Internet DRAFT - draft-jmiller-jose-json-proof-algorithms

draft-jmiller-jose-json-proof-algorithms







jose                                                           J. Miller
Internet-Draft                                             Ping Identity
Intended status: Standards Track                                M. Jones
Expires: 11 September 2023                                     Microsoft
                                                           10 March 2023


                         JSON Proof Algorithms
              draft-jmiller-jose-json-proof-algorithms-01

Abstract

   The JSON Proof Algorithms (JPA) specification registers cryptographic
   algorithms and identifiers to be used with the JSON Web Proof (JWP)
   (https://www.ietf.org/archive/id/draft-jmiller-jose-json-web-proof-
   01.html) and JSON Web Key (JWK) specifications.  It defines several
   IANA registries for these identifiers.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 11 September 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Algorithm Basics  . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Issue . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.2.  Confirm . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.3.  Present . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.4.  Verify  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Algorithm Specifications  . . . . . . . . . . . . . . . . . .   6
     6.1.  Single Use  . . . . . . . . . . . . . . . . . . . . . . .   6
       6.1.1.  JWS Algorithm . . . . . . . . . . . . . . . . . . . .   6
       6.1.2.  Holder Setup  . . . . . . . . . . . . . . . . . . . .   6
       6.1.3.  Issuer Setup  . . . . . . . . . . . . . . . . . . . .   7
       6.1.4.  Using JWS . . . . . . . . . . . . . . . . . . . . . .   7
       6.1.5.  Issuer Protected Header . . . . . . . . . . . . . . .   7
       6.1.6.  Payloads  . . . . . . . . . . . . . . . . . . . . . .   7
       6.1.7.  Presentation Protected Header . . . . . . . . . . . .   8
       6.1.8.  Presentation  . . . . . . . . . . . . . . . . . . . .   8
       6.1.9.  Verification  . . . . . . . . . . . . . . . . . . . .   9
       6.1.10. JPA Registration  . . . . . . . . . . . . . . . . . .   9
       6.1.11. Example . . . . . . . . . . . . . . . . . . . . . . .   9
     6.2.  BBS . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
       6.2.1.  BLS Curve . . . . . . . . . . . . . . . . . . . . . .  10
       6.2.2.  Messages  . . . . . . . . . . . . . . . . . . . . . .  10
       6.2.3.  Issuer Protected Header . . . . . . . . . . . . . . .  10
       6.2.4.  Payloads  . . . . . . . . . . . . . . . . . . . . . .  10
       6.2.5.  Issuance  . . . . . . . . . . . . . . . . . . . . . .  11
       6.2.6.  Presentation  . . . . . . . . . . . . . . . . . . . .  11
       6.2.7.  Verification  . . . . . . . . . . . . . . . . . . . .  11
       6.2.8.  JPA Registration  . . . . . . . . . . . . . . . . . .  12
       6.2.9.  Example . . . . . . . . . . . . . . . . . . . . . . .  12
     6.3.  Message Authentication Code . . . . . . . . . . . . . . .  16
       6.3.1.  Holder Setup  . . . . . . . . . . . . . . . . . . . .  17
       6.3.2.  Issuer Setup  . . . . . . . . . . . . . . . . . . . .  17
       6.3.3.  Issuer Protected Header . . . . . . . . . . . . . . .  18
       6.3.4.  Payloads  . . . . . . . . . . . . . . . . . . . . . .  18
       6.3.5.  Issuer Proof  . . . . . . . . . . . . . . . . . . . .  18
       6.3.6.  Presentation Protected Header . . . . . . . . . . . .  19
       6.3.7.  Presentation  . . . . . . . . . . . . . . . . . . . .  19
       6.3.8.  Verifier Setup  . . . . . . . . . . . . . . . . . . .  19
       6.3.9.  JPA Registration  . . . . . . . . . . . . . . . . . .  21
       6.3.10. Example . . . . . . . . . . . . . . . . . . . . . . .  21
     6.4.  ZKSnark . . . . . . . . . . . . . . . . . . . . . . . . .  27
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27



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     8.1.  JWP Algorithms Registry . . . . . . . . . . . . . . . . .  27
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  27
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  28
   Appendix B.  Document History . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Introduction

   The JSON Web Proof (JWP) (https://www.ietf.org/archive/id/draft-
   jmiller-jose-json-web-proof-01.html) draft establishes a new secure
   container format that supports selective disclosure and unlinkability
   using Zero-Knowledge Proofs (ZKPs) or other cryptographic algorithms.

   |  Editor's Note: This draft is still early and incomplete, there
   |  will be significant changes to the algorithms as currently defined
   |  here.  Please do not use any of these definitions or examples for
   |  anything except personal experimentation and learning.
   |  Contributions and feedback are welcome at https://github.com/json-
   |  web-proofs/json-web-proofs (https://github.com/json-web-proofs/
   |  json-web-proofs).

2.  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.

   The roles of "issuer", "holder", and "verifier" are used as defined
   by the Verifiable Credentials Data Model v1.1
   (https://www.w3.org/TR/2021/REC-vc-data-model-20211109/).  The term
   "presentation" is also used as defined by this source, but the term
   "credential" is avoided in this specification in order to minimize
   confusion with other definitions.

3.  Terminology

   The terms "JSON Web Signature (JWS)", "Base64url Encoding", "Header
   Parameter", "JOSE Header", "JWS Payload", "JWS Signature", and "JWS
   Protected Header" are defined by [RFC7515].

   The terms "JSON Web Proof (JWP)", "JWP Payload", "JWP Proof", and
   "JWP Protected Header" are defined by the JWP draft.

   These terms are defined by this specification:





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   Stable Key An asymmetric key-pair used by an issuer that is also
   shared via an out-of-band mechanism to a verifier in order to
   validate the signature.

   Ephemeral Key An asymmetric key-pair that is generated for one-time
   use by an issuer and never stored or used again outside of the
   creation of a single JWP.

   Presentation Key An asymmetric key-pair that is generated by a holder
   and used to ensure that a presentation is not able to be replayed by
   any other party.

4.  Background

   JWP defines a container binding together a protected header, one or
   more payloads, and a cryptographic proof.  It does not define any
   details about the interactions between an application and the
   cryptographic libraries that implement proof-supporting algorithms.

   Due to the nature of ZKPs, this specification also documents the
   subtle but important differences in proof algorithms versus those
   defined by the JSON Web Algorithms [RFC7518].  These differences help
   support more advanced capabilities such as blinded signatures and
   predicate proofs.

5.  Algorithm Basics

   The four principal interactions that every proof algorithm MUST
   support are [issue](#issue), [confirm](#confirm),
   [present](#present), and [verify](#verify).

5.1.  Issue

   The JWP is first created as the output of a JPA's issue operation.

   Every algorithm MUST support a JSON issuer protected header along
   with one or more octet string payloads.  The algorithm MAY support
   using additional items provided by the holder for issuance such as
   blinded payloads, keys for replay prevention, etc.

   All algorithms MUST provide integrity protection for the issuer
   header and all payloads and MUST specify all digest and/or hash2curve
   methods used.

5.2.  Confirm

   Performed by the holder to validate the issued JWP is correctly
   formed and protected.



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   Each algorithm MAY support using additional input items options such
   as those sent to the issuer for issuance.  After confirmation, an
   algorithm MAY return a modified JWP for serialized storage without
   the local state (such as with blinded payloads now unblinded).

