The Entity Attestation Token (EAT)
draft-ietf-rats-eat-10
RATS Working Group G. Mandyam
Internet-Draft Qualcomm Technologies Inc.
Intended status: Standards Track L. Lundblade
Expires: December 9, 2021 Security Theory LLC
M. Ballesteros
J. O'Donoghue
Qualcomm Technologies Inc.
June 07, 2021
The Entity Attestation Token (EAT)
draft-ietf-rats-eat-10
Abstract
An Entity Attestation Token (EAT) provides a signed (attested) set of
claims that describe state and characteristics of an entity,
typically a device like a phone or an IoT device. These claims are
used by a relying party to determine how much it wishes to trust the
entity.
An EAT is either a CWT or JWT with some attestation-oriented claims.
To a large degree, all this document does is extend CWT and JWT.
Contributing
TBD
Status of This Memo
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This Internet-Draft will expire on December 9, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. CWT, JWT and UCCS . . . . . . . . . . . . . . . . . . . . 6
1.2. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Entity Overview . . . . . . . . . . . . . . . . . . . . . 6
1.4. Use as Evidence and Attestation Results . . . . . . . . . 7
1.5. EAT Operating Models . . . . . . . . . . . . . . . . . . 7
1.6. What is Not Standardized . . . . . . . . . . . . . . . . 9
1.6.1. Transmission Protocol . . . . . . . . . . . . . . . . 9
1.6.2. Signing Scheme . . . . . . . . . . . . . . . . . . . 9
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 10
3. The Claims . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Token ID Claim (cti and jti) . . . . . . . . . . . . . . 11
3.2. Timestamp claim (iat) . . . . . . . . . . . . . . . . . . 11
3.3. Nonce Claim (nonce) . . . . . . . . . . . . . . . . . . . 12
3.3.1. nonce CDDL . . . . . . . . . . . . . . . . . . . . . 12
3.4. Universal Entity ID Claim (ueid) . . . . . . . . . . . . 12
3.4.1. ueid CDDL . . . . . . . . . . . . . . . . . . . . . . 15
3.5. Semi-permanent UEIDs (SUEIDs) . . . . . . . . . . . . . . 15
3.6. OEM Identification by IEEE (oemid) . . . . . . . . . . . 16
3.6.1. oemid CDDL . . . . . . . . . . . . . . . . . . . . . 16
3.7. Hardware Version Claims (hardware-version-claims) . . . . 16
3.8. Software Description and Version . . . . . . . . . . . . 17
3.9. The Security Level Claim (security-level) . . . . . . . . 17
3.9.1. security-level CDDL . . . . . . . . . . . . . . . . . 18
3.10. Secure Boot Claim (secure-boot) . . . . . . . . . . . . . 19
3.10.1. secure-boot CDDL . . . . . . . . . . . . . . . . . . 19
3.11. Debug Status Claim (debug-status) . . . . . . . . . . . . 19
3.11.1. Enabled . . . . . . . . . . . . . . . . . . . . . . 20
3.11.2. Disabled . . . . . . . . . . . . . . . . . . . . . . 21
3.11.3. Disabled Since Boot . . . . . . . . . . . . . . . . 21
3.11.4. Disabled Permanently . . . . . . . . . . . . . . . . 21
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3.11.5. Disabled Fully and Permanently . . . . . . . . . . . 21
3.11.6. debug-status CDDL . . . . . . . . . . . . . . . . . 21
3.12. Including Keys . . . . . . . . . . . . . . . . . . . . . 22
3.13. The Location Claim (location) . . . . . . . . . . . . . . 22
3.13.1. location CDDL . . . . . . . . . . . . . . . . . . . 23
3.14. The Uptime Claim (uptime) . . . . . . . . . . . . . . . . 24
3.14.1. uptime CDDL . . . . . . . . . . . . . . . . . . . . 24
3.15. The Boot Seed Claim (boot-seed) . . . . . . . . . . . . . 24
3.16. The Intended Use Claim (intended-use) . . . . . . . . . . 24
3.16.1. intended-use CDDL . . . . . . . . . . . . . . . . . 25
3.17. The Profile Claim (profile) . . . . . . . . . . . . . . . 25
3.18. The Software Manifests Claim (manifests) . . . . . . . . 26
3.19. The Software Evidence Claim {swevidence} . . . . . . . . 27
3.20. The Submodules Part of a Token (submods) . . . . . . . . 28
3.20.1. Two Types of Submodules . . . . . . . . . . . . . . 28
3.20.1.1. Non-token Submodules . . . . . . . . . . . . . . 29
3.20.1.2. Nested EATs . . . . . . . . . . . . . . . . . . 29
3.20.1.3. Unsecured JWTs and UCCS Tokens as Submodules . . 30
3.20.2. No Inheritance . . . . . . . . . . . . . . . . . . . 30
3.20.3. Security Levels . . . . . . . . . . . . . . . . . . 31
3.20.4. Submodule Names . . . . . . . . . . . . . . . . . . 31
3.20.5. submods CDDL . . . . . . . . . . . . . . . . . . . . 31
4. Endorsements and Verification Keys . . . . . . . . . . . . . 32
4.1. Identification Methods . . . . . . . . . . . . . . . . . 33
4.1.1. COSE/JWS Key ID . . . . . . . . . . . . . . . . . . . 33
4.1.2. JWS and COSE X.509 Header Parameters . . . . . . . . 34
4.1.3. CBOR Certificate COSE Header Parameters . . . . . . . 34
4.1.4. Claim-Based Key Identification . . . . . . . . . . . 34
4.2. Other Considerations . . . . . . . . . . . . . . . . . . 34
5. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.1. Format of a Profile Document . . . . . . . . . . . . . . 35
5.2. List of Profile Issues . . . . . . . . . . . . . . . . . 35
5.2.1. Use of JSON, CBOR or both . . . . . . . . . . . . . . 35
5.2.2. CBOR Map and Array Encoding . . . . . . . . . . . . . 35
5.2.3. CBOR String Encoding . . . . . . . . . . . . . . . . 36
5.2.4. CBOR Preferred Serialization . . . . . . . . . . . . 36
5.2.5. COSE/JOSE Protection . . . . . . . . . . . . . . . . 36
5.2.6. COSE/JOSE Algorithms . . . . . . . . . . . . . . . . 36
5.2.7. Verification Key Identification . . . . . . . . . . . 37
5.2.8. Endorsement Identification . . . . . . . . . . . . . 37
5.2.9. Freshness . . . . . . . . . . . . . . . . . . . . . . 37
5.2.10. Required Claims . . . . . . . . . . . . . . . . . . . 37
5.2.11. Prohibited Claims . . . . . . . . . . . . . . . . . . 37
5.2.12. Additional Claims . . . . . . . . . . . . . . . . . . 37
5.2.13. Refined Claim Definition . . . . . . . . . . . . . . 37
5.2.14. CBOR Tags . . . . . . . . . . . . . . . . . . . . . . 38
5.2.15. Manifests and Software Evidence Claims . . . . . . . 38
6. Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 38
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6.1. Common CDDL Types . . . . . . . . . . . . . . . . . . . . 38
6.2. CDDL for CWT-defined Claims . . . . . . . . . . . . . . . 38
6.3. JSON . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.3.1. JSON Labels . . . . . . . . . . . . . . . . . . . . . 39
6.3.2. JSON Interoperability . . . . . . . . . . . . . . . . 40
6.4. CBOR . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.4.1. CBOR Interoperability . . . . . . . . . . . . . . . . 41
6.4.1.1. EAT Constrained Device Serialization . . . . . . 41
6.5. Collected CDDL . . . . . . . . . . . . . . . . . . . . . 42
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
7.1. Reuse of CBOR Web Token (CWT) Claims Registry . . . . . . 47
7.2. Claim Characteristics . . . . . . . . . . . . . . . . . . 48
7.2.1. Interoperability and Relying Party Orientation . . . 48
7.2.2. Operating System and Technology Neutral . . . . . . . 48
7.2.3. Security Level Neutral . . . . . . . . . . . . . . . 49
7.2.4. Reuse of Extant Data Formats . . . . . . . . . . . . 49
7.2.5. Proprietary Claims . . . . . . . . . . . . . . . . . 49
7.3. Claims Registered by This Document . . . . . . . . . . . 49
7.3.1. Claims for Early Assignment . . . . . . . . . . . . . 50
7.3.2. To be Assigned Claims . . . . . . . . . . . . . . . . 53
7.3.3. Version Schemes Registered by this Document . . . . . 53
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 53
8.1. UEID and SUEID Privacy Considerations . . . . . . . . . . 53
8.2. Location Privacy Considerations . . . . . . . . . . . . . 54
9. Security Considerations . . . . . . . . . . . . . . . . . . . 54
9.1. Key Provisioning . . . . . . . . . . . . . . . . . . . . 55
9.1.1. Transmission of Key Material . . . . . . . . . . . . 55
9.2. Transport Security . . . . . . . . . . . . . . . . . . . 55
9.3. Multiple EAT Consumers . . . . . . . . . . . . . . . . . 56
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 56
10.1. Normative References . . . . . . . . . . . . . . . . . . 56
10.2. Informative References . . . . . . . . . . . . . . . . . 59
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 61
A.1. Very Simple EAT . . . . . . . . . . . . . . . . . . . . . 61
A.2. Example with Submodules, Nesting and Security Levels . . 61
Appendix B. UEID Design Rationale . . . . . . . . . . . . . . . 61
B.1. Collision Probability . . . . . . . . . . . . . . . . . . 62
B.2. No Use of UUID . . . . . . . . . . . . . . . . . . . . . 64
Appendix C. EAT Relation to IEEE.802.1AR Secure Device Identity
(DevID) . . . . . . . . . . . . . . . . . . . . . . 65
C.1. DevID Used With EAT . . . . . . . . . . . . . . . . . . . 65
C.2. How EAT Provides an Equivalent Secure Device Identity . . 66
C.3. An X.509 Format EAT . . . . . . . . . . . . . . . . . . . 66
C.4. Device Identifier Permanence . . . . . . . . . . . . . . 67
Appendix D. Changes from Previous Drafts . . . . . . . . . . . . 67
D.1. From draft-rats-eat-01 . . . . . . . . . . . . . . . . . 67
D.2. From draft-mandyam-rats-eat-00 . . . . . . . . . . . . . 67
D.3. From draft-ietf-rats-eat-01 . . . . . . . . . . . . . . . 67
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D.4. From draft-ietf-rats-eat-02 . . . . . . . . . . . . . . . 68
D.5. From draft-ietf-rats-eat-03 . . . . . . . . . . . . . . . 68
D.6. From draft-ietf-rats-eat-04 . . . . . . . . . . . . . . . 68
D.7. From draft-ietf-rats-05 . . . . . . . . . . . . . . . . . 69
D.8. From draft-ietf-rats-06 . . . . . . . . . . . . . . . . . 69
D.9. From draft-ietf-rats-07 . . . . . . . . . . . . . . . . . 69
D.10. From draft-ietf-rats-08 . . . . . . . . . . . . . . . . . 69
D.11. From draft-ietf-rats-09 . . . . . . . . . . . . . . . . . 69
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 70
1. Introduction
Remote device attestation is a fundamental service that allows a
remote device such as a mobile phone, an Internet-of-Things (IoT)
device, or other endpoint to prove itself to a relying party, a
server or a service. This allows the relying party to know some
characteristics about the device and decide whether it trusts the
device.
Remote attestation is a fundamental service that can underlie other
protocols and services that need to know about the trustworthiness of
the device before proceeding. One good example is biometric
authentication where the biometric matching is done on the device.
The relying party needs to know that the device is one that is known
to do biometric matching correctly. Another example is content
protection where the relying party wants to know the device will
protect the data. This generalizes on to corporate enterprises that
might want to know that a device is trustworthy before allowing
corporate data to be accessed by it.
The notion of attestation here is large and may include, but is not
limited to the following:
o Proof of the make and model of the device hardware (HW)
o Proof of the make and model of the device processor, particularly
for security-oriented chips
o Measurement of the software (SW) running on the device
o Configuration and state of the device
o Environmental characteristics of the device such as its GPS
location
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1.1. CWT, JWT and UCCS
For flexibility and ease of imlpementation in a wide variety of
environments, EATs can be either CBOR [RFC8949] or JSON [ECMAScript]
format. This specification simultaneously describes both formats.
An EAT is either a CWT as defined in [RFC8392], a UCCS as defined in
[UCCS.Draft], or a JWT as defined in [RFC7519]. This specification
extends those specifications with additional claims for attestation.
The identification of a protocol element as an EAT, whether CBOR or
JSON format, follows the general conventions used by CWT, JWT and
UCCS. Largely this depends on the protocol carrying the EAT. In
some cases it may be by content type (e.g., MIME type). In other
cases it may be through use of CBOR tags. There is no fixed
mechanism across all use cases.
