Evidence Transformations
draft-ietf-rats-evidence-trans-02
| Document | Type | Active Internet-Draft (rats WG) | |
|---|---|---|---|
| Authors | Fabrizio Damato , Andrew Draper , Ned Smith | ||
| Last updated | 2025-10-17 | ||
| Replaces | draft-smith-rats-evidence-trans | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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| Stream | WG state | WG Document | |
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| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
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| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-rats-evidence-trans-02
Remote ATtestation ProcedureS F. D'Amato
Internet-Draft AMD
Intended status: Standards Track A. Draper
Expires: 20 April 2026 N. Smith
Independent
17 October 2025
Evidence Transformations
draft-ietf-rats-evidence-trans-02
Abstract
Remote Attestation Procedures (RATS) enable Relying Parties to assess
the trustworthiness of a remote Attester to decide if continued
interaction is warrented. Evidence structures can vary making
appraisals challenging for Verifiers. Verifiers need to understand
Evidence encoding formats and some of the Evidence semantics to
appraise it. Consequently, Evidence may require format
transformation to an internal representation that preserves original
semantics. This document specifies Evidence transformation methods
for DiceTcbInfo, concise evidence, and SPDM measurements block
structures. These Evidence structures are converted to the CoRIM
internal representation and follow CoRIM defined appraisal
procedures.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 20 April 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language and Terminology . . . . . . . . . . . . 3
3. Verifier Reconciliation . . . . . . . . . . . . . . . . . . . 3
4. Transforming DICE Certificate Extension Evidence . . . . . . 4
4.1. DiceUeid Transformation . . . . . . . . . . . . . . . . . 4
4.2. DiceTcbInfo Transformation . . . . . . . . . . . . . . . 4
4.3. DiceConceptualMessageWrapper Transformation . . . . . . . 8
4.4. Authority field in DICE/SPDM ECTs . . . . . . . . . . . . 8
5. Transforming TCG Concise Evidence . . . . . . . . . . . . . . 8
5.1. Transforming the ce.evidence-triples . . . . . . . . . . 9
5.2. Transforming the ce.identity-triples . . . . . . . . . . 10
5.3. Transforming the ce.attest-key-triples . . . . . . . . . 11
6. DMTF SPDM Structure Definitons . . . . . . . . . . . . . . . 12
7. Transforming SPDM Measurement Block Digest . . . . . . . . . 14
8. Transforming SPDM Measurement Block Raw Value . . . . . . . . 14
9. Transforming SPDM RATS EAT CWT . . . . . . . . . . . . . . . 15
10. Transforming SPDM Evidence . . . . . . . . . . . . . . . . . 15
11. Implementation Status . . . . . . . . . . . . . . . . . . . . 16
12. Security Considerations . . . . . . . . . . . . . . . . . . . 16
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
14.1. Normative References . . . . . . . . . . . . . . . . . . 18
14.2. Informative References . . . . . . . . . . . . . . . . . 19
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Remote Attestation Procedures (RATS) [RFC9334] enable Relying Parties
to assess the trustworthiness of a remote Attester to decide if
continued interaction is warrented. Evidence structures can vary
making appraisals challenging for Verifiers. Verifiers need to
understand Evidence encoding formats and some of the Evidence
semantics to appraise it. Consequently, Evidence may require format
transformation to an internal representation that preserves original
semantics. This document specifies Evidence transformation methods
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for DiceTcbInfo [DICE.Attest], concise evidence [TCG.CE], and SPDM
measurements block [SPDM] structures. These Evidence structures are
converted to the CoRIM internal representation (Section 2.1
[I-D.ietf-rats-corim]) and follow CoRIM defined appraisal procedures
(Section 8 [I-D.ietf-rats-corim]).
2. Requirements Language and 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 uses terms and concepts defined by the RATS
architecture. For a complete glossary. See Section 4 of [RFC9334].