   The algorithm MUST fully verify the issued proof value against the
   issuer protected header and all payloads.  If given a presented JWP
   instead of an issued one the confirm process MUST return an error.

5.3.  Present

   Used to apply any selective disclosure choices and perform any
   unlinkability transformations.

   An algorithm MAY support additional input options from the requesting
   party such as for predicate proofs and verifiable computation
   requests.

   Every algorithm MUST support the ability to hide any or all payloads.
   It MUST always include the issuer protected header unmodified in the
   presentation.

   The algorithm MUST replace the issued proof value and generate a new
   presented proof value.  It also MUST include a new presentation
   protected header that provides replay protection.

5.4.  Verify

   Performed by the verifier to verify the protected headers along with
   any disclosed payloads and/or assertions about them from the proving
   party, while also verifying they are the same payloads and ordering
   as witnessed by the issuer.

   The algorithm MUST verify the integrity of all disclosed payloads and
   MUST also verify the integrity of both the issuer and presentation
   protected headers.

   If the presented proof contains any assertions about the hidden
   payloads, the algorithm MUST also verify all of those assertions.  It
   MAY support additional options such as those sent to the holder to
   generate the presentation.

   If given an issued JWP for verification, the algorithm MUST return an
   error.







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6.  Algorithm Specifications

   This section defines how to use specific algorithms for JWPs.

6.1.  Single Use

   |  Editor's Note: This algorithm is going to be renamed and slightly
   |  refactored; the new name is still TBD.

   The Single Use (SU) algorithm is based on composing multiple
   traditional JWS values into a single JWP proof value.  It enables a
   very simple form of selective disclosure without requiring any
   advanced cryptographic techniques.

   It does not support unlinkability if the same JWP is presented
   multiple times, therefore when privacy is required the holder will
   need to interact with the issuer again to receive new single-use JWPs
   (dynamically or in batches).

6.1.1.  JWS Algorithm

   The Single Use algorithm is based on using multiple JWS values, all
   of which are generated with the same JSON Web Algorithm (JWA) for
   signing.  This JWA identifier is included as part of the Single Use
   identifier for JWP.

   The chosen JWA MUST be an asymmetric signing algorithm so that each
   signature can be verified without sharing any private values between
   the parties.  This ensures that the verifier cannot brute force any
   non-disclosed payloads based only on their disclosed individual
   signatures.

6.1.2.  Holder Setup

   In order to support the protection of a presentation by a holder to a
   verifier, the holder MUST use a Presentation Key during the issuance
   and the presentation of every Single Use JWP.  This Presentation Key
   MUST be generated and used for only one JWP.

   The issuer MUST verify that the holder has possession of this key.
   The holder-issuer communication to exchange this information is out
   of scope of this specification but can be easily accomplished by the
   holder using this key to generate a JWS that signs a value the issuer
   can verify as unique.







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6.1.3.  Issuer Setup

   To create a Single Use JWP the issuer first generates a unique
   Ephemeral Key using the selected JWS algorithm.  This key-pair will
   be used to sign each of the payloads of a single JWP and then
   discarded.

6.1.4.  Using JWS

   JSON Web Signatures are used to create all of the signature values
   used by the SU algorithm.  This allows an implementation to use an
   existing JWS library directly for all necessary cryptographic
   operations without requiring any additional primitives.

   Each individual JWS uses a fixed protected header containing only the
   minimum required alg value.  Since this JWS protected header itself
   is the same for every JWS, it SHOULD be a static value in the form of
   {"alg":"***"} where *** is the JWA asymmetric signing key algorithm
   identifier being used.  This value is recreated by a verifier using
   the correct JWA algorithm value included in the SU algorithm
   identifier.

   If an implementation uses an alternative JWS protected header than
   this fixed value, a base64url encoded serialized form of the
   alternate fixed header MUST be included using the jws_header claim in
   the issuer protected header.

6.1.5.  Issuer Protected Header

   The JWK of the issuer's Ephemeral Key MUST be included in the issuer
   protected header with the property name of proof_jwk and contain only
   the REQUIRED values to represent the public key.

   The holder's Presentation Key JWK MUST be included in issuer
   protected header using the presentation_jwk claim.

   The final issuer protected header is then used directly as the body
   of a JWS and signed using the issuer's Stable Key.  The resulting JWS
   signature value unencoded octet string is the first value in the JWP
   proof.

6.1.6.  Payloads

   Each JWP payload is processed in order and signed as a JWS body using
   the issuer's Ephemeral Key.  The resulting JWS signature value
   unencoded octet string is appended to the JWP proof.





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   The proof value as an octet string will have a total length that is
   the sum of the fixed length of the issuer protected header signature
   plus the fixed length of each of the payload Ephemeral Key
   signatures.  For example, the signature for the ES256 algorithm is 64
   octets and for a JWP with five payloads the total proof value length
   would be 64 * (1 + 5) = 384 octets).

6.1.7.  Presentation Protected Header

   In order to generate a new presentation, the holder first creates a
   presentation protected header that is specific to the verifier being
   presented to.  This header MUST contain a claim that both the holder
   and verifier trust as being unique and non-replayable.

   This specification registers a nonce claim for the presentation
   protected header that contains a string value either generated by the
   verifier or derived from values provided by the verifier.  When
   present, the verifier MUST ensure the nonce value matches during
   verification.

   The presentation protected header MAY contain other claims that are
   either provided by the verifier or by the holder.  These presentation
   claims SHOULD NOT contain values that are common across multiple
   presentations and SHOULD be unique to a single presentation and
   verifier.

6.1.8.  Presentation

   |  Editor's Note: The current definition here is incomplete, the
   |  holder's signature needs to also incorporate the presented proof.

   The holder derives a new proof value when presenting it to a
   verifier.  The presented proof value will always contain the issuer's
   Stable Key signature for the issuer protected header as the first
   element.

   The second element of the presented proof value is always the
   holder's Presentation Key signature of the presentation protected
   header, constructed identically to the issuer protected header by
   using the serialized JSON value octet string as the JWS body.
   Signing only the presentation header with the Presentation Key is
   sufficient to protect the entire presentation since that key is
   private to the holder and only the contents of the presentation
   header are used for replay prevention.

   The two header signatures are then followed by only the issuer's
   Ephemeral Key signatures for each payload that is disclosed.  The
   order of the payload signatures is preserved and MUST be in the same



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   order as the included disclosed payloads in the presented JWP.  Non-
   disclosed payloads will NOT have a signature value included.  For
   example, if the second and fifth payloads are hidden then the
   holder's derived proof value would be of the length 64 * (1 + 1 + the
   1st, 2nd, and 4th payload signatures) = 320 octets.

   Since the individual signatures in the proof value are unique and
   remain unchanged across multiple presentations, a Single Use JWP
   SHOULD only be presented a single time to each verifier in order for
   the holder to remain unlinkable across multiple presentations.

6.1.9.  Verification

   The verifier MUST verify the issuer protected header against the
   first matching JWS signature part in the proof value using the
   issuer's Stable Key.  It MUST also verify the presentation protected
   header against the second JWS signature part in the proof value using
   the holder's Presentation Key as provided in the presentation_jwk
   claim in the issuer protected header.

   With the headers verified, the issuer's Ephemeral Key as given in the
   issuer protected header proof_jwk claim can then be used to verify
   each of the disclosed payload signatures.

