An EAT Profile for Device Attestation
draft-poirier-rats-eat-da-00
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draft-poirier-rats-eat-da-00
Remote ATtestation ProcedureS M. Poirier
Internet-Draft T. Fossati
Intended status: Informational Linaro
Expires: 14 December 2025 12 June 2025
An EAT Profile for Device Attestation
draft-poirier-rats-eat-da-00
Abstract
In confidential computing, device assignment (DA) is the method by
which a device (e.g., network adapter, GPU), whether on-chip or
behind a PCIe Root Port, is assigned to a Trusted Virtual Machine
(TVM). For the TVM to trust the device, the device must provide the
TVM with attestation Evidence confirming its identity and the state
of its firmware and configuration.
Since Evidence claims can be consumed by 3rd party attestation
services external to the TVM, there is a need to standardise the
representation of Evidence to ensure interoperability. This document
defines an attestation Evidence format for DA as an EAT (Entity
Attestation Token) profile.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://rats-
device-attestation.github.io/draft-poirier-rats-eat-da/draft-poirier-
rats-eat-da.html. Status information for this document may be found
at https://datatracker.ietf.org/doc/draft-poirier-rats-eat-da/.
Discussion of this document takes place on the Remote ATtestation
ProcedureS Working Group mailing list (mailto:rats@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/rats/.
Subscribe at https://www.ietf.org/mailman/listinfo/rats/.
Source for this draft and an issue tracker can be found at
https://github.com/rats-device-attestation/draft-poirier-rats-eat-da.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Device Attestation Claims . . . . . . . . . . . . . . . . . . 3
3.1. SPDM Claims . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Measurement Claims . . . . . . . . . . . . . . . . . 4
3.1.2. Measurement Claims Signature . . . . . . . . . . . . 5
3.1.3. Certificate Claims . . . . . . . . . . . . . . . . . 6
3.2. PCIe Legacy Device Claims . . . . . . . . . . . . . . . . 7
4. Collated CDDL . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6.1. New CWT Claims Registrations . . . . . . . . . . . . . . 9
6.2. New CBOR Tags Registrations . . . . . . . . . . . . . . . 9
7. Normative References . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 10
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
In confidential computing, device assignment (DA) is the method by
which a device (e.g., network adapter, GPU), whether on-chip or
behind a PCIe Root Port, is assigned to a Trusted Virtual Machine
(TVM). Most confidential computing platforms (e.g., Arm CCA, AMD
SEV-SNP, Intel TDX) provide DA capabilities. Such capabilities
prevent agents which are untrusted by the TVM (including other TVMs
and the host hypervisor) from accessing or controlling a device that
has been assigned to the TVM. This includes, for example, protection
of device MMIO interfaces and device caches. From a trust
perspective, DA allows a device to be included in the TVM's Trusted
Computing Base (TCB). For the TVM to trust the device, the device
must provide the TVM with attestation Evidence confirming its
identity and the state of its firmware and configuration.
This document defines an attestation Evidence format for DA as an EAT
[RFC9711] profile. The format is designed to be generic, extensible
and architecture agnostic. Ongoing work on DA concentrates on PCIe
devices that support the SPDM protocol, but other bus architecture
and protocols are expected to be supported as the technology gains
wider adoption. As such we focus on the formalization of an Evidence
format for SPDM compliant devices while leaving room for the
definition of other Evidence format such as CXL and CHI. This list
is by no means exhaustive and is expected to expand.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Device Attestation Claims
The Device Attestation claim is the encompassing envelope for the
individual device claims to be presented. It can be used as a
standalone entity but typically enclosed in a wider platform specific
attestation token. The Device attestation claim consists of an EAT
profile identifier, a nonce and an EAT submodule (Section 4.2.18 of
[RFC9711]) that contains any number of individual device claims.