Addintional RATS architecture and terminology is found in
[I-D.ietf-rats-endorsements]. RATS architecture terms and concepts
are always referenced as proper nouns, i.e., with Capital Letters.
Additional terminology from CoRIM [I-D.ietf-rats-corim],
[DICE.CoRIM], CBOR [STD94], CDDL [RFC8610] and COSE [STD96] may also
apply.
In this document, Evidence structures are expressed in their
respective "external representations". There are many possible
Evidence structures including those mentioned above.
The CoRIM specification defines an "internal representation" for
Evidence (Section 8.2.1.3 [I-D.ietf-rats-corim]). This document
defines mapping operations that convert from an external
representation to an internal representation. The conversion steps
are also known as "transformation".
3. Verifier Reconciliation
This document assumes the reader is familiar with Verifier
reconciliation as described in Section 2 of [I-D.ietf-rats-corim].
It describes how a Verifier should process the CoRIM to enable CoRIM
authors to convey their intended meaning and how a Verifier
reconciles its various inputs. Evidence is one of its inputs. The
Verifier is expected to create an internal representation from an
external representation. By using an internal representation, the
Verifier processes Evidence inputs such that they can be appraised
consistently.
This document defines format transformations for Evidence in DICE
[DICE.Attest], SPDM [SPDM], and concise evidence [TCG.CE] formats
that are transformed into a Verifier's internal representation. This
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document uses the CoMID internal representation (Section 8.2.1 of
[I-D.ietf-rats-corim]) as the transformation target. Other internal
representations are possible but out of scope for this document.
4. Transforming DICE Certificate Extension Evidence
This section defines how Evidence from an X.509 certificate [RFC5280]
containing a DICE certificate extension [DICE.Attest] is transformed
into an internal representation that can be processed by Verifiers.
Verifiers supporting the DICE certificate Evidence extensions SHOULD
implement this transformation.
4.1. DiceUeid Transformation
This section defines the transformation method for the DiceUeid
certificate extension. This extension is identified by the following
object identifier:
* tcg-dice-Ueid - "2.23.133.5.4.4"
The DiceUeid extension does not create evidence directly. The ueid
OCTET STRING within this extension is used to populate the instance-
id field within evidence created by other extensions.
Section Section 4.2 describes extensions which use this value.
4.2. DiceTcbInfo Transformation
This section defines transformation methods for DICE certificate
extensions DiceTcbInfo, DiceMultiTcbInfo, and DiceMultiTcbInfoComp.
These extensions are identified by the following object identifiers:
* tcg-dice-TcbInfo - "2.23.133.5.4.1"
* tcg-dice-MultiTcbInfo - "2.23.133.5.4.5"
* tcg-dice-MultiTcbInfoComp - "2.23.133.5.4.8"
Each DiceTcbInfo entry in a MultiTcbInfo is converted to a CoRIM ECT
(see Section 8.2.1 of [I-D.ietf-rats-corim]) using the transformation
steps in this section. Each DiceMultiTcbInfo entry is independent of
the others such that each is transformed to a separate ECT entry. A
list of Evidence ECTs (i.e., ae = [ + ECT]) is constructed using
CoRIM attestation evidence internal representation (see
Section 8.2.1.1 of [I-D.ietf-rats-corim]). Each DiceMultiTcbInfoComp
entry is converted to a DiceMultiTcbInfo entry then processed as a
DiceMultiTcbInfo.
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For each DiceTcbInfo (DTI) entry in a DiceMultiTcbInfo allocate an
ECT structure.
Step 1. An ae entry is allocated.
Step 2. The cmtype of the ECT is set to evidence.
Step 3. The DiceTcbInfo (DTI) entry populates the ae ECT.
i The DTI entry populates the ae ECT environment-map
*copy*(DTI.type, ECT.environment.environment-map.class-
map.class-id). The binary representation of DTI.type MUST be
equivalent to the binary representation of class-id without the
CBOR tag.
