ssmith-acdc-03.txt

Internet DRAFT - draft-ssmith-acdc

draft-ssmith-acdc

Last Version:	draft-ssmith-acdc-03.txt	Tracker Entry
Date:	`01-Aug-2023`
Disposition:	expired
Previous Versions:	draft-ssmith-acdc-02.txt (diff) - 17-May-2022
	draft-ssmith-acdc-01.txt (diff) - 26-Apr-2022
	draft-ssmith-acdc-00.txt (diff) - 06-Apr-2022

TODO Working Group S. Smith
Internet-Draft ProSapien LLC
Intended status: Informational 28 July 2023
Expires: 29 January 2024

Authentic Chained Data Containers (ACDC)
draft-ssmith-acdc-03

Abstract

An authentic chained data container (ACDC) [ACDC_ID][ACDC_WP][VCEnh]
is an IETF [IETF] internet draft focused specification being
incubated at the ToIP (Trust over IP) foundation [TOIP][ACDC_TF]. An
ACDC is a variant of the W3C Verifiable Credential (VC) specification
[W3C_VC]. The W3C VC specification depends on the W3C DID
(Decentralized IDentifier) specification [W3C_DID]. A major use case
for the ACDC specification is to provide GLEIF vLEIs (verifiable
Legal Entity Identifiers) [vLEI][GLEIF_vLEI][GLEIF_KERI]. GLEIF is
the Global Legal Entity Identifier Foundation [GLEIF]. ACDCs are
dependent on a suite of related IETF focused standards associated
with the KERI (Key Event Receipt Infrastructure) [KERI_ID][KERI]
specification. These include CESR [CESR_ID], SAID [SAID_ID], PTEL
[PTEL_ID], CESR-Proof [Proof_ID], IPEX [IPEX_ID], did:keri [DIDK_ID],
and OOBI [OOBI_ID]. Some of the major distinguishing features of
ACDCs include normative support for chaining, use of composable JSON
Schema [JSch][JSchCp], multiple serialization formats, namely, JSON
[JSON][RFC4627], CBOR [CBOR][RFC8949], MGPK [MGPK], and CESR
[CESR_ID], support for Ricardian contracts [RC], support for chain-
link confidentiality [CLC], a well defined security model derived
from KERI [KERI][KERI_ID], _compact_ formats for resource constrained
applications, simple _partial disclosure_ mechanisms and simple
_selective disclosure_ mechanisms. ACDCs provision data using a
synergy of provenance, protection, and performance.

Discussion Venues

This note is to be removed before publishing as an RFC.

Source for this draft and an issue tracker can be found at
https://github.com/trustoverip/tswg-acdc-specification.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on 29 January 2024.

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Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. ACDC Fields . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Field Label Tables . . . . . . . . . . . . . . . . . . . 7
2.1.1. Top-Level Fields . . . . . . . . . . . . . . . . . . 7
2.1.2. Other Fields . . . . . . . . . . . . . . . . . . . . 8
2.2. Compact Labels . . . . . . . . . . . . . . . . . . . . . 9
2.3. Version String Field . . . . . . . . . . . . . . . . . . 10
2.4. SAID (Self-Addressing IDentifier) Fields . . . . . . . . 11
2.5. UUID (Universally Unique IDentifier) Fields . . . . . . . 11
2.6. AID (Autonomic IDentifier) and Derived IDentifier
Fields . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.6.1. Namespaced AIDs . . . . . . . . . . . . . . . . . . . 13
2.7. Selectively Disclosable Attribute Aggregate Field . . . . 13
2.8. Graduated Disclosure and Contractually Protected
Disclosure . . . . . . . . . . . . . . . . . . . . . . . 13
2.8.1. Types of Graduated Disclosure . . . . . . . . . . . . 15
3. Schema Section . . . . . . . . . . . . . . . . . . . . . . . 16
3.1. Type-is-Schema . . . . . . . . . . . . . . . . . . . . . 17
3.2. Schema ID Field Label . . . . . . . . . . . . . . . . . . 17
3.3. Static (Immutable) Schema . . . . . . . . . . . . . . . . 18

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3.4. Schema Dialect . . . . . . . . . . . . . . . . . . . . . 21
3.5. Schema Availablity . . . . . . . . . . . . . . . . . . . 21
3.6. Composable JSON Schema . . . . . . . . . . . . . . . . . 21
4. ACDC Variants . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. Public ACDC . . . . . . . . . . . . . . . . . . . . . . . 24
4.2. Private ACDC . . . . . . . . . . . . . . . . . . . . . . 24
4.3. Metadata ACDC . . . . . . . . . . . . . . . . . . . . . . 24
5. Unpermissioned Exploitation of Data . . . . . . . . . . . . . 26
5.1. Graduated Disclosure and the Principle of Least
Disclosure . . . . . . . . . . . . . . . . . . . . . . . 26
5.2. Exploitation Protection Mechanisms . . . . . . . . . . . 26
5.3. Three-Party Exploitation Model . . . . . . . . . . . . . 27
5.3.1. Second-Party (Disclosee) Exploitation . . . . . . . . 27
5.3.2. Third-Party (Observer) Exploitation . . . . . . . . . 27
5.4. Chain-link Confidentiality Exchange . . . . . . . . . . . 28
6. Field Ordering . . . . . . . . . . . . . . . . . . . . . . . 28
7. Compact ACDC . . . . . . . . . . . . . . . . . . . . . . . . 28
7.1. Compact Public ACDC . . . . . . . . . . . . . . . . . . . 28
7.2. Compact Private ACDC . . . . . . . . . . . . . . . . . . 29
7.2.1. Compact Private ACDC Schema . . . . . . . . . . . . . 29
8. Attribute Section . . . . . . . . . . . . . . . . . . . . . . 31
8.1. Public-Attribute ACDC . . . . . . . . . . . . . . . . . . 31
8.2. Public Uncompacted Attribute Section Schema . . . . . . . 32
8.3. Composed Schema for both Public Compact and Uncompacted
Attribute Section Variants . . . . . . . . . . . . . . . 33
8.4. Private-Attribute ACDC . . . . . . . . . . . . . . . . . 35
8.4.1. Composed Schema for Both Compact and Uncompacted
Private-Attribute ACDC . . . . . . . . . . . . . . . 36
8.5. Untargeted ACDC . . . . . . . . . . . . . . . . . . . . . 37
8.6. Targeted ACDC . . . . . . . . . . . . . . . . . . . . . . 38
9. Edge Section . . . . . . . . . . . . . . . . . . . . . . . . 39
9.1. Edge Sub-block Reserved Fields . . . . . . . . . . . . . 40
9.1.1. SAID Field . . . . . . . . . . . . . . . . . . . . . 41
9.1.2. UUID Field . . . . . . . . . . . . . . . . . . . . . 42
9.1.3. Node Field . . . . . . . . . . . . . . . . . . . . . 42
9.1.4. Schema Field . . . . . . . . . . . . . . . . . . . . 42
9.1.5. Operator Field . . . . . . . . . . . . . . . . . . . 43
9.1.6. Weight Field . . . . . . . . . . . . . . . . . . . . 43
9.2. Globally Distributed Secure Graph Fragments . . . . . . . 43
9.3. Compact Edge . . . . . . . . . . . . . . . . . . . . . . 44
9.4. Private Edge . . . . . . . . . . . . . . . . . . . . . . 44
9.5. Simple Compact Edge . . . . . . . . . . . . . . . . . . . 45
9.6. Operations on Edges and Edge-Groups . . . . . . . . . . . 46
9.6.1. Label Types . . . . . . . . . . . . . . . . . . . . . 46
9.6.2. Block Types . . . . . . . . . . . . . . . . . . . . . 46
9.6.3. Operator, o, Field . . . . . . . . . . . . . . . . . 47
9.6.4. Weight, w, field. . . . . . . . . . . . . . . . . . . 47
9.6.5. M-ary Operators . . . . . . . . . . . . . . . . . . . 48

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9.6.6. Special Unary Operators . . . . . . . . . . . . . . . 48
9.6.7. Defaults for missing operators . . . . . . . . . . . 50
9.6.8. Examples . . . . . . . . . . . . . . . . . . . . . . 50
9.6.9. Explicit AND . . . . . . . . . . . . . . . . . . . . 51
9.6.10. Unary I2I . . . . . . . . . . . . . . . . . . . . . . 51
9.6.11. Unary NI2I . . . . . . . . . . . . . . . . . . . . . 51
9.6.12. Nested Edge-Group . . . . . . . . . . . . . . . . . . 52
9.6.13. vLEI ECR issued by QVI example . . . . . . . . . . . 53
9.6.14. Commentary . . . . . . . . . . . . . . . . . . . . . 54
9.7. Node Discovery . . . . . . . . . . . . . . . . . . . . . 55
10. Rule Section . . . . . . . . . . . . . . . . . . . . . . . . 55
10.1. Compact Clauses . . . . . . . . . . . . . . . . . . . . 57
10.2. Private Clause . . . . . . . . . . . . . . . . . . . . . 57
10.3. Simple Compact Clause . . . . . . . . . . . . . . . . . 58
10.4. Clause Discovery . . . . . . . . . . . . . . . . . . . . 58
11. Disclosure-Specific (Bespoke) Issued ACDCs . . . . . . . . . 59
11.1. Example Bespoke Issued ACDC . . . . . . . . . . . . . . 59
12. Informative Examples . . . . . . . . . . . . . . . . . . . . 60
12.1. Public ACDC with Compact and Uncompated Variants . . . . 60
12.1.1. Public Uncompacted Variant . . . . . . . . . . . . . 61
12.1.2. Composed Schema that Supports both Public Compact and
Uncompacted Variants . . . . . . . . . . . . . . . . 62
13. Selective Disclosure . . . . . . . . . . . . . . . . . . . . 68
13.1. Tiered Selective Disclosure Mechanisms . . . . . . . . . 69
13.2. Basic Selective Disclosure Mechanism . . . . . . . . . . 69
13.3. Selectively Disclosable Attribute ACDC . . . . . . . . . 70
13.3.1. Blinded Attribute Array . . . . . . . . . . . . . . 72
13.3.2. Composed Schema for Selectively Disclosable Attribute
Section . . . . . . . . . . . . . . . . . . . . . . . 73
13.3.3. Inclusion Proof via Aggregated List Digest . . . . . 75
13.3.4. Inclusion Proof via Merkle Tree Root Digest . . . . 78
13.3.5. Hierarchical Derivation at Issuance of Selectively
Disclosable Attribute ACDCs . . . . . . . . . . . . . 79
13.4. Bulk-Issued Private ACDCs . . . . . . . . . . . . . . . 80
13.5. Basic Bulk Issuance . . . . . . . . . . . . . . . . . . 82
13.5.1. Inclusion Proof via Merkle Tree . . . . . . . . . . 88
13.5.2. Bulk Issuance of Private ACDCs with Unique Issuee
AIDs . . . . . . . . . . . . . . . . . . . . . . . . 89
13.6. Blindable State TEL . . . . . . . . . . . . . . . . . . 90
13.6.1. Blindable State TEL Top-Level Fields . . . . . . . . 91
13.6.2. Blindable State TEL Attribute (state) Fields . . . . 91
13.7. Independent TEL Bulk-Issued ACDCs . . . . . . . . . . . 92
14. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 93
15. Appendix: Performance and Scalability . . . . . . . . . . . . 94
16. Appendix: Cryptographic Strength and Security . . . . . . . . 94
16.1. Cryptographic Strength . . . . . . . . . . . . . . . . . 94
16.2. Information Theoretic Security and Perfect Security . . 95
17. Conventions and Definitions . . . . . . . . . . . . . . . . . 96

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18. Security Considerations . . . . . . . . . . . . . . . . . . . 96
19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 96
20. References . . . . . . . . . . . . . . . . . . . . . . . . . 96
20.1. Normative References . . . . . . . . . . . . . . . . . . 96
20.2. Informative References . . . . . . . . . . . . . . . . . 98
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 102
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 102

1. Introduction

One primary purpose of the ACDC protocol is to provide granular
provenanced proof-of-authorship (authenticity) of their contained
data via a tree or chain of linked ACDCs (technically a directed
acyclic graph or DAG). Similar to the concept of a chain-of-custody,
ACDCs provide a verifiable chain of proof-of-authorship of the
contained data. With a little additional syntactic sugar, this
primary facility of chained (treed) proof-of-authorship
(authenticity) is extensible to a chained (treed) verifiable
authentic proof-of-authority (proof-of-authorship-of-authority). A
proof-of-authority may be used to provide verifiable authorizations
or permissions or rights or credentials. A chained (treed) proof-of-
authority enables delegation of authority and delegated
authorizations. These proofs of authorship and/or authority provide
provenance of an ACDC itself and by association any data that is so
conveyed.

The dictionary definition of *_credential_* is _evidence of
authority, status, rights, entitlement to privileges, or the like_.
Appropriately structured ACDCs may be used as credentials when their
semantics provide verifiable evidence of authority. Chained ACDCs
may provide delegated credentials.

Chains of ACDCs that merely provide proof-of-authorship
(authenticity) of data may be appended to chains of ACDCs that
provide proof-of-authority (delegation) to enable verifiable
delegated authorized authorship of data. This is a vital facility
for authentic data supply chains. Furthermore, any physical supply
chain may be measured, monitored, regulated, audited, and/or archived
by a data supply chain acting as a digital twin [Twin]. Therefore
ACDCs provide the critical enabling facility for an authentic data
economy and by association an authentic real (twinned) economy.

ACDCs act as securely attributed (authentic) fragments of a
distributed _property graph_ (PG) [PGM][Dots]. Thus they may be used
to construct knowledge graphs expressed as property graphs [KG].
ACDCs enable securely-attributed and privacy-protecting knowledge
graphs.

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The ACDC specification (including its partial and selective
disclosure mechanisms) leverages two primary cryptographic operations
namely digests and digital signatures [Hash][DSig]. These operations
when used in an ACDC MUST have a security level, cryptographic
strength, or entropy of approximately 128 bits [Level]. (See the
appendix for a discussion of cryptographic strength and security)

An important property of high-strength cryptographic digests is that
a verifiable cryptographic commitment (such as a digital signature)
to the digest of some data is equivalent to a commitment to the data
itself. ACDCs leverage this property to enable compact chains of
ACDCs that anchor data via digests. The data _contained_ in an ACDC
may therefore be merely its equivalent anchoring digest. The
anchored data is thereby equivalently authenticated or authorized by
the chain of ACDCs.

2. ACDC Fields

An ACDC may be abstractly modeled as a nested key: value mapping. To
avoid confusion with the cryptographic use of the term _key_ we
instead use the term _field_ to refer to a mapping pair and the terms
_field label_ and _field value_ for each member of a pair. These
pairs can be represented by two tuples e.g (label, value). We
qualify this terminology when necessary by using the term _field map_
to reference such a mapping. _Field maps_ may be nested where a given
_field value_ is itself a reference to another _field map_. We call
this nested set of fields a _nested field map_ or simply a _nested
map_ for short. A _field_ may be represented by a framing code or
block delimited serialization. In a block delimited serialization,
such as JSON, each _field map_ is represented by an object block with
block delimiters such as {} [RFC8259][JSON][RFC4627]. Given this
equivalence, we may also use the term _block_ or _nested block_ as
synonymous with _field map_ or _nested field map_. In many
programming languages, a field map is implemented as a dictionary or
hash table in order to enable performant asynchronous lookup of a
_field value_ from its _field label_. Reproducible serialization of
_field maps_ requires a canonical ordering of those fields. One such
canonical ordering is called insertion or field creation order. A
list of (field, value) pairs provides an ordered representation of
any field map. Most programming languages now support ordered
dictionaries or hash tables that provide reproducible iteration over
a list of ordered field (label, value) pairs where the ordering is
the insertion or field creation order. This enables reproducible
round trip serialization/deserialization of _field maps_. ACDCs
depend on insertion ordered field maps for canonical serialization/
deserialization. ACDCs support multiple serialization types, namely
JSON, CBOR, MGPK, and CESR but for the sake of simplicity, we will
only use JSON herein for examples [RFC8259][JSON]. The basic set of

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normative field labels in ACDC field maps is defined in the following
table.

2.1. Field Label Tables

2.1.1. Top-Level Fields

These are reserved field labels at the top level of an ACDC.

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Table 1

2.1.2. Other Fields

These may appear at other levels besides the top-level of an ACDC but
are nonetheless reserved.

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Table 2

2.2. Compact Labels

The primary field labels are compact in that they use only one or two
characters. ACDCs are meant to support resource-constrained
applications such as supply chain or IoT (Internet of Things)
applications. Compact labels better support resource-constrained
applications in general. With compact labels, the over-the-wire
verifiable signed serialization consumes a minimum amount of
bandwidth. Nevertheless, without loss of generality, a one-to-one
normative semantic overlay using more verbose expressive field labels
may be applied to the normative compact labels after verification of
the over-the-wire serialization. This approach better supports

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bandwidth and storage constraints on transmission while not
precluding any later semantic post-processing. This is a well-known
design pattern for resource-constrained applications.

2.3. Version String Field

The version string, v, field MUST be the first field in any top-level
ACDC field map. It provides a regular expression target for
determining the serialization format and size (character count) of a
serialized ACDC. A stream-parser may use the version string to
extract and deserialize (deterministically) any serialized ACDC in a
stream of serialized ACDCs. Each ACDC in a stream may use a
different serialization type.

The format of the version string is ACDCvvSSSShhhhhh_. The first four
characters ACDC indicate the enclosing field map serialization. The
next two characters, vv provide the lowercase hexadecimal notation
for the major and minor version numbers of the version of the ACDC
specification used for the serialization. The first v provides the
major version number and the second v provides the minor version
number. For example, 01 indicates major version 0 and minor version
1 or in dotted-decimal notation 0.1. Likewise 1c indicates major
version 1 and minor version decimal 12 or in dotted-decimal notation
1.12. The next four characters SSSS indicate the serialization type
in uppercase. The four supported serialization types are JSON, CBOR,
MGPK, and CESR for the JSON, CBOR, MessagePack, and CESR
serialization standards respectively
[JSON][RFC4627][CBOR][RFC8949][MGPK][CESR_ID]. The next six
characters provide in lowercase hexadecimal notation the total number
of characters in the serialization of the ACDC. The maximum length
of a given ACDC is thereby constrained to be _2^24 = 16,777,216_
characters in length. The final character - is the version string
terminator. This enables later versions of ACDC to change the total
version string size and thereby enable versioned changes to the
composition of the fields in the version string while preserving
deterministic regular expression extractability of the version
string. Although a given ACDC serialization type may have a field
map delimiter or framing code characters that appear before (i.e.
prefix) the version string field in a serialization, the set of
possible prefixes is sufficiently constrained by the allowed
serialization protocols to guarantee that a regular expression can
determine unambiguously the start of any ordered field map
serialization that includes the version string as the first field
value. Given the version string, a parser may then determine the end
of the serialization so that it can extract the full ACDC from the
stream without first deserializing it. This enables performant
stream parsing and off-loading of ACDC streams that include any or
all of the supported serialization types.

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2.4. SAID (Self-Addressing IDentifier) Fields

Some fields in ACDCs may have for their value either a _field map_ or
a SAID. A SAID follows the SAID protocol [SAID_ID]. Essentially a
SAID is a Self-Addressing IDentifier (self-referential content
addressable). A SAID is a special type of cryptographic digest of
its encapsulating _field map_ (block). The encapsulating block of a
SAID is called a SAD (Self-Addressed Data). Using a SAID as a _field
value_ enables a more compact but secure representation of the
associated block (SAD) from which the SAID is derived. Any nested
field map that includes a SAID field (i.e. is, therefore, a SAD) may
be compacted into its SAID. The uncompacted blocks for each
associated SAID may be attached or cached to optimize bandwidth and
availability without decreasing security.

Several top-level ACDC fields may have for their value either a
serialized _field map_ or the SAID of that _field map_. Each SAID
provides a stable universal cryptographically verifiable and agile
reference to its encapsulating block (serialized _field map_).
Specifically, the value of top-level s, a, e, and r fields may be
replaced by the SAID of their associated _field map_. When replaced
by their SAID, these top-level sections are in _compact_ form.

