Internet DRAFT - draft-birkholz-attestation-terminology
draft-birkholz-attestation-terminology
Network Working Group H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Informational M. Wiseman
Expires: January 3, 2019 GE Global Research
H. Tschofenig
ARM Ltd.
July 02, 2018
Reference Terminology for Remote Attestation Procedures
draft-birkholz-attestation-terminology-02
Abstract
This document is intended to illustrate and remediate the impedance
mismatch of terms related to remote attestation procedures used in
different domains today. New terms defined by this document provide
a consolidated basis to support future work on attestation procedures
in the IETF and beyond.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 3, 2019.
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Copyright (c) 2018 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4
2. Basic Roles of RATS . . . . . . . . . . . . . . . . . . . . . 4
3. Computing Context . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Formal Semantic Relationships . . . . . . . . . . . . . . 5
3.2. Characteristics of a Computing Context . . . . . . . . . 6
4. Computing Context Identity . . . . . . . . . . . . . . . . . 7
5. Attestation Workflow . . . . . . . . . . . . . . . . . . . . 7
6. Reference Use Cases . . . . . . . . . . . . . . . . . . . . . 8
6.1. The Lying Endpoint Problem . . . . . . . . . . . . . . . 10
6.2. Who am I a talking to? . . . . . . . . . . . . . . . . . 11
7. Trustworthiness . . . . . . . . . . . . . . . . . . . . . . . 11
8. Remote Attestation . . . . . . . . . . . . . . . . . . . . . 12
8.1. Building Block Terms . . . . . . . . . . . . . . . . . . 12
9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 13
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
13.1. Normative References . . . . . . . . . . . . . . . . . . 14
13.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
During its evolution, the term Remote Attestation has been used in
multiple contexts and multiple scopes and in consequence accumulated
various connotations with slightly different semantic meaning.
Correspondingly, Remote Attestation Procedures (RATS) are employed in
various usage scenarios and different environments.
In order to better understand and grasp the intend and meaning of
specific RATS in the scope of the security area - including the
requirements that are addressed by them - this document provides an
overview of existing work, its background, and common terminology.
As the contribution, from that state-of-the-art a set of terms that
provides a stable basis for future work on RATS in the IETF is
derived.
The primary application of RATS is to increase the trust and
confidence in the integrity of the object characteristics and
properties of a system entity that is intended to interact and
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exchange data with other system entities remotely. How an objects's
characteristics are attested remotely and which characteristics are
actually chosen to be attested varies with the requirements of the
use cases, or -- in essence -- depends on the risk that is intended
to be mitigated via RATS. Effectively, RATS are a vital tool to be
used to increase the confidence in the level of trust of a system
that is supposed to be a trusted system.
In the remainder of this document a system that is capable to provide
an appropriate amount of information about its integrity is
considered to be a trustworthy system - or simply trustworthy.
The primary characteristics of a trustworthy system are commonly
based on information about the integrity of its intended composition,
its enrolled and subsequently installed software components, and the
scope of known valid states that a trustworthy system is supposed to
operate in.
It is important to note that the activity of attestation itself in
principle only provides the evidence that proves the integrity of a
(subset) of a system's object characteristics. The provided evidence
is used as a basis for further activities. Specific RATS define the
higher semantic context about how the evidence is utilized and what
RATS actually can accomplish; and what they cannot accomplish,
correspondingly. Hence, this document is also intended to provide a
map of terms, concepts and applications that illustrate the ecosystem
of current applications of RATS.
In essence, a prerequisite for providing an adequate set of terms and
definitions in the domain of RATS is a general understanding and a
common definitions of "what" RATS can accomplish "how" RATS can to be
used.
Please note that this document is still missing multiple reference
and is considered "under construction". The majority of definitions
is still only originating from IETF work. Future iterations will
pull in more complementary definitions from other SDO (e.g. Global
Platform, TCG, etc.) and a general structure template to highlight
semantic relationships and capable of resolving potential
discrepancies will be introduced. A section of context awareness
will provide further insight on how attestation procedures are vital
to ongoing work in the IETF (e.g. I2NSF & tokbind). The definitions
in the section about RATS are still self-describing in this version.