6.1.10.  JPA Registration

   Proposed JWP alg value is of the format "SU-" appended with the
   relevant JWS alg value for the chosen public and ephemeral key-pair
   algorithm, for example "SU-ES256".

6.1.11.  Example

   See the example in the appendix of the JSON Web Proof draft.

6.2.  BBS

   The BBS Signature Scheme under active standards development as a work
   item (https://github.com/decentralized-identity/bbs-signature) within
   the DIF Applied Cryptography Working Group
   (https://identity.foundation/working-groups/crypto.html).  Prior to
   this effort, a V1 implementation of BBS
   (https://github.com/mattrglobal/bbs-signatures) has been released and
   maintained by a community of individuals with notable adoption in
   multiple early stage decentralized identity projects.







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   This JSON Proof Algorithm definition for BBS is based on the already
   released implementation and relies on the provided software API.  A
   future definition with a different alg value will be created to
   succeed this version as the BBS standardization effort progresses.

   This algorithm supports both selective disclosure and unlinkability,
   enabling the holder to generate multiple presentations from one
   issued JWP without any verifier being able to correlate those
   presentations together.

6.2.1.  BLS Curve

   The pairing friendly elliptic curve used for the BBS software
   implementation is part of the BLS family with an embedding degree of
   12 over a 381-bit prime field.  For this JPA, only the group G2 is
   used.

   In the implementation the method used to generate the key pairs is
   generateBls12381G2KeyPair().

6.2.2.  Messages

   BBS is a multi-message scheme and operates on an array of individual
   messages for signing and proof generation.  Each message is a single
   binary octet string.  The BBS implementation uses a hash-to-curve
   method to map each message to a point.

6.2.3.  Issuer Protected Header

   The UTF-8 octet string of the issuer protected header is the first
   message in the input array at index 0.

6.2.4.  Payloads

   The octet strings of each payload are placed into the BBS message
   array following the issuer protected header message.  For example,
   the first payload is at index 1 of the array and the last payload is
   always the last message in the array.

   In future versions of this algorithm, there will be additional
   methods defined for transforming a payload into a point such that
   additional Zero-Knowledge Proof types can be supported by the holder
   such as range and membership predicates.








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6.2.5.  Issuance

   The issuer's BLS12-381 G2 Stable Key is used to sign the completed
   message array input containing the octet strings of the issuer
   protected header and every payload.  The result is a signature octet
   string that is used as the initial JWP proof value.

   In the implementation, the method used to perform the signing is
   blsSign({keyPair, [header, payload1, payload2, ...]}) and returns a
   binary signature value.

6.2.6.  Presentation

   The holder must decode the issuer protected header and payload values
   in order to generate the identical message array that the issuer
   used.

   To generate a presented JWP for a verifier, the holder must use a
   cryptographic nonce that is provided by that verifier as input.  This
   nonce MUST be a 32-byte octet string that the verifier generated by a
   secure RNG.  How this nonce value is communicated to the holder is
   out of scope of this presentation.  The nonce claim in the
   presentation protected header is used to store the verifier's given
   nonce value.

   The holder also applies selective disclosure preferences by creating
   an array of indices of which messages in the input array are to be
   revealed to the verifier.  The revealed indices MUST include the
   value 0 so that the issuer protected header message is always
   revealed to the verifier.

   The result of creating a proof is an octet string that is used as the
   presented JWP proof value.

   In the implementation, the method used to generate the proof is
   blsCreateProof({signedProof, publicKey, [issuer_header, payload1,
   payload2, ...], presentation_header, [0, 2, ...]).

6.2.7.  Verification

   The verifier decodes the JWP issuer protected header and payload
   values into a messages array, skipping any non-revealed payloads.
   The current BBS implementation embeds the revealed indices into the
   output proof value, so the verification messages array only needs to
   include the disclosed messages.






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   In the implementation, the method used to verify the proof is
   blsVerifyProof({verifyProof, publicKey, [issuer_header, payload2,
   ...], presentation_header).

6.2.8.  JPA Registration

   Proposed JWP alg value for BBS based on the software implementation
   is "BBS-X".

6.2.9.  Example

   The following example uses the given BLS12-384 key-pair:

   Public:

   [179, 209, 122, 60, 230, 37, 188, 86, 19, 19, 4, 36, 240, 230, 79,
   178, 230, 147, 9, 60, 239, 41, 233, 167, 190, 252, 154, 35, 39, 201,
   238, 73, 77, 228, 20, 47, 109, 174, 15, 168, 187, 145, 126, 85, 83,
   151, 48, 30, 13, 237, 92, 179, 124, 181, 211, 204, 187, 222, 229,
   234, 182, 94, 60, 157, 19, 148, 162, 48, 185, 134, 177, 168, 68,
   115, 167, 48, 92, 181, 168, 53, 52, 246, 201, 112, 103, 23, 159,
   138, 225, 13, 165, 171, 251, 112, 163, 96]

                     Figure 1: bbs-issuer-public-octets

   Private:

   [72, 125, 227, 97, 150, 148, 186, 145, 110, 46, 135, 232, 104, 204,
   128, 242, 73, 151, 72, 162, 0, 54, 139, 146, 221, 137, 34, 74, 1,
   42, 140, 206]

                    Figure 2: bbs-issuer-private-octets

   The protected header used is:

   {
     "iss": "https://issuer.example",
     "claims": [
       "family_name",
       "given_name",
       "email",
       "age"
     ],
     "typ": "JPT",
     "alg": "BBS-X"
   }

                   Figure 3: bbs-issuer-protected-header



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   The first payload is the string "Doe" with the octet sequence of [
   34, 68, 111, 101, 34 ] and base64url-encoded as IkRvZSI.

   The second payload is the string "Jay" with the octet sequence of [
   34, 74, 97, 121, 34 ] and base64url-encoded as IkpheSI.

   The third payload is the string "jaydoe@example.org" with the octet
   sequence of [ 34, 106, 97, 121, 100, 111, 101, 64, 101, 120, 97, 109,
   112, 108, 101, 46, 111, 114, 103, 34 ] and base64url-encoded as
   ImpheWRvZUBleGFtcGxlLm9yZyI.

   The fourth payload is the string 42 with the octet sequence of [ 52,
   50 ] and base64url-encoded as NDI.

   The message array used as an input to the BLS implementation is:

   [
    [123, 34, 105, 115, 115, 34, 58, 34, 104, 116, 116, 112, 115, 58,
     47, 47, 105, 115, 115, 117, 101, 114, 46, 101, 120, 97, 109, 112,
     108, 101, 34, 44, 34, 99, 108, 97, 105, 109, 115, 34, 58, 91, 34,
     102, 97, 109, 105, 108, 121, 95, 110, 97, 109, 101, 34, 44, 34,
     103, 105, 118, 101, 110, 95, 110, 97, 109, 101, 34, 44, 34, 101,
     109, 97, 105, 108, 34, 44, 34, 97, 103, 101, 34, 93, 44, 34, 116,
     121, 112, 34, 58, 34, 74, 80, 84, 34, 44, 34, 97, 108, 103, 34, 58,
     34, 66, 66, 83, 45, 88, 34, 125],
    [ 34, 68, 111, 101, 34 ],
    [ 34, 74, 97, 121, 34 ],
    [34, 106, 97, 121, 100, 111, 101, 64, 101, 120, 97, 109, 112, 108,
    101, 46, 111, 114, 103, 34], [ 52, 50 ]
   ]