1.2. CDDL
This specification uses CDDL, [RFC8610], as the primary formalism to
define each claim. The implementor then interprets the CDDL to come
to either the CBOR [RFC8949] or JSON [ECMAScript] representation. In
the case of JSON, Appendix E of [RFC8610] is followed. Additional
rules are given in Section 6.3.2 of this document where Appendix E is
insufficient. (Note that this is not to define a general means to
translate between CBOR and JSON, but only to define enough such that
the claims defined in this document can be rendered unambiguously in
JSON).
The CWT specification was authored before CDDL was available and did
not use it. This specification includes a CDDL definition of most of
what is described in [RFC8392].
1.3. Entity Overview
An "entity" can be any device or device subassembly ("submodule")
that can generate its own attestation in the form of an EAT. The
attestation should be cryptographically verifiable by the EAT
consumer. An EAT at the device-level can be composed of several
submodule EAT's.
Modern devices such as a mobile phone have many different execution
environments operating with different security levels. For example,
it is common for a mobile phone to have an "apps" environment that
runs an operating system (OS) that hosts a plethora of downloadable
apps. It may also have a TEE (Trusted Execution Environment) that is
distinct, isolated, and hosts security-oriented functionality like
biometric authentication. Additionally, it may have an eSE (embedded
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Secure Element) - a high security chip with defenses against HW
attacks that is used to produce attestations. This device
attestation format allows the attested data to be tagged at a
security level from which it originates. In general, any discrete
execution environment that has an identifiable security level can be
considered an entity.
1.4. Use as Evidence and Attestation Results
Here, normative reference is made to [RATS-Architecture],
particularly the definition of Evidence, the Verifier, Attestation
Results and the Relying Party. Per Figure 1 in [RATS-Architecture],
Evidence is a protocol message that goes from the Attester to the
Verifier and Attestation Results a message that goes from the
Verifier to the Relying Party. EAT is defined such that it can be
used to represent either Evidence, Attestation Results or both. No
claims defined here are considered exclusive to or are prohibited in
either use. It is useful to create EAT profiles as described in
Section 5 for either use.
It is useful to characterize the relationship of claims in Evidence
to those in Attestation Results.
Many claims in Evidence simply will pass through the Verifier to the
Relying Party without modification. They will be verified as
authentic from the device by the Verifier just through normal
verification of the Attester's signature. They will be protected
from modification when they are conveyed to the Relying Party by
whatever means is used to protect Attestation Results. (The details
of that protection are out of scope of this document.)
Some claims in Evidence will be verified by the Verifier by
comparison to Reference Values. In this case the claims in Evidence
will not likely be conveyed to the Relying Party. Instead, some
claim indicating they were checked may be added to the Attestation
Results or it may be tacitly known that the Verifier always does this
check.
In some cases the Verifier may provide privacy-preserving
functionality by stripping or modifying claims that do not posses
sufficient privacy-preserving characteristics.
1.5. EAT Operating Models
TODO: Rewrite (or eliminate) this section in light of the RATS
architecture draft.
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At least the following three participants exist in all EAT operating
models. Some operating models have additional participants.
The Entity. This is the phone, the IoT device, the sensor, the sub-
assembly or such that the attestation provides information about.
The Manufacturer. The company that made the entity. This may be a
chip vendor, a circuit board module vendor or a vendor of finished
consumer products.
The Relying Party. The server, service or company that makes use of
the information in the EAT about the entity.
In all operating models, the manufacturer provisions some secret
attestation key material (AKM) into the entity during manufacturing.
This might be during the manufacturer of a chip at a fabrication
facility (fab) or during final assembly of a consumer product or any
time in between. This attestation key material is used for signing
EATs.
In all operating models, hardware and/or software on the entity
create an EAT of the format described in this document. The EAT is
always signed by the attestation key material provisioned by the
manufacturer.
In all operating models, the relying party must end up knowing that
the signature on the EAT is valid and consistent with data from
claims in the EAT. This can happen in many different ways. Here are
some examples.
o The EAT is transmitted to the relying party. The relying party
gets corresponding key material (e.g. a root certificate) from the
manufacturer. The relying party performs the verification.
o The EAT is transmitted to the relying party. The relying party
transmits the EAT to a verification service offered by the
manufacturer. The server returns the validated claims.
o The EAT is transmitted directly to a verification service, perhaps
operated by the manufacturer or perhaps by another party. It
verifies the EAT and makes the validated claims available to the
relying party. It may even modify the claims in some way and re-
sign the EAT (with a different signing key).
All these operating models are supported and there is no preference
of one over the other. It is important to support this variety of
operating models to generally facilitate deployment and to allow for
some special scenarios. One special scenario has a validation
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service that is monetized, most likely by the manufacturer. In
another, a privacy proxy service processes the EAT before it is
transmitted to the relying party. In yet another, symmetric key
material is used for signing. In this case the manufacturer should
perform the verification, because any release of the key material
would enable a participant other than the entity to create valid
signed EATs.
1.6. What is Not Standardized
The following is not standardized for EAT, just the same they are not
standardized for CWT or JWT.
1.6.1. Transmission Protocol
EATs may be transmitted by any protocol the same as CWTs and JWTs.
For example, they might be added in extension fields of other
protocols, bundled into an HTTP header, or just transmitted as files.
This flexibility is intentional to allow broader adoption. This
flexibility is possible because EAT's are self-secured with signing
(and possibly additionally with encryption and anti-replay). The
transmission protocol is not required to fulfill any additional
security requirements.
For certain devices, a direct connection may not exist between the
EAT-producing device and the Relying Party. In such cases, the EAT
should be protected against malicious access. The use of COSE and
JOSE allows for signing and encryption of the EAT. Therefore, even
if the EAT is conveyed through intermediaries between the device and
Relying Party, such intermediaries cannot easily modify the EAT
payload or alter the signature.
1.6.2. Signing Scheme
The term "signing scheme" is used to refer to the system that
includes end-end process of establishing signing attestation key
material in the entity, signing the EAT, and verifying it. This
might involve key IDs and X.509 certificate chains or something
similar but different. The term "signing algorithm" refers just to
the algorithm ID in the COSE signing structure. No particular
signing algorithm or signing scheme is required by this standard.
There are three main implementation issues driving this. First,
secure non-volatile storage space in the entity for the attestation
key material may be highly limited, perhaps to only a few hundred
bits, on some small IoT chips. Second, the factory cost of
provisioning key material in each chip or device may be high, with
even millisecond delays adding to the cost of a chip. Third,
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privacy-preserving signing schemes like ECDAA (Elliptic Curve Direct
Anonymous Attestation) are complex and not suitable for all use
cases.
Over time to faciliate interoperability, some signing schemes may be
defined in EAT profiles or other documents either in the IETF or
outside.
2. Terminology
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.
This document reuses terminology from JWT [RFC7519], COSE [RFC8152],
and CWT [RFC8392].
Claim Name. The human-readable name used to identify a claim.
Claim Key. The CBOR map key or JSON name used to identify a claim.
Claim Value. The value portion of the claim. A claim value can be
any CBOR data item or JSON value.
CWT Claims Set. The CBOR map or JSON object that contains the claims
conveyed by the CWT or JWT.
Attestation Key Material (AKM). The key material used to sign the
EAT token. If it is done symmetrically with HMAC, then this is a
simple symmetric key. If it is done with ECC, such as an IEEE
DevID [IEEE.802.1AR], then this is the private part of the EC key
pair. If ECDAA is used, (e.g., as used by Enhanced Privacy ID,
i.e. EPID) then it is the key material needed for ECDAA.
3. The Claims
This section describes new claims defined for attestation. It also
mentions several claims defined by CWT and JWT that are particularly
important for EAT.
Note also: * Any claim defined for CWT or JWT may be used in an EAT
including those in the CWT [IANA.CWT.Claims] and JWT IANA
[IANA.JWT.Claims] claims registries.
o All claims are optional
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o No claims are mandatory
o All claims that are not understood by implementations MUST be
ignored
There are no default values or meanings assigned to absent claims
other than they are not reported. The reason for a claim's absence
may be the implementation not supporting the claim, an inability to
determine its value, or a preference to report in a different way
such as a proprietary claim.
CDDL along with text descriptions is used to define each claim
indepdent of encoding. Each claim is defined as a CDDL group (the
group is a general aggregation and type definition feature of CDDL).
In the encoding section Section 6, the CDDL groups turn into CBOR map
entries and JSON name/value pairs.
Map labels are assigned both an integer and string value. CBOR
encoded tokens MUST use only integer labels. JSON encoded tokens
MUST use only string labels.
TODO: add paragraph here about use for Attestation Evidence and for
Results.
3.1. Token ID Claim (cti and jti)
CWT defines the "cti" claim. JWT defines the "jti" claim. These are
equivalent to each other in EAT and carry a unique token identifier
as they do in JWT and CWT. They may be used to defend against re use
of the token but are distinct from the nonce that is used by the
relying party to guarantee freshness and defend against replay.
3.2. Timestamp claim (iat)
The "iat" claim defined in CWT and JWT is used to indicate the date-
of-creation of the token, the time at which the claims are collected
and the token is composed and signed.
The data for some claims may be held or cached for some period of
time before the token is created. This period may be long, even
days. Examples are measurements taken at boot or a geographic
position fix taken the last time a satellite signal was received.
There are individual timestamps associated with these claims to
indicate their age is older than the "iat" timestamp.
CWT allows the use floating-point for this claim. EAT disallows the
use of floating-point. No token may contain an iat claim in float-
point format. Any recipient of a token with a floating-point format
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iat claim may consider it an error. A 64-bit integer representation
of epoch time can represent a range of +/- 500 billion years, so the
only point of a floating-point timestamp is to have precession
greater than one second. This is not needed for EAT.
3.3. Nonce Claim (nonce)
All EATs should have a nonce to prevent replay attacks. The nonce is
generated by the relying party, the end consumer of the token. It is
conveyed to the entity over whatever transport is in use before the
token is generated and then included in the token as the nonce claim.
This documents the nonce claim for registration in the IANA CWT
claims registry. This is equivalent to the JWT nonce claim that is
already registered.
The nonce must be at least 8 bytes (64 bits) as fewer are unlikely to
be secure. A maximum of 64 bytes is set to limit the memory a
constrained implementation uses. This size range is not set for the
already-registered JWT nonce, but it should follow this size
recommendation when used in an EAT.
Multiple nonces are allowed to accommodate multistage verification
and consumption.
3.3.1. nonce CDDL
nonce-type = bstr .size (8..64)
nonce-claim = (
nonce => nonce-type / [ 2* nonce-type ]
)
3.4. Universal Entity ID Claim (ueid)
UEID's identify individual manufactured entities / devices such as a
mobile phone, a water meter, a Bluetooth speaker or a networked
security camera. It may identify the entire device or a submodule or
subsystem. It does not identify types, models or classes of devices.
It is akin to a serial number, though it does not have to be
sequential.
UEID's must be universally and globally unique across manufacturers
and countries. UEIDs must also be unique across protocols and
systems, as tokens are intended to be embedded in many different
protocols and systems. No two products anywhere, even in completely
different industries made by two different manufacturers in two
different countries should have the same UEID (if they are not global
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and universal in this way, then relying parties receiving them will
have to track other characteristics of the device to keep devices
distinct between manufacturers).
There are privacy considerations for UEID's. See Section 8.1.
The UEID is permanent. It never change for a given device / entity.
UEIDs are variable length. All implementations MUST be able to
receive UEIDs that are 33 bytes long (1 type byte and 256 bits). The
recommended maximum sent is also 33 bytes.
When the entity constructs the UEID, the first byte is a type and the
following bytes the ID for that type. Several types are allowed to
accommodate different industries and different manufacturing
processes and to give options to avoid paying fees for certain types
of manufacturer registrations.
Creation of new types requires a Standards Action [RFC8126].
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+------+------+-----------------------------------------------------+
| Type | Type | Specification |
| Byte | Name | |
+------+------+-----------------------------------------------------+
| 0x01 | RAND | This is a 128, 192 or 256 bit random number |
| | | generated once and stored in the device. This may |
| | | be constructed by concatenating enough identifiers |
| | | to make up an equivalent number of random bits and |
| | | then feeding the concatenation through a |
| | | cryptographic hash function. It may also be a |
| | | cryptographic quality random number generated once |
| | | at the beginning of the life of the device and |
| | | stored. It may not be smaller than 128 bits. |
| 0x02 | IEEE | This makes use of the IEEE company identification |
| | EUI | registry. An EUI is either an EUI-48, EUI-60 or |
| | | EUI-64 and made up of an OUI, OUI-36 or a CID, |
| | | different registered company identifiers, and some |
| | | unique per-device identifier. EUIs are often the |
| | | same as or similar to MAC addresses. This type |
| | | includes MAC-48, an obsolete name for EUI-48. (Note |
| | | that while devices with multiple network interfaces |
| | | may have multiple MAC addresses, there is only one |
| | | UEID for a device) [IEEE.802-2001], [OUI.Guide] |
| 0x03 | IMEI | This is a 14-digit identifier consisting of an |
| | | 8-digit Type Allocation Code and a 6-digit serial |
| | | number allocated by the manufacturer, which SHALL |
| | | be encoded as byte string of length 14 with each |
| | | byte as the digit's value (not the ASCII encoding |
| | | of the digit; the digit 3 encodes as 0x03, not |
| | | 0x33). The IMEI value encoded SHALL NOT include |
| | | Luhn checksum or SVN information. [ThreeGPP.IMEI] |
+------+------+-----------------------------------------------------+
Table 1: UEID Composition Types
UEID's are not designed for direct use by humans (e.g., printing on
the case of a device), so no textual representation is defined.