Additional explanatory text will be added to provide more context and
coherence.
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1.1. Requirements notation
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 RFC
2119, BCP 14 [RFC2119].
2. Basic Roles of RATS
The use of the term Remote Attestation Procedures always implies the
involvement of at least two parties that each take on a specific role
in corresponding RATS - the Attestor role and the Verifier role.
Depending on the object characteristics attested and the nature of
the parties, information is exchanged via specific types of
Interconnects between them. The type of interconnect ranges from GIO
pins, to a bus component, to the Internet, or from a direct physical
connection, to a wireless association, to a world wide mesh of peers.
In other words, virtually every kind communication path
(Interconnect) can be used by system entities that take on the role
of Attestor and Verifier (in fact, a single party can take on both
roles at the same time, but there is only a limited use to this
architecture).
Attestor: The role that designates the subject of the remote
attestation. A system entity that is the provider of evidence
takes on the role of an Attestor.
Verifier: The role that designates the system entity that is the
appraiser of the evidence provided by the Attestor. A system
entity that is the consumer of evidence takes on the role of a
Verifier.
Interconnect: A channel of communication between Attestor and
Verifier that enables the appraisal of evidence created by the
Attestor by a remote Verifier.
3. Computing Context
This section introduces the term Computing Context in order to
simplify the definition of RATS terminology.
The number of approaches and solutions to create things that provide
the same capabilities as a "simple physical device" continuously
increases. Examples include but are not limited to: the
compartmentalization of physical resources, the separation of
software instances with different dependencies in dedicated
containers, and the nesting of virtual components via hardware-based
and software-based solutions.
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System entities are composed of system entities. In essence, every
physical or logical device is a composite of system entities. In
consequence, a composite device also constitutes a system entity.
Every component in that composite is a potential Computing Context
capable of taking on the roles of Attestor or Verifier. The scope
and application of these roles can range from:
o continuous mutual attestation procedures of every system entity
inside a composite device, to
o sporadic remote attestation of unknown parties via heterogeneous
Interconnects.
Analogously, the increasing number of features and functions that
constitute components of a device start to blur the lines that are
required to categorize each solution and approach precisely. To
address this increasingly challenging categorization, the term
Computing Context defines the characteristics of the system entities
that can take on the role of an Attestor and/or the role of a
Verifier. This approach is intended to provide a stable basis of
definitions for future solutions that continuous to remain viable
long-term.
Computing Context : An umbrella term that combines the scope of the
definitions of endpoint [ref NEA], device [ref 1ar], and thing
[ref t2trg], including hardware-based and software-based sub-
contexts that constitute independent, isolated and distinguishable
slices of a Computing Context created by compartmentalization
mechanisms, such as Trusted Execution Environments (TEE), Hardware
Security Modules (HSM) or Virtual Network Function (VNF) contexts.
3.1. Formal Semantic Relationships
The formal semantic relationship of a Computing Context and the
definitions provided by RFC 4949 is a as follows.
The scope of the term computing context encompasses
o an information system,
o an object and in consequence a system component or a composite of
system sub-components, and
o a system entity or a composite of system entities.
Analogously, a sub-context is a subsystem and as with system
components, computing contexts can be nested and therefore be
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physical system components or logical ("virtual") system
(sub-)components.
The formal semantic relationship is based on the following
definitions from RFC 4949.
(Information) System: An organized assembly of computing and
communication resources and procedures - i.e., equipment and
services, together with their supporting infrastructure,
facilities, and personnel - that create, collect, record, process,
store, transport, retrieve, display, disseminate, control, or
dispose of information to accomplish a specified set of functions.
Object: A system component that contains or receives information.
Subsystem: A collection of related system components that together
perform a system function or deliver a system service.
System Component: A collection of system resources that (a) forms a
physical or logical part of the system, (b) has specified
functions and interfaces, and (c) is treated (e.g., by policies or
specifications) as existing independently of other parts of the
system. (See: subsystem.)