Recall that a cryptographic commitment (such as a digital signature
or cryptographic digest) on a given digest with sufficient
cryptographic strength including collision resistance [HCR][QCHC] is
equivalent to a commitment to the block from which the given digest
was derived. Specifically, a digital signature on a SAID makes a
verifiable cryptographic non-repudiable commitment that is equivalent
to a commitment on the full serialization of the associated block
from which the SAID was derived. This enables reasoning about ACDCs
in whole or in part via their SAIDS in a fully interoperable,
verifiable, compact, and secure manner. This also supports the well-
known bow-tie model of Ricardian Contracts [RC]. This includes
reasoning about the whole ACDC given by its top-level SAID, d, field
as well as reasoning about any nested sections using their SAIDS.

2.5. UUID (Universally Unique IDentifier) Fields

The purpose of the UUID, u, field in any block is to provide
sufficient entropy to the SAID, d, field of the associated block to
make computationally infeasible any brute force attacks on that block
that attempt to discover the block contents from the schema and the
SAID. The UUID, u, field may be considered a salty nonce [Salt].
Without the entropy provided the UUID, u, field, an adversary may be
able to reconstruct the block contents merely from the SAID of the
block and the schema of the block using a rainbow or dictionary
attack on the set of field values allowed by the schema [RB][DRB].

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The effective security level, entropy, or cryptographic strength of
the schema-compliant field values may be much less than the
cryptographic strength of the SAID digest. Another way of saying
this is that the cardinality of the power set of all combinations of
allowed field values may be much less than the cryptographic strength
of the SAID. Thus an adversary could successfully discover via brute
force the exact block by creating digests of all the elements of the
power set which may be small enough to be computationally feasible
instead of inverting the SAID itself. Sufficient entropy in the u
field ensures that the cardinality of the power set allowed by the
schema is at least as great as the entropy of the SAID digest
algorithm itself.

A UUID, u field may optionally appear in any block (field map) at any
level of an ACDC. Whenever a block in an ACDC includes a UUID, u,
field then its associated SAID, d, field makes a blinded commitment
to the contents of that block. The UUID, u, field is the blinding
factor. This makes that block securely partially disclosable or even
selectively disclosable notwithstanding disclosure of the associated
schema of the block. The block contents can only be discovered given
disclosure of the included UUID field. Likewise when a UUID, u,
field appears at the top level of an ACDC then that top-level SAID,
d, field makes a blinded commitment to the contents of the whole ACDC
itself. Thus the whole ACDC, not merely some block within the ACDC,
may be disclosed in a privacy-preserving (correlation minimizing)
manner.

2.6. AID (Autonomic IDentifier) and Derived IDentifier Fields

Some fields, such as the i, Issuer identifier field MUST each have an
AID (Autonomic IDentifier) as its value. An AID is a fully qualified
Self-Certifying IDentifier (SCID) that follows the KERI protocol
[KERI][KERI_ID]. A related type of identifier field is the ri,
registry identifier field. The ri field is cryptographically derived
from the Issuer identifier field value so has securely attributable
control authority via the AID from which it is derived. A SCID is
derived from one or more (public, private) key pairs using asymmetric
or public-key cryptography to create verifiable digital signatures
[DSig]. Each AID has a set of one or more controllers who each
control a private key. By virtue of their private key(s), the set of
controllers may make statements on behalf of the associated AID that
is backed by uniquely verifiable commitments via digital signatures
on those statements. Any entity may then verify those signatures
using the associated set of public keys. No shared or trusted
relationship between the controllers and verifiers is required. The
verifiable key state for AIDs is established with the KERI protocol
[KERI][KERI_ID]. The use of AIDS enables ACDCs to be used in a
portable but securely attributable, fully decentralized manner in an

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ecosystem that spans trust domains.

2.6.1. Namespaced AIDs

Because KERI is agnostic about the namespace for any particular AID,
different namespace standards may be used to express KERI AIDs or
identifiers derived from AIDs as the value of thes AID related fields
in an ACDC. The examples below use the W3C DID namespace
specification with the did:keri method [DIDK_ID]. But the examples
would have the same validity from a KERI perspective if some other
supported namespace was used or no namespace was used at all. The
latter case consists of a bare KERI AID (identifier prefix) expressed
in CESR format [CESR_ID].

2.7. Selectively Disclosable Attribute Aggregate Field

The top-level selectively-disclosable attribute aggregate section, A,
field value is an aggregate of cryptographic commitments used to make
a commitment to a set (bundle) of selectively-disclosable attributes.
The value of the attribute aggregate, A, field depends on the type of
selective disclosure mechanism employed. For example, the aggregate
value could be the cryptographic digest of the concatenation of an
ordered set of cryptographic digests, a Merkle tree root digest of an
ordered set of cryptographic digests, or a cryptographic accumulator.

2.8. Graduated Disclosure and Contractually Protected Disclosure

ACDC leverages several closely related mechanisms for what can be
called *_graduated disclosure_*. _Graduated disclosure_ enables
adherence to the principle of least disclosure which is expressed as
follows:

The system should disclose only the minimum amount of information
about a given party needed to facilitate a transaction and no
more. [IDSys]

To clarify, _graduated disclosure_ enables a potential Discloser to
follow the principle of _least disclosure_ by providing the least
amount of information i.e. partial, incomplete, or uncorrelatable
information needed to further a transaction.

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The important insight is that one type of transaction enabled by
least disclosure is a transaction that specifically enables further
disclosure. In other words, disclose enough to enable more
disclosure which in turn may enable even more disclosure. This is
the essence of _graduated disclosure_. This progression of successive
least graduated disclosures to enable a transaction that itself
enables a farther least graduated disclosure forms a recursive loop
of least disclosure enabled transactions. In other words, the
principle of least disclosure may be applied recursively.

A type of transaction that leverages _graduated disclosure_ to enable
further disclosure we call a *_contractually protected disclosure_*
transaction. In a contractually protected disclosure, the potential
Discloser first makes an offer using the least (partial) disclosure
of some information about other information to be disclosed (full
disclosure) contingent on the potential Disclosee first agreeing to
the contractual terms provided in the offer. The contractual terms
could, for example, limit the disclosure to third parties of the yet
to be disclosed information. But those contractual terms may also
include provisions that protect against liability or other concerns
not merely disclosure to third parties.

One special case of a _contractually protected disclosure_ is a
*_chain-link confidential disclosure_* [CLC].

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Another special case of _contractually protected disclosure_ is a
*_contingent-disclosure_*. In a _contingent disclosure_ some
contingency is specified in the rule section that places an
obligation by some party to make a disclosure when the contingency is
satisfied. This might be recourse given the breach of some other
term of the contract. When that contingency is met then the
contingent disclosure MUST be made by the party whose responsibility
it is to satisfy that disclosure obligation. The responsible party
may be the Discloser of the ACDC or it may be some other party such
as an escrow agent. The contingent disclosure clause may reference a
cryptographic commitment to a private ACDC or private attribute ACDC
(partial disclosure) that satisfies via its full disclosure the
contingent disclosure requirement. Contingent disclosure may be used
to limit the actual disclosure of personally identifying information
(PII) to a just-in-time, need-to-know basis (i.e upon the
contingency) and not a priori. As long as the Discloser and
Disclosee trust the escrow agent and the verifiability of the
committment, there is no need to disclose PII about the discloser in
order to enable a transaction, but merely an agreement to the terms
of the contingency. This enables something called *_latent
accountability_*. Recourse via PII is latent in the contingent
disclosure but is not ever realized (actualized) until recourse is
truly needed. The minimizes inadvertent leakage while protecting the
Disclosee.

2.8.1. Types of Graduated Disclosure

ACDCs employ three specific closely related types of _graduated
disclosure_. These are *_compact disclosure_*, *_partial
disclosure_*, and *_selective disclosure_*. The mechanism for
_compact disclosure_ is a cryptographic digest of the content
expressed in the form of a SAID of that content. Both partial and
selective disclosure rely on the compact disclosure of content that
is also cryptographically blinded or hidden. Content in terms of an
ACDC means a block (field map or field map array).

The difference between *_partial disclosure_* and *_selective
disclosure_* of a given block is determined by the correlatability of
the disclosed field(s) after *_full disclosure_* of the detailed
field value with respect to its enclosing block (field map or field
map array). A _partially disclosable_ field becomes correlatable
after _full disclosure_. Whereas a _selectively disclosable_ field
may be excluded from the _full disclosure_ of any other _selectively
disclosable_ fields in the _selectively disclosable_ block (usually a
field map array). After such _selective disclosure_, the selectively
disclosed fields are not correlatable to the so-far undisclosed but
selectively disclosable fields in that block (field map array).

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When used in the context of _selective disclosure_, _full disclosure_
means detailed disclosure of the selectively disclosed attributes not
detailed disclosure of all selectively disclosable attributes.
Whereas when used in the context of _partial disclosure_, _full
disclosure_ means detailed disclosure of the field map that was so
far only partially disclosed.

_Partial disclosure_ is an essential mechanism needed to support both
performant exchange of information and contractually protected
disclosure such as chain-link confidentiality on exchanged
information [CLC]. The exchange of only the SAID of a given field
map is a type of _partial disclosure_. Another type of _partial
disclosure_ is the disclosure of validatable metadata about a
detailed field map e.g. the schema of a field map.

The SAID of a field map provides a _compact_ cryptographically
equivalent commitment to the yet to be undisclosed field map details.
A later exchange of the uncompacted field map detail provides _full
disclosure_. Any later _full disclosure_ is verifiable to an earlier
_partial disclosure_. Partial disclosure via compact SAIDs enables
the scalable repeated verifiable exchange of SAID references to
cached full disclosures. Multiple SAID references to cached fully
disclosed field maps may be transmitted compactly without redundant
retransmission of the full details each time a new reference is
transmitted. Likewise, _partial disclosure_ via SAIDs also supports
the bow-tie model of Ricardian contracts [RC]. Similarly, the schema
of a field map is metadata about the structure of the field map this
is validatable given the full disclosure of the field map. The
details of_compact_ and/or confidential exchange mechanisms that
leverage partial disclosure are explained later. When the field map
includes sufficient cryptographic entropy such as through a UUID
field (salty nonce), then the SAID of that field map effectively
blinds the contents of the field map. This enables the field map
contents identified by its SAID and characterized by its schema (i.e.
partial disclosure) to remain private until later full disclosure.

_Selective disclosure_, on the other hand, is an essential mechanism
needed to unbundle in a correlation minimizing way a single
commitment by an Issuer to a bundle of fields (i.e. a nested array or
list or tuple of fields) as a whole. This allows separating a "stew"
(bundle) of "ingredients" (attributes) into its constituent
"ingredients" (attributes) without correlating the constituents via
the Issuer's commitment to the "stew" (bundle) as a whole.

3. Schema Section

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3.1. Type-is-Schema

Notable is the fact that there are no top-level type fields in an
ACDC. This is because the schema, s, field itself is the type field
for the ACDC and its parts. ACDCs follow the design principle of
separation of concerns between a data container's actual payload
information and the type information of that container's payload. In
this sense, type information is metadata, not data. The schema
dialect used by ACDCs is JSON Schema 2020-12 [JSch][JSch_202012].
JSON Schema supports composable schema (sub-schema), conditional
schema (sub-schema), and regular expressions in the schema.
Composability enables a validator to ask and answer complex questions
about the type of even optional payload elements while maintaining
isolation between payload information and type (structure)
information about the payload [JSchCp][JSchRE][JSchId][JSchCx]. A
static but composed schema allows a verifiably immutable set of
variants. Although the set is immutable, the variants enable
graduated but secure disclosure. ACDC's use of JSON Schema MUST be
in accordance with the ACDC defined profile as defined herein. The
exceptions are defined below.

3.2. Schema ID Field Label

The usual field label for SAID fields in ACDCs is d. In the case of
the schema section, however, the field label for the SAID of the
schema section is $id. This repurposes the schema id field label,
$id as defined by JSON Schema [JSchId][JSchCx]. The top-level id,
$id, field value in a JSON Schema provides a unique identifier of the
schema instance. In a usual (non-ACDC) schema the value of the id,
$id, field is expressed as a URI. This is called the _Base URI_ of
the schema. In an ACDC schema, however, the top-level id, $id, field
value is repurposed. Its value MUST include the SAID of the schema.
This ensures that the ACDC schema is static and verifiable to their
SAIDS. A verifiably static schema satisfies one of the essential
security properties of ACDCs as discussed below. There are several
ACDC supported formats for the value of the top-level id, $id, field
but all of the formats MUST include the SAID of the schema (see
below). Correspondingly, the value of the top-level schema, s, field
MUST be the SAID included in the schema's top-level $id field. The
detailed schema is either attached or cached and maybe discovered via
its SAIDified, id, $id, field value.

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When an id, '$id', field appears in a sub-schema it indicates a
bundled sub-schema called a schema resource [JSchId][JSchCx]. The
value of the id, '$id', field in any ACDC bundled sub-schema resource
MUST include the SAID of that sub-schema using one of the formats
described below. The sub-schema so bundled MUST be verifiable
against its referenced and embedded SAID value. This ensures secure
bundling.

3.3. Static (Immutable) Schema

For security reasons, the full schema of an ACDC must be completely
self-contained and statically fixed (immutable) for that ACDC. By
this, we mean that no dynamic schema references or dynamic schema
generation mechanisms are allowed.

Should an adversary successfully attack the source that provides the
dynamic schema resource and change the result provided by that
reference, then the schema validation on any ACDC that uses that
dynamic schema reference may fail. Such an attack effectively
revokes all the ACDCs that use that dynamic schema reference. We
call this a *_schema revocation_* attack.

More insidiously, an attacker could shift the semantics of the
dynamic schema in such a way that although the ACDC still passes its
schema validation, the behavior of the downstream processing of that
ACDC is changed by the semantic shift. This we call a *_semantic
malleability_* attack. It may be considered a new type of
_transaction malleability_ attack [TMal].

To prevent both forms of attack, all schema must be static, i.e.
schema MUST be SADs and therefore verifiable against their SAIDs.

To elaborate, the serialization of a static schema may be self-
contained. A compact commitment to the detailed static schema may be
provided by its SAID. In other words, the SAID of a static schema is
a verifiable cryptographic identifier for its SAD. Therefore all
ACDC compliant schema must be SADs. In other words, they MUST
therefore be _SAIDified_. The associated detailed static schema
(uncompacted SAD) is cryptographically bound and verifiable to its
SAID.

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The JSON Schema specification allows complex schema references that
may include non-local URI references
[JSchId][JSchCx][RFC3986][RFC8820]. These references may use the $id
or $ref keywords. A relative URI reference provided by a $ref
keyword is resolved against the _Base URI_ provided by the top-level
$id field. When this top-level _Base URI_ is non-local then all
relative $ref references are therefore also non-local. A non-local
URI reference provided by a $ref keyword may be resolved without
reference to the _Base URI_.

In general, schema indicated by non-local URI references ($id or
$ref) MUST NOT be used because they are not cryptographically end-
verifiable. The value of the underlying schema resource so
referenced may change (mutate). To restate, a non-local URI schema
resource is not end-verifiable to its URI reference because there is
no cryptographic binding between URI and resource [RFC3986][RFC8820].

This does not preclude the use of remotely cached SAIDified schema
resources because those resources are end-verifiable to their
embedded SAID references. Said another way, a SAIDified schema
resource is itself a SAD (Self-Address Data) referenced by its SAID.
A URI that includes a SAID may be used to securely reference a remote
or distributed SAIDified schema resource because that resource is
fixed (immutable, nonmalleable) and verifiable to both the SAID in
the reference and the embedded SAID in the resource so referenced.
To elaborate, a non-local URI reference that includes an embedded
cryptographic commitment such as a SAID is verifiable to the
underlying resource when that resource is a SAD. This applies to
JSON Schema as a whole as well as bundled sub-schema resources.

There ACDC supported formats for the value of the top-level id, $id,
field are as follows:

* Bare SAIDs may be used to refer to a SAIDified schema as long as
the JSON schema validator supports bare SAID references. By
default, many if not all JSON schema validators support bare
strings (non-URIs) for the _Base URI_ provided by the top-level
$id field value.

* The sad: URI scheme may be used to directly indicate a URI
resource that safely returns a verifiable SAD. For example
sad:SAID where _SAID_ is replaced with the actual SAID of a SAD
that provides a verifiable non-local reference to JSON Schema as
indicated by the mime-type of schema+json.

* The IETF KERI OOBI internet draft specification provides a URL
syntax that references a SAD resource by its SAID at the service
endpoint indicated by that URL [OOBI_ID]. Such remote OOBI URLs

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are also safe because the provided SAD resource is verifiable
against the SAID in the OOBI URL. Therefore OOBI URLs are also
acceptable non-local URI references for JSON Schema
[OOBI_ID][RFC3986][RFC8820].

* The did: URI scheme may be used safely to prefix non-local URI
references that act to namespace SAIDs expressed as DID URIs or
DID URLs. DID resolvers resolve DID URLs for a given DID method
such as did:keri [DIDK_ID] and may return DID docs or DID doc
metadata with SAIDified schema or service endpoints that return
SAIDified schema or OOBIs that return SAIDified schema
[RFC3986][RFC8820][OOBI_ID]. A verifiable non-local reference in
the form of DID URL that includes the schema SAID is resolved
safely when it dereferences to the SAD of that SAID. For example,
the resolution result returns an ACDC JSON Schema whose id, $id,
field includes the SAID and returns a resource with JSON Schema
mime-type of schema+json.

To clarify, ACDCs MUST NOT use complex JSON Schema references which
allow *dynamically generated *schema resources to be obtained from
online JSON Schema Libraries [JSchId][JSchCx]. The latter approach
may be difficult or impossible to secure because a cryptographic
commitment to the base schema that includes complex schema (non-
relative URI-based) references only commits to the non-relative URI
reference and not to the actual schema resource which may change (is
dynamic, mutable, malleable). To restate, this approach is insecure
because a cryptographic commitment to a complex (non-relative URI-
based) reference is NOT equivalent to a commitment to the detailed
associated schema resource so referenced if it may change.

ACDCs MUST use static JSON Schema (i.e. _SAIDifiable_ schema). These
may include internal relative references to other parts of a fully
self-contained static (_SAIDified_) schema or references to static
(_SAIDified_) external schema parts. As indicated above, these
references may be bare SAIDs, DID URIs or URLs (did: scheme), SAD
URIs (sad: scheme), or OOBI URLs [OOBI_ID]. Recall that a commitment
to a SAID with sufficient collision resistance makes an equivalent
secure commitment to its encapsulating block SAD. Thus static schema
may be either fully self-contained or distributed in parts but the
value of any reference to a part must be verifiably static
(immutable, nonmalleable) by virtue of either being relative to the
self-contained whole or being referenced by its SAID. The static
schema in whole or in parts may be attached to the ACDC itself or
provided via a highly available cache or data store. To restate,
this approach is securely end-verifiable (zero-trust) because a
cryptographic commitment to the SAID of a SAIDified schema is
equivalent to a commitment to the detailed associated schema itself
(SAD).

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3.4. Schema Dialect

The schema dialect for ACDC 1.0 is JSON Schema 2020-12 and is
indicated by the identifier "https://json-schema.org/draft/2020-12/
schema" [JSch][JSch_202012]. This is indicated in a JSON Schema via
the value of the top-level $schema field. Although the value of
$schema is expressed as a URI, de-referencing does not provide
dynamically downloadable schema dialect validation code. This would
be an attack vector. The validator MUST control the tooling code
dialect used for schema validation and hence the tooling dialect
version actually used. A mismatch between the supported tooling code
dialect version and the $schema string value should cause the
validation to fail. The string is simply an identifier that
communicates the intended dialect to be processed by the schema
validation tool. When provided, the top-level $schema field value
for ACDC version 1.0 must be "https://json-schema.org/draft/2020-12/
schema".

3.5. Schema Availablity

The composed detailed (uncompacted) (bundled) static schema for an
ACDC may be cached or attached. But cached, and/or attached static
schema is not to be confused with dynamic schema. Nonetheless, while
securely verifiable, a remotely cached, _SAIDified_, schema resource
may be unavailable. Availability is a separate concern. Unavailable
does not mean insecure or unverifiable. ACDCs MUST be verifiable
when available. Availability is typically solvable through
redundancy. Although a given ACDC application domain or eco-system
governance framework may impose schema availability constraints, the
ACDC specification itself does not impose any specific availability
requirements on Issuers other than schema caches SHOULD be
sufficiently available for the intended application of their
associated ACDCs. It's up to the Issuer of an ACDC to satisfy any
availability constraints on its schema that may be imposed by the
application domain or eco-system.