                       Figure 4: bbs-issuer-messages

   Using the above inputs, the output of the blsSign() call is the octet
   string:

   [180, 3, 66, 254, 9, 205, 20, 88, 175, 82, 90, 34, 26, 178, 80, 225,
   91, 209, 120, 23, 185, 159, 76, 73, 189, 236, 115, 141, 31, 83, 43,
   42, 186, 247, 196, 236, 70, 19, 123, 80, 249, 146, 237, 172, 48,
   208, 193, 62, 100, 59, 154, 22, 52, 165, 184, 250, 71, 52, 106, 233,
   26, 240, 251, 214, 122, 133, 61, 241, 70, 127, 83, 240, 112, 130,
   181, 151, 160, 214, 43, 213, 83, 211, 238, 191, 1, 65, 135, 147,
   226, 197, 24, 104, 183, 9, 141, 207, 21, 106, 136, 161, 115, 142, 3,
   196, 155, 52, 174, 205, 212, 13, 174, 220]

                       Figure 5: bbs-issuer-signature

   The resulting signed JWP in JSON serialization is:



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   {
     "protected": "eyJpc3MiOiJodHRwczovL2lzc3Vlci5leGFtcGxlIiwiY2xhaW1z
     IjpbImZhbWlseV9uYW1lIiwiZ2l2ZW5fbmFtZSIsImVtYWlsIiwiYWdlIl0sInR5cC
     I6IkpQVCIsImFsZyI6IkJCUy1YIn0",
     "payloads": [
       "IkRvZSI",
       "IkpheSI",
       "ImpheWRvZUBleGFtcGxlLm9yZyI",
       "NDI"
     ],
     "proof": "tANC_gnNFFivUloiGrJQ4VvReBe5n0xJvexzjR9TKyq698TsRhN7UPmS
     7aww0ME-ZDuaFjSluPpHNGrpGvD71nqFPfFGf1PwcIK1l6DWK9VT0-6_AUGHk-LFGG
     i3CY3PFWqIoXOOA8SbNK7N1A2u3A"
   }

                          Figure 6: bbs-issued-jwp

   The same JWP in compact serialization:

   ImV5SnBjM01pT2lKb2RIUndjem92TDJsemMzVmxjaTVsZUdGdGNHeGxJaXdpWTJ4aGFX
   MXpJanBiSW1aaGJXbHNlVjl1WVcxbElpd2laMmwyWlc1ZmJtRnRaU0lzSW1WdFlXbHNJ
   aXdpWVdkbElsMHNJblI1Y0NJNklrcFFWQ0lzSW1Gc1p5STZJa0pDVXkxWUluMCI.IkRv
   ZSI~IkpheSI~ImpheWRvZUBleGFtcGxlLm9yZyI~NDI.tANC_gnNFFivUloiGrJQ4VvR
   eBe5n0xJvexzjR9TKyq698TsRhN7UPmS7aww0ME-ZDuaFjSluPpHNGrpGvD71nqFPfFG
   f1PwcIK1l6DWK9VT0-6_AUGHk-LFGGi3CY3PFWqIoXOOA8SbNK7N1A2u3A

                        Figure 7: bbs-issued-compact

   For verification, a nonce is needed:

   [137, 103, 248, 147, 211, 133, 97, 190, 130, 157, 110, 64, 244, 250,
   100, 151, 7, 36, 164, 109, 146, 195, 190, 75, 32, 255, 6, 128, 44,
   128, 96, 9]

                        Figure 8: bbs-present-nonce

   To generate a proof, the blsCreateProof() method is used with a
   revealed indexes array argument of [ 0, 2, 4 ] and results in the
   octet string:












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   [0, 5, 21, 169, 73, 242, 49, 111, 234, 26, 186, 194, 204, 174, 241,
   30, 165, 50, 117, 236, 144, 95, 147, 186, 219, 190, 135, 205, 66,
   179, 227, 86, 151, 246, 174, 234, 204, 46, 171, 249, 225, 198, 135,
   81, 131, 225, 141, 217, 47, 217, 127, 176, 15, 98, 110, 233, 74,
   220, 230, 27, 201, 117, 114, 211, 41, 183, 44, 64, 185, 45, 140,
   153, 49, 73, 199, 93, 208, 248, 212, 175, 106, 199, 83, 255, 128,
   77, 152, 250, 166, 101, 78, 248, 10, 106, 236, 24, 238, 21, 34, 134,
   128, 186, 132, 153, 123, 86, 88, 156, 246, 203, 23, 253, 248, 217,
   233, 1, 168, 208, 12, 193, 222, 142, 90, 28, 223, 241, 130, 164,
   144, 83, 0, 15, 165, 25, 156, 145, 243, 39, 88, 249, 246, 185, 152,
   3, 220, 72, 180, 0, 0, 0, 116, 133, 180, 58, 53, 105, 120, 124, 227,
   160, 78, 229, 74, 209, 111, 164, 101, 183, 86, 122, 212, 126, 90,
   23, 228, 109, 184, 73, 75, 114, 177, 142, 178, 89, 107, 100, 189,
   187, 74, 143, 167, 218, 186, 193, 189, 247, 14, 134, 40, 0, 0, 0, 2,
   5, 130, 120, 86, 255, 28, 33, 145, 20, 149, 195, 8, 4, 200, 212,
   178, 67, 147, 230, 174, 192, 9, 158, 94, 179, 144, 63, 60, 82, 255,
   216, 4, 85, 108, 209, 194, 209, 177, 106, 69, 215, 235, 177, 83,
   244, 1, 195, 102, 135, 99, 20, 121, 7, 252, 26, 187, 206, 16, 250,
   134, 1, 255, 197, 92, 130, 105, 241, 175, 35, 22, 210, 101, 158,
   113, 214, 222, 3, 4, 168, 188, 251, 34, 213, 211, 224, 150, 147, 38,
   164, 229, 151, 226, 223, 188, 181, 180, 204, 228, 58, 107, 55, 232,
   148, 180, 199, 42, 181, 127, 59, 233, 234, 188, 0, 0, 0, 4, 93, 196,
   31, 38, 151, 105, 231, 46, 228, 46, 86, 196, 136, 212, 175, 170, 83,
   21, 78, 19, 224, 211, 122, 7, 92, 71, 17, 171, 66, 122, 56, 130, 45,
   19, 172, 217, 65, 63, 246, 39, 6, 30, 77, 132, 86, 36, 41, 3, 234,
   72, 146, 200, 101, 150, 159, 108, 140, 15, 195, 57, 249, 154, 191,
   204, 91, 30, 159, 32, 157, 24, 3, 110, 90, 102, 99, 206, 42, 58, 1,
   181, 215, 85, 29, 32, 131, 46, 76, 25, 5, 43, 203, 32, 215, 167,
   169, 108, 56, 174, 146, 51, 174, 40, 190, 22, 37, 93, 156, 245,
   208, 26, 55, 180, 135, 115, 70, 96, 106, 243, 213, 131, 196, 63,
   165, 42, 157, 22, 94, 46]

                        Figure 9: bbs-present-proof

   The resulting verifiable JWP in JSON serialization is:
















