Remote ATtestation ProcedureS T. Fossati Internet-Draft Y. Deshpande Intended status: Informational Arm Ltd Expires: 11 September 2023 H. Birkholz Fraunhofer SIT 10 March 2023 A CoRIM Profile for Arm's Platform Security Architecture (PSA) draft-fdb-rats-psa-endorsements-02 Abstract PSA Endorsements include reference values, endorsed values, cryptographic key material and certification status information that a Verifier may need in order to appraise attestation Evidence produced by a PSA device. This memo defines PSA Endorsements as a profile of the CoRIM data model. Discussion Venues This note is to be removed before publishing as an RFC. Discussion of this document takes place on the Remote ATtestation ProcedureS Working Group mailing list (rats@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/rats/. Source for this draft and an issue tracker can be found at https://github.com/thomas-fossati/corim-psa. 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- Drafts is at https://datatracker.ietf.org/drafts/current/. 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 11 September 2023. Fossati, et al. Expires 11 September 2023 [Page 1] Internet-Draft CoRIM PSA Profile March 2023 Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. PSA Endorsements . . . . . . . . . . . . . . . . . . . . . . 3 3.1. PSA Endorsement Profile . . . . . . . . . . . . . . . . . 3 3.2. PSA Endorsements to PSA RoT Linkage . . . . . . . . . . . 4 3.3. Reference Values . . . . . . . . . . . . . . . . . . . . 5 3.4. Attestation Verification Claims . . . . . . . . . . . . . 7 3.5. Certification Claims . . . . . . . . . . . . . . . . . . 9 3.6. Software Upgrades and Patches . . . . . . . . . . . . . . 12 4. Security Considerations . . . . . . . . . . . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 5.1. CBOR Tag Registrations . . . . . . . . . . . . . . . . . 15 5.2. CoRIM Profile Registration . . . . . . . . . . . . . . . 15 5.3. CoMID Codepoints . . . . . . . . . . . . . . . . . . . . 15 5.3.1. CoMID Triples Map Extension . . . . . . . . . . . . . 15 5.3.2. CoMID Measurement Values Map Extension . . . . . . . 16 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Normative References . . . . . . . . . . . . . . . . . . . . . 16 Informative References . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 1. Introduction PSA Endorsements include reference values, endorsed values, cryptographic key material and certification status information that a Verifier needs in order to appraise attestation Evidence produced by a PSA device [PSA-TOKEN]. This memo defines PSA Endorsements as a profile of the CoRIM data model [CoRIM]. Fossati, et al. Expires 11 September 2023 [Page 2] Internet-Draft CoRIM PSA Profile March 2023 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. An understanding of the [CoRIM] data model is a prerequisite. The reader is also assumed to be familiar with the terms defined in Section 2.1 of [PSA-TOKEN] and in Section 4 of [RATS-ARCH]. 3. PSA Endorsements PSA Endorsements describe an attesting device in terms of the hardware and firmware components that make up its PSA Root of Trust (RoT). This includes the identification and expected state of the device as well as the cryptographic key material needed to verify Evidence signed by the device's PSA RoT. Additionally, PSA Endorsements can include information related to the certification status of the attesting device. There are three basic types of PSA Endorsements: * Reference Values (Section 3.3), i.e., measurements of the PSA RoT firmware; * Attestation Verification Claims (Section 3.4), i.e., cryptographic keys that are used to verify signed Evidence produced by the PSA RoT, along with the identifiers that bind the keys to their device instances; * Certification Claims (Section 3.5), i.e., metadata that describe the certification status associated with a PSA device; There is a fourth PSA Endorsement type that aims at covering more advanced Verifier use cases (e.g., the one described in Section 7 of [TEEP]): * Software Relations (Section 3.6), used to model upgrade and patch relationships between software components. 