3.6. Composable JSON Schema

A composable JSON Schema enables the use of any combination of
compacted/uncompacted attribute, edge, and rule sections in a
provided ACDC. When compact, any one of these sections may be
represented merely by its SAID [JSch][JSchCp]. When used for the
top-level attribute, a, edge, e, or rule, r, section field values,
the oneOf sub-schema composition operator provides both compact and
uncompacted variants. The provided ACDC MUST validate against an
allowed combination of the composed variants, either the compact SAID
of a block or the full detailed (uncompacted) block for each section.
The validator determines what decomposed variants the provided ACDC

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MUST also validate against. Decomposed variants may be dependent on
the type of graduated disclosure, partial, full, or selective.
Essentially a composable schema is a verifiable bundle of metadata
(composed) about content that then can be verifiably unbundled
(decomposed) later. The Issuer makes a single verifiable commitment
to the bundle (composed schema) and a recipient may then safely
unbundle (decompose) the schema to validate any of the graduated
disclosures variants allowed by the composition.

Unlike the other compactifiable sections, it is impossible to define
recursively the exact detailed schema as a variant of a oneOf
composition operator contained in itself. Nonetheless, the provided
schema, whether self-contained, attached, or cached MUST validate as
a SAD against its provided SAID. It MUST also validate against one
of its specified oneOf variants.

The compliance of the provided non-schema attribute, a, edge, e, and
rule, r, sections MUST be enforced by validating against the composed
schema. In contrast, the compliance of the provided composed schema
for an expected ACDC type MUST be enforced by the validator. This is
because it is not possible to enforce strict compliance of the schema
by validating it against itself.

ACDC specific schema compliance requirements are usually specified in
the eco-system governance framework for a given ACDC type. Because
the SAID of a schema is a unique content-addressable identifier of
the schema itself, compliance can be enforced by comparison to the
allowed schema SAID in a well-known publication or registry of ACDC
types for a given ecosystem governance framework (EGF). The EGF may
be solely specified by the Issuer for the ACDCs it generates or be
specified by some mutually agreed upon eco-system governance
mechanism. Typically the business logic for making a decision about
a presentation of an ACDC starts by specifying the SAID of the
composed schema for the ACDC type that the business logic is
expecting from the presentation. The verified SAID of the actually
presented schema is then compared against the expected SAID. If they
match then the actually presented ACDC may be validated against any
desired decomposition of the expected (composed) schema.

To elaborate, a validator can confirm compliance of any non-schema
section of the ACDC against its schema both before and after
uncompacted disclosure of that section by using a composed base
schema with oneOf pre-disclosure and a decomposed schema post-
disclosure with the compact oneOf option removed. This capability
provides a mechanism for secure schema validation of both compact and
uncompacted variants that require the Issuer to only commit to the
composed schema and not to all the different schema variants for each
combination of a given compact/uncompacted section in an ACDC.

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One of the most important features of ACDCs is support for Chain-Link
Confidentiality [CLC]. This provides a powerful mechanism for
protecting against un-permissioned exploitation of the data disclosed
via an ACDC. Essentially an exchange of information compatible with
chain-link confidentiality starts with an offer by the discloser to
disclose confidential information to a potential disclosee. This
offer includes sufficient metadata about the information to be
disclosed such that the disclosee can agree to those terms.
Specifically, the metadata includes both the schema of the
information to be disclosed and the terms of use of that data once
disclosed. Once the disclosee has accepted the terms then full
disclosure is made. A full disclosure that happens after contractual
acceptance of the terms of use we call _permissioned_ disclosure.
The pre-acceptance disclosure of metadata is a form of partial
disclosure.

As is the case for compact (uncompacted) ACDC disclosure, Composable
JSON Schema, enables the use of the same base schema for both the
validation of the partial disclosure of the offer metadata prior to
contract acceptance and validation of full or detailed disclosure
after contract acceptance [JSch][JSchCp]. A cryptographic commitment
to the base schema securely specifies the allowable semantics for
both partial and full disclosure. Decomposition of the base schema
enables a validator to impose more specific semantics at later stages
of the exchange process. Specifically, the oneOf sub-schema
composition operator validates against either the compact SAID of a
block or the full block. Decomposing the schema to remove the
optional compact variant enables a validator to ensure complaint full
disclosure. To clarify, a validator can confirm schema compliance
both before and after detailed disclosure by using a composed base
schema pre-disclosure and a decomposed schema post-disclosure with
the undisclosed options removed. These features provide a mechanism
for secure schema-validated contractually-bound partial (and/or
selective) disclosure of confidential data via ACDCs.

4. ACDC Variants

There are several variants of ACDCs determined by the presence/
absence of certain fields and/or the value of those fields. At the
top level, the presence (absence), of the UUID, u, field produces two
variants. These are private (public) respectively. In addition, a
present but empty UUID, u, field produces a private metadata variant.

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4.1. Public ACDC

Given that there is no top-level UUID, u, field in an ACDC, then
knowledge of both the schema of the ACDC and the top-level SAID, d,
field may enable the discovery of the remaining contents of the ACDC
via a rainbow table attack [RB][DRB]. Therefore, although the top-
level, d, field is a cryptographic digest, it may not securely blind
the contents of the ACDC when knowledge of the schema is available.
The field values may be discoverable. Consequently, any
cryptographic commitment to the top-level SAID, d, field may provide
a fixed point of correlation potentially to the ACDC field values
themselves in spite of non-disclosure of those field values. Thus an
ACDC without a top-level UUID, u, field must be considered a
*_public_* (non-confidential) ACDC.

4.2. Private ACDC

Given a top-level UUID, u, field, whose value has sufficient
cryptographic entropy, then the top-level SAID, d, field of an ACDC
may provide a secure cryptographic digest that blinds the contents of
the ACDC [Hash]. An adversary when given both the schema of the ACDC
and the top-level SAID, d, field, is not able to discover the
remaining contents of the ACDC in a computationally feasible manner
such as through a rainbow table attack [RB][DRB]. Therefore the top-
level, UUID, u, field may be used to securely blind the contents of
the ACDC notwithstanding knowledge of the schema and top-level, SAID,
d, field. Moreover, a cryptographic commitment to that that top-
level SAID, d, field does not provide a fixed point of correlation to
the other ACDC field values themselves unless and until there has
been a disclosure of those field values. Thus an ACDC with a
sufficiently high entropy top-level UUID, u, field may be considered
a *_private_* (confidential) ACDC. enables a verifiable commitment to
the top-level SAID of a private ACDC to be made prior to the
disclosure of the details of the ACDC itself without leaking those
contents. This is called _partial_ disclosure. Furthermore, the
inclusion of a UUID, u, field in a block also enables _selective_
disclosure mechanisms described later in the section on selective
disclosure.

4.3. Metadata ACDC

An empty, top-level UUID, u, field appearing in an ACDC indicates
that the ACDC is a *_metadata_* ACDC. The purpose of a _metadata_
ACDC is to provide a mechanism for a _Discloser_ to make
cryptographic commitments to the metadata of a yet to be disclosed
private ACDC without providing any point of correlation to the actual
top-level SAID, d, field of that yet to be disclosed ACDC. The top-
level SAID, d, field, of the metadata ACDC, is cryptographically

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derived from an ACDC with an empty top-level UUID, u, field so its
value will necessarily be different from that of an ACDC with a high
entropy top-level UUID, u, field value. Nonetheless, the _Discloser_
may make a non-repudiable cryptographic commitment to the metadata
SAID in order to initiate a chain-link confidentiality exchange
without leaking correlation to the actual ACDC to be disclosed [CLC].
A _Disclosee_ (verifier) may validate the other metadata information
in the metadata ACDC before agreeing to any restrictions imposed by
the future disclosure. The metadata includes the _Issuer_, the
_schema_, the provenancing _edges_, and the _rules_ (terms-of-use).
The top-level attribute section, a, field value of a _metadata_ ACDC
may be empty so that its value is not correlatable across disclosures
(presentations). Should the potential _Disclosee_ refuse to agree to
the rules then the _Discloser_ has not leaked the SAID of the actual
ACDC or the SAID of the attribute block that would have been
disclosed.

Given the _metadata_ ACDC, the potential _Disclosee_ is able to
verify the _Issuer_, the schema, the provenanced edges, and rules
prior to agreeing to the rules. Similarly, an _Issuer_ may use a
_metadata_ ACDC to get agreement to a contractual waiver expressed in
the rule section with a potential _Issuee_ prior to issuance. Should
the _Issuee_ refuse to accept the terms of the waiver then the
_Issuer_ has not leaked the SAID of the actual ACDC that would have
been issued nor the SAID of its attributes block nor the attribute
values themselves.

When a _metadata_ ACDC is disclosed (presented) only the
_Discloser's_ signature(s) is attached not the _Issuer's_
signature(s). This precludes the _Issuer's_ signature(s) from being
used as a point of correlation until after the _Disclosee_ has agreed
to the terms in the rule section. When chain-link confidentiality is
used, the _Issuer's_ signatures are not disclosed to the _Disclosee_
until after the _Disclosee_ has agreed to keep them confidential.
The _Disclosee_ is protected from forged _Discloser_ because
ultimately verification of the disclosed ACDC will fail if the
_Discloser_ does not eventually provide verifiable _Issuer's_
signatures. Nonetheless, should the potential _Disclosee_ not agree
to the terms of the disclosure expressed in the rule section then the
_Issuer's_ signature(s) is not leaked.

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5. Unpermissioned Exploitation of Data

An important design goal of ACDCs is they support the sharing of
provably authentic data while also protecting against the un-
permissioned exploitation of that data. Often the term _privacy
protection_ is used to describe similar properties. But a narrow
focus on "privacy protection" may lead to problematic design trade-
offs. With ACDCs, the primary design goal is not _data privacy
protection_ per se but the more general goal of protection from the
*_un-permissioned exploitation of data_*. In this light, a _given
privacy protection_ mechanism may be employed to help protect against
_unpermissioned exploitation of data_ but only when it serves that
more general-purpose and not as an end in and of itself.

5.1. Graduated Disclosure and the Principle of Least Disclosure

As described previously, ACDCs employ _graduated disclosure_
mechanisms that satisfy the principle of least disclosure. Requoted
here the principle of least disclosure is as follows:

The system should disclose only the minimum amount of information
about a given party needed to facilitate a transaction and no
more. [IDSys]

For example, compact disclosure, partial disclosure, and selective
disclosure are all graduated disclosure mechanisms. Contractually
protected disclosure leverages graduated disclosure so that
contractual protections can be put into place using the least
disclosure necessary to that end. This minimizes the leakage of
information that can be correlated. One type of contractually
protected disclosure is chain-link confidentiality [CLC].

5.2. Exploitation Protection Mechanisms

An ACDC may employ several mechanisms to protect against
_unpermissioned exploitation of data_. These are:

* Contractually Protected Disclosure

- Chain-link Confidentiality [CLC]

- Contingent Disclosure

* Partial Disclosure

* Selective Disclosure

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For example, the _partial disclosure_ of portions of an ACDC to
enable chain-link confidentiality of the subsequent full disclosure
is an application of the principle of least disclosure. Likewise,
unbundling only the necessary attributes from a bundled commitment
using _selective disclosure_ to enable a correlation minimizing
disclosure from that bundle is an application of the principle of
least disclosure.

5.3. Three-Party Exploitation Model

Unpermission exploitation is characterized using a three-party model.
The three parties are as follows:

* First-Party = _Discloser_ of data.

* Second-Party = _Disclosee_ of data received from First Party
(_Discloser_).

* Third-Party = _Observer_ of data disclosed by First Party
(_Discloser_) to Second Party (_Disclosee_).

5.3.1. Second-Party (Disclosee) Exploitation

* implicit permissioned correlation.

- no contractual restrictions on the use of disclosed data.

* explicit permissioned correlation.

- use as permitted by contract

* explicit unpermissioned correlation with other second parties or
third parties.

- malicious use in violation of contract

5.3.2. Third-Party (Observer) Exploitation

* implicit permissioned correlation.

- no contractual restrictions on the use of observed data.

* explicit unpermissioned correlation via collusion with second
parties.

- malicious use in violation of second-party contract

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5.4. Chain-link Confidentiality Exchange

Chain-link confidentiality imposes contractual restrictions and
liability on any Disclosee (Second-Party) [CLC]. The exchange
provides a fair contract consummation mechanism. The essential steps
in a chain-link confidentiality exchange are shown below. Other
steps may be included in a more comprehensive exchange protocol.

* _Discloser_ provides a non-repudiable _Offer_ with verifiable
metadata (sufficient partial disclosure), which includes any terms
or restrictions on use.

* _Disclosee_ verifies _Offer_ against composed schema and metadata
adherence to desired data.

* _Disclosee_ provides non-repudiable _Accept_ of terms that are
contingent on compliant disclosure.

* _Discloser_ provides non-repudiable _Disclosure_ with sufficient
compliant detail.

* _Disclosee_ verifies _Disclosure_ using decomposed schema and
adherence of disclosed data to _Offer_.

_Disclosee_ may now engage in permissioned use and carries liability
as a deterrent against unpermissioned use.

6. Field Ordering

The ordering of the top-level fields when present in an ACDC MUST be
as follows, v, d, u, i, ri, s, a, e, r.

7. Compact ACDC

The top-level section field values of a compact ACDC are the SAIDs of
each uncompacted top-level section. The section field labels are s,
a, e, and r.

7.1. Compact Public ACDC

A fully compact public ACDC is shown below.

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7.2. Compact Private ACDC

A fully compact private ACDC is shown below.

{
"v": "ACDC10JSON00011c_",
"d": "EBdXt3gIXOf2BBWNHdSXCJnFJL5OuQPyM5K0neuniccM",
"u": "0ANghkDaG7OY1wjaDAE0qHcg",
"i": "did:keri:EmkPreYpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPM",
"ri": "did:keri:EymRy7xMwsxUelUauaXtMxTfPAMPAI6FkekwlOjkggt",
"s": "E46jrVPTzlSkUPqGGeIZ8a8FWS7a6s4reAXRZOkogZ2A",
"a": "EgveY4-9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PY",
"e": "ERH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZIl3MOA",
"r": "Ee71iheqcywJcnjtJtQIYPvAu6DZIl3MORH3dCdoFOLB"
}

7.2.1. Compact Private ACDC Schema

The schema for the compact private ACDC example above is provided
below.

{
"$id": "EBdXt3gIXOf2BBWNHdSXCJnFJL5OuQPyM5K0neuniccM",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"title": "Compact Private ACDC",
"description": "Example JSON Schema for a Compact Private ACDC.",
"credentialType": "CompactPrivateACDCExample",
"type": "object",
"required":
[
"v",
"d",
"u",
"i",
"ri",
"s",
"a",

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"e",
"r"
],
"properties":
{
"v":
{
"description": "ACDC version string",
"type": "string"
},
"d":
{
"description": "ACDC SAID",
"type": "string"
},
"u":
{
"description": "ACDC UUID",
"type": "string"
},
"i":
{
"description": "Issuer AID",
"type": "string"
},
"ri":
{
"description": "credential status registry ID",
"type": "string"
},
"s": {
"description": "schema SAID",
"type": "string"
},
"a": {
"description": "attribute SAID",
"type": "string"
},
"e": {
"description": "edge SAID",
"type": "string"
},
"r": {
"description": "rule SAID",
"type": "string"
}
},
"additionalProperties": false

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}

8. Attribute Section

The attribute section in the examples above has been compacted into
its SAID. The schema of the compacted attribute section is as
follows,

{
"a":
{
"description": "attribute section SAID",
"type": "string"
}
}

Two variants of an ACDC, namely, namely, *_private (public)
attribute_* are defined respectively by the presence (absence) of a
UUID, u, field in the uncompacted attribute section block.

Two other variants of an ACDC, namely, *_targeted (untargeted)_* are
defined respectively by the presence (absence) of an issuee, i, field
in the uncompacted attribute section block.

8.1. Public-Attribute ACDC

Suppose that the un-compacted value of the attribute section as
denoted by the attribute section, a, field is as follows,

{
"a":
{
"d": "EgveY4-9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PY",
"i": "did:keri:EpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPmkPreYA",
"score": 96,
"name": "Jane Doe"
}
}

The SAID, d, field at the top level of the uncompacted attribute
block is the same SAID used as the compacted value of the attribute
section, a, field.

Given the absence of a u field at the top level of the attributes
block, then knowledge of both SAID, d, field at the top level of an
attributes block and the schema of the attributes block may enable
the discovery of the remaining contents of the attributes block via a
rainbow table attack [RB][DRB]. Therefore the SAID, d, field of the

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attributes block, although, a cryptographic digest, does not securely
blind the contents of the attributes block given knowledge of the
schema. It only provides compactness, not privacy. Moreover, any
cryptographic commitment to that SAID, d, field provides a fixed
point of correlation potentially to the attribute block field values
themselves in spite of non-disclosure of those field values via a
compact ACDC. Thus an ACDC without a UUID, u, field in its
attributes block must be considered a *_public-attribute_* ACDC even
when expressed in compact form.

8.2. Public Uncompacted Attribute Section Schema

The subschema for the public uncompacted attribute section is shown
below,

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{
"a":
{
"description": "attribute section",
"type": "object",
"required":
[
"d",
"i",
"score",
"name"
],
"properties":
{
"d":
{
"description": "attribute SAID",
"type": "string"
},
"i":
{
"description": "Issuee AID",
"type": "string"
},
"score":
{
"description": "test score",
"type": "integer"
},
"name":
{
"description": "test taker full name",
"type": "string"
}
},
"additionalProperties": false
}
}

8.3. Composed Schema for both Public Compact and Uncompacted Attribute
Section Variants

Through the use of the JSON Schema oneOf composition operator the
following composed schema will validate against both the compact and
un-compacted value of the attribute section field.

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{
"a":
{
"description": "attribute section",
"oneOf":
[
{
"description": "attribute SAID",
"type": "string"
},
{
"description": "uncompacted attribute section",
"type": "object",
"required":
[
"d",
"i",
"score",
"name"
],
"properties":
{
"d":
{
"description": "attribute SAID",
"type": "string"
},
"i":
{
"description": "Issuee AID",
"type": "string"
},
"score":
{
"description": "test score",
"type": "integer"
},
"name":
{
"description": "test taker full name",
"type": "string"
}
},
"additionalProperties": false
}
]
}
}

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8.4. Private-Attribute ACDC

Consider the following form of an uncompacted private-attribute
block,

{
"a":
{
"d": "EgveY4-9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PY",
"u": "0AwjaDAE0qHcgNghkDaG7OY1",
"i": "did:keri:EpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPmkPreYA",
"score": 96,
"name": "Jane Doe"
}
}

Given the presence of a top-level UUID, u, field of the attribute
block whose value has sufficient cryptographic entropy, then the top-
level SAID, d, field of the attribute block provides a secure
cryptographic digest of the contents of the attribute block [Hash].
An adversary when given both the schema of the attribute block and
its SAID, d, field, is not able to discover the remaining contents of
the attribute block in a computationally feasible manner such as a
rainbow table attack [RB][DRB]. Therefore the attribute block's
UUID, u, field in a compact ACDC enables its attribute block's SAID,
d, field to securely blind the contents of the attribute block
notwithstanding knowledge of the attribute block's schema and SAID, d
field. Moreover, a cryptographic commitment to that attribute
block's, SAID, d, field does not provide a fixed point of correlation
to the attribute field values themselves unless and until there has
been a disclosure of those field values.

To elaborate, when an ACDC includes a sufficiently high entropy UUID,
u, field at the top level of its attributes block then the ACDC may
be considered a *_private-attributes_* ACDC when expressed in compact
form, that is, the attribute block is represented by its SAID, d,
field and the value of its top-level attribute section, a, field is
the value of the nested SAID, d, field from the uncompacted version
of the attribute block. A verifiable commitment may be made to the
compact form of the ACDC without leaking details of the attributes.
Later disclosure of the uncompacted attribute block may be verified
against its SAID, d, field that was provided in the compact form as
the value of the top-level attribute section, a, field.

Because the _Issuee_ AID is nested in the attribute block as that
block's top-level, issuee, i, field, a presentation exchange
(disclosure) could be initiated on behalf of a different AID that has
not yet been correlated to the _Issuee_ AID and then only correlated

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to the Issuee AID after the _Disclosee_ has agreed to the chain-link
confidentiality provisions in the rules section of the private-
attributes ACDC [CLC].