The consumer (the relying party) of a UEID MUST treat a UEID as a
completely opaque string of bytes and not make any use of its
internal structure. For example, they should not use the OUI part of
a type 0x02 UEID to identify the manufacturer of the device. Instead
they should use the oemid claim that is defined elsewhere. The
reasons for this are:
o UEIDs types may vary freely from one manufacturer to the next.
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o New types of UEIDs may be created. For example, a type 0x07 UEID
may be created based on some other manufacturer registration
scheme.
o Device manufacturers are allowed to change from one type of UEID
to another anytime they want. For example, they may find they can
optimize their manufacturing by switching from type 0x01 to type
0x02 or vice versa. The main requirement on the manufacturer is
that UEIDs be universally unique.
3.4.1. ueid CDDL
ueid-type = bstr .size (7..33)
ueid-claim = (
ueid => ueid-type
)
3.5. Semi-permanent UEIDs (SUEIDs)
An SEUID is of the same format as a UEID, but it may change to a
different value on device life-cycle events. Examples of these
events are change of ownership, factory reset and on-boarding into an
IoT device management system. A device may have both a UEID and
SUEIDs, neither, one or the other.
There may be multiple SUEIDs. Each one has a text string label the
purpose of which is to distinguish it from others in the token. The
label may name the purpose, application or type of the SUEID.
Typically, there will be few SUEDs so there is no need for a formal
labeling mechanism like a registry. The EAT profile may describe how
SUEIDs should be labeled. If there is only one SUEID, the claim
remains a map and there still must be a label. For example, the
label for the SUEID used by FIDO Onboarding Protocol could simply be
"FDO".
There are privacy considerations for SUEID's. See Section 8.1.
sueids-type = {
+ tstr => ueid-type
}
sueids-claim = (
sueids => sueids-type
)
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3.6. OEM Identification by IEEE (oemid)
The IEEE operates a global registry for MAC addresses and company
IDs. This claim uses that database to identify OEMs. The contents
of the claim may be either an IEEE MA-L, MA-M, MA-S or an IEEE CID
[IEEE.RA]. An MA-L, formerly known as an OUI, is a 24-bit value used
as the first half of a MAC address. MA-M similarly is a 28-bit value
uses as the first part of a MAC address, and MA-S, formerly known as
OUI-36, a 36-bit value. Many companies already have purchased one of
these. A CID is also a 24-bit value from the same space as an MA-L,
but not for use as a MAC address. IEEE has published Guidelines for
Use of EUI, OUI, and CID [OUI.Guide] and provides a lookup services
[OUI.Lookup]
Companies that have more than one of these IDs or MAC address blocks
should pick one and prefer that for all their devices.
Commonly, these are expressed in Hexadecimal Representation
[IEEE.802-2001] also called the Canonical format. When this claim is
encoded the order of bytes in the bstr are the same as the order in
the Hexadecimal Representation. For example, an MA-L like "AC-DE-48"
would be encoded in 3 bytes with values 0xAC, 0xDE, 0x48. For JSON
encoded tokens, this is further base64url encoded.
3.6.1. oemid CDDL
oemid-claim = (
oemid => bstr
)
3.7. Hardware Version Claims (hardware-version-claims)
The hardware version can be claimed at three different levels, the
chip, the circuit board and the final device assembly. An EAT can
include any combination these claims.
The hardware version is a simple text string the format of which is
set by each manufacturer. The structure and sorting order of this
text string can be specified using the version-scheme item from
CoSWID [CoSWID].
The hardware version can also be given by a 13-digit [EAN-13]. A new
CoSWID version scheme is registered with IANA by this document in
Section 7.3.3. An EAN-13 is also known as an International Article
Number or most commonly as a bar code.
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chip-version-claim = (
chip-version => tstr
)
chip-version-scheme-claim = (
chip-version-scheme => $version-scheme
)
board-version-claim = (
board-version => tstr
)
board-version-scheme-claim = (
board-version-scheme => $version-scheme
)
device-version-claim = (
device-version => tstr
)
device-version-scheme-claim = (
device-version-scheme => $version-scheme
)
hardware-version-claims = (
? chip-version-claim,
? board-version-claim,
? device-version-claim,
? chip-version-scheme-claim,
? board-version-scheme-claim,
? device-version-scheme-claim,
)
3.8. Software Description and Version
TODO: Add claims that reference CoSWID.
3.9. The Security Level Claim (security-level)
This claim characterizes the device/entity ability to defend against
attacks aimed at capturing the signing key, forging claims and at
forging EATs. This is done by defining four security levels as
described below. This is similar to the key protection types defined
by the Fast Identity Online (FIDO) Alliance [FIDO.Registry].
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These claims describe security environment and countermeasures
available on the end-entity / client device where the attestation key
reside and the claims originate.
1 - Unrestricted There is some expectation that implementor will
protect the attestation signing keys at this level. Otherwise the
EAT provides no meaningful security assurances.
2- Restricted Entities at this level should not be general-purpose
operating environments that host features such as app download
systems, web browsers and complex productivity applications. It
is akin to the Secure Restricted level (see below) without the
security orientation. Examples include a Wi-Fi subsystem, an IoT
camera, or sensor device.
3 - Secure Restricted Entities at this level must meet the criteria
defined by FIDO Allowed Restricted Operating Environments
[FIDO.AROE]. Examples include TEE's and schemes using
virtualization-based security. Like the FIDO security goal,
security at this level is aimed at defending well against large-
scale network / remote attacks against the device.
4 - Hardware Entities at this level must include substantial defense
against physical or electrical attacks against the device itself.
It is assumed any potential attacker has captured the device and
can disassemble it. Example include TPMs and Secure Elements.
The entity should claim the highest security level it achieves and no
higher. This set is not extensible so as to provide a common
interoperable description of security level to the relying party. If
a particular implementation considers this claim to be inadequate, it
can define its own proprietary claim. It may consider including both
this claim as a coarse indication of security and its own proprietary
claim as a refined indication.
This claim is not intended as a replacement for a proper end-device
security certification schemes such as those based on FIPS 140
[FIPS-140] or those based on Common Criteria [Common.Criteria]. The
claim made here is solely a self-claim made by the Entity Originator.
3.9.1. security-level CDDL
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security-level-cbor-type = &(
unrestricted: 1,
restricted: 2,
secure-restricted: 3,
hardware: 4
)
security-level-json-type =
"unrestricted" /
"restricted" /
"secure-restricted" /
"hardware"
security-level-claim = (
security-level => security-level-cbor-type / security-level-json-type
)
3.10. Secure Boot Claim (secure-boot)
The value of true indicates secure boot is enabled. Secure boot is
considered enabled when base software, the firmware and operating
system, are under control of the entity manufacturer identified in
the oemid claimd described in Section 3.6. This may because the
software is in ROM or because it is cryptographically authenticated
or some combination of the two or other.
3.10.1. secure-boot CDDL
secure-boot-claim = (
secure-boot => bool
)
3.11. Debug Status Claim (debug-status)
This applies to system-wide or submodule-wide debug facilities of the
target device / submodule like JTAG and diagnostic hardware built
into chips. It applies to any software debug facilities related to
root, operating system or privileged software that allow system-wide
memory inspection, tracing or modification of non-system software
like user mode applications.
This characterization assumes that debug facilities can be enabled
and disabled in a dynamic way or be disabled in some permanent way
such that no enabling is possible. An example of dynamic enabling is
one where some authentication is required to enable debugging. An
example of permanent disabling is blowing a hardware fuse in a chip.
The specific type of the mechanism is not taken into account. For
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example, it does not matter if authentication is by a global password
or by per-device public keys.
As with all claims, the absence of the debug level claim means it is
not reported. A conservative interpretation might assume the Not
Disabled state. It could however be that it is reported in a
proprietary claim.
This claim is not extensible so as to provide a common interoperable
description of debug status to the relying party. If a particular
implementation considers this claim to be inadequate, it can define
its own proprietary claim. It may consider including both this claim
as a coarse indication of debug status and its own proprietary claim
as a refined indication.
The higher levels of debug disabling requires that all debug
disabling of the levels below it be in effect. Since the lowest
level requires that all of the target's debug be currently disabled,
all other levels require that too.
There is no inheritance of claims from a submodule to a superior
module or vice versa. There is no assumption, requirement or
guarantee that the target of a superior module encompasses the
targets of submodules. Thus, every submodule must explicitly
describe its own debug state. The verifier or relying party
receiving an EAT cannot assume that debug is turned off in a
submodule because there is a claim indicating it is turned off in a
superior module.
An individual target device / submodule may have multiple debug
facilities. The use of plural in the description of the states
refers to that, not to any aggregation or inheritance.
The architecture of some chips or devices may be such that a debug
facility operates for the whole chip or device. If the EAT for such
a chip includes submodules, then each submodule should independently
report the status of the whole-chip or whole-device debug facility.
This is the only way the relying party can know the debug status of
the submodules since there is no inheritance.
3.11.1. Enabled
If any debug facility, even manufacturer hardware diagnostics, is
currently enabled, then this level must be indicated.
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3.11.2. Disabled
This level indicates all debug facilities are currently disabled. It
may be possible to enable them in the future, and it may also be
possible that they were enabled in the past after the target device/
sub-system booted/started, but they are currently disabled.
3.11.3. Disabled Since Boot
This level indicates all debug facilities are currently disabled and
have been so since the target device/sub-system booted/started.
3.11.4. Disabled Permanently
This level indicates all non-manufacturer facilities are permanently
disabled such that no end user or developer cannot enable them. Only
the manufacturer indicated in the OEMID claim can enable them. This
also indicates that all debug facilities are currently disabled and
have been so since boot/start.
3.11.5. Disabled Fully and Permanently
This level indicates that all debug capabilities for the target
device/sub-module are permanently disabled.
3.11.6. debug-status CDDL
debug-status-cbor-type = &(
enabled: 0,
disabled: 1,
disabled-since-boot: 2,
disabled-permanently: 3,
disabled-fully-and-permanently: 4
)
debug-status-json-type =
"enabled" /
"disabled" /
"disabled-since-boot" /
"disabled-permanently" /
"disabled-fully-and-permanently"
debug-status-claim = (
debug-status => debug-status-cbor-type / debug-status-json-type
)
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3.12. Including Keys
An EAT may include a cryptographic key such as a public key. The
signing of the EAT binds the key to all the other claims in the
token.
The purpose for inclusion of the key may vary by use case. For
example, the key may be included as part of an IoT device onboarding
protocol. When the FIDO protocol includes a pubic key in its
attestation message, the key represents the binding of a user, device
and relying party. This document describes how claims containing
keys should be defined for the various use cases. It does not define
specific claims for specific use cases.
Keys in CBOR format tokens SHOULD be the COSE_Key format [RFC8152]
and keys in JSON format tokens SHOULD be the JSON Web Key format
[RFC7517]. These two formats support many common key types. Their
use avoids the need to decode other serialization formats. These two
formats can be extended to support further key types through their
IANA registries.
The general confirmation claim format [RFC8747], [RFC7800] may also
be used. It provides key encryption. It also allows for inclusion
by reference through a key ID. The confirmation claim format may
employed in the definition of some new claim for a a particular use
case.
When the actual confirmation claim is included in an EAT, this
document associates no use case semantics other than proof of
posession. Different EAT use cases may choose to associate further
semantics. The key in the confirmation claim MUST be protected the
same as the key used to sign the EAT. That is, the same, equivalent
or better hardware defenses, access controls, key generation and such
must be used.
3.13. The Location Claim (location)
The location claim gives the location of the device entity from which
the attestation originates. It is derived from the W3C Geolocation
API [W3C.GeoLoc]. The latitude, longitude, altitude and accuracy
must conform to [WGS84]. The altitude is in meters above the [WGS84]
ellipsoid. The two accuracy values are positive numbers in meters.
The heading is in degrees relative to true north. If the device is
stationary, the heading is NaN (floating-point not-a-number). The
speed is the horizontal component of the device velocity in meters
per second.