An identifiable and self-contained part of a Target of Evaluation.
System Entity: An active part of a system - [...] (see: subsystem) -
that has a specific set of capabilities.
3.2. Characteristics of a Computing Context
While the semantic relationships highlighted above constitute the
fundamental basis to provide a define Computing Context, the
following list of object characteristics is intended to improve the
application of the term and provide a better understanding of its
meaning:
A computing context:
o provides its own independent environment in regard to executing
and running software,
o provides its own isolated control plane state (by potentially
interacting with other Computing
o Contexts) and may provide a dedicated management interface by
which control plane behavior can be effected,
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o can be identified uniquely and therefore reliably differentiated
in a given scope, and
o does not necessarily has to include a network interface with
associated network addresses (as required, e.g. by the definition
of an endpoint) - although it is very likely to have (access to)
one.
In contrast, a docker [ref docker, find a more general term here]
context is not a distinguishable isolated slice of an information
system and therefore is not an independent Computing Context. [more
feedback on this statement is required as the capabilities of docker-
like functions evolve continuously]
Examples include: a smart phone, a nested virtual machine, a
virtualized firewall function running distributed on a cluster of
physical and virtual nodes, or a trust-zone.
4. Computing Context Identity
The identity of a Computing Context provides the basis for creating
evidence about data origin authenticity. Confidence in the identity
assurance level [NIST SP-800-63-3] or the assurance levels for
identity authentication [RFC4949] impacts the confidence in the
evidence an Attestor provides.
5. Attestation Workflow
This section introduces terms and definitions that are required to
illustrate the scope and the granularity of RATS workflows in the
domain of security automation. Terms defined in the following
sections will be based on this workflow-related definitions.
In general, RATS are composed of iterative activities that can be
conducted in intervals. It is neither a generic set of actions nor
simply a task, because the actual actions to be conducted by RATS can
vary significantly depending on the protocols employed and types of
Computing Contexts involved.
Activity: A sequence of actions conducted by Computing Contexts that
compose a remote attestation procedure. The actual composition of
actions can vary, depending on the characteristics of the
Computing Context they are conducted by/in and the protocols used
to utilize an Interconnect. A single activity provides only a
minimal amount of semantic context, e.g.defined by the activity's
requirements imposed on the Computing Context, or via the set of
actions it is composed of. Example: The conveyance of
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cryptographic evidence or the appraisal of evidence via imperative
guidance.
Task: "A piece of work to be done or undertaken."
In the scope of RATS, a task is a procedure to be conducted.
Example: A Verifier can be tasked with the appraisal of evidence
originating from a specific type of Computing Contexts providing
appropriate identities.
Action: "The accomplishment of a thing usually over a period of
time, in stages, or with the possibility of repetition."
In the scope of RATS, an action is the execution of an operation
or function in the scope of an activity conducted by a Computing
Context. A single action provides no semantic context by itself,
although it can limit potential semantic contexts of RATS to a
specific scope. Example: Signing an existing public key via a
specific openssl library, transmitting data, or receiving data are
actions.
Procedure: "A series of actions that are done in a certain way or
order."
In the scope of RATS, a procedure is a composition of activities
(sequences of actions) that is intended to create a well specified
result with a well established semantic context. Example: The
activities of attestation, conveyance and verification compose a
remote attestation procedure.
6. Reference Use Cases
This document provides NNN prominent examples of use cases
attestation procedures are intended to address:
o Verification of the source integrity of a computing context via
data integrity proofing of installed software instances that are
executed, and
o Verification of the identity proofing of a computing context.
These use case summary highlighted above is based in the following
terms defined in RFC4949 and complementary sources of terminology:
Assurance: An attribute of an information system that provides
grounds for having confidence that the system operates such that
the system's security policy is enforced [RFC4949] (see Trusted
System below).
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In common criteria, assurance is the basis for the metric level of
assurance, which represents the "confidence that a system's
principal security features are reliably implemented".