*copy*(DTI.vendor, ECT.environment.environment-map.class-
map.vendor).
*copy*(DTI.model, ECT.environment.environment-map.class-
map.model).
*copy*(DTI.layer, ECT.environment.environment-map.class-
map.layer).
*copy*(DTI.index, ECT.environment.environment-map.class-
map.index).
ii If a DiceUeid (UEID) extension is present, then this populates the
instance-id field within the ECT environment-map.
If DiceUeid extension is present: *copy*(UEID.ueid,
ECT.environment-map.instance-id.tagged-ueid-type). The CBOR
tag #6.550 is prepended to the DiceUeid OCTET STRING then
copied to ECT.environment-map.instance-id.
iiiThe DTI entry populates the ae ECT elemenet-list.
*copy*(DTI.version, ECT.element-list.element-map.measurement-
values-map.version-map.version).
*copy*(DTI.svn, ECT.element-list.element-map.measurement-
values-map.svn).
*copy*(DTI.vendorInfo, ECT.element-list.element-
map.measurement-values-map.raw-value).
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Foreach FWID in FWIDLIST: *copy*(DTI.FWID.digest, ECT.element-
list.element-map.measurement-values-map.digests.digest.val).
Foreach FWID in FWIDLIST: *copy*(DTI.FWID.hashAlg, ECT.element-
list.element-map.measurement-values-map.digests.digest.alg).
Foreach INTEGRITYREGISTER in IRLIST:
*copy*(DTI.INTEGRITYREGISTER.registerNum, ECT.element-
list.element-map.measurement-values-map.integrity-
registers.integrity-register-id-type-choice).
Foreach FWID in INTEGRITYREGISTER.FWIDLIST:
*copy*(DTI.FWID.digest, ECT.element-list.element-
map.measurement-values-map.integrity-registers.digest-
type.val).
Foreach FWID in INTEGRITYREGISTER.FWIDLIST:
*copy*(DTI.FWID.alg, ECT.element-list.element-map.measurement-
values-map.integrity-registers.digest-type.alg).
iv The DTI entry populates the ae ECT elemenet-list.flags. Foreach
_f_ in DTI.OperationalFlags and each _m_ in
DTI.OperationalFlagsMask:
If _m_.notConfigured = 1 AND _f_.notConfigured = 1;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-configured = FALSE).
If _m_.notConfigured = 1 AND _f_.notConfigured = 0;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-configured = TRUE).
If _m_.notSecure = 1 AND _f_.notSecure = 1; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-secure =
FALSE).
If _m_.notSecure = 1 AND _f_.notSecure = 0; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-secure =
TRUE).
If _m_.recovery = 1 AND _f_.recovery = 1; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-recovery =
FALSE).
If _m_.recovery = 1 AND _f_.recovery = 0; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-recovery =
TRUE).
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If _m_.debug = 1 AND _f_.debug = 1; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-debug =
FALSE).
If _m_.debug = 1 AND _f_.debug = 0; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-debug = TRUE).
If _m_.notReplayProtected = 1 AND _f_.notReplayProtected = 1;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-replay-protected = FALSE).
If _m_.notReplayProtected = 1 AND _f_.notReplayProtected = 0;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-replay-protected = TRUE).
If _m_.notIntegrityProtected = 1 AND _f_.notIntegrityProtected
= 1; *set*(ECT.element-list.element-map.measurement-values-
map.flags.is-integrity-proteccted = FALSE).
If _m_.notIntegrityProtected = 1 AND _f_.notIntegrityProtected
= 0; *set*(ECT.element-list.element-map.measurement-values-
map.flags.is-integrity-proteccted = TRUE).
If _m_.notRuntimeMeasured = 1 AND _f_.notRuntimeMeasured = 1;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-runtime-meas = FALSE).
If _m_.notRuntimeMeasured = 1 AND _f_.notRuntimeMeasured = 0;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-runtime-meas = TRUE).