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   {
     "protected": "eyJpc3MiOiJodHRwczovL2lzc3Vlci5leGFtcGxlIiwiY2xhaW1z
     IjpbImZhbWlseV9uYW1lIiwiZ2l2ZW5fbmFtZSIsImVtYWlsIiwiYWdlIl0sInR5cC
     I6IkpQVCIsImFsZyI6IkJCUy1YIn0",
     "payloads": [
       null,
       "IkpheSI",
       null,
       "NDI"
     ],
     "proof": "AAUVqUnyMW_qGrrCzK7xHqUydeyQX5O6276HzUKz41aX9q7qzC6r-eHG
     h1GD4Y3ZL9l_sA9ibulK3OYbyXVy0ym3LEC5LYyZMUnHXdD41K9qx1P_gE2Y-qZlTv
     gKauwY7hUihoC6hJl7Vlic9ssX_fjZ6QGo0AzB3o5aHN_xgqSQUwAPpRmckfMnWPn2
     uZgD3Ei0AAAAdIW0OjVpeHzjoE7lStFvpGW3VnrUfloX5G24SUtysY6yWWtkvbtKj6
     fausG99w6GKAAAAAIFgnhW_xwhkRSVwwgEyNSyQ5PmrsAJnl6zkD88Uv_YBFVs0cLR
     sWpF1-uxU_QBw2aHYxR5B_wau84Q-oYB_8VcgmnxryMW0mWecdbeAwSovPsi1dPglp
     MmpOWX4t-8tbTM5DprN-iUtMcqtX876eq8AAAABF3EHyaXaecu5C5WxIjUr6pTFU4T
     4NN6B1xHEatCejiCLROs2UE_9icGHk2EViQpA-pIkshllp9sjA_DOfmav8xbHp8gnR
     gDblpmY84qOgG111UdIIMuTBkFK8sg16epbDiukjOuKL4WJV2c9dAaN7SHc0ZgavPV
     g8Q_pSqdFl4u"
   }

                         Figure 10: bbs-present-jwp

   The same JWP in compact serialization:

   ImV5SnBjM01pT2lKb2RIUndjem92TDJsemMzVmxjaTVsZUdGdGNHeGxJaXdpWTJ4aGFX
   MXpJanBiSW1aaGJXbHNlVjl1WVcxbElpd2laMmwyWlc1ZmJtRnRaU0lzSW1WdFlXbHNJ
   aXdpWVdkbElsMHNJblI1Y0NJNklrcFFWQ0lzSW1Gc1p5STZJa0pDVXkxWUluMCI.~Ikp
   heSI~~NDI.AAUVqUnyMW_qGrrCzK7xHqUydeyQX5O6276HzUKz41aX9q7qzC6r-eHGh1
   GD4Y3ZL9l_sA9ibulK3OYbyXVy0ym3LEC5LYyZMUnHXdD41K9qx1P_gE2Y-qZlTvgKau
   wY7hUihoC6hJl7Vlic9ssX_fjZ6QGo0AzB3o5aHN_xgqSQUwAPpRmckfMnWPn2uZgD3E
   i0AAAAdIW0OjVpeHzjoE7lStFvpGW3VnrUfloX5G24SUtysY6yWWtkvbtKj6fausG99w
   6GKAAAAAIFgnhW_xwhkRSVwwgEyNSyQ5PmrsAJnl6zkD88Uv_YBFVs0cLRsWpF1-uxU_
   QBw2aHYxR5B_wau84Q-oYB_8VcgmnxryMW0mWecdbeAwSovPsi1dPglpMmpOWX4t-8tb
   TM5DprN-iUtMcqtX876eq8AAAABF3EHyaXaecu5C5WxIjUr6pTFU4T4NN6B1xHEatCej
   iCLROs2UE_9icGHk2EViQpA-pIkshllp9sjA_DOfmav8xbHp8gnRgDblpmY84qOgG111
   UdIIMuTBkFK8sg16epbDiukjOuKL4WJV2c9dAaN7SHc0ZgavPVg8Q_pSqdFl4u

                       Figure 11: bbs-present-compact

6.3.  Message Authentication Code

   The Message Authentication Code (MAC) JPA uses a MAC to both generate
   ephemeral keys and compute authentication codes to protect the issuer
   header and each payload individually.





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   Like the JWS-based JPA, it also does not support unlinkability if the
   same JWP is presented multiple times and requires an individually
   issued JWP for each presentation in order to fully protect privacy.
   When compared to the JWS approach, using a MAC requires less
   computation but can result in potentially larger presentation proof
   values.

   The design is intentionally minimal and only involves using a single
   standardized MAC method instead of a mix of MAC/hash methods or a
   custom hash-based construct.  It is able to use any published
   cryptographic MAC method such as HMAC
   (https://datatracker.ietf.org/doc/html/rfc2104) or KMAC
   (https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
   NIST.SP.800-185.pdf).  It uses traditional public-key based
   signatures to verify the authenticity of the issuer and holder.

6.3.1.  Holder Setup

   Prior to the issuer creating a new JWP it must have presentation
   binding information provided by the holder.  This enables the holder
   to perform replay prevention while presenting the JWP.

   The presentation key used by the holder must be transferred to the
   issuer and verified, likely through a challenge and self-signing
   mechanism.  If the holder requires unlinkability it must also
   generate a new key that is verified and bound to each new JWP.

   How these holder presentation keys are transferred and verified is
   out of scope of this specification, protocols such as OpenID Connect
   can be used to accomplish this.  What is required by this definition
   is that the holder's presentation key MUST be included in the
   issuer's protected header using the pjwk claim with a JWK as the
   value.

6.3.2.  Issuer Setup

   To use the MAC algorithm the issuer must have a stable public key
   pair to perform signing.  To start the issuance process, a single
   32-byte random Shared Secret must first be generated.  This value
   will be shared privately to the holder as part of the issuer's JWP
   proof value.

   The Shared Secret is used by both the issuer and holder as the MAC
   method's key to generate a new set of unique ephemeral keys.  These
   keys are then used as the input to generate a MAC that protects each
   payload.





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6.3.3.  Issuer Protected Header

   The holder's presentation key JWK MUST be included in the issuer
   protected header using the pjwk claim.  The issuer MUST validate that
   the holder has possession of this key through a trusted mechanism
   such as verifying the signature of a unique nonce value from the
   holder.

   For consistency, the issuer header is also protected by a MAC by
   using the fixed value "issuer_header" as the input key.  The issuer
   header JSON is serialized using UTF-8 and encoded with base64url into
   an octet array.  The final issuer header MAC is generated from the
   octet array and the fixed key, and the resulting value becomes the
   first input into the larger octet array that will be signed by the
   issuer.

6.3.4.  Payloads

   A unique key is generated for each payload using the MAC with the
   Shared Secret as the key and the values "payload_X" where "X" is
   replaced by the zero-based array index of the payload, for example
   "payload_0", "payload_1", etc.

   Each payload is serialized using UTF-8 and encoded with base64url
   into an octet array.  The generated key for that payload based on its
   index is used to generate the MAC for the payload's encoded octet
   array.  The resulting value is appended to the larger octet array
   that will be signed by the issuer.

6.3.5.  Issuer Proof

   The issuer proof consists of two items appended together, the
   issuer's signature of the appended array of MACs, and the Shared
   Secret used to generate the set of payload keys.