Each individual device claim is the combination of a device name and
a standard claims format based on the bus or protocol the device
supports. As previously mentioned, this draft currently defines the
claims set for SPDM compliant devices and PCIe legacy devices that do
not support the SPDM protocol. Careful condideration was also given
to the overall design in order to leave room for future expansion.
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da-token = {
&(eat_profile: 265) => "tag:linaro.org,2025:device#1.0.0"
&(eat_nonce: 10) => bytes .size 64 ; same as realm nonce
&(eat_submods: 266) => {
+ device-name => $device-claims
}
}
device-name = text .regexp "dev-[A-Za-z0-9]+"
$device-claims /= #6.1000000(spdm-claims)
$device-claims /= #6.1000001(cxl-claims)
$device-claims /= #6.1000002(chi-claims)
$device-claims /= #6.1000003(pcie-legacy-claims)
3.1. SPDM Claims
A SPDM claim instance is expected to be present for each SPDM
compatible device to be attested. Each instance consists of
measurements and a certificates section. There can be up to 239
measurements per device with the entire measurement log optionally
signed by the certificate populated in one of the 8 certificate
slots. It should be noted that measurements formalized herein follow
the DMTF measurement specification.
spdm-claims = {
&(measurements: 1) => {
+ block-id => spdm-measurement
? "signature" => spdm-measurement-blocks-signature
}
&(certificates: 2) => spdm-certificates
}
block-id = 1..239
3.1.1. Measurement Claims
SPDM measurements start with a component type that reflects one of
the 10 categories defined by the SPDM specification. Following is
the measurement itself represented by either a raw bitstream or a
digest. The size of the digest value is derived from the measurement
hash algorithm conveyed by the SPDM ALGORITHMS message response.
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spdm-measurement = {
&(component-type: 1) => component-type
measurement
}
measurement //= ( &(digest-measurement: 2) => digest-measurement )
measurement //= ( &(raw-measurement: 3) => raw-measurement )
component-type /= &(immutable-rom: 0)
component-type /= &(mutable-firmware: 1)
component-type /= &(hardware-config: 2)
component-type /= &(firmware-config: 3)
component-type /= &(freeform-measurement-manifest: 4)
component-type /= &(device-mode: 5)
component-type /= &(mutable-firmware-version: 6)
component-type /= &(mutable-firmware-svn: 7)
component-type /= &(hash-extend-measurement: 8)
component-type /= &(informational: 9)
component-type /= &(structured-measurement-manifest: 10)
raw-measurement = bytes
digest-measurement = digest
digest = [
alg: uint / text
val: bytes
]
3.1.2. Measurement Claims Signature
SPDM compliant devices can optionally support the capability to sign
measurements. Included in the measurement claim signature are all
the elements needed by a third party entity to reconstruct the
original measurement log signed by the device. Those elements
include L1 (see CDDL below), the combined SPDM prefix, the hash
algorithm used to generate a digest of the measurement log and nonces
provided by the requester and responder. The slot number of the leaf
certificate used to sign the measurement log is also provided.
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;
; What follows is based on SPDM v1.3.2 (DSP0274_1.3.2.pdf)
;
;
; Algorithms currently supported by SPDM.
; See "MeasurementHashAlgo", table 21, page 79.
;
hash-algorithm-type /= &(tpm_alg_sha_256: 0)
hash-algorithm-type /= &(tpm_alg_sha_384: 2)
hash-algorithm-type /= &(tpm_alg_sha_512: 4)
hash-algorithm-type /= &(tpm_alg_sha3_256: 8)
hash-algorithm-type /= &(tpm_alg_sha3_384: 16)
hash-algorithm-type /= &(tpm_alg_sha3_512: 32)
hash-algorithm-type /= &(tpm_alg_sm3_256: 64)
;
; See signature generation and verification algorithms for
; MEASUREMENTS messages on page 126.