If _m_.notImmutable = 1 AND _f_.notImmutable = 1;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-immutable = FALSE).
If _m_.notImmutable = 1 AND _f_.notImmutable = 0;
*set*(ECT.element-list.element-map.measurement-values-
map.flags.is-immutable = TRUE).
If _m_.notTcb = 1 AND _f_.notTcb = 1; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-tcb = FALSE).
If _m_.notTcb = 1 AND _f_.notTcb = 0; *set*(ECT.element-
list.element-map.measurement-values-map.flags.is-tcb = TRUE).
Step 4. The ECT.authority field is set up based on the signer of the
certificate containing DTI as described in Section 4.4.
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The completed ECT is added to the ae list.
4.3. DiceConceptualMessageWrapper Transformation
This section defines the transformation method for the
DiceConceptualMessageWrapper certificate extension. This extension
is identified by the following object identifier:
* tcg-dice-Ueid - "2.23.133.5.4.9"
The DiceConceptualMessageWrapper entry OCTET STRING may contain a
CBOR array, JSON array, or CBOR tagged value. If the entry contains
a CBOR tag value of #6.571 or #6.1668557429, or a Content ID of
10571, or a Media Type of "application/ce+cbor", the contents are
transformed according to Section 5.
4.4. Authority field in DICE/SPDM ECTs
The ECT authority field is an array of $crypto-keys-type-choice
values.
When adding Evidence to the ACS, the Verifier SHALL add the public
key representing the signer of that Evidence (for example the DICE
certificate or SPDM MEASUREMENTS response) to the ECT authority
field. The Verifier SHALL add the authority of the signers of each
certificate in the certificate path of the end-entity signing key to
the ECT authority list. Having each authority in a certificate path
in the ECT authority field lets conditional endorsement conditions
match multiple authorities or match an authority that is scoped more
broadly than the immediate signer of the Evidence artifact.
Each signer authority value MUST be represented using tagged-cose-
key-type.
5. Transforming TCG Concise Evidence
This section defines how Evidence from TCG [TCG.CE] is transformed
into an internal representation that can be processed by Verifiers.
Verifiers supporting the TCG Concise Evidence format SHOULD implement
this transformation.
Concise evidence may be recognized by any of the following registered
types:
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+==========+========+===============+=======================+
| CBOR tag | C-F ID | TN Tag | Media Type |
+==========+========+===============+=======================+
| #6.571 | 10571 | #6.1668557429 | "application/ce+cbor" |
+----------+--------+---------------+-----------------------+
Table 1
A Concise Evidence entry is converted to a CoRIM ECT (see
Section 8.2.1 of [I-D.ietf-rats-corim]) using the transformation
steps in this section. A list of Evidence ECTs (i.e., ae = [ + ECT])
is constructed using CoRIM attestation evidence internal
representation (see Section 8.2.1.1 of [I-D.ietf-rats-corim]). The
Concise Evidence scheme uses CoRIM CDDL definitions to define several
Evidence representations called _triples_. Cases where Concise
Evidence CDDL is identical to CoRIM CDDL the transformation logic
uses the structure names in common.
5.1. Transforming the ce.evidence-triples
The ce.evidence-triples structure is a list of evidence-triple-
record. An evidence-triple-record consists of an environment-map and
a list of measurement-map. For each evidence-triple-record an ae ECT
is constructed.
Step 1. An ae ECT entry is allocated.
Step 2. The cmtype of the ECT is set to evidence.
Step 3. The Concise Evidence (CE) entry populates the ae ECT
environment fields.