   To generate the signature, the array containing the final MAC of the
   issuer protected header followed by all of the payload MACs appended
   in order is used as the input to a new JWS.

   jws_payload = [issuer_header_mac, payload_mac_1, ... payload_mac_n]

   The issuer signs the JWS using its stable public key and a fixed
   header containing the alg associated with MAC algorithm in use.

   jws_header = '{"alg":"ES256"}'






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   The resulting signature is decoded and used as the first item in the
   issuer proof value.  The octet array of the Shared Secret is
   appended, resulting in the final issuer proof value.

   issuer_proof = [jws_signature, shared_secret]

6.3.6.  Presentation Protected Header

   See the JWS Presentation Protected Header (#presentation-protected-
   header) section.

6.3.7.  Presentation

   |  Editor's Note: The current definition here is incomplete, the
   |  holder's signature needs to also incorporate the presented proof.

   The presentation proof is constructed as a large octet array
   containing multiple appended items similar to the issuer proof value.
   The first item is the JWS decoded signature value generated when the
   holder uses the presentation key to sign the presentation header.
   The second item is the issuer signature from the issuer's proof
   value.

   These two signatures are then followed by a MAC value for each
   payload.  The MAC values used will depend on if that payload has been
   disclosed or is hidden.  Disclosed payloads will include the MAC key
   input, and hidden payloads will include only their final MAC value.

   presentation_proof = [presentation_signature, issuer_signature,
                         disclosed_key_0, hidden_mac_1, hidden_mac_2,
                         ... disclosed_key_n]

   The size of this value will depend on the underlying cryptographic
   algorithms.  For example, MAC-H256 uses the ES256 JWS with a decoded
   signature of 64 octets, and for a JWP with five payloads using HMAC-
   SHA256 the total presentation proof value length would be 64 + 64 +
   (5 * 32) = 288 octets.

6.3.8.  Verifier Setup

   In order to verify that the presentation was protected from replay
   attacks, the verifier must be able to validate the presentation
   protected header.  This involves the following steps:

   1.  JSON parse the presentation header

   2.  Validate the contained nonce claim




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   3.  JSON parse the issuer header

   4.  Validate the contained pjwk claim

   5.  Create a JWS using the correct fixed header with alg value and
       the presentation header as the body

   6.  Remove the presentation_signature from the beginning of the
       presentation_proof octet array

   7.  Validate the JWS using the JWK from the pjwk claim and the
       presentation_signature value

   Next, the verifier must validate all of the disclosed payloads using
   the following steps:

   1.  JSON parse the issuer header

   2.  Resolve the kid using a trusted mechanism to obtain the correct
       issuer JWK

   3.  Remove the issuer_signature from the beginning of the remaining
       presentation_proof octet array (after the presentation_signature
       was removed)

   4.  Perform the MAC on the presented issuer_header value using the
       "issuer_header" value as the input key

   5.  Store the resulting value as the first entry in a new jws_payload
       octet array

   6.  Iterate on each presented payload (disclosed or hidden)

       1.  Extract the next hash value from the remaining
           presentation_proof octet array

       2.  If the payload was disclosed: perform a MAC using the given
           hash value as the input key and append the result to the
           jws_payload octet array

       3.  If the payload was hidden: append the given hash value to the
           jws_payload octet array

   7.  Create a JWS using a header containing the alg parameter along
       with the generated jws_payload value as the payload

   8.  Validate the JWS using the resolved issuer JWK and the extracted
       issuer_signature value



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6.3.9.  JPA Registration

   Proposed JWP alg value is of the format "MAC-" appended with a unique
   identifier for the set of MAC and signing algorithms used.  Below are
   the initial registrations:

   *  MAC-H256 uses HMAC SHA-256 as the MAC and ECDSA using P-256 and
      SHA-256 for the signatures

   *  MAC-H384 uses HMAC SHA-384 as the MAC and ECDSA using P-384 and
      SHA-384 for the signatures

   *  MAC-H512 uses HMAC SHA-512 as the MAC and ECDSA using P-521 and
      SHA-512 for the signatures

   *  MAC-K25519 uses KMAC SHAKE128 as the MAC and EdDSA using
      Curve25519 for the signatures

   *  MAC-K448 uses KMAC SHAKE256 as the MAC and EdDSA using Curve448
      for the signatures

   *  MAC-H256K uses HMAC SHA-256 as the MAC and ECDSA using secp256k1
      and SHA-256 for the signatures

6.3.10.  Example

   The following example uses the MAC-H256 algorithm.

   This is the Signer's stable private key in the JWK format:

   {
     "crv": "P-256",
     "kty": "EC",
     "x": "ONebN43-G5DOwZX6jCVpEYEe0bYd5WDybXAG0sL3iDA",
     "y": "b0MHuYfSxu3Pj4DAyDXabAc0mPjpB1worEpr3yyrft4",
     "d": "jnE0-9YvxQtLJEKcyUHU6HQ3Y9nSDnh0NstYJFn7RuI"
   }

                       Figure 12: issuer-private-jwk

   This is the Signer's generated Shared Secret:

   [100, 109, 91, 184, 139, 20, 107, 86, 1, 252, 86, 159, 126, 251,
   228, 4, 35, 177, 75, 96, 11, 205, 144, 189, 42, 95, 135, 170, 107,
   58, 99, 142]

                        Figure 13: mac-shared-secret




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   This is the Holder's presentation private key in the JWK format:

   {
     "crv": "P-256",
     "kty": "EC",
     "x": "oB1TPrE_QJIL61fUOOK5DpKgd8j2zbZJtqpILDTJX6I",
     "y": "3JqnrkucLobkdRuOqZXOP9MMlbFyenFOLyGlG-FPACM",
     "d": "AvyDPl1I4xwjrI2iEOi6DxM9ipJe_h_VUN5OvoKvvW8"
   }

                     Figure 14: holder-presentation-jwk

   The first MAC is generated using the key issuer_header and the
   base64url-encoded issuer protected header, resulting in this octet
   array:

   [140, 88, 59, 30, 127, 113, 27, 237, 78, 200, 182, 114, 94, 123,
   198, 128, 102, 232, 178, 88, 252, 248, 57, 2, 231, 19, 145, 8, 160,
   197, 66, 166]

                      Figure 15: mac-issuer-header-mac

   The issuer generates an array of derived keys with one for each
   payload by using the shared secret as the key and the index of the
   payload as the input:

   [
    [180, 129, 55, 94, 125, 158, 179, 245, 30, 199, 148, 60, 184, 28,
    197, 123, 231, 232, 95, 91, 65, 74, 38, 242, 253, 96, 67, 44, 40,
    220, 250, 4],
    [143, 172, 182, 156, 184, 138, 228, 172, 215, 26, 175, 137, 137,
    25, 159, 141, 213, 12, 214, 29, 231, 200, 13, 94, 116, 22, 41, 115,
    72, 214, 57, 98],
    [144, 73, 77, 66, 230, 187, 217, 186, 246, 41, 138, 25, 39, 203,
    101, 76, 156, 161, 244, 130, 203, 166, 184, 154, 7, 4, 218, 84,
    168, 199, 36, 245],
    [70, 55, 182, 105, 101, 130, 254, 234, 68, 224, 219, 97, 119, 98,
    244, 33, 43, 55, 148, 238, 225, 177, 101, 160, 49, 246, 109, 155,
    242, 236, 21, 138]
   ]

                         Figure 16: mac-issuer-keys

   The first payload is the string "Doe" with the octet sequence of [
   34, 68, 111, 101, 34 ] and base64url-encoded as IkRvZSI.

   The second payload is the string "Jay" with the octet sequence of [
   34, 74, 97, 121, 34 ] and base64url-encoded as IkpheSI.