8.4.1. Composed Schema for Both Compact and Uncompacted Private-
Attribute ACDC

Through the use of the JSON Schema oneOf composition operator, the
following composed schema will validate against both the compact and
un-compacted value of the private attribute section, a, field.

{
"a":
{
"description": "attribute section",
"oneOf":
[
{
"description": "attribute SAID",
"type": "string"
},
{
"description": "uncompacted attribute section",
"type": "object",
"required":
[
"d",
"u",
"i",
"score",
"name"
],
"properties":
{
"d":
{
"description": "attribute SAID",
"type": "string"
},
"u":
{
"description": "attribute UUID",
"type": "string"
},
"i":
{
"description": "Issuee AID",
"type": "string"

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},
"score":
{
"description": "test score",
"type": "integer"
},
"name":
{
"description": "test taker full name",
"type": "string"
}
},
"additionalProperties": false
}
]
}
}

As described above in the Schema section of this specification, the
oneOf sub-schema composition operator validates against either the
compact SAID of a block or the full block. A validator can use a
composed schema that has been committed to by the Issuer to securely
confirm schema compliance both before and after detailed disclosure
by using the fully composed base schema pre-disclosure and a specific
decomposed variant post-disclosure. Decomposing the schema to remove
the optional compact variant (i.e. removing the oneOf compact option)
enables a validator to ensure complaint full disclosure.

8.5. Untargeted ACDC

Consider the case where the issuee, i, field is absent at the top
level of the attribute block as shown below,

{
"a":
{
"d": "EgveY4-9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PY",
"temp": 45,
"lat": "N40.3433",
"lon": "W111.7208"
}
}

This ACDC has an _Issuer_ but no _Issuee_. Therefore, there is no
provably controllable _Target_ AID. This may be thought of as an
undirected verifiable attestation or observation of the data in the
attributes block by the _Issuer_. One could say that the attestation
is addressed to "whom it may concern". It is therefore an

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*_untargeted_* ACDC, or equivalently an _unissueed_ ACDC. An
_untargeted_ ACDC enables verifiable authorship by the Issuer of the
data in the attributes block but there is no specified counter-party
and no verifiable mechanism for delegation of authority.
Consequently, the rule section may only provide contractual
obligations of implied counter-parties.

This form of an ACDC provides a container for authentic data only
(not authentic data as authorization). But authentic data is still a
very important use case. To clarify, an untargeted ACDC enables
verifiable authorship of data. An observer such as a sensor that
controls an AID may make verifiable non-repudiable measurements and
publish them as ACDCs. These may be chained together to provide
provenance for or a chain-of-custody of any data. These ACDCs could
be used to provide a verifiable data supply chain for any compliance-
regulated application. This provides a way to protect participants
in a supply chain from imposters. Such data supply chains are also
useful as a verifiable digital twin of a physical supply chain
[Twin].

A hybrid chain of one or more targeted ACDCs ending in a chain of one
or more untargeted ACDCs enables delegated authorized attestations at
the tail of that chain. This may be very useful in many regulated
supply chain applications such as verifiable authorized authentic
datasheets for a given pharmaceutical.

8.6. Targeted ACDC

When present at the top level of the attribute section, the issuee,
i, field value provides the AID of the _Issuee_ of the ACDC. This
_Issuee_ AID is a provably controllable identifier that serves as the
_Target_ AID. This makes the ACDC a *_targeted_* ACDC or
equivalently an _issueed_ ACDC. Targeted ACDCs may be used for many
different purposes such as an authorization or a delegation directed
at the _Issuee_ AID, i.e. the _Target_. In other words, a _targeted
ACDC_ provides a container for authentic data that may also be used
as some form of authorization such as a credential that is verifiably
bound to the _Issuee_ as targeted by the _Issuer_. Furthermore, by
virtue of the targeted _Issuee's_ provable control over its AID, the
_targeted ACDC_ may be verifiably presented (disclosed) by the
controller of the _Issuee_ AID.

For example, the definition of the term *_credential_* is _evidence
of authority, status, rights, entitlement to privileges, or the
like_. To elaborate, the presence of an attribute section top-level
issuee, i, field enables the ACDC to be used as a verifiable
credential given by the _Issuer_ to the _Issuee_.

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One reason the issuee, i, field is nested into the attribute section,
a, block is to enable the _Issuee_ AID to be private or partially or
selectively disclosable. The _Issuee_ may also be called the
_Holder_ or _Subject_ of the ACDC. But here we use the more
semantically precise albeit less common terms of _Issuer_ and
_Issuee_. The ACDC is issued from or by an _Issuer_ and is issued to
or for an _Issuee_. This precise terminology does not bias or color
the role (function) that an _Issuee_ plays in the use of an ACDC.
What the presence of _Issuee_ AID does provide is a mechanism for
control of the subsequent use of the ACDC once it has been issued.
To elaborate, because the issuee, i, field value is an AID, by
definition, there is a provable controller of that AID. Therefore
that _Issuee_ controller may make non-repudiable commitments via
digital signatures on behalf of its AID. Therefore subsequent use of
the ACDC by the _Issuee_ may be securely attributed to the _Issuee_.

Importantly the presence of an issuee, i, field enables the
associated _Issuee_ to make authoritative verifiable presentations or
disclosures of the ACDC. A designated _Issuee_also better enables
the initiation of presentation exchanges of the ACDC between that
_Issuee_ as _Discloser_ and a _Disclosee_ (verifier).

In addition, because the _Issuee_ is a specified counter-party the
_Issuer_ may engage in a contract with the _Issuee_ that the _Issuee_
agrees to by virtue of its non-repudiable signature on an offer of
the ACDC prior to its issuance. This agreement may be a pre-
condition to the issuance and thereby impose liability waivers or
other terms of use on that _Issuee_.

Likewise, the presence of an issuee, i, field, enables the _Issuer_
to use the ACDC as a contractual vehicle for conveying an
authorization to the _Issuee_. This enables verifiable delegation
chains of authority because the _Issuee_ in one ACDC may become the
_Issuer_ in some other ACDC. Thereby an _Issuer_ may delegate
authority to an _Issuee_ who may then become a verifiably authorized
_Issuer_ that then delegates that authority (or an attenuation of
that authority) to some other verifiably authorized _Issuee_ and so
forth.

9. Edge Section

In the compact ACDC examples above, the edge section has been
compacted into merely the SAID of that section. Suppose that the un-
compacted value of the edge section denoted by the top-level edge, e,
field is as follows,

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{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLx,UdY",
"boss":
{
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA"
}
}
}

The edge section's top-level SAID, d, field is the SAID of the edge
block and is the same SAID used as the compacted value of the ACDC's
top-level edge, e, field. Each edge in the edge section gets its own
field with its own local label. The value of the field may be a sub-
block or in the simplest case a string. In the example above, the
edge label is "boss". Note that each edge does NOT include a type
field. The type of each edge is provided by the schema vis-a-vis the
label of that edge. This is in accordance with the design principle
of ACDCs that may be succinctly expressed as "type-is-schema". This
approach varies somewhat from many property graphs which often do not
have a schema [PGM][Dots][KG]. Because ACDCs have a schema for other
reasons, however, they leverage that schema to provide edge types
with a cleaner separation of concerns. Notwithstanding, this
separation, an edge sub-block may include a constraint on the type of
the ACDC to which that edge points by including the SAID of the
schema of the pointed-to ACDC as a property of that edge.

9.1. Edge Sub-block Reserved Fields

A main distinguishing feature of a _property graph_ (PG) is that both
nodes and edges may have a set of properties [PGM][Dots][KG]. These
might include modifiers that influence how the connected node is to
be combined or place a constraint on the allowed type(s) of connected
nodes.

There several reserved field labels for edge sub-blocks. These are
detailed in the table below. Each edge sub-block may have other non-
reserved field labels as needed for a particular edge type.

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Table 3

The node, n, field is required. The SAID, d, UUID, u, schema, s,
operator, o, and weight, w, fields are optional. To clarify, each
edge sub-block MUST have a node, n, field and MAY have any
combination of SAID, d, UUID, u, schema, s, operator, o, or weight,
w, fields.

9.1.1. SAID Field

When present, the SAID, d, field MUST appear as the first field in
the edge sub-block. When present,the value of the SAID, d field MUST
be the SAID of its enclosing edge sub-block.

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9.1.2. UUID Field

A UUID, u, field MUST not appear unless there is also a SAID, d
field. When present, the UUID, u, field must appear immediately
after as the SAID, d, field in the edge sub-block. When present, the
value of the UUID, u is a pseudorandom string with approximately 128
bits of cryptographic entropy. The UUID, u, field acts as a salty
nonce to hide the values of the edge sub-block in spite of knowledge
of the edge sub-blocks SAID, d, field and its, the edge's, actual
near schema (not its far node schema field).

9.1.3. Node Field

When the edge sub-block does NOT include a SAID, d, field then the
node, n, field MUST appear as the first field in the edge sub-block,
i.e. it follows the SAID, d, field which is first. When the edge
sub-block does include a SAID, d, field then the node, n, field MUST
appear as the second field in the edge sub-block.

The value of the required node, n, field is the SAID of the ACDC to
which the edge connects i.e. the node, n, field indicated,
designates, references, or "points to" another ACDC. The edge is
directed _from_ the _near_ node that is the ACDC in which the edge
sub-block resides and is directed _to_ the _far_ node that is the
ACDC indicated by the node, n, field of that edge sub-block. In
order for the edge (chain) to be valid, the ACDC validator MUST
confirm that the SAID of the provided _far_ ACDC matches the node, n,
field value given in the edge sub-block in _near_ ACDC and MUST
confirm that the provided _far_ ACDC satisfies its own schema.

9.1.4. Schema Field

When present, the schema, s field must appear immediately following
the node n, field in the edge sub-block. When present, the value of
the schema, s field MUST be the SAID of the top-level schema, s,
field of the ACDC indicated by the edge's far node, n, field. When
the schema, s, field is present in an edge sub-block, in order for
the edge (chain) to be valid, the ACDC validator, after validating
that the provided _far_ ACDC indicated by the node, n, field
satisfies its (the far ACDC's) own schema, MUST also confirm that the
value of the edge's schema, s, field matches the SAID of the far
ACDC's schema as indicated by its top-level schema, s, field.

The following example adds both SAID, d, and schema, s, fields (edge
properties) to the edge sub-block.

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{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"boss":
{
"d": "E2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NHwY1lkFrn9y",
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"s": "ELIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdYerzw"
}
}
}

9.1.5. Operator Field

When present, the operator, o field must appear immediately following
all of the SAID, d, node, n, or schema, s, fields in the edge sub-
block. The function of the operator field is explained in a later
section.

9.1.6. Weight Field

When present, the weight, w field must appear immediately following
all of the SAID, d, node, n, schema, s, or operator, o, fields in the
edge sub-block. The function of the weight field is explained in a
later section.

9.2. Globally Distributed Secure Graph Fragments

Abstractly, an ACDC with one or more edges may be a fragment of a
distributed property graph. However, the local label does not enable
the direct unique global resolution of a given edge including its
properties other than a trivial edge with only one property, its
node, n field. To enable an edge with additional properties to be
globally uniquely resolvable, that edge's block MUST have a SAID, d,
field. Because a SAID is a cryptographic digest it will universally
and uniquely identify an edge with a given set of properties [Hash].
This allows ACDCs to be used as secure fragments of a globally
distributed property graph (PG). This enables a property graph to
serve as a global knowledge graph in a secure manner that crosses
trust domains [PGM][Dots][KG]. This is shown below.

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{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"boss":
{
"d": "E9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NHwY1lkFrn",
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"w": "high"
}
}
}

9.3. Compact Edge

Given that an individual edge's property block includes a SAID, d,
field then a compact representation of the edge's property block is
provided by replacing it with its SAID. This may be useful for
complex edges with many properties. This is called a *_compact
edge_*. This is shown as follows,

{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"boss": "E9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NHwY1lkFrn"
}
}

9.4. Private Edge

Each edge's properties may be blinded by its SAID, d, field (i.e. be
private) if its properties block includes a UUID, u field. As with
UUID, u, fields used elsewhere in ACDC, if the UUID, u, field value
has sufficient entropy then the values of the properties of its
enclosing block are not discoverable in a computationally feasible
manner merely given the schema for the edge block and its SAID, d
field. This is called a *_private edge_*. When a private edge is
provided in compact form then the edge detail is hidden and is
partially disclosable. An uncompacted private edge is shown below.

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{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"boss":
{
"d": "E9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NHwY1lkFrn",
"u": "0AG7OY1wjaDAE0qHcgNghkDa",
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"w": "high"
}
}
}

When an edge points to a _private_ ACDC, a _Discloser_ may choose to
use a metadata version of that private ACDC when presenting the node,
n, field of that edge prior to acceptance of the terms of disclosure.
The _Disclosee_ can verify the metadata of the private node without
the _Discloser_ exposing the actual node contents via the actual node
SAID or other attributes.

Private ACDCs (nodes) and private edges may be used in combination to
prevent an un-permissioned correlation of the distributed property
graph.

9.5. Simple Compact Edge

When an edge sub-block has only one field that is its node, n, field
then the edge block may use an alternate simplified compact form
where the labeled edge field value is the value of its node, n,
field. The schema for that particular edge label, in this case,
"boss", will indicate that the edge value is a node SAID and not the
edge sub-block SAID as would be the case for the normal compact form
shown above. This alternate compact form is shown below.

{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"boss": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA"
}
}

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9.6. Operations on Edges and Edge-Groups

When the top-level edge section, e, field includes more than one edge
there is a need or opportunity to define the logic for evaluating
those edges with respect to validating the ACDC itself with respect
to the validity of the other ACDCs it is connected two. More than
one edge creates a provenance tree not simply a provenance chain.
The obvious default for a chain is that all links in the chain must
be valid in order for the chain itself to be valid, or more precisely
for the tail of the chain to be valid. If any links between the head
and the tail are broken (invalid) then the tail is not valid. This
default logic may not be so useful in all cases when a given ACDC is
the tail of multiple parallel chains (i.e. a branching node in a tree
of chains). Therefore provided herein is the syntax for exactly
specifying the operations to perform on each edge and groups of edges
in its edge section.

9.6.1. Label Types

There are three types of labels in edge sub-blocks:

* Reserved Field Labels (Metadata). d for SAID of block u for UUID
(salty nonce) n for node SAID (far ACDC) s for schema SAID ( far
ACDC) o for operator w for weight

* Edge Field Map Labels (Single Edges) any value except reserved
values above

* Edge-Group Field Map Labels (Aggregates of Edges) any value except
reserved values above

9.6.2. Block Types

There are two types of field-maps or blocks that may appear as values
of fields within an edge section, e, field either at the top level or
nested:

* Edge-Group. An _*edge-group*_ MUST NOT have a node, n, metadata
field. Its non-metadata field values may include other (sub)
edge-group blocks, edge blocks or other properties.

* Edge. An _*edge*_ MUST have a node, n, metadata field. Its non-
metadata field values MUST NOT include edge-group blocks or other
edge blocks but may include other types of properties. From a
graph perspective, _edge_ blocks terminate at their node, n, field
and are not themselves nestable. An _edge_ block is a leaf with
respect to any nested _edge-group_ blocks in which the edge
appears. It is therefore also a leaf with respect to its

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enclosing top-level edge section, e, field. The ACDC node that an
edge points to may have its own edge-groups or edges in that
node's own top-level edge section.

The top-level edge section, e, field value is always an _edge-group_
block.

With respect to the granularity of a property graph consisting of
ACDCs as nodes, nested edge-groups within a given top-level edge
field, e, field of a given ACDC constitute a sub-graph whose nodes
are edge-groups not ACDCs. One of the attractive features of
property graphs (PGs) is their support for different edge and node
types which enables nested sub-graphs such as is being employed here
to support the expression of complex logical or aggregative
operations on groups of edges (as subnodes) within the top-level edge
section, e, field of an ACDC (as supernode).

9.6.3. Operator, o, Field

The meaning of the operator, o, metadata field label depends on which
type of block it appears in.

* When appearing in an edge-group block then the operator, o, field
value is an aggregating (m-ary) operator, such as, OR, AND, AVG,
NAND, NOR etc. Its operator applies to all the edges or edge-
groups that appear in that edge-group block.

* When appearing in an edge block then the operator, o, field value
is a unary operator like NOT. When more than one unary operator
applies to a given edge then the value of the operator, o, field
is a list of those unary operators.

9.6.4. Weight, w, field.

Weighted directed edges represent degrees of confidence or
likelihood. PGs with weighted directed edges are commonly used for
machine learning or reasoning under uncertainty. The weight, w field
provides a reserved label for the primary weight. To elaborate, many
aggregating operators used for automated reasoning such as the
weighted average, WAVG, operator or ranking aggregation operators,
depend on each edge having a weight. To simplify the semantics for
such operators, the weight, w, field is the reserved field label for
weighting. Other fields with other labels could provide other types
of weights but having a default label, namely w, simplifies the
default definitions of weighted operators.

The following example adds a weight property to the edge sub-block as
indicated by the weight, w, field.

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{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"boss":
{
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"w": "high"
}
}
}

9.6.5. M-ary Operators

There are two basic m-ary operators defined for ACDCs. These are,

Table 4

9.6.6. Special Unary Operators

There are three special unary operators defined for ACDCs. These
are,

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Table 5

Many ACDC chains use targeted ACDCs (i.e. have Issuees). A chain of
Issuer-To-Issuee-To-Issuer targeted ACDCs in which each Issuee
becomes the Issuer of the next ACDC in the chain can be used to
provide a chain-of-authority. A common use case of a chain-of-
authority is a delegation chain for authorization.

The I2I unary operator when present means that the Issuer AID of the
current ACDC in which the edge resides MUST be the Issuee AID of the
node that the edge points to. This also means therefore that the
ACDC node pointed to by the edge must also be a targeted ACDC. This
is the default value when none of I2I, NI2I, or DI2I is present.

The NI2I unary operator when present removes or nullifies any
requirement expressed by the dual I2I operator described above. In
other words, any requirement that the Issuer AID of the current ACDC
in which the edge resides MUST be the Issuee AID, if any, of the node
the edge points to is relaxed (not applicable). To clarify, when
operative (present), the NI2I operator means that both an untargeted
ACDC or targeted ACDC as the node pointed to by the edge may still be
valid even when untargeted or if targeted even when the Issuer of the
ACDC in which the edge appears is not the Issuee AID, of that node
the edge points to.

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The DI2I unary operator when present expands the class of allowed
Issuer AIDs of the node the edge resides in to include not only the
Issuee AID but also any delegated AIDS of the Issuee of the node the
edge points to. This also means therefore that the ACDC node pointed
to by the edge must also be a targeted ACDC.

If more than one of the I2I, NI2I, or DI2I operators appear in an
operator, o, field list then the last one appearing in the list is
the operative one.

9.6.7. Defaults for missing operators

When the operator, o, field is missing in an edge-group block. The
default value for the operator, o, field is AND.

When the operator, o, field is missing or empty in an edge block, or
is present but does not include any of the I2I, NI2I or DI2I
operators then,

If the node pointed to by the edge is a targeted ACDC, i.e. has an
Issuee, by default it is assumed that the I2I operator is appended to
the operator, o, field's effective list value.

If the node pointed to by the edge block is a non-targeted ACDC i.e.,
does not have an Issuee, by default, it is assumed that the NI2I
operator is appended to the operator, o, field's effective list
value.

9.6.8. Examples

9.6.8.1. Defaults

{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLx,UdY",
"boss":
{
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"power": "high"
},
"baby":
{
"n": "EORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZAIl3A",
"power": "low"
}
}
}

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9.6.9. Explicit AND

{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLx,UdY",
"o": "AND",
"boss":
{
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"power": "high"
},
"baby":
{
"n": "EORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZAIl3A",
"o": "NOT",
"power": "low"
}
}
}

9.6.10. Unary I2I

9.6.11. Unary NI2I

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{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLx,UdY",
"o": "OR",
"boss":
{
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"o": "NI2I",
"power": "high"
},
"baby":
{
"n": "EORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZAIl3A",
"o": "I2I",
"power": "low"
}
}
}

9.6.12. Nested Edge-Group

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{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLx,UdY",
"o": "AND",
"boss":
{
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"o": ["NI2I", "NOT"],
"power": "high"
},
"baby":
{
"n": "EORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZAIl3A",
"o": "I2I",
"power": "low"
},
"food":
{
"o": "OR",
"power": "med",
"plum":
{
"n": "EQIYPvAu6DZAIl3AORH3dCdoFOLe71iheqcywJcnjtJt",
"o": "NI2I"
},
"pear":
{
"n": "EJtQIYPvAu6DZAIl3AORH3dCdoFOLe71iheqcywJcnjt",
"o": "NI2I"
}
}
}
}

9.6.13. vLEI ECR issued by QVI example

When an ECR vLEI is issued by the QVI it is not chained, Issuer-to-
Issuee, via the LE credential. A more accurate way of expressing the
chaining would be to use the AND operator to include both the LE and
QVI credentials as edges in the ECR and also to apply the unary NI2I
to the LE credential instead of only chaining the ECR to the LE and
not chaining to ECR to the QVI at all.