*copy*(CE.evidence-triple-record.environment-map,
ECT.environment.environment-map).
i For each ce in CE.[ + measurement-map]; and each ect in ECT.[ +
element-list]:
*copy*(ce.mkey, ect.element-map.element-id)
*copy*(ce.mval, ect.element-map.element-claims`)
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Step 4. The signer of the envelope containing CE is copied to the
ECT.authority field as described in Section 4.4. For
example, a CE may be wrapped by an EAT token [RFC9711] or
DICE certificate [DICE.Attest]. The signer identity MUST be
expressed using $crypto-key-type-choice. A profile or other
arrangement is used to coordinate which $crypto-key-type-
choice is used for both Evidence and Reference Values.
Step 5. If CE has a profile, the profile is converted to a $profile-
type-choice then copied to the ECT.profile` field.
The completed ECT is added to the ae list.
5.2. Transforming the ce.identity-triples
The ce.identity-triples structure is a list of ev-identity-triple-
record. An ev-identity-triple-record consists of an environment-map
and a list of $crypto-key-type-choice. For each ev-identity-triple-
record an ae ECT is constructed where the $crypto-key-type-choice
values are copied as ECT Evidence measurement values. The ECT
internal representation accommodates keys as a type of measurement.
In order for the $crypto-key-type-choice keys to be verified a CoRIM
identity-triples claim MUST be asserted.
Step 1. An ae ECT entry is allocated.
Step 2. The cmtype of the ECT is set to evidence.
Step 3. The Concise Evidence (CE) entry populates the ae ECT
environment fields.
*copy*(CE.ce-identity-triple-record.environment-map,
ECT.environment.environment-map).
*copy*(_null_, ECT.element-list.element-map.element-id).
i For each cek in CE.[ + $crypto-key-type-choice ]; and each ect in
ECT.element-list.element-map.element-claims.intrep-keys.[ + typed-
crypto-key ]:
*copy*(cek, ect.key)
*set*( &(identity-key: 1), ect.key-type)
Step 4. The signer of the envelope containing CE is copied to the
ECT.authority field. For example, a CE may be wrapped by an
EAT token [RFC9711] or DICE certificate [DICE.Attest]. The
signer identity MUST be expressed using $crypto-key-type-
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choice. A profile or other arrangement is used to
coordinate which $crypto-key-type-choice is used for both
Evidence and Reference Values.
Step 5. If CE has a profile, the profile is converted to a $profile-
type-choice then copied to the ECT.profile` field.
The completed ECT is added to the ae list.
5.3. Transforming the ce.attest-key-triples
The ce.attest-key-triples structure is a list of ev-attest-key-
triple-record. An ev-attest-key-triple-record consists of an
environment-map and a list of $crypto-key-type-choice. For each ev-
attest-key-triple-record an ae ECT is constructed where the $crypto-
key-type-choice values are copied as ECT Evidence measurement values.
The ECT internal representation accommodates keys as a type of
measurement. In order for the $crypto-key-type-choice keys to be
verified a CoRIM attest-key-triples claim MUST be asserted.
Step 1. An ae ECT entry is allocated.
Step 2. The cmtype of the ECT is set to evidence.
Step 3. The Concise Evidence (CE) entry populates the ae ECT
environment fields.
*copy*(CE.ce-attest-key-triple-record.environment-map,
ECT.environment.environment-map).
*copy*(_null_, ECT.element-list.element-map.element-id).
i For each cek in CE.[ + $crypto-key-type-choice ]; and each ect in
ECT.element-list.element-map.element-claims.intrep-keys.[ + typed-
crypto-key ]:
*copy*(cek, ect.key)
*set*( &(attest-key: 0), ect.key-type)
Step 4. The signer of the envelope containing CE is copied to the
ECT.authority field. For example, a CE may be wrapped by an
EAT token [RFC9711] or DICE certificate [DICE.Attest]. The
signer identity MUST be expressed using $crypto-key-type-
choice. A profile or other arrangement is used to
coordinate which $crypto-key-type-choice is used for both
Evidence and Reference Values.
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Step 5. If CE has a profile, the profile is converted to a $profile-
type-choice then copied to the ECT.profile` field.
The completed ECT is added to the ae list.