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   The third payload is the string "jaydoe@example.org" with the octet
   sequence of [ 34, 106, 97, 121, 100, 111, 101, 64, 101, 120, 97, 109,
   112, 108, 101, 46, 111, 114, 103, 34 ] and base64url-encoded as
   ImpheWRvZUBleGFtcGxlLm9yZyI.

   The fourth payload is the string 42 with the octet sequence of [ 52,
   50 ] and base64url-encoded as NDI.

   A MAC is generated for each payload using the generated key for its
   given index, resulting in an array of MACs:

   [
    [156, 53, 90, 125, 139, 226, 60, 168, 100, 220, 79, 255, 8, 87, 28,
    220, 237, 112, 161, 91, 39, 68, 137, 203, 92, 243, 16, 116, 64,
    129, 61, 172],
    [239, 17, 12, 35, 111, 129, 51, 87, 43, 86, 234, 38, 89, 149, 169,
    157, 33, 104, 81, 246, 190, 154, 74, 195, 194, 158, 50, 208, 203,
    203, 249, 237],
    [162, 174, 12, 27, 190, 250, 112, 1, 139, 177, 49, 124, 110, 201,
    83, 233, 14, 109, 60, 253, 121, 184, 126, 121, 26, 138, 5, 214, 97,
    96, 216, 80],
    [61, 109, 78, 172, 255, 189, 67, 83, 247, 65, 234, 128, 30, 47,
    145, 70, 129, 26, 41, 41, 78, 4, 151, 230, 232, 127, 135, 230, 14,
    208, 178, 50]
   ]

                         Figure 17: mac-issuer-macs

   Concatenating the issuer protected header MAC with the array of
   payload MACs produces a single octet array that is signed using the
   issuer's stable key, resulting in the following signature:

   [120, 172, 15, 230, 138, 230, 150, 139, 241, 196, 79, 134, 122, 43,
   149, 11, 253, 104, 58, 199, 49, 87, 32, 64, 237, 50, 86, 155, 153,
   58, 63, 116, 245, 130, 136, 197, 164, 207, 232, 238, 106, 171, 246,
   98, 149, 254, 22, 1, 114, 187, 233, 168, 116, 173, 211, 208, 234,
   245, 76, 238, 143, 157, 83, 202]

                      Figure 18: mac-issuer-signature

   The original shared secret octet string is then concatenated to the
   end of the issuer signature octet string and the result is base64url-
   encoded as the issuer's proof value.

   The final issued JWP in JSON serialization is:






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   {
     "payloads": [
       "IkRvZSI",
       "IkpheSI",
       "ImpheWRvZUBleGFtcGxlLm9yZyI",
       "NDI"
     ],
     "issuer": "eyJpc3MiOiJodHRwczovL2lzc3Vlci50bGQiLCJjbGFpbXMiOlsiZmF
     taWx5X25hbWUiLCJnaXZlbl9uYW1lIiwiZW1haWwiLCJhZ2UiXSwidHlwIjoiSlBUI
     iwicGp3ayI6eyJjcnYiOiJQLTI1NiIsImt0eSI6IkVDIiwieCI6Im9CMVRQckVfUUp
     JTDYxZlVPT0s1RHBLZ2Q4ajJ6YlpKdHFwSUxEVEpYNkkiLCJ5IjoiM0pxbnJrdWNMb
     2JrZFJ1T3FaWE9QOU1NbGJGeWVuRk9MeUdsRy1GUEFDTSJ9LCJhbGciOiJNQUMtSDI
     1NiJ9",
     "proof": "eKwP5ormlovxxE-GeiuVC_1oOscxVyBA7TJWm5k6P3T1gojFpM_o7mqr
     9mKV_hYBcrvpqHSt09Dq9Uzuj51TymRtW7iLFGtWAfxWn3775AQjsUtgC82QvSpfh6
     prOmOO"
   }

                         Figure 19: mac-issued-jwp

   The same JWP in compact serialization:

   eyJpc3MiOiJodHRwczovL2lzc3Vlci50bGQiLCJjbGFpbXMiOlsiZmFtaWx5X25hbWUi
   LCJnaXZlbl9uYW1lIiwiZW1haWwiLCJhZ2UiXSwidHlwIjoiSlBUIiwicGp3ayI6eyJj
   cnYiOiJQLTI1NiIsImt0eSI6IkVDIiwieCI6Im9CMVRQckVfUUpJTDYxZlVPT0s1RHBL
   Z2Q4ajJ6YlpKdHFwSUxEVEpYNkkiLCJ5IjoiM0pxbnJrdWNMb2JrZFJ1T3FaWE9QOU1N
   bGJGeWVuRk9MeUdsRy1GUEFDTSJ9LCJhbGciOiJNQUMtSDI1NiJ9.IkRvZSI~IkpheSI
   ~ImpheWRvZUBleGFtcGxlLm9yZyI~NDI.eKwP5ormlovxxE-GeiuVC_1oOscxVyBA7TJ
   Wm5k6P3T1gojFpM_o7mqr9mKV_hYBcrvpqHSt09Dq9Uzuj51TymRtW7iLFGtWAfxWn37
   75AQjsUtgC82QvSpfh6prOmOO

                       Figure 20: mac-issued-compact

   Next, we show the presentation of the JWP with selective disclosure.

   We start with this presentation header using a nonce provided by the
   Verifier:

   {
     "nonce": "uTEB371l1pzWJl7afB0wi0HWUNk1Le-bComFLxa8K-s"
   }

                     Figure 21: mac-presentation-header

   When signed with the holder's presentation key, the resulting
   signature octets are:





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   [126, 134, 175, 2, 165, 12, 103, 11, 116, 72, 94, 228, 240, 142,
   107, 195, 198, 238, 218, 203, 63, 198, 105, 175, 1, 69, 182, 5, 204,
   239, 35, 149, 85, 55, 4, 169, 109, 243, 88, 213, 12, 1, 167, 235,
   222, 17, 232, 118, 110, 111, 47, 165, 102, 142, 0, 1, 226, 117, 143,
   125, 132, 62, 231, 145]

                Figure 22: mac-presentation-header-signature

   Then by applying selective disclosure of only the given name and age
   claims (family name and email hidden, payload array indexes 0 and 2),
   the holder builds a mixed array of either the payload key (if
   disclosed) or MAC (if hidden):

   [
    [156, 53, 90, 125, 139, 226, 60, 168, 100, 220, 79, 255, 8, 87, 28,
    220, 237, 112, 161, 91, 39, 68, 137, 203, 92, 243, 16, 116, 64,
    129, 61, 172],
    [143, 172, 182, 156, 184, 138, 228, 172, 215, 26, 175, 137, 137,
    25, 159, 141, 213, 12, 214, 29, 231, 200, 13, 94, 116, 22, 41, 115,
    72, 214, 57, 98],
    [162, 174, 12, 27, 190, 250, 112, 1, 139, 177, 49, 124, 110, 201,
    83, 233, 14, 109, 60, 253, 121, 184, 126, 121, 26, 138, 5, 214, 97,
    96, 216, 80],
    [70, 55, 182, 105, 101, 130, 254, 234, 68, 224, 219, 97, 119, 98,
    244, 33, 43, 55, 148, 238, 225, 177, 101, 160, 49, 246, 109, 155,
    242, 236, 21, 138]
   ]