The NIST Handbook [get ref from 4949] notes that the levels of
assurance defined in Common Criteria represent "a degree of
confidence, not a true measure of how secure the system actually
is. This distinction is necessary because it is extremely
difficult-and in many cases, virtually impossible-to know exactly
how secure a system is."
Historically, assurance was well-defined in the Orange Book
[http://csrc.nist.gov/publications/history/dod85.pdf] as
"guaranteeing or providing confidence that the security policy has
been implemented correctly and that the protection-relevant
elements of the system do, indeed, accurately mediate and enforce
the intent of that policy. By extension, assurance must include a
guarantee that the trusted portion of the system works only as
intended."
Confidence: The definition of correctness integrity in [RFC4949]
notes that "source integrity refers to confidence in data values".
Hence, confidence in an attestation procedure is referring to the
degree of trustworthiness of an attestation activity that produces
evidence (Attestor), of an conveyance activity that transfers
evidence (interconnect), and of a verification activity that
appraises evidence (Verifier), in respect to correctness
integrity.
Identity: Defined by [RFC4949] as the collective aspect of a set of
attribute values (i.e., a set of characteristics) by which a
system user or other system entity is recognizable or known.
(See: authenticate, registration. Compare: identifier.)
There are different scopes an identity can apply to:
Singular identity: An identity that is registered for an entity
that is one person or one process.
Shared identity: An identity that is registered for an entity that
is a set of singular entities in which each member is authorized
to assume the identity individually, and for which the registering
system maintains a record of the singular entities that comprise
the set. In this case, we would expect each member entity to be
registered with a singular identity before becoming associated
with the shared identity.
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Group identity: An identity that is registered for an entity that
is a set of entities (2) for which the registering system does not
maintain a record of singular entities that comprise the set.
Identity Proofing: A process that vets and verifies the information
that is used to establish the identity of a system entity.
Source Integrity: The property that data is trustworthy (i.e.,
worthy of reliance or trust), based on the trustworthiness of its
sources and the trustworthiness of any procedures used for
handling data in the system.
Data Integrity: (a) The property that data has not been changed,
destroyed, or lost in an unauthorized or accidental manner. (See:
data integrity service. Compare: correctness integrity, source
integrity.)
(b) The property that information has not been modified or
destroyed in an unauthorized manner.
Correctness: The property of a system that is guaranteed as the
result of formal verification activities.
Correctness integrity: The property that the information represented
by data is accurate and consistent.
Verification: (a) The process of examining information to establish
the truth of a claimed fact or value.
(b) The process of comparing two levels of system specification
for proper correspondence, such as comparing a security model with
a top-level specification, a top-level specification with source
code, or source code with object code.
Forward Authenticity (FA): A property of secure communication
protocols, in which later compromise of the long-term keys of a
data origin does not compromise past authentication of data from
that origin. FA is achieved by timely recording of assessments of
the authenticity from entities (via "audit logs" during "audit
sessions") that are authorized for this purpose, in a time frame
much shorter than that expected for the compromise of the long-
term keys.
6.1. The Lying Endpoint Problem
A very prominent goal of attestation procedures - and therefore a
suitable example used as reference in this document - is to address
the "lying endpoint problem".
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Information created, relayed, or, in essence, emitted by a computing
context does not have to be correct. There can be multiple reasons
why that is the case and the "lying endpoint problem" represents a
scenario, in which the reason is the compromization of computing
contexts with malicious intend. A compromised computing context
could try to "pretend" to be integer, while actually feeding
manipulated information into a security domain, therefore
compromising the effectiveness of automated security functions.
Attestation - and remote attestation procedures specifically - is an
approach intended to identify compromised software instances in
computing contexts.
Per definition, a "lying endpoint" cannot be "trusted system".
Trusted System: A system that operates as expected, according to
design and policy, doing what is required - despite environmental
disruption, human user and operator errors, and attacks by hostile
parties - and not doing other things.
Remote attestation procedures are intended to enable the consumer of
information emitted by an computing context to assess the validity
and integrity of the information transferred. The approach is based
on the assumption that if evidence can be provided in order to prove
the integrity of every software instance installed involved in the
activity of creating the emitted information in question, the emitted
information can be considered valid and integer.