6. DMTF SPDM Structure Definitons
This section defines how a Verifier shall parse a DMTF Measurement
Block.
DMTF Measurement Block Definition:
* Byte Offset 0: DMTFSpecMeasurementValueType
- Bit 7 = 0b Digest / 1b Raw bit stream
- Bit [6:0] = Indicate what is measured
o 0x0 Immutable Rom
o 0x1 Mutable FW
o 0x2 HW Config
o 0x3 FW config
o 0x4 Freeform Manifest
o 0x5 Structured Representation of debug and device mode
o 0x6 Mutable FW Version Number
o 0x7 Mutable FW Secure Version Number
o 0x8 Hash-Extend Measurement (new in SPDM 1.3)
o 0x9 Informational (new in SPDM 1.3)
o 0xA Structured Measurement Manifest (new in SPDM 1.3)
* Byte Offset 1: DMTFSpecMeasurementValueSize
* Byte Offset 3: DMTFSpecMeasurementValue
Structured Manifest Block Definition (only for >=SPDM 1.3):
* Byte Offset 0: Standard Body or Vendor Defined Header (SVH)
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* Byte Offset 2 + VendorIdLen: Manifest
Standard Body or Vendor Defined Header (SVH) Definition (only for
>=SPDM 1.3):
* Byte Offset 0: ID
* Byte Offset 1: VendorIdLen
* Byte Offset 2: VendorId
DMTF Header for Concise Evidence Manifest Block:
If SPDM Version 1.2:
* DMTFSpecMeasurementValueType = 0x84 (Raw Bit / Freeform Manifest)
* DMTFSpecMeasurementValueSize = Size of tagged-spdm-toc CBOR Tag
* DMTFSpecMeasurementValue = tagged-spdm-toc CBOR Tag
if SPDM >=Version 1.3:
* DMTFSpecMeasurementValueType = 0x8A (Raw Bit / Structured
Manifest)
* DMTFSpecMeasurementValueSize = Size of Structured Manifest
* DMTFSpecMeasurementValue = Structured Manifest
SVH for Concise Evidence Manifest Block:
* ID = 0xA (IANA CBOR)
* VendorIdLen = 2
* VendorId = 0x570 #6.570(spdm-toc-map)
Structured Manifest Block Definition for Concise Evidence:
* SVH = SVH for Concise Evidence Manifest Block
* Manifest = tagged-spdm-toc CBOR Tag Payload
DMTF Header for CBor Web Token (CWT):
If SPDM Version 1.2:
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* DMTFSpecMeasurementValueType = 0x84 (Raw Bit / Freeform Manifest)
* DMTFSpecMeasurementValueSize = Size of CWT
* DMTFSpecMeasurementValue = CWT # COSE_Sign1
if SPDM = Version 1.3:
* DMTFSpecMeasurementValueType = 0x8A (Raw Bit / Structured
Manifest)
* DMTFSpecMeasurementValueSize = Size of Structured Manifest
* DMTFSpecMeasurementValue = Structured Manifest
SVH for CBor Web Token (CWT):
* ID = 0xA (IANA CBOR)
* VendorIdLen = 2
* VendorId = 0x18 #6.18
Structured Manifest Block Definition for CBor Web Token (CWT):
* SVH = SVH for CBor Web Token (CWT)
* Manifest = COSE_Sign1 Payload
7. Transforming SPDM Measurement Block Digest
Step 1. if DMTFSpecMeasurementValueType is in range [0x80 - 0x83]:
*copy*(SPDM.MeasurementBlock.DMTFSpecMeasurementValue ,
ECT.environment.measurement-map.mval.digests).
Step 2. if DMTFSpecMeasurementValueType is in range [0x88]:
*copy*(SPDM.MeasurementBlock.DMTFSpecMeasurementValue ,
ECT.environment.measurement-map.mval.integrity-
registers).