                    Figure 23: mac-presentation-keyormac

   The final presented proof value is generated by concatenating first
   the presentation header signature octet string, followed by the
   issuer signature octet string, then followed by the mixed array of
   keys and MACs:

















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   [126, 134, 175, 2, 165, 12, 103, 11, 116, 72, 94, 228, 240, 142,
   107, 195, 198, 238, 218, 203, 63, 198, 105, 175, 1, 69, 182, 5, 204,
   239, 35, 149, 85, 55, 4, 169, 109, 243, 88, 213, 12, 1, 167, 235,
   222, 17, 232, 118, 110, 111, 47, 165, 102, 142, 0, 1, 226, 117, 143,
   125, 132, 62, 231, 145, 120, 172, 15, 230, 138, 230, 150, 139, 241,
   196, 79, 134, 122, 43, 149, 11, 253, 104, 58, 199, 49, 87, 32, 64,
   237, 50, 86, 155, 153, 58, 63, 116, 245, 130, 136, 197, 164, 207,
   232, 238, 106, 171, 246, 98, 149, 254, 22, 1, 114, 187, 233, 168,
   116, 173, 211, 208, 234, 245, 76, 238, 143, 157, 83, 202, 156, 53,
   90, 125, 139, 226, 60, 168, 100, 220, 79, 255, 8, 87, 28, 220, 237,
   112, 161, 91, 39, 68, 137, 203, 92, 243, 16, 116, 64, 129, 61, 172,
   143, 172, 182, 156, 184, 138, 228, 172, 215, 26, 175, 137, 137, 25,
   159, 141, 213, 12, 214, 29, 231, 200, 13, 94, 116, 22, 41, 115, 72,
   214, 57, 98, 162, 174, 12, 27, 190, 250, 112, 1, 139, 177, 49, 124,
   110, 201, 83, 233, 14, 109, 60, 253, 121, 184, 126, 121, 26, 138, 5,
   214, 97, 96, 216, 80, 70, 55, 182, 105, 101, 130, 254, 234, 68, 224,
   219, 97, 119, 98, 244, 33, 43, 55, 148, 238, 225, 177, 101, 160, 49,
   246, 109, 155, 242, 236, 21, 138]

                     Figure 24: mac-presentation-proof

   The resulting presented JWP in JSON serialization is:

   {
     "payloads": [
       null,
       "IkpheSI",
       null,
       "NDI"
     ],
     "issuer": "eyJpc3MiOiJodHRwczovL2lzc3Vlci50bGQiLCJjbGFpbXMiOlsiZmF
     taWx5X25hbWUiLCJnaXZlbl9uYW1lIiwiZW1haWwiLCJhZ2UiXSwidHlwIjoiSlBUI
     iwicGp3ayI6eyJjcnYiOiJQLTI1NiIsImt0eSI6IkVDIiwieCI6Im9CMVRQckVfUUp
     JTDYxZlVPT0s1RHBLZ2Q4ajJ6YlpKdHFwSUxEVEpYNkkiLCJ5IjoiM0pxbnJrdWNMb
     2JrZFJ1T3FaWE9QOU1NbGJGeWVuRk9MeUdsRy1GUEFDTSJ9LCJhbGciOiJNQUMtSDI
     1NiJ9",
     "proof": "foavAqUMZwt0SF7k8I5rw8bu2ss_xmmvAUW2BczvI5VVNwSpbfNY1QwB
     p-veEeh2bm8vpWaOAAHidY99hD7nkXisD-aK5paL8cRPhnorlQv9aDrHMVcgQO0yVp
     uZOj909YKIxaTP6O5qq_Zilf4WAXK76ah0rdPQ6vVM7o-dU8qcNVp9i-I8qGTcT_8I
     Vxzc7XChWydEictc8xB0QIE9rI-stpy4iuSs1xqviYkZn43VDNYd58gNXnQWKXNI1j
     lioq4MG776cAGLsTF8bslT6Q5tPP15uH55GooF1mFg2FBGN7ZpZYL-6kTg22F3YvQh
     KzeU7uGxZaAx9m2b8uwVig",
     "presentation": "eyJub25jZSI6InVURUIzNzFsMXB6V0psN2FmQjB3aTBIV1VOa
     zFMZS1iQ29tRkx4YThLLXMifQ"
   }

                      Figure 25: mac-presentation-jwp




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   The same JWP in compact serialization:

   eyJpc3MiOiJodHRwczovL2lzc3Vlci50bGQiLCJjbGFpbXMiOlsiZmFtaWx5X25hbWUi
   LCJnaXZlbl9uYW1lIiwiZW1haWwiLCJhZ2UiXSwidHlwIjoiSlBUIiwicGp3ayI6eyJj
   cnYiOiJQLTI1NiIsImt0eSI6IkVDIiwieCI6Im9CMVRQckVfUUpJTDYxZlVPT0s1RHBL
   Z2Q4ajJ6YlpKdHFwSUxEVEpYNkkiLCJ5IjoiM0pxbnJrdWNMb2JrZFJ1T3FaWE9QOU1N
   bGJGeWVuRk9MeUdsRy1GUEFDTSJ9LCJhbGciOiJNQUMtSDI1NiJ9.eyJub25jZSI6InV
   URUIzNzFsMXB6V0psN2FmQjB3aTBIV1VOazFMZS1iQ29tRkx4YThLLXMifQ.~IkpheSI
   ~~NDI.foavAqUMZwt0SF7k8I5rw8bu2ss_xmmvAUW2BczvI5VVNwSpbfNY1QwBp-veEe
   h2bm8vpWaOAAHidY99hD7nkXisD-aK5paL8cRPhnorlQv9aDrHMVcgQO0yVpuZOj909Y
   KIxaTP6O5qq_Zilf4WAXK76ah0rdPQ6vVM7o-dU8qcNVp9i-I8qGTcT_8IVxzc7XChWy
   dEictc8xB0QIE9rI-stpy4iuSs1xqviYkZn43VDNYd58gNXnQWKXNI1jlioq4MG776cA
   GLsTF8bslT6Q5tPP15uH55GooF1mFg2FBGN7ZpZYL-6kTg22F3YvQhKzeU7uGxZaAx9m
   2b8uwVig

                    Figure 26: mac-presentation-compact

6.4.  ZKSnark

   |  Editor's Note: This is just a placeholder for a future definition
   |  that is in the early stages of development as part of the
   |  Decentralized Identity Foundation (https://github.com/
   |  decentralized-identity/spartan_zkSNARK_signatures).

7.  Security Considerations

   |  Editor's Note: This will follow once the algorithms defined here
   |  have become more stable.

   *  Data minimization of the proof value

   *  Unlinkability of the protected header contents

8.  IANA Considerations

8.1.  JWP Algorithms Registry

   This section establishes the IANA JWP Algorithms Registry.  It also
   registers the following algorithms.

   TBD

9.  Informative References

   [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/info/rfc2119>.



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   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [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/info/rfc8174>.

Appendix A.  Acknowledgements

   TBD

Appendix B.  Document History

   [[ To be removed from the final specification ]]

   -01

   *  Applied editorial improvements

   -00

   *  First individual draft targeting JOSE working group

Authors' Addresses

   Jeremie Miller
   Ping Identity
   Email: jmiller@pingidentity.com


   Michael B. Jones
   Microsoft
   Email: mbj@microsoft.com
   URI:   https://self-issued.info/












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