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When encoding floating-point numbers half-precision should not be
used. It usually does not provide enough precision for a geographic
location. It is not a requirement that the receiver of an EAT
implement half-precision, so the receiver may not be able to decode
the location.
The location may have been cached for a period of time before token
creation. For example, it might have been minutes or hours or more
since the last contact with a GPS satellite. Either the timestamp or
age data item can be used to quantify the cached period. The
timestamp data item is preferred as it a non-relative time.
The age data item can be used when the entity doesn't know what time
it is either because it doesn't have a clock or it isn't set. The
entity must still have a "ticker" that can measure a time interval.
The age is the interval between acquisition of the location data and
token creation.
See location-related privacy considerations in Section 8.2 below.
3.13.1. location CDDL
location-type = {
latitude => number,
longitude => number,
? altitude => number,
? accuracy => number,
? altitude-accuracy => number,
? heading => number,
? speed => number,
? timestamp => ~time-int,
? age => uint
}
latitude = 1 / "latitude"
longitude = 2 / "longitude"
altitude = 3 / "altitude"
accuracy = 4 / "accuracy"
altitude-accuracy = 5 / "altitude-accuracy"
heading = 6 / "heading"
speed = 7 / "speed"
timestamp = 8 / "timestamp"
age = 9 / "age"
location-claim = (
location-label => location-type
)
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3.14. The Uptime Claim (uptime)
The "uptime" claim contains a value that represents the number of
seconds that have elapsed since the entity or submod was last booted.
3.14.1. uptime CDDL
uptime-claim = (
uptime => uint
)
3.15. The Boot Seed Claim (boot-seed)
The Boot Seed claim is a random value created at system boot time
that will allow differentiation of reports from different boot
sessions. This value is usually public and not protected. It is not
the same as a seed for a random number generator which must be kept
secret.
boot-seed-claim = (
boot-seed => bytes
)
3.16. The Intended Use Claim (intended-use)
EAT's may be used in the context of several different applications.
The intended-use claim provides an indication to an EAT consumer
about the intended usage of the token. This claim can be used as a
way for an application using EAT to internally distinguish between
different ways it uses EAT.
1 - Generic Generic attestation describes an application where the
EAT consumer requres the most up-to-date security assessment of
the attesting entity. It is expected that this is the most
commonly-used application of EAT.
2- Registration Entities that are registering for a new service may
be expected to provide an attestation as part of the registration
process. This intended-use setting indicates that the attestation
is not intended for any use but registration.
3 - Provisioning Entities may be provisioned with different values
or settings by an EAT consumer. Examples include key material or
device management trees. The consumer may require an EAT to
assess device security state of the entity prior to provisioning.
4 - Certificate Issuance (Certificate Signing Request) Certifying
authorities (CA's) may require attestations prior to the issuance
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of certificates related to keypairs hosted at the entity. An EAT
may be used as part of the certificate signing request (CSR).
5 - Proof-of-Possession An EAT consumer may require an attestation
as part of an accompanying proof-of-possession (PoP) appication.
More precisely, a PoP transaction is intended to provide to the
recipient cryptographically-verifiable proof that the sender has
posession of a key. This kind of attestation may be neceesary to
verify the security state of the entity storing the private key
used in a PoP application.
3.16.1. intended-use CDDL
intended-use-cbor-type = &(
generic: 1,
registration: 2,
provisioning: 3,
csr: 4,
pop: 5
)
intended-use-json-type =
"generic" /
"registration" /
"provisioning" /
"csr" /
"pop"
intended-use-claim = (
intended-use => intended-use-cbor-type / intended-use-json-type
)
3.17. The Profile Claim (profile)
See Section 5 for the detailed description of a profile.
A profile is identified by either a URL or an OID. Typically, the
URI will reference a document describing the profile. An OID is just
a unique identifier for the profile. It may exist anywhere in the
OID tree. There is no requirement that the named document be
publicly accessible. The primary purpose of the profile claim is to
uniquely identify the profile even if it is a private profile.
The OID is encoded in CBOR according to [CBOR-OID] and the URI
according to [RFC8949]. Both are unwrapped and thus not tags. The
OID is always absolute and never relative. If the claims CBOR type
is a text string it is a URI and if a byte string it is an OID.
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Note that this named "eat_profile" for JWT and is distinct from the
already registered "profile" claim in the JWT claims registry.
oid = #6.4000(bstr) ; TODO: fill this in with correct CDDL from OID RFC
profile-claim = (
profile => ~uri / ~oid
)
3.18. The Software Manifests Claim (manifests)
This claim contains descriptions of software that is present on the
device. These manifests are installed on the device when the
software is installed or are created as part of the installation
process. Installation is anything that adds software to the device,
possibly factory installation, the user installing elective
applications and so on. The defining characteristic is that they are
created by the software manufacturer. The purpose of these claims in
an EAT is to relay them without modification to the Verifier and/or
the Relying Party.
In some cases these will be signed by the software manufacturer
independent of any signing for the purpose of EAT attestation.
Manifest claims should include the manufacturer's signature (which
will be signed over by the attestation signature). In other cases
the attestation signature will be the only one.
This claim allows multiple formats for the manifest. For example the
manifest may be a CBOR-format CoSWID, an XML-format SWID or other.
Identification of the type of manifest is always by a CBOR tag. In
many cases, for examples CoSWID, a tag will already be registered
with IANA. If not, a tag MUST be registered. It can be in the
first-come-first-served space which has minimal requirements for
registration.
The claim is an array of one or more manifests. To facilitate hand
off of the manifest to a decoding library, each manifest is contained
in a byte string. This occurs for CBOR-format manifests as well as
non-CBOR format manifests.
If a particular manifest type uses CBOR encoding, then the item in
the array for it MUST be a byte string that contains a CBOR tag. The
EAT decoder must decode the byte string and then the CBOR within it
to find the tag number to identify the type of manifest. The
contents of the byte string is then handed to the particular manifest
processor for that type of manifest. CoSWID and SUIT manifest are
examples of this.
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If a particular manifest type does not use CBOR encoding, then the
item in the array for it must be a CBOR tag that contains a byte
string. The EAT decoder uses the tag to identify the processor for
that type of manifest. The contents of the tag, the byte string, are
handed to the manifest processor. Note that a byte string is used to
contain the manifest whether it is a text based format or not. An
example of this is an XML format ISO/IEC 19770 SWID.
It is not possible to describe the above requirements in CDDL so the
type for an individual manifest is any in the CDDL below. The above
text sets the encoding requirement.
This claim allows for multiple manifests in one token since multiple
software packages are likely to be present. The multiple manifests
may be of multiple formats. In some cases EAT submodules may be used
instead of the array structure in this claim for multiple manifests.
When the [CoSWID] format is used, it MUST be a payload CoSWID, not an
evidence CoSWID.
manifests-claim = (
manifests => manifests-type
)
manifests-type = [+ $manifest-formats]
; Must be a CoSWID payload type
$manifest-formats /= bytes .cbor concise-swid-tag
$manifest-formats /= bytes .cbor SUIT_Envelope_Tagged
3.19. The Software Evidence Claim {swevidence}
This claim contains descriptions, lists, evidence or measurements of
the software that exists on the device. The defining characteristic
of this claim is that its contents are created by processes on the
device that inventory, measure or otherwise characterize the software
on the device. The contents of this claim do not originate from the
software manufacturer.
In most cases the contents of this claim are signed as part of
attestation signing, but independent signing in addition to the
attestation signing is not ruled out when a particular evidence
format supports it.
This claim uses the same mechanism for identification of the type of
the swevidence as is used for the type of the manifest in the
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manifests claim. It also uses the same byte string based mechanism
for containing the claim and easing the hand off to a processing
library. See the discussion above in the manifests claim.
When the [CoSWID] format is used, it MUST be evidence CoSWIDs, not
payload CoSWIDS.
swevidence-claim = (
swevidence => swevidence-type
)
swevidence-type = [+ $swevidence-formats]
; Must be a CoSWID evidence type
$swevidence-formats /= bytes .cbor concise-swid-tag
3.20. The Submodules Part of a Token (submods)
Some devices are complex, having many subsystems or submodules. A
mobile phone is a good example. It may have several connectivity
submodules for communications (e.g., Wi-Fi and cellular). It may
have subsystems for low-power audio and video playback. It may have
one or more security-oriented subsystems like a TEE or a Secure
Element.
The claims for each these can be grouped together in a submodule.
The submods part of a token are in a single map/object with many
entries, one per submodule. There is only one submods map in a
token. It is identified by its specific label. It is a peer to
other claims, but it is not called a claim because it is a container
for a claim set rather than an individual claim. This submods part
of a token allows what might be called recursion. It allows claim
sets inside of claim sets inside of claims sets...
3.20.1. Two Types of Submodules
Each entry in the submod map is one of two types:
o A non-token submodule that is a map or object directly containing
claims for the submodule.
o A nested EAT that is a fully formed, independently signed EAT
token
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3.20.1.1. Non-token Submodules
This is simply a map or object containing claims about the submodule.
It may contain claims that are the same as its surrounding token or
superior submodules. For example, the top-level of the token may
have a UEID, a submod may have a different UEID and a further
subordinate submodule may also have a UEID.
It is signed/encrypted along with the rest of the token and thus the
claims are secured by the same Attester with the same signing key as
the rest of the token.
If a token is in CBOR format (a CWT or a UCCS), all non-token
submodules must be CBOR format. If a token in in JSON format (a
JWT), all non-token submodules must be in JSON format.
When decoding, this type of submodule is recognized from the other
type by being a data item of type map for CBOR or type object for
JSON.
3.20.1.2. Nested EATs
This type of submodule is a fully formed secured EAT as defined in
this document except that it MUST NOT be a UCCS or an unsecured JWT.
A nested token that is one that is always secured using COSE or JOSE,
usually by an independent Attester. When the surrounding EAT is a
CWT or secured JWT, the nested token becomes securely bound with the
other claims in the surrounding token.
It is allowed to have a CWT as a submodule in a JWT and vice versa,
but this SHOULD be avoided unless necessary.
3.20.1.2.1. Surrounding EAT is CBOR format
They type of an EAT nested in a CWT is determined by whether the CBOR
type is a text string or a byte string. If a text string, then it is
a JWT. If a byte string, then it is a CWT.
A CWT nested in a CBOR-format token is always wrapped by a byte
string for easier handling with standard CBOR decoders and token
processing APIs that will typically take a byte buffer as input.
Nested CWTs may be either a CWT CBOR tag or a CWT Protocol Message.
COSE layers in nested CWT EATs MUST be a COSE_Tagged_Message, never a
COSE_Untagged_Message. If a nested EAT has more than one level of
COSE, for example one that is both encrypted and signed, a
COSE_Tagged_message must be used at every level.
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3.20.1.2.2. Surrounding EAT is JSON format
When a CWT is nested in a JWT, it must be as a 55799 tag in order to
distinguish it from a nested JWT.
When a nested EAT in a JWT is decoded, first remove the base64url
encoding. Next, check to see if it starts with the bytes 0xd9d9f7.
If so, then it is a CWT as a JWT will never start with these four
bytes. If not if it is a JWT.
Other than the 55799 tag requirement, tag usage for CWT's nested in a
JSON format token follow the same rules as for CWTs nested in CBOR-
format tokens. It may be a CWT CBOR tag or a CWT Protocol Message
and COSE_Tagged_Message MUST be used at all COSE layers.
3.20.1.3. Unsecured JWTs and UCCS Tokens as Submodules
To incorporate a UCCS token as a submodule, it MUST be as a non-token
submodule. This can be accomplished inserting the content of the
UCCS Tag into the submodule map. The content of a UCCS tag is
exactly a map of claims as required for a non-token submodule. If
the UCCS is not a UCCS tag, then it can just be inserted into the
submodule map directly.
The definition of a nested EAT type of submodule is that it is one
that is secured (signed) by an Attester. Since UCCS tokens are
unsecured, they do not fulfill this definition and must be non-token
submodules.
To incorporate an Unsecured JWT as a submodule, the null-security
JOSE wrapping should be removed. The resulting claims set should be
inserted as a non-token submodule.
To incorporate a UCCS token in a surrounding JSON token, the UCCS
token claims should be translated from CBOR to JSON. To incorporate
an Unsecured JWT into a surrounding CBOR-format token, the null-
security JOSE should be removed and the claims translated from JSON
to CBOR.
3.20.2. No Inheritance
The subordinate modules do not inherit anything from the containing
token. The subordinate modules must explicitly include all of their
claims. This is the case even for claims like the nonce and age.
This rule is in place for simplicity. It avoids complex inheritance
rules that might vary from one type of claim to another.
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3.20.3. Security Levels
The security level of the non-token subordinate modules should always
be less than or equal to that of the containing modules in the case
of non-token submodules. It makes no sense for a module of lesser
security to be signing claims of a module of higher security. An
example of this is a TEE signing claims made by the non-TEE parts
(e.g. the high-level OS) of the device.