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In the following example: The top-level edge-block uses the default
of AND and the qvi edge uses the default of I2I because it points to
a targeted ACDC. The le edge, on the other hand, points to a
targeted ACDC. It uses the unary operator, NI2I in its operator, o,
field so that it will be accepted it even though its targeted Issuee
is not the Issuer of the current credential.

{
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLx,UdY",
"qvi":
{
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA"
},
"le":
{
"n": "EORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZAIl3A",
"o": "NI2I"
}
}
}

9.6.14. Commentary

This provides a simple but highly expressive syntax for applying
(m-ary) aggregating operators to nestable groups of edges and unary
operators to edges individually within those groups. This is a
general approach with high expressive power. It satisfies many
business logic requirements similar to that of SGL.

Certainly, an even more expressive syntax could be developed. The
proposed syntax, however, is relatively simple and compact. It has
intelligent defaults and is sufficiently general in scope to satisfy
all the currently contemplated use cases.

The intelligent defaults for the operator, o, field, including the
default application of the I2I or NI2I unary operator, means that in
most current use cases, the operator, o, field, does not even need to
be present.

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9.7. Node Discovery

In general, the discovery of the details of an ACDC referenced as a
node, n field value, in an edge sub-block begins with the node SAID
or the SAID of the associated edge sub-block. Because a SAID is a
cryptographic digest with high collision resistance it provides a
universally unique identifier to the referenced ACDC as a node. The
Discovery of a service endpoint URL that provides database access to
a copy of the ACDC may be bootstrapped via an OOBI (Out-Of-Band-
Introduction) that links the service endpoint URL to the SAID of the
ACDC [OOBI_ID]. Alternatively, the _Issuer_ may provide as an
attachment at the time of issuance a copy of the referenced ACDC. In
either case, after a successful exchange, the _Issuee_ or recipient
of any ACDC will have either a copy or a means of obtaining a copy of
any referenced ACDCs as nodes in the edge sections of all ACDCs so
chained. That Issuee or recipient will then have everything it needs
to make a successful disclosure to some other _Disclosee_. This is
the essence of _percolated_ discovery.

10. Rule Section

In the compact ACDC examples above, the rule section has been
compacted into merely the SAID of that section. Suppose that the un-
compacted value of the rule section denoted by the top-level rule, r,
field is as follows,

{
"r":
{
"d": "EwY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NA",
"warrantyDisclaimer":
{
"l": "Issuer provides this credential on an \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE"
},
"liabilityDisclaimer":
{
"l": "In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the Issuer be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this credential. "
}
}
}

The purpose of the rule section is to provide a Ricardian Contract
[RC]. The important features of a Ricardian contract are that it be
both human and machine-readable and referenceable by a cryptographic
digest. A JSON encoded document or block such as the rule section
block is a practical example of both a human and machine-readable
document. The rule section's top-level SAID, d, field provides the
digest. This provision supports the bow-tie model of Ricardian

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Contracts [RC]. Ricardian legal contracts may be hierarchically
structured into sections and subsections with named or numbered
clauses in each section. The labels on the clauses may follow such a
hierarchical structure using nested maps or blocks. These provisions
enable the rule section to satisfy the features of a Ricardian
contract.

To elaborate, the rule section's top-level SAID, d, field is the SAID
of that block and is the same SAID used as the compacted value of the
rule section, r, field that appears at the top level of the ACDC.
Each clause in the rule section gets its own field. Each clause also
has its own local label.

The legal, l, field in each block provides the associated legal
language.

Note there are no type fields in the rule section. The type of a
contract and the type of each clause is provided by the schema vis-
a-vis the label of that clause. This follows the ACDC design
principle that may be succinctly expressed as "type-is-schema".

Each rule section clause may also have its own clause SAID, d, field.
Clause SAIDs enable reference to individual clauses, not merely the
whole contract as given by the rule section's top-level SAID, d,
field.

An example rule section with clause SAIDs is provided below.

{
"r":
{
"d": "EwY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NA",
"warrantyDisclaimer":
{
"d": "EXgOcLxUdYerzwLIr9Bf7V_NAwY1lkFrn9y2PgveY4-9",
"l": "Issuer provides this credential on an \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE"
},
"liabilityDisclaimer":
{
"d": "EY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NAw",
"l": "In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the Issuer be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this credential. "
}
}
}

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10.1. Compact Clauses

The use of clause SAIDS enables a compact form of a set of clauses
where each clause value is the SAID of the corresponding clause. For
example,

{
"r":
{
"d": "EwY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NA",
"warrantyDisclaimer": "EXgOcLxUdYerzwLIr9Bf7V_NAwY1lkFrn9y2PgveY4-9",
"liabilityDisclaimer": "EY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NAw"
}
}

10.2. Private Clause

The disclosure of some clauses may be pre-conditioned on acceptance
of chain-link confidentiality. In this case, some clauses may
benefit from partial disclosure. Thus clauses may be blinded by
their SAID, d, field when the clause block includes a sufficiently
high entropy UUID, u, field. The use of a clause UUID enables the
compact form of a clause to NOT be discoverable merely from the
schema for the clause and its SAID via rainbow table attack
[RB][DRB]. Therefore such a clause may be partially disclosable.
These are called *_private clauses_*. A private clause example is
shown below.

{
"r":
{
"d": "EwY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NA",
"warrantyDisclaimer":
{
"d": "EXgOcLxUdYerzwLIr9Bf7V_NAwY1lkFrn9y2PgveY4-9",
"u": "0AG7OY1wjaDAE0qHcgNghkDa",
"l": "Issuer provides this credential on an \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE"
},
"liabilityDisclaimer":
{
"d": "EY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NAw",
"u": "0AHcgNghkDaG7OY1wjaDAE0q",
"l": "In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the Issuer be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this credential. "
}
}
}

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10.3. Simple Compact Clause

An alternate simplified compact form uses the value of the legal, l,
field as the value of the clause field label. The schema for a
specific clause label will indicate that the field value, for a given
clause label is the legal language itself and not the clause block's
SAID, d, field as is the normal compact form shown above. This
alternate simple compact form is shown below. In this form
individual clauses are not compactifiable and are fully self-
contained.

{
"r":
{
"d": "EwY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NA",
"warrantyDisclaimer": "Issuer provides this credential on an \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE",
"liabilityDisclaimer": "In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the Issuer be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this credential. "
}
}

10.4. Clause Discovery

In compact form, the discovery of either the rule section as a whole
or a given clause begins with the provided SAID. Because the SAID,
d, field of any block is a cryptographic digest with high collision
resistance it provides a universally unique identifier to the
referenced block details (whole rule section or individual clause).
The discovery of a service endpoint URL that provides database access
to a copy of the rule section or to any of its clauses may be
bootstrapped via an OOBI (Out-Of-Band-Introduction) that links the
service endpoint URL to the SAID of the respective block [OOBI_ID].
Alternatively, the issuer may provide as an attachment at issuance a
copy of the referenced contract associated with the whole rule
section or any clause. In either case, after a successful issuance
exchange, the Issuee or holder of any ACDC will have either a copy or
a means of obtaining a copy of any referenced contracts in whole or
in part of all ACDCs so issued. That Issuee or recipient will then
have everything it needs to subsequently make a successful
presentation or disclosure to a Disclosee. This is the essence of
percolated discovery.

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11. Disclosure-Specific (Bespoke) Issued ACDCs

The ACDC chaining enables disclosure-specific issuance of bespoke
ACDCs. A given Discloser of an ACDC issued by some Issuer may want
to augment the disclosure with additional contractual obligations or
additional information sourced by the Discloser where those
augmentations are specific to a given context such as a specific
Disclosee. Instead of complicating the presentation exchange to
accommodate such disclosure-specific augmentations, a given Disloser
issues its own bespoke ACDC that includes the other ACDC of the other
Issuer by reference via an edge in the bespoke ACDC. This means that
the normal validation logic and tooling for a chained ACDC can be
applied without complicating the presentation exchange logic.
Furthermore, attributes in other ACDCs pointed to by edges in the
bespoke ACDC may be addressed by attributes in the bespoke ACDC using
JSON Pointer or CESR-Proof SAD Path references that are relative to
the node SAID in the edge [RFC6901][Proof_ID].

For example, this approach enables the bespoke ACDC to identify
(name) the Disclosee directly as the Issuee of the bespoke ACDC.
This enables contractual legal language in the rule section of the
bespoke ACDC that reference the Issuee of that ACDC as a named party.
Signing the agreement to the offer of that bespoke ACDC consummates a
contract between named Issuer and named Issuee. This approach means
that custom or bespoke presentations do not need additional
complexity or extensions. Extensibility comes from reusing the
tooling for issuing ACDCs to issue a bespoke or disclosure-specific
ACDC. When the only purpose of the bespoke ACDC is to augment the
contractual obligations associated with the disclosure then the
attribute section, a, field value of the bespoke ACD may be empty or
it may include properties whose only purpose is to support the
bespoke contractual language.

Similarly, this approach effectively enables a type of _rich
presentation_ or combined disclosure where multiple ACDCs may be
referenced by edges in the bespoke ACDC that each contributes some
attribute(s) to the effective set of attributes referenced in the
bespoke ACDC. The bespoke ACDC enables the equivalent of a _rich
presentation_ without requiring any new tooling [Abuse].

11.1. Example Bespoke Issued ACDC

Consider the following disclosure-specific ACDC. The Issuer is the
Discloser, the Issuee is the Disclosee. The rule section includes a
context-specific (anti) assimilation clause that limits the use of
the information to a single one-time usage purpose, that is in this
case, admittance to a restaurant. The ACDC includes an edge that
references some other ACDC that may for example be a coupon or gift

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card. The attribute section includes the date and place of
admittance.

{
"v": "ACDC10JSON00011c_",
"d": "EBdXt3gIXOf2BBWNHdSXCJnFJL5OuQPyM5K0neuniccM",
"i": "did:keri:EmkPreYpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPM",
"s": "EGGeIZ8a8FWS7a646jrVPTzlSkUPqs4reAXRZOkogZ2A",
"a":
{
"d": "EgveY4-9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PY",
"i": "did:keri:EpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPmkPreYA",
"date": "2022-08-22T17:50:09.988921+00:00",
"place": "GoodFood Restaurant, 953 East Sheridan Ave, Cody WY 82414 USA"
},
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"other":
{
"d": "E9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NHwY1lkFrn",
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA"
}
},
"r":
{
"d": "EwY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NA",
"Assimilation":
{
"d": "EXgOcLxUdYerzwLIr9Bf7V_NAwY1lkFrn9y2PgveY4-9",
"l": "Issuee hereby explicitly and unambiguously agrees to NOT assimilate, aggregate, correlate, or otherwise use in combination with other information available to the Issuee, the information, in whole or in part, referenced by this container or any containers recursively referenced by the edge section, for any purpose other than that expressly permitted by the Purpose clause."
},
"Purpose":
{
"d": "EY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NAw",
"l": "One-time admittance of Issuer by Issuee to eat at place on date as specified in attribute section."
}
}
}

12. Informative Examples

12.1. Public ACDC with Compact and Uncompated Variants

### Public Compact Variant

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12.1.1. Public Uncompacted Variant

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{
"v": "ACDC10JSON00011c_",
"d": "EBdXt3gIXOf2BBWNHdSXCJnFJL5OuQPyM5K0neuniccM",
"i": "did:keri:EmkPreYpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPM",
"ri": "did:keri:EymRy7xMwsxUelUauaXtMxTfPAMPAI6FkekwlOjkggt",
"s": "E46jrVPTzlSkUPqGGeIZ8a8FWS7a6s4reAXRZOkogZ2A",
"a":
{
"d": "EgveY4-9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PY",
"i": "did:keri:EpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPmkPreYA",
"score": 96,
"name": "Jane Doe"
},
"e":
{
"d": "EerzwLIr9Bf7V_NHwY1lkFrn9y2PgveY4-9XgOcLxUdY",
"boss":
{
"d": "E9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NHwY1lkFrn",
"n": "EIl3MORH3dCdoFOLe71iheqcywJcnjtJtQIYPvAu6DZA",
"s": "EiheqcywJcnjtJtQIYPvAu6DZAIl3MORH3dCdoFOLe71",
"w": "high"
}
},
"r":
{
"d": "EwY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NA",
"warrantyDisclaimer":
{
"d": "EXgOcLxUdYerzwLIr9Bf7V_NAwY1lkFrn9y2PgveY4-9",
"l": "Issuer provides this credential on an \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE"
},
"liabilityDisclaimer":
{
"d": "EY1lkFrn9y2PgveY4-9XgOcLxUdYerzwLIr9Bf7V_NAw",
"l": "In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the Issuer be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this credential. "
}
}
}

12.1.2. Composed Schema that Supports both Public Compact and
Uncompacted Variants

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{
"$id": "E46jrVPTzlSkUPqGGeIZ8a8FWS7a6s4reAXRZOkogZ2A",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"title": "Public ACDC",
"description": "Example JSON Schema Public ACDC.",
"credentialType": "PublicACDCExample",
"type": "object",
"required":
[
"v",
"d",
"i",
"ri",
"s",
"a",
"e",
"r"
],
"properties":
{
"v":
{
"description": "ACDC version string",
"type": "string"
},
"d":
{
"description": "ACDC SAID",
"type": "string"
},
"i":
{
"description": "Issuer AID",
"type": "string"
},
"ri":
{
"description": "credential status registry ID",
"type": "string"
},
"s":
{
"description": "schema section",
"oneOf":
[
{
"description": "schema section SAID",
"type": "string"

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},
{
"description": "schema detail",
"type": "object"
}
]
},
"a":
{
"description": "attribute section",
"oneOf":
[
{
"description": "attribute section SAID",
"type": "string"
},
{
"description": "attribute detail",
"type": "object",
"required":
[
"d",
"i",
"score",
"name"
],
"properties":
{
"d":
{
"description": "attribute section SAID",
"type": "string"
},
"i":
{
"description": "Issuee AID",
"type": "string"
},
"score":
{
"description": "test score",
"type": "integer"
},
"name":
{
"description": "test taker full name",
"type": "string"
}

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},
"additionalProperties": false
}
]
},
"e":
{
"description": "edge section",
"oneOf":
[
{
"description": "edge section SAID",
"type": "string"
},
{
"description": "edge detail",
"type": "object",
"required":
[
"d",
"boss"
],
"properties":
{
"d":
{
"description": "edge section SAID",
"type": "string"
},
"boss":
{
"description": "boss edge",
"type": "object",
"required":
[
"d",
"n",
"s",
"w"
],
"properties":
{
"d":
{
"description": "edge SAID",
"type": "string"
},
"n":

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{
"description": "far node SAID",
"type": "string"
},
"s":
{
"description": "far node schema SAID",
"type": "string",
"const": "EiheqcywJcnjtJtQIYPvAu6DZAIl3MORH3dCdoFOLe71"
},
"w":
{
"description": "edge weight",
"type": "string"
}
},
"additionalProperties": false
}
},
"additionalProperties": false
}
]
},
"r":
{
"description": "rule section",
"oneOf":
[
{
"description": "rule section SAID",
"type": "string"
},
{
"description": "rule detail",
"type": "object",
"required":
[
"d",
"warrantyDisclaimer",
"liabilityDisclaimer"
],
"properties":
{
"d":
{
"description": "edge section SAID",
"type": "string"
},

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"warrantyDisclaimer":
{
"description": "warranty disclaimer clause",
"type": "object",
"required":
[
"d",
"l"
],
"properties":
{
"d":
{
"description": "clause SAID",
"type": "string"
},
"l":
{
"description": "legal language",
"type": "string"
}
},
"additionalProperties": false
},
"liabilityDisclaimer":
{
"description": "liability disclaimer clause",
"type": "object",
"required":
[
"d",
"l"
],
"properties":
{
"d":
{
"description": "clause SAID",
"type": "string"
},
"l":
{
"description": "legal language",
"type": "string"
}
},
"additionalProperties": false
}

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},
"additionalProperties": false
}
]
}
},
"additionalProperties": false
}

13. Selective Disclosure

As explained previously, the primary difference between _partial
disclosure_ and _selective disclosure_ is determined by the
correlatability with respect to its encompassing block after _full
disclosure_ of the detailed field value. A _partially disclosable_
field becomes correlatable to its encompassing block after its _full
disclosure_. Whereas a _selectively disclosable_ field may be
excluded from the _full disclosure_ of any other selectively
disclosable fields in its encompassing block. After selective
disclosure, the selectively disclosed fields are not correlatable to
the so-far undisclosed but selectively disclosable fields in the same
encompassing block. In this sense, _full disclosure_ means detailed
disclosure of the selectively disclosed attributes not detailed
disclosure of all selectively disclosable attributes.

Recall that _partial_ disclosure is an essential mechanism needed to
support chain-link confidentiality [CLC]. The chain-link
confidentiality exchange _offer_ requires _partial disclosure_, and
_full disclosure_ only happens after _acceptance_ of the _offer_.
_Selective_ disclosure, on the other hand, is an essential mechanism
needed to unbundle in a correlation minimizing way a single
commitment by an Issuer to a bundle of fields (i.e. a nested block or
array of fields). This allows separating a "stew" of "ingredients"
(attributes) into its constituent "ingredients" (attributes) without
correlating the constituents via the stew.

ACDCs, as a standard, benefit from a minimally sufficient approach to
selective disclosure that is simple enough to be universally
implementable and adoptable. This does not preclude support for
other more sophisticated but optional approaches. But the minimally
sufficient approach should be universal so that at least one
selective disclosure mechanism be made available in all ACDC
implementations. To clarify, not all instances of an ACDC must
employ the minimal selective disclosure mechanisms as described
herein but all ACDC implementations must support any instance of an
ACDC that employs the minimal selective disclosure mechanisms as
described above.

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13.1. Tiered Selective Disclosure Mechanisms

The ACDC chaining mechanism reduces the need for selective disclosure
in some applications. Many non-ACDC verifiable credentials provide
bundled precisely because there is no other way to associate the
attributes in the bundle. These bundled credentials could be
refactored into a graph of ACDCs. Each of which is separately
disclosable and verifiable thereby obviating the need for selective
disclosure.

Nonetheless, some applications require bundled attributes and
therefore may benefit from the independent selective disclosure of
bundled attributes. This is provided by *_selectively disclosable
attribute_* ACDCs.

The use of a revocation registry is an example of a type of bundling,
not of attributes in a credential, but uses of a credential in
different contexts. Unbundling the usage contexts may be beneficial.
This is provided by *_bulk-issued_* ACDCs.

Finally, in the case where the correlation of activity of an Issuee
across contexts even when the ACDC used in those contexts is not
correlatable may be addressed of a variant of bulk-issued ACDCs that
have *_unique issuee AIDs_* with an independent TEL registry per
issuee instance. This provides non-repudiable (recourse supporting)
disclosure while protecting from the malicious correlation between
second parties and other second and/or third-parties as to who
(Issuee) is involved in a presentation.

In any case, the set of selective disclosure mechanisms we call
tiered selective disclosure which allows a user or implementer to
better trade-off protection vs. complexity and performance. A tiered
selective disclosure me

13.2. Basic Selective Disclosure Mechanism

The basic selective disclosure mechanism shared by all is comprised
of a single aggregated blinded commitment to a list of blinded
commitments to undisclosed values. Membership of any blinded
commitment to a value in the list of aggregated blinded commitments
may be proven without leaking (disclosing) the unblinded value
belonging to any other blinded commitment in the list. This enables
provable selective disclosure of the unblinded values. When a non-
repudiable digital signature is created on the aggregated blinded
commitment then any disclosure of a given value belonging to a given
blinded commitment in the list is also non-repudiable. This approach
does not require any more complex cryptography than digests and
digital signatures. This satisfies the design ethos of minimally

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sufficient means. The primary drawback of this approach is
verbosity. It trades ease and simplicity and _adoptability_ of
implementation for size. Its verbosity may be mitigated by replacing
the list of blinded commitments with a Merkle tree of those
commitments where the Merkle tree root becomes the aggregated blinded
commitment.