;
; L1 = Concatenate(VCA, GET_MEASUREMENTS_REQUEST1,
; MEASUREMENTS_RESPONSE1, ...,
; GET_MEASUREMENTS_REQUESTn-1,
; MEASUREMENTS_RESPONSEn-1,
; GET_MEASUREMENTS_REQUESTn, MEASUREMENTS_RESPONSEn)
;
spdm-measurement-blocks-signature = {
&(slot: 1) => 0..7, ; Slot of the certificate chain used to
; authenticate the measurement. Default
; should be 0.
&(requester-nonce: 2) => bytes .size 32,
&(responder-nonce: 3) => bytes .size 32,
&(combined-spdm-prefix: 4) => bytes .size 100,
&(IL1: 5) => bytes, ; L1 (see comment above)
&(base-hash-algo: 6) => hash-algorithm-type,
&(signature: 7) => bytes
}
3.1.3. Certificate Claims
According to the specification, SPDM compliant devices should support
at most 8 slots, with slot 0 populated by default. Slot 0 SHALL
contain a certificate chain that follows the Device certificate model
or the Alias certificate model. Regardless of the certificate model
used, a certificate chain comprises one or more DER-encoded X.509 v3
certificates [RFC5280]. The certificates MUST be concatenated with
no intermediate padding.
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spdm-certificates = {
default-cert-slot => cert-chain
? aux-cert-slots => cert-chain
}
; ASN.1 DER-encoded certificates concatenated with no intermediate
; padding.
cert-chain = bytes
default-cert-slot = 0
aux-cert-slots = 1..7
3.2. PCIe Legacy Device Claims
The definition of a device claims set for PCIe legacy devices that do
not implement the extensions needed to attest for their provenance
and configuration is provided, making it is possible to keep using
current assets as secures ones are being provisioned. This legacy
device claims set simply mirrors the type 0/1 common registers of the
PCIe configuration space, mandating only that the vendor and device
identification code be provided. Other fields of the configuration
space header may optionally be included should they add value.
pcie-legacy-claims = {
&(legacy-header: 1) => pcie-type-0-1-config-space
? $$pcie-legacy-claim-extension
}
pcie-type-0-1-config-space = {
&(vendorID: 1) => bytes .size 2
&(deviceID: 2) => bytes .size 2
? &(command: 3) => bytes .size 2
? &(status: 4) => bytes .size 2
? &(revisionID: 5) => bytes .size 1
? &(classCode: 6) => bytes .size 3
? &(cacheLineSize: 7) => bytes .size 1
? &(latencyTimer: 8) => bytes .size 1
? &(headerType: 9) => bytes .size 1
? &(BITS: 10) => bytes .size 1
}
4. Collated CDDL
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=============== NOTE: '\' line wrapping per RFC 8792 ================
da-token = {
&(eat_profile: 265) => "tag:linaro.org,2025:device#1.0.0",
&(eat_nonce: 10) => bytes .size 64,
&(eat_submods: 266) => {+ device-name => $device-claims},
}
device-name = text .regexp "dev-[A-Za-z0-9]+"
$device-claims /= #6.1000000(spdm-claims) / #6.1000001(cxl-claims) \
/ #6.1000002(chi-claims) / #6.1000003(pcie-legacy-claims)
spdm-claims = {
&(measurements: 1) => {
+ block-id => spdm-measurement,
? "signature" => spdm-measurement-blocks-signature,
},
&(certificates: 2) => spdm-certificates,
}
block-id = 1 .. 239
spdm-measurement = {
&(component-type: 1) => component-type,
measurement,
}
measurement //= (&(digest-measurement: 2) => digest-measurement // &\
(raw-measurement: 3) => raw-measurement)
component-type /= &(immutable-rom: 0) / &(mutable-firmware: 1) / &(\