The opposite may be true for the nested tokens. They usually have
their own more secure key material. An example of this is an
embedded secure element.
3.20.4. Submodule Names
The label or name for each submodule in the submods map is a text
string naming the submodule. No submodules may have the same name.
3.20.5. submods CDDL
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; The part of a token that contains all the submodules. It is a peer
; with the claims in the token, but not a claim, only a map/object to
; hold all the submodules.
submods-part = (
submods => submods-type
)
submods-type = { + submod-type }
; The type of a submodule which can either be a nested claim set or a
; nested separately signed token. Nested tokens are wrapped in a bstr
; or a tstr.
submod-type = (
submod-name => eat-claim-set / nested-token
)
; When this is a bstr, the contents are an eat-token in CWT or UCCS
; format. When this is a tstr, the contents are an eat-token in JWT
; format.
nested-token = bstr / tstr;
; Each submodule has a unique text string name.
submod-name = tstr
4. Endorsements and Verification Keys
The Verifier must possess the correct key when it performs the
cryptographic part of an EAT verification (e.g., verifying the COSE
signature). This section describes several ways to identify the
verification key. There is not one standard method.
The verification key itself may be a public key, a symmetric key or
something complicated in the case of a scheme like Direct Anonymous
Attestation (DAA).
RATS Architecture [RATS.Architecture] describes what is called an
Endorsement. This is an input to the Verifier that is usually the
basis of the trust placed in an EAT and the Attester that generated
it. It may contain the public key for verification of the signature
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on the EAT. It may contain Reference Values to which EAT claims are
compared as part of the verification process. It may contain implied
claims, those that are passed on to the Relying Party in Attestation
Results.
There is not yet any standard format(s) for an Endorsement. One
format that may be used for an Endorsement is an X.509 certificate.
Endorsement data like Reference Values and implied claims can be
carried in X.509 v3 extensions. In this use, the public key in the
X.509 certificate becomes the verification key, so identification of
the Endorsement is also identification of the verification key.
The verification key identification and establishment of trust in the
EAT and the attester may also be by some other means than an
Endorsement.
For the components (Attester, Verifier, Relying Party,...) of a
particular end-end attestation system to reliably interoperate, its
definition should specify how the verification key is identified.
Usually, this will be in the profile document for a particular
attestation system.
4.1. Identification Methods
Following is a list of possible methods of key identification. A
specific attestation system may employ any one of these or one not
listed here.
The following assumes Endorsements are X.509 certificates or
equivalent and thus does not mention or define any identifier for
Endorsements in other formats. If such an Endorsement format is
created, new identifiers for them will also need to be created.
4.1.1. COSE/JWS Key ID
The COSE standard header parameter for Key ID (kid) may be used. See
[RFC8152] and [RFC7515]
COSE leaves the semantics of the key ID open-ended. It could be a
record locator in a database, a hash of a public key, an input to a
KDF, an authority key identifier (AKI) for an X.509 certificate or
other. The profile document should specify what the key ID's
semantics are.
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4.1.2. JWS and COSE X.509 Header Parameters
COSE X.509 [COSE.X509.Draft] and JSON Web Siganture [RFC7515] define
several header parameters (x5t, x5u,...) for referencing or carrying
X.509 certificates any of which may be used.
The X.509 certificate may be an Endorsement and thus carrying
additional input to the Verifier. It may be just an X.509
certificate, not an Endorsement. The same header parameters are used
in both cases. It is up to the attestation system design and the
Verifier to determine which.
4.1.3. CBOR Certificate COSE Header Parameters
Compressed X.509 and CBOR Native certificates are defined by CBOR
Certificates [CBOR.Cert.Draft]. These are semantically compatible
with X.509 and therefore can be used as an equivalent to X.509 as
described above.
These are identified by their own header parameters (c5t, c5u,...).
4.1.4. Claim-Based Key Identification
For some attestation systems, a claim may be re-used as a key
identifier. For example, the UEID uniquely identifies the device and
therefore can work well as a key identifier or Endorsement
identifier.
This has the advantage that key identification requires no additional
bytes in the EAT and makes the EAT smaller.
This has the disadvantage that the unverified EAT must be
substantially decoded to obtain the identifier since the identifier
is in the COSE/JOSE payload, not in the headers.
4.2. Other Considerations
In all cases there must be some way that the verification key is
itself verified or determined to be trustworthy. The key
identification itself is never enough. This will always be by some
out-of-band mechanism that is not described here. For example, the
Verifier may be configured with a root certificate or a master key by
the Verifier system administrator.
Often an X.509 certificate or an Endorsement carries more than just
the verification key. For example, an X.509 certificate might have
key usage constraints and an Endorsement might have Reference Values.
When this is the case, the key identifier must be either a protected
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header or in the payload such that it is cryptographically bound to
the EAT. This is in line with the requirements in section 6 on Key
Identification in JSON Web Signature [RFC7515].
5. Profiles
This EAT specification does not gaurantee that implementations of it
will interoperate. The variability in this specification is
necessary to accommodate the widely varying use cases. An EAT
profile narrows the specification for a specific use case. An ideal
EAT profile will gauarantee interoperability.
The profile can be named in the token using the profile claim
described in Section 3.17.
5.1. Format of a Profile Document
A profile document doesn't have to be in any particular format. It
may be simple text, something more formal or a combination.
In some cases CDDL may be created that replaces CDDL in this or other
document to express some profile requirements. For example, to
require the altitude data item in the location claim, CDDL can be
written that replicates the location claim with the altitude no
longer optional.
5.2. List of Profile Issues
The following is a list of EAT, CWT, UCCS, JWS, COSE, JOSE and CBOR
options that a profile should address.
5.2.1. Use of JSON, CBOR or both
The profile should indicate whether the token format should be CBOR,
JSON, both or even some other encoding. If some other encoding, a
specification for how the CDDL described here is serialized in that
encoding is necessary.
This should be addressed for the top-level token and for any nested
tokens. For example, a profile might require all nested tokens to be
of the same encoding of the top level token.
5.2.2. CBOR Map and Array Encoding
The profile should indicate whether definite-length arrays/maps,
indefinite-length arrays/maps or both are allowed. A good default is
to allow only definite-length arrays/maps.
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An alternate is to allow both definite and indefinite-length arrays/
maps. The decoder should accept either. Encoders that need to fit
on very small hardware or be actually implement in hardware can use
indefinite-length encoding.
This applies to individual EAT claims, CWT and COSE parts of the
implementation.
5.2.3. CBOR String Encoding
The profile should indicate whether definite-length strings,
indefinite-length strings or both are allowed. A good default is to
allow only definite-length strings. As with map and array encoding,
allowing indefinite-length strings can be beneficial for some smaller
implementations.
5.2.4. CBOR Preferred Serialization
The profile should indicate whether encoders must use preferred
serialization. The profile should indicate whether decoders must
accept non-preferred serialization.
5.2.5. COSE/JOSE Protection
COSE and JOSE have several options for signed, MACed and encrypted
messages. EAT/CWT has the option to have no protection using UCCS
and JOSE has a NULL protection option. It is possible to implement
no protection, sign only, MAC only, sign then encrypt and so on. All
combinations allowed by COSE, JOSE, JWT, CWT and UCCS are allowed by
EAT.
The profile should list the protections that must be supported by all
decoders implementing the profile. The encoders them must implement
a subset of what is listed for the decoders, perhaps only one.
Implementations may choose to sign or MAC before encryption so that
the implementation layer doing the signing or MACing can be the
smallest. It is often easier to make smaller implementations more
secure, perhaps even implementing in solely in hardware. The key
material for a signature or MAC is a private key, while for
encryption it is likely to be a public key. The key for encryption
requires less protection.
5.2.6. COSE/JOSE Algorithms
The profile document should list the COSE algorithms that a Verifier
must implement. The Attester will select one of them. Since there
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is no negotiation, the Verifier should implement all algorithms
listed in the profile.
5.2.7. Verification Key Identification
Section Section 4 describes a number of methods for identifying a
verification key. The profile document should specify one of these
or one that is not described. The ones described in this document
are only roughly described. The profile document should go into the
full detail.
5.2.8. Endorsement Identification
Similar to, or perhaps the same as Verification Key Identification,
the profile may wish to specify how Endorsements are to be
identified. However note that Endorsement Identification is
optional, where as key identification is not.
5.2.9. Freshness
Just about every use case will require some means of knowing the EAT
is recent enough and not a replay of an old token. The profile
should describe how freshness is achieved. The section on Freshness
in [RATS-Architecture] describes some of the possible solutions to
achieve this.
5.2.10. Required Claims
The profile can list claims whose absence results in Verification
failure.
5.2.11. Prohibited Claims
The profile can list claims whose presence results in Verification
failure.
5.2.12. Additional Claims
The profile may describe entirely new claims. These claims can be
required or optional.
5.2.13. Refined Claim Definition
The profile may lock down optional aspects of individual claims. For
example, it may require altitude in the location claim, or it may
require that HW Versions always be described using EAN-13.
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5.2.14. CBOR Tags
The profile should specify whether the token should be a CWT Tag or
not. Similarly, the profile should specify whether the token should
be a UCCS tag or not.
When COSE protection is used, the profile should specify whether COSE
tags are used or not. Note that RFC 8392 requires COSE tags be used
in a CWT tag.
Often a tag is unncessary because the surrounding or carrying
protocol identifies the object as an EAT.
5.2.15. Manifests and Software Evidence Claims
The profile should specify which formats are allowed for the
manifests and software evidence claims. The profile may also go on
to say which parts and options of these formats are used, allowed and
prohibited.
6. Encoding
This makes use of the types defined in CDDL Appendix D, Standard
Prelude.
Some of the CDDL included here is for claims that are defined in CWT
[RFC8392] or JWT [RFC7519] or are in the IANA CWT or JWT registries.
CDDL was not in use when these claims where defined.
6.1. Common CDDL Types
time-int is identical to the epoch-based time, but disallows
floating-point representation.
Note that unless expliclity indicated, URIs are not the URI tag
defined in [RFC8949]. They are just text strings that contain a URI.
string-or-uri = tstr
time-int = #6.1(int)
6.2. CDDL for CWT-defined Claims
This section provides CDDL for the claims defined in CWT. It is non-
normative as [RFC8392] is the authoritative definition of these
claims.
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Note that the subject, issue and audience claims may be a text string
containing a URI per [RFC8392] and [RFC7519]. These are never the
URI tag defined in [RFC8949].
$$eat-extension //= (
? issuer => text,
? subject => text,
? audience => text,
? expiration => time,
? not-before => time,
? issued-at => time,
? cwt-id => bytes,
)
issuer = 1
subject = 2
audience = 3
expiration = 4
not-before = 5
issued-at = 6
cwt-id = 7
6.3. JSON
6.3.1. JSON Labels
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; The following are Claim Keys (labels) assigned for JSON-encoded tokens.
ueid /= "ueid"
sueids /= "sueids"
nonce /= "nonce"
oemid /= "oemid"
security-level /= "seclevel"
secure-boot /= "secboot"
debug-status /= "dbgstat"
location /= "location"
uptime /= "uptime"
profile /= "eat-profile"
intended-use /= "intuse"
boot-seed /= "bootseed"
submods /= "submods"
timestamp /= "timestamp"
manifests /= "manifests"
swevidence /= "swevidence"
latitude /= "lat"
longitude /= "long"
altitude /= "alt"
accuracy /= "accry"
altitude-accuracy /= "alt-accry"
heading /= "heading"
speed /= "speed"
6.3.2. JSON Interoperability
JSON should be encoded per RFC 8610 Appendix E. In addition, the
following CDDL types are encoded in JSON as follows:
o bstr - must be base64url encoded
o time - must be encoded as NumericDate as described section 2 of
[RFC7519].
o string-or-uri - must be encoded as StringOrURI as described
section 2 of [RFC7519].
o uri - must be a URI [RFC3986].
o oid - encoded as a string using the well established dotted-
decimal notation (e.g., the text "1.2.250.1").
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6.4. CBOR
6.4.1. CBOR Interoperability
CBOR allows data items to be serialized in more than one form. If
the sender uses a form that the receiver can't decode, there will not
be interoperability.
This specification gives no blanket requirements to narrow CBOR
serialization for all uses of EAT. This allows individual uses to
tailor serialization to the environment. It also may result in EAT
implementations that don't interoperate.
One way to guarantee interoperability is to clearly specify CBOR
serialization in a profile document. See Section 5 for a list of
serialization issues that should be addressed.
EAT will be commonly used where the device generating the attestation
is constrained and the receiver/verifier of the attestation is a
capacious server. Following is a set of serialization requirements
that work well for that use case and are guaranteed to interoperate.
Use of this serialization is recommended where possible, but not
required. An EAT profile may just reference the following section
rather than spell out serialization details.