8. Transforming SPDM Measurement Block Raw Value
Step 1. if DMTFSpecMeasurementValueType is in range [0x7]:
*copy*(SPDM.MeasurementBlock.DMTFSpecMeasurementValue ,
ECT.environment.measurement-map.mval.svn).
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9. Transforming SPDM RATS EAT CWT
The RATS EAT CWT shall be reported in any of the assigned Measurement
Block 0xFD The Concise Evidence CBOR Tag is serialized inside eat-
measurements (273) claim ($measurements-body-cbor /= bytes .cbor
concise-evidence-map) Subsequently the transformation steps defined
in Section 5.
10. Transforming SPDM Evidence
This section defines how Evidence from SPDM [SPDM] is transformed
into an internal representation that can be processed by Verifiers.
Verifiers supporting the SPDM Evidence format SHOULD implement this
transformation. SPDM Responders SHALL support a minimum version of
1.2
Theory of Operations:
* The SPDM Requestor SHALL retrieve the measurement Manifest at
Block 0xFD (Manifest Block) and send its payload to the Verifier
- The Verifier SHALL decode the payload as a tagged-spdm-toc CBOR
tag.
- The Verifier SHALL extract the tagged-concise-evidence CBOR TAG
from the tagged-spdm-toc CBOR tag
Theconcise-evidence has a format that is similar to CoRIM triples-map
(their semantics follows the matching rules described above).
* For every spdm-indirect measurement the Verifier shall ask the
SPDM Requestor to retrieve the measurement block indicated by the
index
- if the index is in range [0x1 - 0xEF] (refer to #Transforming
SPDM Measurement Block Digest)
- if the index is 0xFD (refer to #Transforming SPDM RATS EAT CWT]
)
The TCG DICE Concise Evidence Binding for SPDM specification [TCG.CE]
describes a process for converting the SPDM Measurement Block to
Concise Evidence. Subsequently the transformation steps defined in
Section 5.
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The keys provided in the ECT.authority field SHOULD include the key
which signed the SPDM MEASUREMENTS response carrying the Evidence and
keys which authorized that key as described in Section 4.4.```
11. Implementation Status
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalogue of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as Evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
12. Security Considerations
Evidence appraisal is at the core of any RATS protocol flow,
mediating all interactions between Attesters and their Relying
Parties. The Verifier is effectively part of the Attesters' and
Relying Parties' trusted computing base (TCB). Any mistake in the
appraisal process could have security implications. For instance, it
could lead to the subversion of an access control function, which
creates a chance for privilege escalation.
Therefore, the Verifier’s code and configuration, especially those of
the CoRIM processor, are primary security assets that must be built
and maintained as securely as possible.
The protection of both the Attester and Verifier systems should be
considered throughout their entire lifecycle, from design to
operation. This includes the following aspects:
* Minimizing implementation complexity (see also Section 6.1 of
[I-D.ietf-rats-endorsements]);
* Using memory-safe programming languages;
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* Using secure defaults;
* Minimizing the attack surface by avoiding unnecessary features
that could be exploited by attackers;
* Applying the principle of least privilege to the system's users;
* Minimizing the potential impact of security breaches by
implementing separation of duties in both the software and
operational architecture;
* Conducting regular, automated audits and reviews of the system,
such as ensuring that users' privileges are correctly configured
and that any new code has been audited and approved by independent
parties;
* Failing securely in the event of errors to avoid compromising the
security of the system.
The appraisal process should be auditable and reproducible. The
integrity of the code and data during execution should be made an
explicit objective, for example ensuring that the appraisal functions
are computed in an attestable trusted execution environment (TEE).
The integrity of public and private key material and the secrecy of
private key material must be ensured at all times. This includes key
material carried in attestation key triples and key material used to
assert or verify the authority of triples (such as public keys that
identify trusted supply chain actors). For more detailed information
on protecting Trust Anchors, refer to Section 12.4 of [RFC9334].