hardware-config: 2) / &(firmware-config: 3) / &(freeform-measurement\
-manifest: 4) / &(device-mode: 5) / &(mutable-firmware-version: 6) \
/ &(mutable-firmware-svn: 7) / &(hash-extend-measurement: 8) / &(\
informational: 9) / &(structured-measurement-manifest: 10)
raw-measurement = bytes
digest-measurement = digest
digest = [
alg: uint / text,
val: bytes,
]
spdm-certificates = {
default-cert-slot => cert-chain,
? aux-cert-slots => cert-chain,
}
cert-chain = bytes
default-cert-slot = 0
aux-cert-slots = 1 .. 7
hash-algorithm-type /= &(tpm_alg_sha_256: 0) / &(tpm_alg_sha_384: 2\
) / &(tpm_alg_sha_512: 4) / &(tpm_alg_sha3_256: 8) / &(\
tpm_alg_sha3_384: 16) / &(tpm_alg_sha3_512: 32) / &(tpm_alg_sm3_256\
: 64)
spdm-measurement-blocks-signature = {
&(slot: 1) => 0 .. 7,
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&(requester-nonce: 2) => bytes .size 32,
&(responder-nonce: 3) => bytes .size 32,
&(combined-spdm-prefix: 4) => bytes .size 100,
&(IL1: 5) => bytes,
&(base-hash-algo: 6) => hash-algorithm-type,
&(signature: 7) => bytes,
}
cxl-claims = {}
chi-claims = {}
pcie-legacy-claims = {
&(legacy-header: 1) => pcie-type-0-1-config-space,
? $$pcie-legacy-claim-extension,
}
pcie-type-0-1-config-space = {
&(vendorID: 1) => bytes .size 2,
&(deviceID: 2) => bytes .size 2,
? &(command: 3) => bytes .size 2,
? &(status: 4) => bytes .size 2,
? &(revisionID: 5) => bytes .size 1,
? &(classCode: 6) => bytes .size 3,
? &(cacheLineSize: 7) => bytes .size 1,
? &(latencyTimer: 8) => bytes .size 1,
? &(headerType: 9) => bytes .size 1,
? &(BITS: 10) => bytes .size 1,
}
5. Security Considerations
TODO Security
6. IANA Considerations
6.1. New CWT Claims Registrations
TODO IANA CWT allocations
6.2. New CBOR Tags Registrations
TODO IANA CBOR Tag allocations
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
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[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>.
[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>.
[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>.
Appendix A. Examples
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=============== NOTE: '\' line wrapping per RFC 8792 ================
{
/ profile / 265: "tag:linaro.org,2025:device#1.0.0",
/ nonce / 10: h'\
f9efc3341597f75f8d94432ad39566a8c5704b2004ba001c094f475bfc057f9f25d7\
aa40cd86cd30ebaae746fb19f008c1e6a1f23ad6a178e18dceda918f7f6e',
/ submods / 266: {
"dev-a": 1000000({
/ measurements / 1: {
1: {
/ component-type / 1: 2, / hardware config /
/ raw-measurement / 3: h'4f6d616861'
}
},
/ certificates / 2: {
/ device certs / 0: h'\
676f616e6e61747261646974696f6e6d6f6e676572'
/ no aux certs /
}
}),
"dev-b": 1000000({
/ measurements / 1: {
1: {
/ component-type / 1: 1, / mutable firmware /
/ digest-measurement / 2: [
/ alg / 1,
/ val / h'6b656e6e656c6c79'
]
},
6: {
/ component-type / 1: 2, / hardware config /
/ digest measurement / 2: [
/ alg / 0,
/ val / h'756e646572637279'
]
}
},
/ certificates / 2: {
/ device certs / 0: h'61746865697A656178696C6C6172',
/ aux certs (slot=2) / 2: h'23451576923AE99106783948598A'
}
})
}
}
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Acknowledgments
TODO acknowledge.
Authors' Addresses
Mathieu Poirier
Linaro
Email: mathieu.poirier@linaro.org
Thomas Fossati
Linaro
Email: thomas.fossati@linaro.org
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