6.4.1.1. EAT Constrained Device Serialization
o Preferred serialization described in section 4.1 of [RFC8949] is
not required. The EAT decoder must accept all forms of number
serialization. The EAT encoder may use any form it wishes.
o The EAT decoder must accept indefinite length arrays and maps as
described in section 3.2.2 of [RFC8949]. The EAT encoder may use
indefinite length arrays and maps if it wishes.
o The EAT decoder must accept indefinite length strings as described
in section 3.2.3 of [RFC8949]. The EAT encoder may use indefinite
length strings if it wishes.
o Sorting of maps by key is not required. The EAT decoder must not
rely on sorting.
o Deterministic encoding described in Section 4.2 of [RFC8949] is
not required.
o Basic validity described in section 5.3.1 of [RFC8949] must be
followed. The EAT encoder must not send duplicate map keys/labels
or invalid UTF-8 strings.
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6.5. Collected CDDL
; This is the top-level definition of the claims in EAT tokens. To
; form an actual EAT Token, this claim set is enclosed in a COSE, JOSE
; or UCCS message.
eat-claim-set = {
? ueid-claim,
? sueids-claim,
? nonce-claim,
? oemid-claim,
? hardware-version-claims,
? security-level-claim,
? secure-boot-claim,
? debug-status-claim,
? location-claim,
? intended-use-claim,
? profile-claim,
? uptime-claim,
? manifests-claim,
? swevidence-claim,
? submods-part,
* $$eat-extension,
}
; This is the top-level definition of an EAT Token. It is a CWT, JWT
; or UCSS where the payload is an eat-claim-set. A JWT_Message is what
; is defined by JWT in RFC 7519. (RFC 7519 doesn't use CDDL so a there
; is no actual CDDL definition of JWT_Message).
eat-token = EAT_Tagged_Message / EAT_Untagged_Message / JWT_Message
; This is CBOR-format EAT token in the CWT or UCCS format that is a
; tag. COSE_Tagged_message is defined in RFC 8152. Tag 601 is
; proposed by the UCCS draft, but not yet assigned.
EAT_Tagged_Message = #6.61(COSE_Tagged_Message) / #6.601(eat-claim-set)
; This is a CBOR-format EAT token that is a CWT or UCSS that is not a
; tag COSE_Tagged_message and COSE_Untagged_Message are defined in RFC
; 8152.
EAT_Untagged_Message = COSE_Tagged_Message / COSE_Untagged_Message / UCCS_Untagged_Message
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; This is an "unwrapped" UCCS tag. Unwrapping a tag means to use the
; definition of its content without the preceding type 6 tag
; integer. Since a UCCS is nothing but a tag for an unsecured CWT
; claim set, unwrapping reduces to a bare eat-claim-set.
UCCS_Untagged_Message = eat-claim-set
string-or-uri = tstr
time-int = #6.1(int)
$$eat-extension //= (
? issuer => text,
? subject => text,
? audience => text,
? expiration => time,
? not-before => time,
? issued-at => time,
? cwt-id => bytes,
)
issuer = 1
subject = 2
audience = 3
expiration = 4
not-before = 5
issued-at = 6
cwt-id = 7
debug-status-cbor-type = &(
enabled: 0,
disabled: 1,
disabled-since-boot: 2,
disabled-permanently: 3,
disabled-fully-and-permanently: 4
)
debug-status-json-type =
"enabled" /
"disabled" /
"disabled-since-boot" /
"disabled-permanently" /
"disabled-fully-and-permanently"
debug-status-claim = (
debug-status => debug-status-cbor-type / debug-status-json-type
)
location-type = {
latitude => number,
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longitude => number,
? altitude => number,
? accuracy => number,
? altitude-accuracy => number,
? heading => number,
? speed => number,
? timestamp => ~time-int,
? age => uint
}
latitude = 1 / "latitude"
longitude = 2 / "longitude"
altitude = 3 / "altitude"
accuracy = 4 / "accuracy"
altitude-accuracy = 5 / "altitude-accuracy"
heading = 6 / "heading"
speed = 7 / "speed"
timestamp = 8 / "timestamp"
age = 9 / "age"
location-claim = (
location-label => location-type
)
nonce-type = bstr .size (8..64)
nonce-claim = (
nonce => nonce-type / [ 2* nonce-type ]
)
oemid-claim = (
oemid => bstr
)
chip-version-claim = (
chip-version => tstr
)
chip-version-scheme-claim = (
chip-version-scheme => $version-scheme
)
board-version-claim = (
board-version => tstr
)
board-version-scheme-claim = (
board-version-scheme => $version-scheme
)
device-version-claim = (
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device-version => tstr
)
device-version-scheme-claim = (
device-version-scheme => $version-scheme
)
hardware-version-claims = (
? chip-version-claim,
? board-version-claim,
? device-version-claim,
? chip-version-scheme-claim,
? board-version-scheme-claim,
? device-version-scheme-claim,
)
secure-boot-claim = (
secure-boot => bool
)
security-level-cbor-type = &(
unrestricted: 1,
restricted: 2,
secure-restricted: 3,
hardware: 4
)
security-level-json-type =
"unrestricted" /
"restricted" /
"secure-restricted" /
"hardware"
security-level-claim = (
security-level => security-level-cbor-type / security-level-json-type
)
; The part of a token that contains all the submodules. It is a peer
; with the claims in the token, but not a claim, only a map/object to
; hold all the submodules.
submods-part = (
submods => submods-type
)
submods-type = { + submod-type }
; The type of a submodule which can either be a nested claim set or a
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; nested separately signed token. Nested tokens are wrapped in a bstr
; or a tstr.
submod-type = (
submod-name => eat-claim-set / nested-token
)
; When this is a bstr, the contents are an eat-token in CWT or UCCS
; format. When this is a tstr, the contents are an eat-token in JWT
; format.
nested-token = bstr / tstr;
; Each submodule has a unique text string name.
submod-name = tstr
ueid-type = bstr .size (7..33)
ueid-claim = (
ueid => ueid-type
)
sueids-type = {
+ tstr => ueid-type
}
sueids-claim = (
sueids => sueids-type
)
intended-use-cbor-type = &(
generic: 1,
registration: 2,
provisioning: 3,
csr: 4,
pop: 5
)
intended-use-json-type =
"generic" /
"registration" /
"provisioning" /
"csr" /
"pop"
intended-use-claim = (
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intended-use => intended-use-cbor-type / intended-use-json-type
)
oid = #6.4000(bstr) ; TODO: fill this in with correct CDDL from OID RFC
uptime-claim = (
uptime => uint
)
manifests-claim = (
manifests => manifests-type
)
manifests-type = [+ $manifest-formats]
; Must be a CoSWID payload type
$manifest-formats /= bytes .cbor concise-swid-tag
$manifest-formats /= bytes .cbor SUIT_Envelope_Tagged
swevidence-claim = (
swevidence => swevidence-type
)
swevidence-type = [+ $swevidence-formats]
; Must be a CoSWID evidence type
$swevidence-formats /= bytes .cbor concise-swid-tag
oid = #6.4000(bstr) ; TODO: fill this in with correct CDDL from OID RFC
profile-claim = (
profile => ~uri / ~oid
)
boot-seed-claim = (
boot-seed => bytes
)
7. IANA Considerations
7.1. Reuse of CBOR Web Token (CWT) Claims Registry
Claims defined for EAT are compatible with those of CWT so the CWT
Claims Registry is re used. No new IANA registry is created. All
EAT claims should be registered in the CWT and JWT Claims Registries.
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7.2. Claim Characteristics
The following is design guidance for creating new EAT claims,
particularly those to be registered with IANA.
Much of this guidance is generic and could also be considered when
designing new CWT or JWT claims.
7.2.1. Interoperability and Relying Party Orientation
It is a broad goal that EATs can be processed by relying parties in a
general way regardless of the type, manufacturer or technology of the
device from which they originate. It is a goal that there be
general-purpose verification implementations that can verify tokens
for large numbers of use cases with special cases and configurations
for different device types. This is a goal of interoperability of
the semantics of claims themselves, not just of the signing, encoding
and serialization formats.
This is a lofty goal and difficult to achieve broadly requiring
careful definition of claims in a technology neutral way. Sometimes
it will be difficult to design a claim that can represent the
semantics of data from very different device types. However, the
goal remains even when difficult.
7.2.2. Operating System and Technology Neutral
Claims should be defined such that they are not specific to an
operating system. They should be applicable to multiple large high-
level operating systems from different vendors. They should also be
applicable to multiple small embedded operating systems from multiple
vendors and everything in between.
Claims should not be defined such that they are specific to a SW
environment or programming language.
Claims should not be defined such that they are specific to a chip or
particular hardware. For example, they should not just be the
contents of some HW status register as it is unlikely that the same
HW status register with the same bits exists on a chip of a different
manufacturer.
The boot and debug state claims in this document are an example of a
claim that has been defined in this neutral way.
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7.2.3. Security Level Neutral
Many use cases will have EATs generated by some of the most secure
hardware and software that exists. Secure Elements and smart cards
are examples of this. However, EAT is intended for use in low-
security use cases the same as high-security use case. For example,
an app on a mobile device may generate EATs on its own.
Claims should be defined and registered on the basis of whether they
are useful and interoperable, not based on security level. In
particular, there should be no exclusion of claims because they are
just used only in low-security environments.
7.2.4. Reuse of Extant Data Formats
Where possible, claims should use already standardized data items,
identifiers and formats. This takes advantage of the expertise put
into creating those formats and improves interoperability.
Often extant claims will not be defined in an encoding or
serialization format used by EAT. It is preferred to define a CBOR
and JSON format for them so that EAT implementations do not require a
plethora of encoders and decoders for serialization formats.
In some cases, it may be better to use the encoding and serialization
as is. For example, signed X.509 certificates and CRLs can be
carried as-is in a byte string. This retains interoperability with
the extensive infrastructure for creating and processing X.509
certificates and CRLs.
7.2.5. Proprietary Claims
EAT allows the definition and use of proprietary claims.
For example, a device manufacturer may generate a token with
proprietary claims intended only for verification by a service
offered by that device manufacturer. This is a supported use case.
In many cases proprietary claims will be the easiest and most obvious
way to proceed, however for better interoperability, use of general
standardized claims is preferred.
7.3. Claims Registered by This Document
This specification adds the following values to the "JSON Web Token
Claims" registry established by [RFC7519] and the "CBOR Web Token
Claims Registry" established by [RFC8392]. Each entry below is an
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addition to both registries (except for the nonce claim which is
already registered for JWT, but not registered for CWT).
The "Claim Description", "Change Controller" and "Specification
Documents" are common and equivalent for the JWT and CWT registries.
The "Claim Key" and "Claim Value Types(s)" are for the CWT registry
only. The "Claim Name" is as defined for the CWT registry, not the
JWT registry. The "JWT Claim Name" is equivalent to the "Claim Name"
in the JWT registry.
7.3.1. Claims for Early Assignment
RFC Editor: in the final publication this section should be combined
with the following section as it will no longer be necessary to
distinguish claims with early assignment. Also, the following
paragraph should be removed.
The claims in this section have been (requested for / given) early
assignment according to [RFC7120]. They have been assigned values
and registered before final publication of this document. While
their semantics is not expected to change in final publication, it is
possible that they will. The JWT Claim Names and CWT Claim Keys are
not expected to change.
o Claim Name: Nonce
o Claim Description: Nonce
o JWT Claim Name: "nonce" (already registered for JWT)
o Claim Key: 10
o Claim Value Type(s): byte string
o Change Controller: IESG
o Specification Document(s): [OpenIDConnectCore], *this document*
o Claim Name: UEID
o Claim Description: The Universal Entity ID
o JWT Claim Name: "ueid"
o CWT Claim Key: 11
o Claim Value Type(s): byte string
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o Change Controller: IESG
o Specification Document(s): *this document*
o Claim Name: OEMID
o Claim Description: IEEE-based OEM ID
o JWT Claim Name: "oemid"
o Claim Key: 13
o Claim Value Type(s): byte string
o Change Controller: IESG
o Specification Document(s): *this document*
o Claim Name: Security Level
o Claim Description: Characterization of the security of an Attester
or submodule
o JWT Claim Name: "seclevel"
o Claim Key: 14
o Claim Value Type(s): integer
o Change Controller: IESG
o Specification Document(s): *this document*
o Claim Name: Secure Boot
o Claim Description: Indicate whether the boot was secure
o JWT Claim Name: "secboot"
o Claim Key: 15
o Claim Value Type(s): Boolean
o Change Controller: IESG
o Specification Document(s): *this document*
o Claim Name: Debug Status
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o Claim Description: Indicate status of debug facilities
o JWT Claim Name: "dbgstat"
o Claim Key: 16
o Claim Value Type(s): integer
o Change Controller: IESG
o Specification Document(s): *this document*
o Claim Name: Location
o Claim Description: The geographic location
o JWT Claim Name: "location"
o Claim Key: 17
o Claim Value Type(s): map
o Change Controller: IESG
o Specification Document(s): *this document*
o Claim Name: Profile
o Claim Description: Indicates the EAT profile followed
o JWT Claim Name: "eat_profile"
o Claim Key: 18
o Claim Value Type(s): map
o Change Controller: IESG
o Specification Document(s): *this document*
o Claim Name: Submodules Section
o Claim Description: The section containing submodules (not actually
a claim)
o JWT Claim Name: "submods"
o Claim Key: 20
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o Claim Value Type(s): map
o Change Controller: IESG
o Specification Document(s): *this document*
7.3.2. To be Assigned Claims
TODO: add the rest of the claims in here
7.3.3. Version Schemes Registered by this Document
IANA is requested to register a new value in the "Software Tag
Version Scheme Values" established by [CoSWID].