In contrast, such evidence has to be impossible to create if the
software instances used in a computing context are compromised.
Attestation activities that are intended to create this evidence
therefore also to also provide guarantees about the validity of the
evidence they can create.
6.2. Who am I a talking to?
[working title, write up use case here, ref teep requirements]
7. Trustworthiness
A "lying endpoint" is not trustworthy.
Trusted System: A system that operates as expected, according to
design and policy, doing what is required - despite environmental
disruption, human user and operator errors, and attacks by hostile
parties - and not doing other things.
Trustworthy: pull in text here
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8. Remote Attestation
Attestation: An object integrity authentication facilitated via the
creation of a claim about the properties of an Attestor, such that
the claim can be used as evidence.
Conveyance: The transfer of evidence from the Attestor to the
Verifier.
Verification: The appraisal of evidence by evaluating it against
declarative guidance.
Remote Attestation: A procedure composed of the activities
attestation, conveyance and verification.
8.1. Building Block Terms
[working title, pulled from various sources, vital]
Attestation Identity Key (AIK): A special purpose signature
(therefore asymmetric) key that supports identity related
operations. The private portion of the key pair is maintained
confidential to the computing context via appropriate measures
(that have a direct impact on the level of confidence). The
public portion of the key pair may be included in AIK credentials
that provide a claim about the computing context.
Claim: A piece of information asserted about a subject. A claim is
represented as a name/value pair consisting of a Claim Name and a
Claim Value [RFC7519]
In the context of SACM, a claim is also specialized as an
attribute/value pair that is intended to be related to a statement
[I-D.ietf-sacm-terminology].
Computing Context Characteristics: The composition, configuration
and state of a computing context.
Evidence: A trustworthy set of claims about an computing context's
characteristics.
Identity: A set of claims that is intended to be related to an
entity. [merge with RFC4949 defintion above]
Integrity Measurements: Metrics of computing context characteristics
(i.e. composition, configuration and state) that affect the
confidence in the trustworthiness of a computing context. Digests
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of integrity measurements can be stored in shielded locations
(e.g. a PCR of a TPM).
Reference Integrity Measurements: Signed measurements about a
computing context's characteristics that are provided by a vendor
or manufacturer and are intended to be used as declarative
guidannce [I-D.ietf-sacm-terminology] (e.g. a signed CoSWID).
Trustworthiness: The qualities of computing context characteristics
that guarantee a specific behavior specified by declarative
guidance. Trustworthiness is not an absolute property but defined
with respect to a computing context, corresponding declarative
guidance, and has a scope of confidence. A trusted system is
trustworthy. [refactor defintion with RFC4949 terms]
Trustworthy Computing Context: a computing context that guarantees
trustworthy behavior and/or composition (with respect to certain
declarative guidance and a scope of confideence). A trustworthy
computing context is a trusted system.
Trustworthy Statement: evidence that trustworthy conveyed by a
computing context that is not necessarily trustworthy. [update
with tamper related terms]
9. IANA considerations
This document will include requests to IANA:
o first item
o second item
10. Security Considerations
There are always some.
11. Acknowledgements
Maybe.
12. Change Log
No changes yet.
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13. References
13.1. Normative 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>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
13.2. Informative References
[I-D.ietf-sacm-terminology]
Birkholz, H., Lu, J., Strassner, J., Cam-Winget, N., and
A. Montville, "Security Automation and Continuous
Monitoring (SACM) Terminology", draft-ietf-sacm-
terminology-14 (work in progress), December 2017.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
Authors' Addresses
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
Darmstadt 64295
Germany
Email: henk.birkholz@sit.fraunhofer.de
Monty Wiseman
GE Global Research
USA
Email: monty.wiseman@ge.com
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Hannes Tschofenig
ARM Ltd.
110 Fulbourn Rd
Cambridge CB1 9NJ
UK
Email: hannes.tschofenig@gmx.net
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