Given sufficient cryptographic entropy of the blinding factors,
collision resistance of the digests, and unforgeability of the
digital signatures, either inclusion proof format (list or Merkle
tree digest) prevents a potential disclosee or adversary from
discovering in a computationally feasible way the values of any
undisclosed blinded value details from the combination of the schema
of those value details and either the aggregated blinded commitment
and/or the list of aggregated blinded commitments
[Hash][HCR][QCHC][Mrkl][TwoPI][MTSec]. A potential disclosee or
adversary would also need both the blinding factor and the actual
value details.

Selective disclosure in combination with partial disclosure for
chain-link confidentiality provides comprehensive correlation
minimization because a discloser may use a non-disclosing metadata
ACDC prior to acceptance by the disclosee of the terms of the chain-
link confidentiality expressed in the rule section [CLC]. Thus only
malicious disclosees who violate chain-link confidentiality may
correlate between independent disclosures of the value details of
distinct members in the list of aggregated blinded commitments.
Nonetheless, they are not able to discover any as-of-yet undisclosed
(unblinded) value details.

13.3. Selectively Disclosable Attribute ACDC

In a *_selectively disclosable attribute_* ACDC, the set of
attributes is provided as an array of blinded blocks. Each attribute
in the set has its own dedicated blinded block. Each block has its
own SAID, d, field and UUID, u, field in addition to its attribute
field or fields. When an attribute block has more than one attribute
field then the set of fields in that block are not independently
selectively disclosable but MUST be disclosed together as a set.
Notable is that the field labels of the selectively disclosable
attributes are also blinded because they only appear within the
blinded block. This prevents un-permissioned correlation via
contextualized variants of a field label that appear in a selectively
disclosable block. For example, localized or internationalized
variants where each variant's field label(s) each use a different
language or some other context correlatable information in the field
labels themselves.

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A selectively-disclosable attribute section appears at the top level
using the field label A. This is distinct from the field label a for
a non-selectively-disclosable attribute section. This makes clear
(unambiguous) the semantics of the attribute section's associated
schema. This also clearly reflects the fact that the value of a
compact variant of selectively-disclosable attribute section is an
"aggregate" not a SAID. As described previously, the top-level
selectively-disclosable attribute aggregate section, A, field value
is an aggregate of cryptographic commitments used to make a
commitment to a set (bundle) of selectively-disclosable attributes.
The derivation of its value depends on the type of selective
disclosure mechanism employed. For example, the aggregate value
could be the cryptographic digest of the concatenation of an ordered
set of cryptographic digests, a Merkle tree root digest of an ordered
set of cryptographic digests, or a cryptographic accumulator.

The _Issuee_ attribute block is absent from an uncompacted untargeted
selectively disclosable ACDC as follows:

{
"A":
[
{
"d": "ELIr9Bf7V_NHwY1lkgveY4-Frn9y2PY9XgOcLxUderzw",
"u": "0AG7OY1wjaDAE0qHcgNghkDa",
"score": 96
},
{
"d": "E9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PYgveY4-",
"u": "0AghkDaG7OY1wjaDAE0qHcgN",
"name": "Jane Doe"
}
]
}

The _Issuee_ attribute block is present in an uncompacted untargeted
selectively disclosable ACDC as follows:

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{
"A":
[
{
"d": "ErzwLIr9Bf7V_NHwY1lkFrn9y2PYgveY4-9XgOcLxUde",
"u": "0AqHcgNghkDaG7OY1wjaDAE0",
"i": "did:keri:EpZfFk66jpf3uFv7vklXKhzBrAqjsKAn2EDIPmkPreYA"
},
{
"d": "ELIr9Bf7V_NHwY1lkgveY4-Frn9y2PY9XgOcLxUderzw",
"u": "0AG7OY1wjaDAE0qHcgNghkDa",
"score": 96
},
{
"d": "E9XgOcLxUderzwLIr9Bf7V_NHwY1lkFrn9y2PYgveY4-",
"u": "0AghkDaG7OY1wjaDAE0qHcgN",
"name": "Jane Doe"
}
]
}

13.3.1. Blinded Attribute Array

Given that each attribute block's UUID, u, field has sufficient
cryptographic entropy, then each attribute block's SAID, d, field
provides a secure cryptographic digest of its contents that
effectively blinds the attribute value from discovery given only its
Schema and SAID. To clarify, the adversary despite being given both
the schema of the attribute block and its SAID, d, field, is not able
to discover the remaining contents of the attribute block in a
computationally feasible manner such as a rainbow table attack
[RB][DRB]. Therefore the UUID, u, field of each attribute block
enables the associated SAID, d, field to securely blind the block's
contents notwithstanding knowledge of the block's schema and that
SAID, d, field. Moreover, a cryptographic commitment to that SAID,
d, field does not provide a fixed point of correlation to the
associated attribute (SAD) field values themselves unless and until
there has been specific disclosure of those field values themselves.

Given a total of _N_ elements in the attributes array, let _a_i_
represent the SAID, d, field of the attribute at zero-based index
_i_. More precisely the set of attributes is expressed as the ordered
set,

_{a_i for all i in {0, ..., N-1}}_.

The ordered set of _a_i_ may be also expressed as a list, that is,

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_[a_0, a_1, ...., a_(N-1)]_.

13.3.2. Composed Schema for Selectively Disclosable Attribute Section

Because the selectively-disclosable attributes are provided by an
array (list), the uncompacted variant in the schema uses an array of
items and the anyOf composition operator to allow one or more of the
items to be disclosed without requiring all to be disclosed. Thus
both the oneOf and anyOf composition operators are used. The oneOf
is used to provide compact partial disclosure of the aggregate, _A_,
as the value of the top-level selectively-disclosable attribute
section, A, field in its compact variant and the nested anyOf
operator is used to enable selective disclosure in the uncompacted
selectively-disclosable variant.

{
"A":
{
"description": "selectively disclosable attribute aggregate section",
"oneOf":
[
{
"description": "attribute aggregate",
"type": "string"
},
{
"description": "selectively disclosable attribute details",
"type": "array",
"uniqueItems": true,
"items":
{
"anyOf":
[
{
"description": "issuer attribute",
"type": "object",
"required":
[
"d",
"u",
"i"
],
"properties":
{
"d":
{
"description": "attribute SAID",
"type": "string"

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},
"u":
{
"description": "attribute UUID",
"type": "string"
},
"i":
{
"description": "issuer SAID",
"type": "string"
}
},
"additionalProperties": false
},
{
"description": "score attribute",
"type": "object",
"required":
[
"d",
"u",
"score"
],
"properties":
{
"d":
{
"description": "attribute SAID",
"type": "string"
},
"u":
{
"description": "attribute UUID",
"type": "string"
},
"score":
{
"description": "score value",
"type": "integer"
}
},
"additionalProperties": false
},
{
"description": "name attribute",
"type": "object",
"required":
[

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"d",
"u",
"name"
],
"properties":
{
"d":
{
"description": "attribute SAID",
"type": "string"
},
"u":
{
"description": "attribute UUID",
"type": "string"
},
"name":
{
"description": "name value",
"type": "string"
}
},
"additionalProperties": false
}
]
}
}
],
"additionalProperties": false
}
}

13.3.3. Inclusion Proof via Aggregated List Digest

All the _a_i_ in the list are aggregated into a single aggregate
digest denoted _A_ by computing the digest of their ordered
concatenation. This is expressed as follows:

_A = H(C(a_i for all i in {0, ..., N-1}))_ where _H_ is the digest
(hash) operator and _C_ is the concatentation operator.

To be explicit, using the targeted example above, let _a_0_ denote
the SAID of the _Issuee_ attribute, _a_1_ denote the SAID of the
_score_ attribute, and _a_2_ denote the SAID of the _name_ attribute
then the aggregated digest _A_ is computed as follows:

_A = H(C(a_0, a_1, a_2))_.

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Equivalently using _+_ as the infix concatenation operator, we have,

_A = H(a_0 + a_1 + a_2)_

Given sufficient collision resistance of the digest operator, the
digest of an ordered concatenation is not subject to a birthday
attack on its concatenated elements [BDC][BDay][QCHC][HCR][Hash].

In compact form, the value of the selectively-disclosable top-level
attribute section, A, field is set to the aggregated value _A_. This
aggregate _A_ makes a blinded cryptographic commitment to the all the
ordered elements in the list,

_[a_0, a_1, ...., a_(N-1)]_.

Moreover because each _a_i_ element also makes a blinded commitment
to its block's (SAD) attribute value(s), disclosure of any given
_a_i_ element does not expose or disclose any discoverable
information detail about either its own or another block's attribute
value(s). Therefore one may safely disclose the full list of _a_i_
elements without exposing the blinded block attribute values.

Proof of inclusion in the list consists of checking the list for a
matching value. A computationally efficient way to do this is to
create a hash table or B-tree of the list and then check for
inclusion via lookup in the hash table or B-tree.

To protect against later forgery given a later compromise of the
signing keys of the Issuer, the issuer MUST anchor an issuance proof
digest seal to the ACDC in its KEL. This seal binds the signing key
state to the issuance. There are two cases. In the first case, an
issuance/revocation registry is used. In the second case, an
issuance/revocation registry is not used.

When the ACDC is registered using an issuance/revocation TEL
(Transaction Event Log) then the issuance proof seal digest is the
SAID of the issuance (inception) event in the ACDC's TEL entry. The
issuance event in the TEL includes the SAID of the ACDC. This binds
the ACDC to the issuance proof seal in the Issuer's KEL through the
TEL entry.

When the ACDC is not registered using an issuance/revocation TEL then
the issuance proof seal digest is the SAID of the ACDC itself.

In either case, this issuance proof seal makes a verifiable binding
between the issuance of the ACDC and the key state of the Issuer at
the time of issuance. Because aggregated value _A_ provided as the
attribute section, A, field, value is bound to the SAID of the ACDC

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which is also bound to the key state via the issuance proof seal, the
attribute details of each attribute block are also bound to the key
state.

The requirement of an anchored issuance proof seal means that the
forger Must first successfully publish in the KEL of the issuer an
inclusion proof digest seal bound to a forged ACDC. This makes any
forgery attempt detectable. To elaborate, the only way to
successfully publish such a seal is in a subsequent interaction event
in a KEL that has not yet changed its key state via a rotation event.
Whereas any KEL that has changed its key state via a rotation must be
forked before the rotation. This makes the forgery attempt either
both detectable and recoverable via rotation in any KEL that has not
yet changed its key state or detectable as duplicity in any KEL that
has changed its key state. In any event, the issuance proof seal
ensures detectability of any later attempt at forgery using
compromised keys.

Given that aggregate value _A_ appears as the compact value of the
top-level attribute section, A, field, the selective disclosure of
the attribute at index _j_ may be proven to the disclosee with four
items of information. These are:

* The actual detailed disclosed attribute block itself (at index
_j_) with all its fields.

* The list of all attribute block digests, _[a_0, a_1, ....,
a_(N-1)]_ that includes _a_j_.

* The ACDC in compact form with selectively-disclosable attribute
section, A, field value set to aggregate _A_.

* The signature(s), _s_, of the Issuee on the ACDC's top-level SAID,
d, field.

The actual detailed disclosed attribute block is only disclosed after
the disclosee has agreed to the terms of the rules section.
Therefore, in the event the potential disclosee declines to accept
the terms of disclosure, then a presentation of the compact version
of the ACDC and/or the list of attribute digests, _[a_0, a_1, ....,
a_(N-1)]_. does not provide any point of correlation to any of the
attribute values themselves. The attributes of block _j_ are hidden
by _a_j_ and the list of attribute digests _[a_0, a_1, ....,
a_(N-1)]_ is hidden by the aggregate _A_. The partial disclosure
needed to enable chain-link confidentiality does not leak any of the
selectively disclosable details.

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The disclosee may then verify the disclosure by: * computing _a_j_ on
the selectively disclosed attribute block details. * confirming that
the computed _a_j_ appears in the provided list _[a_0, a_1, ....,
a_(N-1)]_. * computing _A_ from the provided list _[a_0, a_1, ....,
a_(N-1)]_. * confirming that the computed _A_ matches the value, _A_,
of the selectively-disclosable attribute section, A, field value in
the provided ACDC. * computing the top-level SAID, d, field of the
provided ACDC. * confirming the presence of the issuance seal digest
in the Issuer's KEL * confirming that the issuance seal digest in the
Issuer's KEL is bound to the ACDC top-level SAID, d, field either
directly or indirectly through a TEL registry entry. * verifying the
provided signature(s) of the Issuee on the provided top-level SAID, d
field value.

The last 3 steps that culminate with verifying the signature(s)
require determining the key state of the Issuer at the time of
issuance, this may require additional verification steps as per the
KERI, PTEL, and CESR-Proof protocols.

A private selectively disclosable ACDC provides significant
correlation minimization because a presenter may use a metadata ACDC
prior to acceptance by the disclosee of the terms of the chain-link
confidentiality expressed in the rule section [CLC]. Thus only
malicious disclosees who violate chain-link confidentiality may
correlate between presentations of a given private selectively
disclosable ACDC. Nonetheless, they are not able to discover any
undisclosed attributes.

13.3.4. Inclusion Proof via Merkle Tree Root Digest

The inclusion proof via aggregated list may be somewhat verbose when
there are a large number of attribute blocks in the selectively
disclosable attribute section. A more efficient approach is to
create a Merkle tree of the attribute block digests and let the
aggregate, _A_, be the Merkle tree root digest [Mrkl]. Specifically,
set the value of the top-level selectively-disclosable attribute
section, A, field to the aggregate, _A_ whose value is the Merkle
tree root digest [Mrkl].

The Merkle tree needs to have appropriate second-pre-image attack
protection of interior branch nodes [TwoPI][MTSec]. The discloser
then only needs to provide a subset of digests from the Merkle tree
to prove that a given digest, _a_j_ contributed to the Merkle tree
root digest, _A_. For ACDCs with a small number of attributes the
added complexity of the Merkle tree approach may not be worth the
savings in verbosity.

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13.3.5. Hierarchical Derivation at Issuance of Selectively Disclosable
Attribute ACDCs

The amount of data transferred between the Issuer and Issuee (or
recipient in the case of an untargeted ACDC) at issuance of a
selectively disclosable attribute ACDC may be minimized by using a
hierarchical deterministic derivation function to derive the value of
the UUDI, u, fields from a shared secret salt [Salt].

There are several ways that the Issuer may securely share that secret
salt. Given that an Ed25519 key pair(s) controls each of the Issuer
and Issuee AIDs, (or recipient AID in the case of an untargeted ACDC)
a corresponding X15519 asymmetric encryption key pair(s) may be
derived from each controlling Ed25519 key pair(s)
[EdSC][PSEd][TMEd][SKEM]. An X25519 public key may be securely
derived from an Ed25519 public key [KeyEx][SKEM]. Likewise, an
X25519 private key may be securely derived from an Ed25519 private
key [KeyEx][SKEM].

In an interactive approach, the Issuer derives a public asymmetric
X25519 encryption key from the Issuee's published Ed25519 public key
and the Issuee derives a public asymmetric X25519 encryption key from
the Issuer's published Ed25519 public key. The two then interact via
a Diffie-Hellman (DH) key exchange to create a shared symmetric
encryption key [KeyEx][DHKE]. The shared symmetric encryption key
may be used to encrypt the secret salt or the shared symmetric
encryption key itself may be used has high entropy cryptographic
material from which the secret salt may be derived.

In a non-interactive approach, the Issuer derives an X25519
asymmetric public encryption key from the Issuee's (recipient's)
public Ed25519 public key. The Issuer then encrypts the secret salt
with that public asymmetric encryption key and signs the encryption
with the Issuer's private Ed25519 signing key. This is transmitted
to the Issuee, who verifies the signature and decrypts the secret
salt using the private X25519 decryption key derived from the
Issuee's private Ed25519 key. This non-interactive approach is more
scalable for AIDs that are controlled with a multi-sig group of
signing keys. The Issuer can broadcast to all members of the
Issuee's (or recipient's) multi-sig signing group individually
asymmetrically encrypted and signed copies of the secret salt.

In addition to the secret salt, the Issuer provides to the Issuee
(recipient) a template of the ACDC but with empty UUID, u, and SAID,
d, fields in each block with such fields. Each UUID, u, field value
is then derived from the shared salt with a path prefix that indexes
a specific block. Given the UUID, u, field value, the SAID, d, field
value may then be derived. Likewise, both compact and uncompacted

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versions of the ACDC may then be generated. The derivation path for
the top-level UUID, u, field (for private ACDCS), is the string "0"
and derivation path the the the zeroth indexed attribute in the
attributes array is the string "0/0". Likewise, the next attribute's
derivation path is the string "0/1" and so forth.

In addition to the shared salt and ACDC template, the Issuer also
provides its signature(s) on its own generated compact version ACDC.
The Issuer may also provide references to the anchoring issuance
proof seals. Everything else an Issuee (recipient) needs to make a
verifiable presentation/disclosure can be computed at the time of
presentation/disclosure by the Issuee.

13.4. Bulk-Issued Private ACDCs

The purpose of bulk issuance is to enable the Issuee to more
efficiently use ACDCs with unique SAIDs to isolate and minimize
correlation across different usage contexts. Each member of a set of
bulk-issued ACDCs is essentially the same ACDC but with a unique
SAID. This enables public commitments to each of the unqiue ACDC
SAIDs without correlating between them. A private ACDC may be
effectively issued in bulk as a set. In its basic form, the only
difference between each ACDC is the top-level SAID, _d_, and UUID,
_u_ field values. To elaborate, bulk issuance enables the use of un-
correlatable copies while minimizing the associated data transfer and
storage requirements involved in the issuance. Essentially each copy
(member) of a bulk issued ACDC set shares a template that both the
Issuer and Issuee use to generate on-the-fly a given ACDC in that set
without requiring that the Issuer and Issuee exchange and store a
unique copy of each member of the set independently. This minimizes
the data transfer and storage requirements for both the Issuer and
the Issuee. The Issuer is only required to provide a single
signature for the bulk issued aggregate value _B_ defined below. The
same signature may be used to provide proof of issuance of any member
of the bulk issued set. The signature on _B_ and _B_ itself are
points of correlation but these need only be disclosed after
contractually protected disclosure is in place, i.e no permissioned
correlation. Thus correlation requires a colluding second party who
enagages in unpermissioned correlation.

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An ACDC provenance chain is connected via references to the SAIDs
given by the top-level SAID, d, fields of the ACDCs in that chain. A
given ACDC thereby makes commitments to other ACDCs. Expressed
another way, an ACDC may be a node in a directed graph of ACDCs.
Each directed edge in that graph emanating from one ACDC includes a
reference to the SAID of some other connected ACDC. These edges
provide points of correlation to an ACDC via their SAID reference.
Private bulk issued ACDCs enable the Issuee to better control the
correlatability of presentations using different presentation
strategies.

For example, the Issuee could use one copy of a bulk-issued private
ACDC per presentation even to the same verifier. This strategy would
consume the most copies. It is essentially a one-time-use ACDC
strategy. Alternatively, the Issuee could use the same copy for all
presentations to the same verifier and thereby only permit the
verifier to correlate between presentations it received directly but
not between other verifiers. This limits the consumption to one copy
per verifier. In yet another alternative, the Issuee could use one
copy for all presentations in a given context with a group of
verifiers, thereby only permitting correlation among that group.

In this context, we are talking about permissioned correlation. Any
verifier that has received a complete presentation of a private ACDC
has access to all the fields disclosed by the presentation but the
terms of the chain-link confidentiality agreement may forbid sharing
those field values outside a given context. Thus an Issuee may use a
combination of bulk issued ACDCs with chain-link confidentiality to
control permissioned correlation of the contents of an ACDC while
allowing the SAID of the ACDC to be more public. The SAID of a
private ACDC does not expose the ACDC contents to an un-permissioned
third party. Unique SAIDs belonging to bulk issued ACDCs prevent
third parties from making a provable correlation between ACDCs via
their SAIDs in spite of those SAIDs being public. This does not stop
malicious verifiers (as second parties) from colluding and
correlating against the disclosed fields but it does limit provable
correlation to the information disclosed to a given group of
malicious colluding verifiers. To restate unique SAIDs per copy of a
set of private bulk issued ACDC prevent un-permissioned third parties
from making provable correlations, in spite of those SAIDs being
public, unless they collude with malicious verifiers (second
parties).