The new value is a version scheme a 13-digit European Article Number
[EAN-13]. An EAN-13 is also known as an International Article Number
or most commonly as a bar code. This version scheme is the ASCII
text representation of EAN-13 digits, the same ones often printed
with a bar code. This version scheme must comply with the EAN
allocation and assignment rules. For example, this requires the
manufacturer to obtain a manufacture code from GS1.
+-------+---------------------+---------------+
| Index | Version Scheme Name | Specification |
+-------+---------------------+---------------+
| 5 | ean-13 | This document |
+-------+---------------------+---------------+
8. Privacy Considerations
Certain EAT claims can be used to track the owner of an entity and
therefore, implementations should consider providing privacy-
preserving options dependent on the intended usage of the EAT.
Examples would include suppression of location claims for EAT's
provided to unauthenticated consumers.
8.1. UEID and SUEID Privacy Considerations
A UEID is usually not privacy-preserving. Any set of relying parties
that receives tokens that happen to be from a single device will be
able to know the tokens are all from the same device and be able to
track the device. Thus, in many usage situations UEID violates
governmental privacy regulation. In other usage situations a UEID
will not be allowed for certain products like browsers that give
privacy for the end user. It will often be the case that tokens will
not have a UEID for these reasons.
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An SUEID is also usually not privacy-preserving. In some cases it
may have fewer privacy issues than a UEID depending on when and how
and when it is generated.
There are several strategies that can be used to still be able to put
UEIDs and SUEIDs in tokens:
o The device obtains explicit permission from the user of the device
to use the UEID/SUEID. This may be through a prompt. It may also
be through a license agreement. For example, agreements for some
online banking and brokerage services might already cover use of a
UEID/SUEID.
o The UEID/SUEID is used only in a particular context or particular
use case. It is used only by one relying party.
o The device authenticates the relying party and generates a derived
UEID/SUEID just for that particular relying party. For example,
the relying party could prove their identity cryptographically to
the device, then the device generates a UEID just for that relying
party by hashing a proofed relying party ID with the main device
UEID/SUEID.
Note that some of these privacy preservation strategies result in
multiple UEIDs and SUEIDs per device. Each UEID/SUEID is used in a
different context, use case or system on the device. However, from
the view of the relying party, there is just one UEID and it is still
globally universal across manufacturers.
8.2. Location Privacy Considerations
Geographic location is most always considered personally identifiable
information. Implementers should consider laws and regulations
governing the transmission of location data from end user devices to
servers and services. Implementers should consider using location
management facilities offered by the operating system on the device
generating the attestation. For example, many mobile phones prompt
the user for permission when before sending location data.
9. Security Considerations
The security considerations provided in Section 8 of [RFC8392] and
Section 11 of [RFC7519] apply to EAT in its CWT and JWT form,
respectively. In addition, implementors should consider the
following.
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9.1. Key Provisioning
Private key material can be used to sign and/or encrypt the EAT, or
can be used to derive the keys used for signing and/or encryption.
In some instances, the manufacturer of the entity may create the key
material separately and provision the key material in the entity
itself. The manfuacturer of any entity that is capable of producing
an EAT should take care to ensure that any private key material be
suitably protected prior to provisioning the key material in the
entity itself. This can require creation of key material in an
enclave (see [RFC4949] for definition of "enclave"), secure
transmission of the key material from the enclave to the entity using
an appropriate protocol, and persistence of the private key material
in some form of secure storage to which (preferably) only the entity
has access.
9.1.1. Transmission of Key Material
Regarding transmission of key material from the enclave to the
entity, the key material may pass through one or more intermediaries.
Therefore some form of protection ("key wrapping") may be necessary.
The transmission itself may be performed electronically, but can also
be done by human courier. In the latter case, there should be
minimal to no exposure of the key material to the human (e.g.
encrypted portable memory). Moreover, the human should transport the
key material directly from the secure enclave where it was created to
a destination secure enclave where it can be provisioned.
9.2. Transport Security
As stated in Section 8 of [RFC8392], "The security of the CWT relies
upon on the protections offered by COSE". Similar considerations
apply to EAT when sent as a CWT. However, EAT introduces the concept
of a nonce to protect against replay. Since an EAT may be created by
an entity that may not support the same type of transport security as
the consumer of the EAT, intermediaries may be required to bridge
communications between the entity and consumer. As a result, it is
RECOMMENDED that both the consumer create a nonce, and the entity
leverage the nonce along with COSE mechanisms for encryption and/or
signing to create the EAT.
Similar considerations apply to the use of EAT as a JWT. Although
the security of a JWT leverages the JSON Web Encryption (JWE) and
JSON Web Signature (JWS) specifications, it is still recommended to
make use of the EAT nonce.
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9.3. Multiple EAT Consumers
In many cases, more than one EAT consumer may be required to fully
verify the entity attestation. Examples include individual consumers
for nested EATs, or consumers for individual claims with an EAT.
When multiple consumers are required for verification of an EAT, it
is important to minimize information exposure to each consumer. In
addition, the communication between multiple consumers should be
secure.
For instance, consider the example of an encrypted and signed EAT
with multiple claims. A consumer may receive the EAT (denoted as the
"receiving consumer"), decrypt its payload, verify its signature, but
then pass specific subsets of claims to other consumers for
evaluation ("downstream consumers"). Since any COSE encryption will
be removed by the receiving consumer, the communication of claim
subsets to any downstream consumer should leverage a secure protocol
(e.g.one that uses transport-layer security, i.e. TLS),
However, assume the EAT of the previous example is hierarchical and
each claim subset for a downstream consumer is created in the form of
a nested EAT. Then transport security between the receiving and
downstream consumers is not strictly required. Nevertheless,
downstream consumers of a nested EAT should provide a nonce unique to
the EAT they are consuming.
10. References
10.1. Normative References
[CBOR-OID]
Bormann, C., "Concise Binary Object Representation (CBOR)
Tags for Object Identifiers", draft-ietf-cbor-tags-oid-06
(work in progress), March 2021.
[CBOR.Cert.Draft]
Raza, S., "CBOR Encoding of X.509 Certificates (CBOR
Certificates)", 2020, <https://tools.ietf.org/html/draft-
mattsson-cose-cbor-cert-compress-05>.
[COSE.X509.Draft]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header parameters for carrying and referencing X.509
certificates", 2020,
<https://tools.ietf.org/html/draft-ietf-cose-x509-08>.
[CoSWID] "Concise Software Identification Tags", November 2020,
<https://tools.ietf.org/html/draft-ietf-sacm-coswid-16>.
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[EAN-13] GS1, "International Article Number - EAN/UPC barcodes",
2019, <https://www.gs1.org/standards/barcodes/ean-upc>.
[FIDO.AROE]
The FIDO Alliance, "FIDO Authenticator Allowed Restricted
Operating Environments List", November 2019,
<https://fidoalliance.org/specs/fido-uaf-v1.0-fd-20191115/
fido-allowed-AROE-v1.0-fd-20191115.html>.
[IANA.CWT.Claims]
IANA, "CBOR Web Token (CWT) Claims",
<http://www.iana.org/assignments/cwt>.
[IANA.JWT.Claims]
IANA, "JSON Web Token (JWT) Claims",
<https://www.iana.org/assignments/jwt>.
[OpenIDConnectCore]
Sakimura, N., Bradley, J., Jones, M., Medeiros, B. D., and
C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 1", November 2014,
<https://openid.net/specs/openid-connect-core-1_0.html>.
[RATS-Architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture",
draft-ietf-rats-architecture-12 (work in progress), April
2021.
[RATS.Architecture]
Birkholz, H., "Remote Attestation Procedures
Architecture", 2020, <https://tools.ietf.org/html/draft-
ietf-rats-architecture-08>.
[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>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[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>.
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[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
[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>.
[RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
Possession Key Semantics for JSON Web Tokens (JWTs)",
RFC 7800, DOI 10.17487/RFC7800, April 2016,
<https://www.rfc-editor.org/info/rfc7800>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[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>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/info/rfc8747>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
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[ThreeGPP.IMEI]
3GPP, "3rd Generation Partnership Project; Technical
Specification Group Core Network and Terminals; Numbering,
addressing and identification", 2019,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=729>.
[UCCS.Draft]
Birkholz, H., "A CBOR Tag for Unprotected CWT Claims
Sets", 2020,
<https://tools.ietf.org/html/draft-birkholz-rats-uccs-01>.
[WGS84] National Imagery and Mapping Agency, "National Imagery and
Mapping Agency Technical Report 8350.2, Third Edition",
2000, <http://earth-
info.nga.mil/GandG/publications/tr8350.2/wgs84fin.pdf>.
10.2. Informative References
[BirthdayAttack]
"Birthday attack",
<https://en.wikipedia.org/wiki/Birthday_attack.>.
[Common.Criteria]
"Common Criteria for Information Technology Security
Evaluation", April 2017,
<https://www.commoncriteriaportal.org/cc/>.
[ECMAScript]
"Ecma International, "ECMAScript Language Specification,
5.1 Edition", ECMA Standard 262", June 2011,
<http://www.ecma-international.org/ecma-262/5.1/ECMA-
262.pdf>.
[FIDO.Registry]
The FIDO Alliance, "FIDO Registry of Predefined Values",
December 2019, <https://fidoalliance.org/specs/common-
specs/fido-registry-v2.1-ps-20191217.html>.
[FIPS-140]
National Institue of Standards, "Security Requirements for
Cryptographic Modules", May 2001,
<https://csrc.nist.gov/publications/detail/fips/140/2/
final>.
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[IEEE.802-2001]
"IEEE Standard For Local And Metropolitan Area Networks
Overview And Architecture", 2007,
<https://webstore.ansi.org/standards/ieee/
ieee8022001r2007>.
[IEEE.802.1AR]
"IEEE Standard, "IEEE 802.1AR Secure Device Identifier"",
December 2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[IEEE.RA] "IEEE Registration Authority",
<https://standards.ieee.org/products-services/regauth/
index.html>.
[OUI.Guide]
"Guidelines for Use of Extended Unique Identifier (EUI),
Organizationally Unique Identifier (OUI), and Company ID
(CID)", August 2017,
<https://standards.ieee.org/content/dam/ieee-
standards/standards/web/documents/tutorials/eui.pdf>.
[OUI.Lookup]
"IEEE Registration Authority Assignments",
<https://regauth.standards.ieee.org/standards-ra-web/pub/
view.html#registries>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[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>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <https://www.rfc-editor.org/info/rfc7120>.
[W3C.GeoLoc]
Worldwide Web Consortium, "Geolocation API Specification
2nd Edition", January 2018, <https://www.w3.org/TR/
geolocation-API/#coordinates_interface>.
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Appendix A. Examples
A.1. Very Simple EAT
This is shown in CBOR diagnostic form. Only the payload signed by
COSE is shown.
{
/ issuer / 1: "joe",
/ nonce / 10: h'948f8860d13a463e8e',
/ UEID / 11: h'0198f50a4ff6c05861c8860d13a638ea',
/ secure-boot / 15: true,
/ debug-disable / 16: 3, / permanent-disable /
/ timestamp (iat) / 6: 1(1526542894)
}
A.2. Example with Submodules, Nesting and Security Levels
{
/ nonce / 10: h'948f8860d13a463e8e',
/ UEID / 11: h'0198f50a4ff6c05861c8860d13a638ea',
/ secure-boot / 15: true,
/ debug-disable / 16: 3, / permanent-disable /
/ timestamp (iat) / 6: 1(1526542894),
/ security-level / 14: 3, / secure restricted OS /
/ submods / 20: {
/ first submod, an Android Application /
"Android App Foo" : {
/ security-level / 14: 1 / unrestricted /
},
/ 2nd submod, A nested EAT from a secure element /
"Secure Element Eat" :
/ an embedded EAT, bytes of which are not shown /
h'420123',
/ 3rd submod, information about Linux Android /
"Linux Android": {
/ security-level / 14: 1 / unrestricted /
}
}
}
Appendix B. UEID Design Rationale
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B.1. Collision Probability
This calculation is to determine the probability of a collision of
UEIDs given the total possible entity population and the number of
entities in a particular entity management database.