The Verifier should use cryptographically protected, mutually
authenticated secure channels to all its trusted input sources (i.e.,
Attesters, Endorsers, RVPs, Verifier Owners). The Attester should
use cryptographically protected, mutually authenticated secure
channels to all its trusted input sources (i.e., Verifiers, Relying
Parties). These links must reach as deep as possible - possibly
terminating within the Attesting Environment of an Attester or within
the appraisal session context of a Verifier - to avoid man-in-the-
middle attacks. Also consider minimizing the use of intermediaries:
each intermediary becomes another party that needs to be trusted and
therefore factored in the Attesters and Relying Parties' TCBs. Refer
to Section 12.2 of [RFC9334] for information on Conceptual Messages
protection.
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13. IANA Considerations
There are no IANA considerations.
14. References
14.1. Normative References
[DICE.Attest]
Trusted Computing Group (TCG), "DICE Attestation
Architecture", Version 1.2, Revision 1 , January 2025,
<https://trustedcomputinggroup.org/wp-content/uploads/
DICE-Attestation-Architecture-Version-1.2-rc-
1_9January25.pdf>.
[DICE.CoRIM]
Trusted Computing Group (TCG), "DICE Endorsement
Architecture for Devices", Version 1.0, Revision 0.38 ,
November 2022, <https://trustedcomputinggroup.org/wp-
content/uploads/TCG-Endorsement-Architecture-for-Devices-
V1-R38_pub.pdf>.
[I-D.ietf-rats-corim]
Birkholz, H., Fossati, T., Deshpande, Y., Smith, N., and
W. Pan, "Concise Reference Integrity Manifest", Work in
Progress, Internet-Draft, draft-ietf-rats-corim-08, 7 July
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
rats-corim-08>.
[I-D.ietf-rats-endorsements]
Thaler, D., Birkholz, H., and T. Fossati, "RATS
Endorsements", Work in Progress, Internet-Draft, draft-
ietf-rats-endorsements-07, 25 August 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-rats-
endorsements-07>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
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[RFC9334] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", RFC 9334, DOI 10.17487/RFC9334, January
2023, <https://www.rfc-editor.org/rfc/rfc9334>.
[SPDM] Distributed Management Task Force, "Security Protocol and
Data Model (SPDM)", Version 1.3.0 , May 2023,
<https://www.dmtf.org/sites/default/files/standards/
documents/DSP0274_1.3.0.pdf>.
[TCG.CE] Trusted Computing Group, "TCG DICE Concise Evidence
Binding for SPDM", Version 1.00, Revision 0.54 , January
2024, <https://trustedcomputinggroup.org/wp-
content/uploads/TCG-DICE-Concise-Evidence-Binding-for-
SPDM-Version-1.0-Revision-54_pub.pdf>.
14.2. Informative References
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/rfc/rfc7942>.
[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/rfc/rfc8610>.
[RFC9711] Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
Wallace, "The Entity Attestation Token (EAT)", RFC 9711,
DOI 10.17487/RFC9711, April 2025,
<https://www.rfc-editor.org/rfc/rfc9711>.
[STD94] 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/rfc/rfc8949>.
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[STD96] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
Contributors
The authors would like to thank the following people for their
valuable contributions to the specification.
Henk Birkholz
Email: henk.birkholz@ietf.contact
Yogesh Deshpande
Email: yogesh.deshpande@arm.com
Thomas Fossati
Email: Thomas.Fossati@linaro.org
Dionna Glaze
Email: dionnaglaze@google.com
Acknowledgments
The authors would like to thank James D. Beaney, Francisco J.
Chinchilla, Vincent R. Scarlata, and Piotr Zmijewski for review
feedback.
Authors' Addresses
Fabrizio D'Amato
AMD
Email: fabrizio.damato@amd.com
Andrew Draper
Independent
Email: andrew.draper@freeside.org.uk
Ned Smith
Independent
Email: ned.smith.ietf@outlook.com
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