In some applications, chain-link-confidentiality is insufficient to
deter un-permissioned correlation. Some verifiers may be malicious
with sufficient malicious incentives to overcome whatever counter
incentives the terms of the contractual chain-link confidentiality
may impose. In these cases, more aggressive technological anti-

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correlation mechanisms such as bulk issued ACDCs may be useful. To
elaborate, in spite of the fact that chain-link confidentiality terms
of use may forbid such malicious correlation, making such correlation
more difficult technically may provide better protection than chain-
link confidentiality alone [CLC].

It is important to note that any group of colluding malicious
verifiers may always make a statistical correlation between
presentations despite technical barriers to cryptographically
provable correlation. We call this contextual linkability. In
general, there is no cryptographic mechanism that precludes
statistical correlation among a set of colluding verifiers because
they may make cryptographically unverifiable or unprovable assertions
about information presented to them that may be proven as likely true
using merely statistical correlation techniques. Linkability due the
context of the disclosure itself may defeat any unlinkability
guarantees of a cryptographic technique. Thus without contractually
protected disclosure, contextual linkability in spite of
cryptographic unlinkability may make the complexity of using advanced
cryptographic mechanisms to provide unlinkability an exercise in
diminishing returns.

13.5. Basic Bulk Issuance

The amount of data transferred between the Issuer and Issuee (or
recipient of an untargeted ACDC) at issuance of a set of bulk issued
ACDCs may be minimized by using a hierarchical deterministic
derivation function to derive the value of the UUID, u, fields from a
shared secret salt [Salt].

As described above, there are several ways that the Issuer may
securely share a secret salt. Given that the Issuer and Issuee (or
recipient when untargeted) AIDs are each controlled by an Ed25519 key
pair(s), a corresponding X15519 asymmetric encryption key pair(s) may
be derived from the controlling Ed25519 key pair(s)
[EdSC][PSEd][TMEd]. An X25519 public key may be securely derived
from an Ed25519 public key [KeyEx][SKEM]. Likewise, an X25519
private key may be securely derived from an Ed25519 private key
[KeyEx][SKEM].

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In a non-interactive approach, the Issuer derives an X25519
asymmetric public encryption key from the Issuee's (or recipient's)
public Ed25519 public key. The Issuer then encrypts the secret salt
with that public asymmetric encryption key and signs the encryption
with the Issuer's private Ed25519 signing key. This is transmitted
to the Issuee, who verifies the signature and decrypts the secret
salt using the private X25519 decryption key derived from the
Issuee's private Ed25519 key. This non-interactive approach is more
scalable for AIDs that are controlled with a multi-sig group of
signing keys. The Issuer can broadcast to all members of the
Issuee's (or recipient's) multi-sig signing group individually
asymmetrically encrypted and signed copies of the secret salt.

In addition to the secret salt, the Issuer also provides a template
of the private ACDC but with empty UUID, u, and SAID, d, fields at
the top-level of each nested block with such fields. Each UUID, u,
field value is then derived from the shared salt with a deterministic
path prefix that indexes both its membership in the bulk issued set
and its location in the ACDC. Given the UUID, u, field value, the
associated SAID, d, field value may then be derived. Likewise, both
full and compact versions of the ACDC may then be generated. This
generation is analogous to that described in the section for
selective disclosure ACDCs but extended to a set of private ACDCs.

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The initial element in each deterministic derivation path is the
string value of the bulk-issued member's copy index _k_, such as "0",
"1", "2" etc. Specifically, if _k_ denotes the index of an ordered
set of bulk issued private ACDCs of size _M_, the derivation path
starts with the string _"k"_ where _k_ is replaced with the decimal
or hexadecimal textual representation of the numeric index _k_.
Furthermore, a bulk-issued private ACDC with a private attribute
section uses _"k"_ to derive its top-level UUID and _"k/0"_ to derive
its attribute section UUID. This hierarchical path is extended to
any nested private attribute blocks. This approach is further
extended to enable bulk issued selective disclosure ACDCs by using a
similar hierarchical derivation path for the UUID field value in each
of the selectively disclosable blocks in the array of attributes.
For example, the path _"k/j"_ is used to generate the UUID of
attribute index _j_ at bulk-issued ACDC index _k_.

In addition to the shared salt and ACDC template, the Issuer also
provides a list of signatures of SAIDs, one for each SAID of each
copy of the associated compact bulk-issued ACDC. The Issuee (or
recipient) can generate on-demand each compact or uncompacted ACDC
from the template, the salt, and its index _k_. The Issuee does not
need to store a copy of each bulk issued ACDC, merely the template,
the salt, and the list of signatures.

The Issuer MUST also anchor in its KEL an issuance proof digest seal
of the set of bulk issued ACDCs. The issuance proof digest seal
makes a cryptographic commitment to the set of top-level SAIDS
belonging to the bulk issued ACDCs. This protects against later
forgery of ACDCs in the event the Issuer's signing keys become
compromised. A later attempt at forgery requires a new event or new
version of an event that includes a new anchoring issuance proof
digest seal that makes a cryptographic commitment to the set of newly
forged ACDC SAIDS. This new anchoring event of the forgery is
therefore detectable.

Similarly, to the process of generating a selective disclosure
attribute ACDC, the issuance proof digest is an aggregate that is
aggregated from all members in the bulk-issued set of ACDCs. The
complication of this approach is that it must be done in such a way
as to not enable provable correlation by a third party of the actual
SAIDS of the bulk-issued set of ACDCs. Therefore the actual SAIDs
must not be aggregated but blinded commitments to those SAIDs
instead. With blinded commitments, knowledge of any or all members
of such a set does not disclose the membership of any SAID unless and
until it is unblinded. Recall that the purpose of bulk issuance is
to allow the SAID of an ACDC in a bulk issued set to be used publicly
without correlating it in an un-permissioned provable way to the
SAIDs of the other members.

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The basic approach is to compute the aggregate denoted, _B_, as the
digest of the concatenation of a set of blinded digests of bulk
issued ACDC SAIDS. Each ACDC SAID is first blinded via concatenation
to a UUID (salty nonce) and then the digest of that concatenation is
concatenated with the other blinded SAID digests. Finally, a digest
of that concatenation provides the aggregate.

Suppose there are _M_ ACDCs in a bulk issued set. Using zero-based
indexing for each member of the bulk issued set of ACDCs, such that
index _k_ satisfies _k in {0, ..., M-1}, let *d_k_ denote the top-
level SAID of an ACDC in an ordered set of bulk-issued ACDCs. Let
_v_k_ denote the UUID (salty nonce) or blinding factor that is used
to blind that said. The blinding factor, _v_k_, is NOT the top-level
UUID, u, field of the ACDC itself but an entirely different UUID used
to blind the ACDC's SAID for the purpose of aggregation. The
derivation path for _v_k_ from the shared secret salt is _"k."_ where
_k_ is the index of the bulk-issued ACDC.

Let _c_k = v_k + d_k_, denote the blinding concatenation where _+_ is
the infix concatenation operator. Then the blinded digest, _b_k_, is
given by, _b_k = H(c_k) = H(v_k + d_k)_, where _H_ is the digest
operator. Blinding is performed by a digest of the concatenation of
the binding factor, _v_k_, with the SAID, _d_k_ instead of XORing the
two. An XOR of two elements whose bit count is much greater than 2
is not vulnerable to a birthday table attack [BDay][DRB][BDC]. In
order to XOR, however, the two must be of the same length. Different
SAIDs MAY be of different lengths, however, and MAY therefore require
different length blinding factors. Because concatenation is length
independent it is simpler to implement.

The aggregation of blinded digests, _B_, is given by, _B = H(C(b_k
for all k in {0, ..., M-1}))_, where _C_ is the concatenation
operator and _H_ is the digest operator. This aggregate, _B_,
provides the issuance proof digest.

The aggregate, _B_, makes a blinded cryptographic commitment to the
ordered elements in the list _[b_0, b_1, ...., b_(M-1)]_. A
commitment to _B_ is a commitment to all the _b_k_ and hence all the
d_k.

Given sufficient collision resistance of the digest operator, the
digest of an ordered concatenation is not subject to a birthday
attack on its concatenated elements [BDC][BDay][QCHC][HCR][Hash].

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Disclosure of any given _b_k_ element does not expose or disclose any
discoverable information detail about either the SAID of its
associated ACDC or any other ACDC's SAID. Therefore one may safely
disclose the full list of _b_k_ elements without exposing the blinded
bulk issued SAID values, d_k.

Proof of inclusion in the list of blinded digests consists of
checking the list for a matching value. A computationally efficient
way to do this is to create a hash table or B-tree of the list and
then check for inclusion via lookup in the hash table or B-tree.

A proof of inclusion of an ACDC in a bulk-issued set requires
disclosure of _v_k_ which is only disclosed after the disclosee has
accepted (agreed to) the terms of the rule section. Therefore, in
the event the _Disclosee_ declines to accept the terms of disclosure,
then a presentation/disclosure of the compact version of the ACDC
does not provide any point of correlation to any other SAID of any
other ACDC from the bulk set that contributes to the aggregate _B_.
In addition, because the other SAIDs are hidden by each _b_k_ inside
the aggregate, _B_, even a presentation/disclosure of, _[b_0, b_1,
...., b_(M-1)]_ does not provide any point of correlation to the
actual bulk-issued ACDC without disclosure of its _v_k_. Indeed if
the _Discloser_ uses a metadata version of the ACDC in its _offer_
then even its SAID is not disclosed until after acceptance of terms
in the rule section.

To protect against later forgery given a later compromise of the
signing keys of the Issuer, the issuer MUST anchor an issuance proof
seal to the ACDC in its KEL. This seal binds the signing key state
to the issuance. There are two cases. In the first case, an
issuance/revocation registry is used. In the second case, an
issuance/revocation registry is not used.

When the ACDC is registered using an issuance/revocation TEL
(Transaction Event Log) then the issuance proof seal digest is the
SAID of the issuance (inception) event in the ACDC's TEL entry. The
issuance event in the TEL uses the aggregate value, _B_, as its
identifier value. This binds the aggregate, _B_, to the issuance
proof seal in the Issuer's KEL through the TEL.

Recall that the usual purpose of a TEL is to provide a verifiable
data registry that enables dynamic revocation of an ACDC via a state
of the TEL. A verifier checks the state at the time of use to check
if the associated ACDC has been revoked. The Issuer controls the
state of the TEL. The registry identifier, ri, field is used to
identify the public registry which usually provides a unique TEL
entry for each ACDC. Typically the identifier of each TEL entry is
the SAID of the TEL's inception event which is a digest of the

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event's contents which include the SAID of the ACDC. In the bulk
issuance case, however, the TEL's inception event contents include
the aggregate, _B_, instead of the SAID of a given ACDC. Recall that
the goal is to generate an aggregate value that enables an Issuee to
selectively disclose one ACDC in a bulk-issued set without leaking
the other members of the set to un-permissioned parties (second or
third). Using the aggregate, _B_ of blinded ACDC saids as the TEL
registry entry identifier allows all members of the bulk-issued set
to share the same TEL without any third party being able to discover
which TEL any ACDC is using in an un-permissioned provable way.
Moreover, a second party may not discover in an un-permissioned way
any other ACDCs from the bulk-issued set not specifically disclosed
to that second party. In order to prove to which TEL a specific bulk
issued ACDC belongs, the full inclusion proof must be disclosed.

When the ACDC is not registered using an issuance/revocation TEL then
the issuance proof seal digest is the aggregate, _B_, itself.

In either case, this issuance proof seal makes a verifiable binding
between the issuance of all the ACDCs in the bulk issued set and the
key state of the Issuer at the time of issuance.

A _Discloser_ may make a basic provable non-repudiable selective
disclosure of a given bulk issued ACDC, at index _k_ by providing to
the _Disclosee_ four items of information (proof of inclusion).
These are as follows:

* The ACDC in compact form (at index _k_) where _d_k_ as the value
of its top-level SAID, d, field.

* The blinding factor, _v_k_ from which _b_k = H(v_k + d_k)_ may be
computed.

* The list of all blinded SAIDs, _[b_0, b_1, ...., b_(M-1)]_ that
includes _b_k_.

* A reference to the anchoring seal in the Issuer's KEL or TEL that
references the aggregate _B_. The event that references the seal
or the TEL event that references _B_ must be signed by the issuer
so the signature on either event itself is sufficient to prove
authorized issuance.

The aggregate _B_ is a point of unpermissioned correlation but not
permissioned correlation. To remove _B_ as a point of unpermissioned
correlation requires using _independent TEL bulk-issued ACDCs_
described in the section so named below.

A _Disclosee_ may then verify the disclosure by:

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* computing _d_j_ on the disclosed compact ACDC.

* computing _b_k = H(v_k + d_k)_

* confirming that the computed _b_k_ appears in the provided list
_[b_0, b_1, ...., b_(M-1)]_.

* computing the aggregate _B_ from the provided list _[b_0, b_1,
...., b_(M-1)]_..

* confirming the presence of an issuance seal digest in the Issuer's
KEL that makes a commitment to the aggregate, _B_, either directly
or indirectly through a TEL registry entry. This provides proof
of authorized issuance.

The last 3 steps that culminate with verifying the anchoring seal
also require verifying the key state of the Issuer at the time of
issuance, this may require additional verification steps as per the
KERI, PTEL, and CESR-Proof protocols.

The requirement of an anchored issuance proof seal of the aggregate
_B_ means that the forger MUST first successfully publish in the KEL
of the issuer an inclusion proof digest seal bound to a set of forged
bulk issued ACDCs. This makes any forgery attempt detectable. To
elaborate, the only way to successfully publish such a seal is in a
subsequent interaction event in a KEL that has not yet changed its
key state via a rotation event. Whereas any KEL that has changed its
key state via a rotation must be forked before the rotation. This
makes the forgery attempt either both detectable and recoverable via
rotation in any KEL that has not yet changed its key state or
detectable as duplicity in any KEL that has changed its key state.
In any event, the issuance proof seal makes any later attempt at
forgery using compromised keys detectable.

13.5.1. Inclusion Proof via Merkle Tree

The inclusion proof via aggregated list may be somewhat verbose when
there are a very large number of bulk issued ACDCs in a given set. A
more efficient approach is to create a Merkle tree of the blinded
SAID digests, _b_k_ and set the aggregate _B_ value as the Merkle
tree root digest [Mrkl].

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The Merkle tree needs to have appropriate second-pre-image attack
protection of interior branch nodes [TwoPI][MTSec]. The discloser
then only needs to provide a subset of digests from the Merkle tree
to prove that a given digest, _b_k_ contributed to the Merkle tree
root digest. For a small numbered bulk-issued set of ACDCs, the
added complexity of the Merkle tree approach may not be worth the
savings in verbosity.

13.5.2. Bulk Issuance of Private ACDCs with Unique Issuee AIDs

One potential point of provable but un-permissioned correlation among
any group of colluding malicious _Disclosees_ (Second-Party
verifiers) may arise when the same Issuee AID is used for
presentation/disclosure to all _Disclosees_ in that group. Recall
that the contents of private ACDCs are not disclosed except to
permissioned _Disclosees_ (Second-Parties). Thus a common _Issuee_
AID would only be a point of correlation for a group of colluding
malicious verifiers. But in some cases removing this un-permissioned
point of correlation may be desirable.

One solution to this problem is for the _Issuee_ to use a unique AID
for the copy of a bulk-issued ACDC presented to each _Disclosee_ in a
given context. This requires that each ACDC copy in the bulk-issued
set use a unique _Issuee_ AID. This would enable the _Issuee_ in a
given context to minimize provable correlation by malicious
_Disclosees_ against any given _Issuee_ AID. In this case, the bulk
issuance process may be augmented to include the derivation of a
unique Issuee AID in each copy of the bulk-issued ACDC by including
in the inception event that defines a given Issuee's self-addressing
AID, a digest seal derived from the shared salt and copy index _k_.
The derivation path for the digest seal is _"k/0."_ where _k_ is the
index of the ACDC. To clarify _"k/0."_ specifies the path to
generate the UUID to be included in the inception event that
generates the Issuee AID for the ACDC at index _k_. This can be
generated on-demand by the _Issuee_. Each unique _Issuee_ AID would
also need its own KEL. But generation and publication of the
associated KEL can be delayed until the bulk-issued ACDC is actually
used. This approach completely isolates a given _Issuee_ AID to a
given context with respect to the use of a bulk-issued private ACDC.
This protects against even the un-permissioned correlation among a
group of malicious Disclosees (Second Parties) via the Issuee AID.

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13.6. Blindable State TEL

In some applications, it is desirable that the current state of a
transaction event log (TEL) be hidden or blinded such that the only
way for a potential verifier of the state to observe that state is
when the controller of a designated AID discloses it at the time of
presentation. This designated AID we call the Discloser. Typically
for ACDCs that have an Issuee, the Discloser is the Issuee, but the
Issuer could designate any AID as the Discloser. Only the Discloser
will be able to unblind the state to a potential Disclosee.

In a blindable state TEL, the state disclosure is interactive. A
Disclosee may only observe the state when unblinded via an
interactive exchange with the Discloser. After disclosure, the
Discloser may then request that the Issuer update the state with a
new blinding factor (_the blind_). The Disclosee cannot then observe
the current state of the TEL without yet another disclosure
interaction with the Discloser.

The blind is derived from a secret salt shared between the Issuer and
the designated Discloser. The current blind is derived from this
salt, and the sequence number of the TEL event is so blinded. To
elaborate, the derivation path for the blind is the sequence number
of the TEL event, which in combination with the salt, produces a
universally unique salty nonce for the blind. Only the Issuer and
Discloser have a copy of the secret salt, so only they can derive the
current blind. The Issuer provides a service endpoint to which the
Discloser can make a signed request to update the blind. Each new
event in the TEL MUST change the blinding factor but MAY or MAY NOT
change the actual blinded state. Only the Issuer can change the
actual blinded state. Because each updated event in the TEL has a
new blinding factor regardless of an actual change of state or not,
an observer can not correlate state changes to event updates as long
as the Issuer regularly updates the blinding factor by issuing a new
TEL event.

Blindable State TEL events use a unique event type, upd. The event
state is hidden in the a field, whose value is the blinded SAID of a
field map that holds the TEL state. The field map's SAID is its d
field. The blinding factor is provided in the field map's u field.
The SAID of the associated ACDC is in the field map's i field or else
the aggregate value for bulk issued ACDCs. The actual state of the
TEL for that ACDC is provided by other fields in the a, field map. A
simple state could use the s field for state or status.

When the u field is missing or empty, then the event is not
blindable. When the u field has sufficient entropy, then the SAID of
the enclosing field map effectively blinds the state provided by that

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map. The discloser must disclose the field map to the Disclosee, who
can verify that its SAID matches the SAID in the TEL. A subsequent
update event entered into that TEL will then re-blind the state of
the TEL so that any prior Disclosees may no longer verify the current
state of the TEL.

13.6.1. Blindable State TEL Top-Level Fields

+=======+=========================================+=======+
| Label | Description | Notes |
+=======+=========================================+=======+
| v | version string | |
+-------+-----------------------------------------+-------+
| d | event digest | SAID |
+-------+-----------------------------------------+-------+
| s | sequence number of event | |
+-------+-----------------------------------------+-------+
| t | message type of event | upd |
+-------+-----------------------------------------+-------+
| dt | issuer system data/time in iso format | |
+-------+-----------------------------------------+-------+
| p | prior event digest | SAID |
+-------+-----------------------------------------+-------+
| ri | registry identifier from management TEL | |
+-------+-----------------------------------------+-------+
| ra | registry anchor to management TEL | |
+-------+-----------------------------------------+-------+
| a | state attributed digest | SAID |
+-------+-----------------------------------------+-------+

Table 6

13.6.2. Blindable State TEL Attribute (state) Fields

+=======+===============================+===========+
| Label | Description | Notes |
+=======+===============================+===========+
| d | attribute digest | SAID |
+-------+-------------------------------+-----------+
| u | salty nonce blinding factor | UUID |
+-------+-------------------------------+-----------+
| i | namespaced identifier of VC | SAID or |
| | or aggregate when bulk issued | Aggregate |
+-------+-------------------------------+-----------+
| s | state value | issued or |
| | | revoked |
+-------+-------------------------------+-----------+

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Table 7

13.7. Independent TEL Bulk-Issued ACDCs

Recall that the purpose of using the aggregate _B_ for a bulk-issued
set from which the TEL identifier is derived is to enable a set of
bulk-issued ACDCs to share a single public TEL and/or a single
anchoring seal in the Issuer's KEL without enabling un-permissioned
correlation to any other members of the bulk set by virtue of the
shared aggregate _B_ used for either the TEL or anchoring seal in the
KEL. When using a TEL this enables the issuance/revocation/transfer
state of all copies of a set of bulk-issued ACDCs to be provided by a
single TEL which minimizes the storage and compute requirements on
the TEL registry while providing selective disclosure to prevent un-
permissioned correlation via the public TEL. When using an anchoring
seal, this enables one signature to provide proof of inclusion in the
bulk-issued aggregate _B_.