Three different sized databases are considered. The number of
devices per person roughly models non-personal devices such as
traffic lights, devices in stores they shop in, facilities they work
in and so on, even considering individual light bulbs. A device may
have individually attested subsystems, for example parts of a car or
a mobile phone. It is assumed that the largest database will have at
most 10% of the world's population of devices. Note that databases
that handle more than a trillion records exist today.
The trillion-record database size models an easy-to-imagine reality
over the next decades. The quadrillion-record database is roughly at
the limit of what is imaginable and should probably be accommodated.
The 100 quadrillion datadbase is highly speculative perhaps involving
nanorobots for every person, livestock animal and domesticated bird.
It is included to round out the analysis.
Note that the items counted here certainly do not have IP address and
are not individually connected to the network. They may be connected
to internal buses, via serial links, Bluetooth and so on. This is
not the same problem as sizing IP addresses.
+---------+------------+--------------+------------+----------------+
| People | Devices / | Subsystems / | Database | Database Size |
| | Person | Device | Portion | |
+---------+------------+--------------+------------+----------------+
| 10 | 100 | 10 | 10% | trillion |
| billion | | | | (10^12) |
| 10 | 100,000 | 10 | 10% | quadrillion |
| billion | | | | (10^15) |
| 100 | 1,000,000 | 10 | 10% | 100 |
| billion | | | | quadrillion |
| | | | | (10^17) |
+---------+------------+--------------+------------+----------------+
This is conceptually similar to the Birthday Problem where m is the
number of possible birthdays, always 365, and k is the number of
people. It is also conceptually similar to the Birthday Attack where
collisions of the output of hash functions are considered.
The proper formula for the collision calculation is
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p = 1 - e^{-k^2/(2n)}
p Collision Probability
n Total possible population
k Actual population
However, for the very large values involved here, this formula
requires floating point precision higher than commonly available in
calculators and SW so this simple approximation is used. See
[BirthdayAttack].
p = k^2 / 2n
For this calculation:
p Collision Probability
n Total population based on number of bits in UEID
k Population in a database
+----------------------+--------------+--------------+--------------+
| Database Size | 128-bit UEID | 192-bit UEID | 256-bit UEID |
+----------------------+--------------+--------------+--------------+
| trillion (10^12) | 2 * 10^-15 | 8 * 10^-35 | 5 * 10^-55 |
| quadrillion (10^15) | 2 * 10^-09 | 8 * 10^-29 | 5 * 10^-49 |
| 100 quadrillion | 2 * 10^-05 | 8 * 10^-25 | 5 * 10^-45 |
| (10^17) | | | |
+----------------------+--------------+--------------+--------------+
Next, to calculate the probability of a collision occurring in one
year's operation of a database, it is assumed that the database size
is in a steady state and that 10% of the database changes per year.
For example, a trillion record database would have 100 billion states
per year. Each of those states has the above calculated probability
of a collision.
This assumption is a worst-case since it assumes that each state of
the database is completely independent from the previous state. In
reality this is unlikely as state changes will be the addition or
deletion of a few records.
The following tables gives the time interval until there is a
probability of a collision based on there being one tenth the number
of states per year as the number of records in the database.
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t = 1 / ((k / 10) * p)
t Time until a collision
p Collision probability for UEID size
k Database size
+---------------------+---------------+--------------+--------------+
| Database Size | 128-bit UEID | 192-bit UEID | 256-bit UEID |
+---------------------+---------------+--------------+--------------+
| trillion (10^12) | 60,000 years | 10^24 years | 10^44 years |
| quadrillion (10^15) | 8 seconds | 10^14 years | 10^34 years |
| 100 quadrillion | 8 | 10^11 years | 10^31 years |
| (10^17) | microseconds | | |
+---------------------+---------------+--------------+--------------+
Clearly, 128 bits is enough for the near future thus the requirement
that UEIDs be a minimum of 128 bits.
There is no requirement for 256 bits today as quadrillion-record
databases are not expected in the near future and because this time-
to-collision calculation is a very worst case. A future update of
the standard may increase the requirement to 256 bits, so there is a
requirement that implementations be able to receive 256-bit UEIDs.
B.2. No Use of UUID
A UEID is not a UUID [RFC4122] by conscious choice for the following
reasons.
UUIDs are limited to 128 bits which may not be enough for some future
use cases.
Today, cryptographic-quality random numbers are available from common
CPUs and hardware. This hardware was introduced between 2010 and
2015. Operating systems and cryptographic libraries give access to
this hardware. Consequently, there is little need for
implementations to construct such random values from multiple sources
on their own.
Version 4 UUIDs do allow for use of such cryptographic-quality random
numbers, but do so by mapping into the overall UUID structure of time
and clock values. This structure is of no value here yet adds
complexity. It also slightly reduces the number of actual bits with
entropy.
UUIDs seem to have been designed for scenarios where the implementor
does not have full control over the environment and uniqueness has to
be constructed from identifiers at hand. UEID takes the view that
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hardware, software and/or manufacturing process directly implement
UEID in a simple and direct way. It takes the view that
cryptographic quality random number generators are readily available
as they are implemented in commonly used CPU hardware.
Appendix C. EAT Relation to IEEE.802.1AR Secure Device Identity (DevID)
This section describes several distinct ways in which an IEEE IDevID
[IEEE.802.1AR] relates to EAT, particularly to UEID and SUEID.
[IEEE.802.1AR] orients around the definition of an implementation
called a "DevID Module." It describes how IDevIDs and LDevIDs are
stored, protected and accessed using a DevID Module. A particular
level of defense against attack that should be achieved to be a DevID
is defined. The intent is that IDevIDs and LDevIDs are used with an
open set of network protocols for authentication and such. In these
protocols the DevID secret is used to sign a nonce or similar to
proof the association of the DevID certificates with the device.
By contrast, EAT defines network protocol for proving trustworthiness
to a relying party, the very thing that is not defined in
[IEEE.802.1AR]. Nor does not give details on how keys, data and such
are stored protected and accessed. EAT is intended to work with a
variety of different on-device implementations ranging from minimal
protection of assets to the highest levels of asset protection. It
does not define any particular level of defense against attack,
instead providing a set of security considerations.
EAT and DevID can be viewed as complimentary when used together or as
competing to provide a device identity service.
C.1. DevID Used With EAT
As just described, EAT defines a network protocol and [IEEE.802.1AR]
doesn't. Vice versa, EAT doesn't define a an device implementation
and DevID does.
Hence, EAT can be the network protocol that a DevID is used with.
The DevID secret becomes the attestation key used to sign EATs. The
DevID and its certificate chain become the Endorsement sent to the
Verifier.
In this case the EAT and the DevID are likely to both provide a
device identifier (e.g. a serial number). In the EAT it is the UEID
(or SUEID). In the DevID (used as an endorsement), it is a device
serial number included in the subject field of the DevID certificate.
It is probably a good idea in this use for them to be the same serial
number or for the UEID to be a hash of the DevID serial number.
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C.2. How EAT Provides an Equivalent Secure Device Identity
The UEID, SUEID and other claims like OEM ID are equivalent to the
secure device identity put into the subject field of a DevID
certificate. These EAT claims can represent all the same fields and
values that can be put in a DevID certificate subject. EAT
explicitly and carefully defines a variety of useful claims.
EAT secures the conveyance of these claims by having them signed on
the device by the attestation key when the EAT is generated. EAT
also signs the nonce that gives freshness at this time. Since these
claims are signed for every EAT generated, they can include things
that vary over time like GPS location.
DevID secures the device identity fields by having them signed by the
manufacturer of the device sign them into a certificate. That
certificate is created once during the manufacturing of the device
and never changes so the fields cannot change.
So in one case the signing of the identity happens on the device and
the other in a manufacturing facility, but in both cases the signing
of the nonce that proves the binding to the actual device happens on
the device.
While EAT does not specify how the signing keys, signature process
and storage of the identity values should be secured against attack,
an EAT implementation may have equal defenses against attack. One
reason EAT uses CBOR is because it is simple enough that a basic EAT
implementation can be constructed entirely in hardware. This allows
EAT to be implemented with the strongest defenses possible.
C.3. An X.509 Format EAT
It is possible to define a way to encode EAT claims in an X.509
certificate. For example, the EAT claims might be mapped to X.509 v3
extensions. It is even possible to stuff a whole CBOR-encoded
unsigned EAT token into a X.509 certificate.
If that X.509 certificate is an IDevID or LDevID, this becomes
another way to use EAT and DevID together.
Note that the DevID must still be used with an authentication
protocol that has a nonce or equivalent. The EAT here is not being
used as the protocol to interact with the rely party.
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C.4. Device Identifier Permanence
In terms of permanence, an IDevID is similar to a UEID in that they
do not change over the life of the device. They cease to exist only
when the device is destroyed.
An SUEID is similar to an LDevID. They change on device life-cycle
events.
[IEEE.802.1AR] describes much of this permanence as resistant to
attacks that seek to change the ID. IDevID permanence can be
described this way because [IEEE.802.1AR] is oriented around the
definition of an implementation with a particular level of defense
against attack.
EAT is not defined around a particular implementation and must work
on a range of devices that have a range of defenses against attack.
EAT thus can't be defined permanence in terms of defense against
attack. EAT's definition of permanence is in terms of operations and
device lifecycle.
Appendix D. Changes from Previous Drafts
The following is a list of known changes from the previous drafts.
This list is non-authoritative. It is meant to help reviewers see
the significant differences.
D.1. From draft-rats-eat-01
o Added UEID design rationale appendix
D.2. From draft-mandyam-rats-eat-00
This is a fairly large change in the orientation of the document, but
no new claims have been added.
o Separate information and data model using CDDL.
o Say an EAT is a CWT or JWT
o Use a map to structure the boot_state and location claims
D.3. From draft-ietf-rats-eat-01
o Clarifications and corrections for OEMID claim
o Minor spelling and other fixes
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o Add the nonce claim, clarify jti claim
D.4. From draft-ietf-rats-eat-02
o Roll all EUIs back into one UEID type
o UEIDs can be one of three lengths, 128, 192 and 256.
o Added appendix justifying UEID design and size.
o Submods part now includes nested eat tokens so they can be named
and there can be more tha one of them
o Lots of fixes to the CDDL
o Added security considerations
D.5. From draft-ietf-rats-eat-03
o Split boot_state into secure-boot and debug-disable claims
o Debug disable is an enumerated type rather than Booleans
D.6. From draft-ietf-rats-eat-04
o Change IMEI-based UEIDs to be encoded as a 14-byte string
o CDDL cleaned up some more
o CDDL allows for JWTs and UCCSs
o CWT format submodules are byte string wrapped
o Allows for JWT nested in CWT and vice versa
o Allows UCCS (unsigned CWTs) and JWT unsecured tokens
o Clarify tag usage when nesting tokens
o Add section on key inclusion
o Add hardware version claims
o Collected CDDL is now filled in. Other CDDL corrections.
o Rename debug-disable to debug-status; clarify that it is not
extensible
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o Security level claim is not extensible
o Improve specification of location claim and added a location
privacy section
o Add intended use claim
D.7. From draft-ietf-rats-05
o CDDL format issues resolved
o Corrected reference to Location Privacy section
D.8. From draft-ietf-rats-06
o Added boot-seed claim
o Rework CBOR interoperability section
o Added profiles claim and section
D.9. From draft-ietf-rats-07
o Filled in IANA and other sections for possible preassignment of
claim keys for well understood claims
D.10. From draft-ietf-rats-08
o Change profile claim to be either a URL or an OID rather than a
test string
D.11. From draft-ietf-rats-09
o Add SUEIDs
o Add appendix comparing IDevID to EAT
o Added section on use for Evidence and Attestation Results
o Fill in the key ID and endorsements identificaiton section
o Remove origination claim as it is replaced by key IDs and
endorsements
o Added manifests and software evidence claims
o Add string labels non-claim labels for use with JSON (e.g. labels
for members of location claim)
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o EAN-13 HW versions are no longer a separate claim. Now they are
folded in as a CoSWID version scheme.
Authors' Addresses
Giridhar Mandyam
Qualcomm Technologies Inc.
5775 Morehouse Drive
San Diego, California
USA
Phone: +1 858 651 7200
EMail: mandyam@qti.qualcomm.com
Laurence Lundblade
Security Theory LLC
EMail: lgl@island-resort.com
Miguel Ballesteros
Qualcomm Technologies Inc.
5775 Morehouse Drive
San Diego, California
USA
Phone: +1 858 651 4299
EMail: mballest@qti.qualcomm.com
Jeremy O'Donoghue
Qualcomm Technologies Inc.
279 Farnborough Road
Farnborough GU14 7LS
United Kingdom
Phone: +44 1252 363189
EMail: jodonogh@qti.qualcomm.com
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