However, in some applications where chain-link confidentiality does
not sufficiently deter malicious provable correlation by Disclosees
(Second-Party verifiers), an Issuee may benefit from using ACDC with
independent TELs or independent aggregates _B_ but that are still
bulk-issued.

In this case, the bulk issuance process must be augmented so that
each uniquely identified copy of the ACDC gets its own TEL entry (or
equivalently its own aggregate _B_) in the registry. Each Disclosee
(verifier) of a full presentation/disclosure of a given copy of the
ACDC only receives proof of one uniquely identified TEL and can NOT
provably correlate the TEL state of one presentation to any other
presentation because the ACDC SAID, the TEL identifier, and the
signature of the issuer on each aggregate _B_ will be different for
each copy. There is, therefore no point of provable correlation,
permissioned or otherwise. One could for example, modulate this
apprach by having a set of smaller bulk issued sets that are more
contextualized than one large bulk issued set.

The obvious drawbacks of this approach (independent unique TELs for
each private ACDC) are that the size of the registry database
increases as a multiple of the number of copies of each bulk-issued
ACDC and every time an Issuer must change the TEL state of a given
set of copies it must change the state of multiple TELs in the
registry. This imposes both a storage and computation burden on the
registry. The primary advantage of this approach, however, is that
each copy of a private ACDC has a uniquely identified TEL. This
minimizes un-permissioned Third-Party exploitation via provable
correlation of TEL identifiers even with colluding Second-Party
verifiers. They are limited to statistical correlation techniques.

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In this case, the set of private ACDCs may or may not share the same
Issuee AID because for all intents and purposes each copy appears to
be a different ACDC even when issued to the same Issuee.
Nonetheless, using unique Issuee AIDs may further reduce correlation
by malicious Disclosees (Second-Party verifiers) beyond using
independent TELs.

To summarize the main benefit of this approach, in spite of its
storage and compute burden, is that in some applications chain-link
confidentiality does not sufficiently deter un-permissioned malicious
collusion. Therefore completely independent bulk-issued ACDCs may be
used.

14. Extensibility

ToDo

Append-only verifiable data structures have strong security
properties that simplify end-verifiability & foster decentralization.

Append-only provides permission-less extensibility by downstream
issuers, presenters, and/or verifiers

Each ACDC has a universally-unique content-based identifier with a
universally-unique content-based schema identifier.

Fully decentralized name-spacing.

Custom fields are appended via chaining via one or more custom ACDCs
defined by custom schema (type-is-schema).

No need for centralized permissioned name-space registries to resolve
name-space collisions.

The purposes of a registry now become merely schema discovery or
schema blessing for a given context or ecosystem.

The reach of the registry is tuned to the reach of desired
interoperability by the ecosystem participants.

Human meaningful labels on SAIDs are local context only.

Versioning is simplified because edges still verify if new schema are
backwards compatible. (persistent data structure model).

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15. Appendix: Performance and Scalability

The compact disclosure and distribute property graph fragment
mechanisms in ACDC can be leveraged to enable high performance at
scale. Simply using SAIDs and signed SAIDs of ACDCs in whole or in
part enables compact but securely attributed and verifiable
references to ACDCs to be employed anywhere performance is an issue.
Only the SAID and its signature need be transmitted to verify secure
attribution of the data represented by the SAID. Later receipt of
the data may be verified against the SAID. The signature does not
need to be re-verified because a signature on a SAID is making a
unique (to within the cryptographic strength of the SAID) commitment
to the data represented by the SAID. The actual detailed ACDC in
whole or in part may then be cached or provided on-demand or just-in-
time.

Hierarchical decomposition of data into a distributed verifiable
property graph, where each ACDC is a distributed graph fragment,
enables performant reuse of data or more compactly performant reuse
of SAIDs and their signatures. The metadata and attribute sections
of each ACDC provide a node in the graph and the edge section of each
ACDC provides the edges to that node. Higher-up nodes in the graph
with many lower-level nodes need only be transmitted, verified, and
cached once per every node or leaf in the branch not redundantly re-
transmitted and re-verified for each node or leaf as is the case for
document-based verifiable credentials where the whole equivalent of
the branched (graph) structure must be contained in one document.
This truly enables the bow-tie model popularized by Ricardian
contracts, not merely for contracts, but for all data authenticated,
authorized, referenced, or conveyed by ACDCs.

16. Appendix: Cryptographic Strength and Security

16.1. Cryptographic Strength

For crypto-systems with _perfect-security_, the critical design
parameter is the number of bits of entropy needed to resist any
practical brute force attack. In other words, when a large random or
pseudo-random number from a cryptographic strength pseudo-random
number generator (CSPRNG) [CSPRNG] expressed as a string of
characters is used as a seed or private key to a cryptosystem with
_perfect-security_, the critical design parameter is determined by
the amount of random entropy in that string needed to withstand a
brute force attack. Any subsequent cryptographic operations must
preserve that minimum level of cryptographic strength. In
information theory [IThry][ITPS] the entropy of a message or string
of characters is measured in bits. Another way of saying this is
that the degree of randomness of a string of characters can be

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measured by the number of bits of entropy in that string. Assuming
conventional non-quantum computers, the convention wisdom is that,
for systems with information-theoretic or perfect security, the seed/
key needs to have on the order of 128 bits (16 bytes, 32 hex
characters) of entropy to practically withstand any brute force
attack. A cryptographic quality random or pseudo-random number
expressed as a string of characters will have essentially as many
bits of entropy as the number of bits in the number. For other
crypto-systems such as digital signatures that do not have perfect
security, the size of the seed/key may need to be much larger than
128 bits in order to maintain 128 bits of cryptographic strength.

An N-bit long base-2 random number has 2^N different possible values.
Given that no other information is available to an attacker with
perfect security, the attacker may need to try every possible value
before finding the correct one. Thus the number of attempts that the
attacker would have to try maybe as much as 2^(N-1). Given available
computing power, one can easily show that 128 is a large enough N to
make brute force attack computationally infeasible.

Let's suppose that the adversary has access to supercomputers.
Current supercomputers can perform on the order of one quadrillion
operations per second. Individual CPU cores can only perform about 4
billion operations per second, but a supercomputer will parallelly
employ many cores. A quadrillion is approximately 2^50 =
1,125,899,906,842,624. Suppose somehow an adversary had control over
one million (2^20 = 1,048,576) supercomputers which could be employed
in parallel when mounting a brute force attack. The adversary could
then try 2^50 * 2^20 = 2^70 values per second (assuming very
conservatively that each try only took one operation). There are
about 3600 * 24 * 365 = 313,536,000 = 2^(log_2313536000)=2^24.91 ~=
2^25 seconds in a year. Thus this set of a million super computers
could try 2^(50+20+25) = 2^95 values per year. For a 128-bit random
number this means that the adversary would need on the order of
2^(128-95) = 2^33 = 8,589,934,592 years to find the right value.
This assumes that the value of breaking the cryptosystem is worth the
expense of that much computing power. Consequently, a cryptosystem
with perfect security and 128 bits of cryptographic strength is
computationally infeasible to break via brute force attack.

16.2. Information Theoretic Security and Perfect Security

The highest level of cryptographic security with respect to a
cryptographic secret (seed, salt, or private key) is called
_information-theoretic security_ [ITPS]. A cryptosystem that has
this level of security cannot be broken algorithmically even if the
adversary has nearly unlimited computing power including quantum
computing. It must be broken by brute force if at all. Brute force

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means that in order to guarantee success the adversary must search
for every combination of key or seed. A special case of
_information-theoretic security_ is called _perfect-security_ [ITPS].
_Perfect-security_ means that the ciphertext provides no information
about the key. There are two well-known cryptosystems that exhibit
_perfect security_. The first is a _one-time-pad_ (OTP) or Vernum
Cipher [OTP][VCphr], the other is _secret splitting_ [SSplt], a type
of secret sharing [SShr] that uses the same technique as a _one-time-
pad_.

17. Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

* SAID - Self-Addressing Identifier - any identifier which is
deterministically generated out of the content, digest of the
content

18. Security Considerations

Refer to the body of the specification. Security considerations are
included in the context of each section. The ACDC specification is
security driven so the specification itself is riddled with
discussions of the security considerations in the context in which
those discussions are most understandable and relevant.

19. IANA Considerations

This document has no IANA actions.

20. References

20.1. Normative References

[ACDC_ID] Smith, S., "IETF ACDC (Authentic Chained Data Containers)
Internet Draft", 2022,
<https://github.com/trustoverip/tswg-acdc-specification>.

[CBOR] "CBOR Mapping Object Codes", n.d.,
<https://en.wikipedia.org/wiki/CBOR>.

[CESR_ID] Smith, S., "IETF CESR (Composable Event Streaming
Representation) Internet Draft", 2022,
<https://github.com/WebOfTrust/ietf-cesr>.

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[DIDK_ID] Feairheller, P., "IETF DID-KERI Internet Draft", 2022,
<https://github.com/WebOfTrust/ietf-did-keri>.

[IPEX_ID] Feairheller, P., "IPEX (Issuance and Presentation
EXchange) Internet Draft", 2022,
<https://github.com/WebOfTrust/ietf-ipex>.

[JSch] "JSON Schema", n.d., <https://json-schema.org>.

[JSch_202012]
"JSON Schema 2020-12", n.d., <https://json-schema.org/
draft/2020-12/release-notes.html>.

[JSON] "JavaScript Object Notation Delimeters", n.d.,
<https://www.json.org/json-en.html>.

[KERI_ID] Smith, S., "IETF KERI (Key Event Receipt Infrastructure)
Internet Draft", 2022,
<https://github.com/WebOfTrust/ietf-keri>.

[MGPK] "Msgpack Mapping Object Codes", n.d.,
<https://github.com/msgpack/msgpack/blob/master/spec.md>.

[OOBI_ID] Smith, S., "IETF OOBI (Out-Of-Band-Introduction) Internet
Draft", 2022, <https://github.com/WebOfTrust/ietf-oobi>.

[Proof_ID] Feairheller, P., "IETF CESR-Proof Internet Draft", 2022,
<https://github.com/WebOfTrust/ietf-cesr-proof>.

[PTEL_ID] Feairheller, P., "IETF PTEL (Public Transaction Event Log)
Internet Draft", 2022,
<https://github.com/WebOfTrust/ietf-ptel>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.

[RFC3986] "Uniform Resource Identifier (URI): Generic Syntax", n.d.,
<https://datatracker.ietf.org/doc/html/rfc3986>.

[RFC4627] "The application/json Media Type for JavaScript Object
Notation (JSON)", n.d.,
<https://datatracker.ietf.org/doc/rfc4627/>.

[RFC6901] Bryan, P. C., Zyp, K., and M. Nottingham, "JavaScript
Object Notation (JSON) Pointer", 2003,
<https://datatracker.ietf.org/doc/html/rfc6901>.

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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

[RFC8259] "JSON (JavaScript Object Notation)", n.d.,
<https://datatracker.ietf.org/doc/html/rfc8259>.

[RFC8820] "URI Design and Ownership", n.d.,
<https://datatracker.ietf.org/doc/html/rfc8820>.

[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", 4 December 2020,
<https://datatracker.ietf.org/doc/rfc8949/>.

[SAID_ID] Smith, S., "IETF SAID (Self-Addressing IDentifier)
Internet Draft", 2022,
<https://github.com/WebOfTrust/ietf-said>.

20.2. Informative References

[Abuse] "Alice Attempts to Abuse a Verifiable Credential", n.d.,
<https://github.com/WebOfTrustInfo/rwot9-
prague/blob/master/final-documents/alice-attempts-abuse-
verifiable-credential.md>.

[ACDC_TF] "ACDC (Authentic Chained Data Container) Task Force",
n.d., <https://wiki.trustoverip.org/display/HOME/
ACDC+%28Authentic+Chained+Data+Container%29+Task+Force>.

[ACDC_WP] "Authentic Chained Data Containers (ACDC) White Paper",
n.d., <https://github.com/SmithSamuelM/Papers/blob/master/
whitepapers/ACDC.web.pdf>.

[BDay] "Birthday Attack", n.d.,
<https://en.wikipedia.org/wiki/Birthday_attack>.

[BDC] "Birthday Attacks, Collisions, And Password Strength",
n.d., <https://auth0.com/blog/birthday-attacks-collisions-
and-password-strength/>.

[CAcc] "Cryptographic Accumulator", n.d.,
<https://en.wikipedia.org/wiki/
Accumulator_(cryptography)>.

[CLC] "Chain-Link Confidentiality", n.d.,
<https://papers.ssrn.com/sol3/
papers.cfm?abstract_id=2045818>.

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[CSPRNG] "Cryptographically-secure pseudorandom number generator
(CSPRNG)", n.d., <https://en.wikipedia.org/wiki/
Cryptographically-secure_pseudorandom_number_generator>.

[DHKE] "Diffie-Hellman Key Exchange", n.d.,
<https://www.infoworld.com/article/3647751/understand-
diffie-hellman-key-exchange.html>.

[Dots] Rodriguez, M. and P. Neubauer, "Constructions from Dots
and Lines", 2010, <https://arxiv.org/pdf/1006.2361.pdf>.

[DRB] "Dictionary Attacks, Rainbow Table Attacks and how
Password Salting defends against them", n.d.,
<https://www.commonlounge.com/
discussion/2ee3f431a19e4deabe4aa30b43710aa7>.

[DSig] "Digital Signature", n.d.,
<https://en.wikipedia.org/wiki/Digital_signature>.

[EdSC] "The Provable Security of Ed25519: Theory and Practice
Report", n.d., <https://eprint.iacr.org/2020/823>.

[GLEIF] "GLEIF (Global Legal Entity Identifier Foundation)", n.d.,
<https://www.gleif.org/en/>.

[GLEIF_KERI]
"GLEIF with KERI Architecture", n.d.,
<https://github.com/WebOfTrust/vLEI>.

[GLEIF_vLEI]
"GLEIF vLEI (verifiable Legal Entity Identifier)", n.d.,
<https://www.gleif.org/en/lei-solutions/gleifs-digital-
strategy-for-the-lei/introducing-the-verifiable-lei-vlei>.

[Hash] "Cryptographic Hash Function", n.d.,
<https://en.wikipedia.org/wiki/
Cryptographic_hash_function>.

[HCR] "Hash Collision Resistance", n.d.,
<https://en.wikipedia.org/wiki/Collision_resistance>.

[IDSys] "Identity System Essentials", n.d.,
<https://github.com/SmithSamuelM/Papers/blob/master/
whitepapers/Identity-System-Essentials.pdf>.

[IETF] "IETF (Internet Engineering Task Force", n.d.,
<https://www.ietf.org>.

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[IThry] "Information Theory", n.d.,
<https://en.wikipedia.org/wiki/Information_theory>.

[ITPS] "Information-Theoretic and Perfect Security", n.d.,
<https://en.wikipedia.org/wiki/Information-
theoretic_security>.

[JSchCp] "Schema Composition in JSON Schema", n.d., <https://json-
schema.org/understanding-json-schema/reference/
combining.html>.

[JSchCx] "Complex JSON Schema Structuring", n.d., <https://json-
schema.org/understanding-json-schema/
structuring.html#base-uri>.

[JSchId] "JSON Schema Identification", n.d., <https://json-
schema.org/understanding-json-schema/
structuring.html#schema-identification>.

[JSchRE] "Regular Expressions in JSON Schema", n.d., <https://json-
schema.org/understanding-json-schema/reference/
regular_expressions.html>.

[KERI] Smith, S., "Key Event Receipt Infrastructure (KERI)",
2021, <https://arxiv.org/abs/1907.02143>.

[KeyEx] "Key Exchange", n.d.,
<https://libsodium.gitbook.io/doc/key_exchange>.

[KG] "Knowledge Graphs", n.d.,
<https://arxiv.org/pdf/2003.02320.pdf>.

[Level] "Security Level", n.d.,
<https://en.wikipedia.org/wiki/Security_level>.

[Mrkl] "Merkle Tree", n.d.,
<https://en.wikipedia.org/wiki/Merkle_tree>.

[MTSec] "Merkle Tree Security", n.d.,
<https://blog.enuma.io/update/2019/06/10/merkle-trees-not-
that-simple.html>.

[OTP] "One-Time-Pad", n.d.,
<https://en.wikipedia.org/wiki/One-time_pad>.

[PGM] Angles, R., "The Property Graph Database Model", 2018,
<http://ceur-ws.org/Vol-2100/paper26.pdf>.

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[PSEd] Brendel, J., Cremers, C., Jackson, D., and M. Zhao, "The
Provable Security of Ed25519: Theory and Practice", 2021
IEEE Symposium on Security and Privacy (SP) , 24 May 2021,
<https://ieeexplore.ieee.org/document/9519456?denied=>.

[QCHC] "Cost analysis of hash collisions: Will quantum computers
make SHARCS obsolete?", n.d.,
<https://cr.yp.to/hash/collisioncost-20090823.pdf>.

[RB] "Rainbow Table", n.d.,
<https://en.wikipedia.org/wiki/Rainbow_table>.

[RC] "Ricardian Contract", n.d.,
<https://en.wikipedia.org/wiki/Ricardian_contract>.

[Salt] "Salts, Nonces, and Initial Values", n.d.,
<https://medium.com/@fridakahsas/salt-nonces-and-ivs-
whats-the-difference-d7a44724a447>.

[SKEM] "On using the same key pair for Ed25519 and an X25519
based KEM", n.d., <https://eprint.iacr.org/2021/509>.

[SShr] "Secret Sharing", n.d.,
<https://en.wikipedia.org/wiki/Secret_sharing>.

[SSplt] "Secret Splitting", n.d.,
<https://www.ciphermachinesandcryptology.com/en/
secretsplitting.htm>.

[TMal] "Transaction Malleability", n.d.,
<https://en.wikipedia.org/wiki/
Transaction_malleability_problem>.

[TMEd] "Taming the many EdDSAs", n.d.,
<https://eprint.iacr.org/2020/1244.pdf>.

[TOIP] "Trust Over IP (ToIP) Foundation", n.d.,
<https://trustoverip.org>.

[Twin] "Digital Twin", n.d.,
<https://en.wikipedia.org/wiki/Digital_twin>.

[TwoPI] "Second Pre-image Attack on Merkle Trees", n.d.,
<https://flawed.net.nz/2018/02/21/attacking-merkle-trees-
with-a-second-preimage-attack/>.

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[VCEnh] "VC Spec Enhancement Strategy Proposal", n.d.,
<https://github.com/SmithSamuelM/Papers/blob/master/
whitepapers/VC_Enhancement_Strategy.md>.

[VCphr] "Vernom Cipher (OTP)", n.d.,
<https://www.ciphermachinesandcryptology.com/en/
onetimepad.htm>.

[vLEI] "vLEI (verifiable Legal Entity Identifier) Definition",
n.d., <https://github.com/WebOfTrust/vLEI>.

[W3C_DID] "W3C Decentralized Identifiers (DIDs) v1.0", n.d.,
<https://w3c-ccg.github.io/did-spec/>.

[W3C_VC] "W3C Verifiable Credentials Data Model v1.1", n.d.,
<https://www.w3.org/TR/vc-data-model/>.

[XORA] "XORA (XORed Accumulator)", n.d.,
<https://github.com/SmithSamuelM/Papers/blob/master/
whitepapers/XORA.md>.

Acknowledgments

ACDC community.

Author's Address

S. Smith
ProSapien LLC
Email: sam@prosapien.com

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