3.1. PSA Endorsement Profile PSA Endorsements are carried in one or more CoMIDs inside a CoRIM. Fossati, et al. Expires 11 September 2023 [Page 3] Internet-Draft CoRIM PSA Profile March 2023 The profile attribute in the CoRIM MUST be present and MUST be set to the URI http://arm.com/psa/iot/1 as shown in Figure 1. / corim-map / { / corim.profile / 3: 32("http://arm.com/psa/iot/1") / ... / } Figure 1: PSA IoT version 1, CoRIM profile The list of all, and only, the CoMIDs that are currently "active" (i.e., CoMIDs that contain triples that can be used for appraisal) is provided in a CoBOM tag. // TODO CoBOM example 3.2. PSA Endorsements to PSA RoT Linkage Each PSA Endorsement - be it a Reference Value, Attestation Verification Claim or Certification Claim - is associated with an immutable PSA RoT. The linkage between a PSA Endorsement and its PSA RoT is made by means of the unique PSA RoT identifier known as Implementation ID (see Section 3.2.2 of [PSA-TOKEN]). In order to support PSA Implementation IDs, the CoMID type $class-id- type-choice is extended as follows: ; from draft-tschofenig-rats-psa-token psa-implementation-id-type = bytes .size 32 tagged-implementation-id-type = #6.600(implementation-id-type) $class-id-type-choice /= tagged-implementation-id-type Besides, a PSA Endorsement can be associated with a specific instance of a certain PSA RoT - as is the case for Attestation Verification Claims. A PSA Endorsement is associated with a PSA RoT instance by means of the Instance ID (see Section 3.2.1 of [PSA-TOKEN]) and its "parent" Implementation ID. These identifiers are typically found in the subject of a CoMID triple, encoded in an environment-map as shown in Figure 2. Fossati, et al. Expires 11 September 2023 [Page 4] Internet-Draft CoRIM PSA Profile March 2023 / environment-map / { / comid.class / 0 : { / comid.class-id / 0 : / tagged-impl-id-type / 600( h'61636d652d696d706c656d656e746174 696f6e2d69642d303030303030303031' ), / comid.vendor / 1 : "ACME Ltd.", / comid.model / 2 : "Roadrunner 1.0" }, / comid.instance / 1 : / tagged-ueid-type / 550( h'01 4ca3e4f50bf248c39787020d68ffd05c 88767751bf2645ca923f57a98becd296' ) } Figure 2: Example PSA RoT Identification Optional vendor and model can be specified as well. Together, they are interpreted as a unique identifier of the product that embeds the PSA RoT. It is RECOMMENDED to consistently provide a product identifier. 3.3. Reference Values Reference Values carry measurements and other metadata associated with the updatable firmware in a PSA RoT. When appraising Evidence, the Verifier compares Reference Values against the values found in the Software Components of the PSA token (see Section 3.4.1 of [PSA-TOKEN]). When there is more than one measurement associated to a certain PSA RoT, the measurements are spread across multiple reference-triple- records and, in certain cases, across multiple CoMIDs. A single CoBOM MUST completely describe the updatable PSA RoT. The elements of the psa-software-component map defined in Section 4.4.1 of [PSA-TOKEN] are matched against CoMID measurement- map entries as follows: Fossati, et al. Expires 11 September 2023 [Page 5] Internet-Draft CoRIM PSA Profile March 2023 +==================+=============================+=================+ | PSA Evidence | PSA Endorsement | Description | +==================+=============================+=================+ | measurement-type | measurement-values-map.name | Section 4.4.1.1 | | | | of [PSA-TOKEN] | +------------------+-----------------------------+-----------------+ | measurement- | measurement-values- | Section 4.4.1.2 | | value | map.digests[*][1] | of [PSA-TOKEN] | +------------------+-----------------------------+-----------------+ | version | measurement-values- | Section 4.4.1.3 | | | map.version.version | of [PSA-TOKEN] | +------------------+-----------------------------+-----------------+ | measurement-desc | measurement-values- | | | | map.digests[*][0] | | +------------------+-----------------------------+-----------------+ | signer-id | authorized-by[0] | Section 4.4.1.4 | | | | of [PSA-TOKEN] | +------------------+-----------------------------+-----------------+ Table 1: PSA Software Component Mappings The digests array MUST contain at least one entry and MAY contain more than one entry if multiple digests (obtained with different hash algorithms) of the same measured component exist. The authorized-by in the measurement-map MUST have exactly one entry of type tagged-thumbprint-type (CBOR tag 557) containing the signer- id. The example in Figure 3 shows a CoMID encoding a PSA Endorsement of type Reference Value for a firmware measurement associated with Implementation ID acme-implementation-id-000000001. / concise-mid-tag / { / comid.tag-identity / 1 : { / comid.tag-id / 0 : h'3f06af63a93c11e4979700505690773f' }, / comid.triples / 4 : { / comid.reference-triples / 0 : [ [ / environment-map / { / comid.class / 0 : { / comid.class-id / 0 : / tagged-impl-id-type / 600( h'61636d652d696d706c656d656e746174 696f6e2d69642d303030303030303031' ), / comid.vendor / 1 : "ACME Ltd.", Fossati, et al. Expires 11 September 2023 [Page 6] Internet-Draft CoRIM PSA Profile March 2023 / comid.model / 2 : "Roadrunner 1.0" } }, [ / measurement-map / { / comid.mval / 1 : { / comid.version / 0 : { / version / 0: "1.3.5" }, / comid.digests / 2 : [ [ / hash-alg-id / "sha-256", / hash-value / h'44aa336af4cb14a8 79432e53dd6571c7 fa9bccafb75f4882 59262d6ea3a4d91b' ] ], / comid.name / 11 : "PRoT" }, / authorized-by / 2 : [ 557([ / hash-alg-id / "sha-256", / hash-value / h'acbb11c7e4da2172 05523ce4ce1a245a e1a239ae3c6bfd9e 7871f7e5d8bae86b' ]) ] } ] ] ] } } Figure 3: Example Reference Value 3.4. Attestation Verification Claims An Attestation Verification Claim carries the verification key associated with the Initial Attestation Key (IAK) of a PSA device. When appraising Evidence, the Verifier can use the Implementation ID and Instance ID claims (see Section 3.2) to look up the verification key that it SHALL use to check the signature on the Evidence. This allows the Verifier to prove (or disprove) the Attester's claimed identity. Fossati, et al. Expires 11 September 2023 [Page 7] Internet-Draft CoRIM PSA Profile March 2023 Each verification key is provided alongside the corresponding device Instance and Implementation IDs (and, possibly, a product identifier) in an attest-key-triple-record. Specifically: * The Instance and Implementation IDs are encoded in the environment-map as shown in Figure 2; * The IAK public key is carried in the comid.key entry in the verification-key-map. The IAK public key is a PEM-encoded SubjectPublicKeyInfo [RFC5280]. There MUST be only one verification-key-map in an attest-key-triple-record; * The optional comid.keychain entry MUST NOT be set by a CoMID producer that uses the profile described in this document, and MUST be ignored by a CoMID consumer that is parsing according to this profile. The example in Figure 4 shows the PSA Endorsement of type Attestation Verification Claim carrying a secp256r1 EC public IAK associated with Instance ID 4ca3...d296. Fossati, et al. Expires 11 September 2023 [Page 8] Internet-Draft CoRIM PSA Profile March 2023 / concise-mid-tag / { / comid.tag-identity / 1 : { / comid.tag-id / 0 : h'3f06af63a93c11e4979700505690773f' }, / comid.triples / 4 : { / comid.attest-key-triples / 3 : [ [ / environment-map / { / comid.class / 0 : { / comid.class-id / 0 : / tagged-impl-id-type / 600( h'61636d652d696d706c656d656e746174 696f6e2d69642d303030303030303031' ), / comid.vendor / 1 : "ACME Ltd.", / comid.model / 2 : "Roadrunner 1.0" }, / comid.instance / 1 : / tagged-ueid-type / 550( h'01 4ca3e4f50bf248c39787020d68ffd05c 88767751bf2645ca923f57a98becd296' ) }, [ / verification-key-map / { / comid.key / 0 : "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgA ETl4iCZ47zrRbRG0TVf0dw7VFlHtv18HInY hnmMNybo+A1wuECyVqrDSmLt4QQzZPBECV8 ANHS5HgGCCSr7E/Lg==" } ] ] ] } } Figure 4: Example Attestation Verification Claim 3.5. Certification Claims PSA Certified [PSA-CERTIFIED] defines a certification scheme for the PSA ecosystem. A product - either a hardware component, a software component, or an entire device - that is verified to meet the security criteria established by the PSA Certified scheme is warranted a PSA Certified Security Assurance Certificate (SAC). A SAC contains information about the certification of a certain product Fossati, et al. Expires 11 September 2023 [Page 9] Internet-Draft CoRIM PSA Profile March 2023 (e.g., the target system, the attained certification level, the test lab that conducted the evaluation, etc.), and has a unique Certificate Number. The linkage between a PSA RoT -- comprising the immutable part as well as zero or more of the mutable components -- and the associated SAC is provided by a Certification Claim, which binds the PSA RoT Implementation ID and the software component identifiers with the SAC unique Certificate Number. When appraising Evidence, the Verifier can use the Certification Claims associated with the identified Attester as ancillary input to the Appraisal Policy, or to enrich the produced Attestation Result. A Certification Claim is encoded as a conditional-endorsement-triple- record. The SAC is encoded in a psa-cert-num that extends the measurement- values-map: $$measurement-values-map-extension //= ( &(psa-cert-num: 100) => psa-cert-num-type ) psa-cert-num-type = text .regexp "[0-9]{13} - [0-9]{5}" The conditional-endorsement-triple-record is constructed as follows: * The Implementation ID of the immutable PSA RoT to which the SAC applies is encoded as a tagged-impl-id-type in the environment-map of the stateful-environment-record; * Any software component that is part of the certified PSA RoT is encoded as a reference value (see Section 3.3) in the measurement- map of the stateful-environment-record; * The unique SAC Certificate Number is encoded as psa-cert-num in the measurement-values-map. The example in Figure 5 shows a Certification Claim that associates Certificate Number 1234567890123 - 12345 to Implementation ID acme- implementation-id-000000001 and a single "PRoT" software component with version "1.3.5". Fossati, et al. Expires 11 September 2023 [Page 10] Internet-Draft CoRIM PSA Profile March 2023 / concise-mid-tag / { / comid.tag-identity / 1 : { / comid.tag-id / 0 : h'dbb0508ac658421c99c904124bab59ca' }, / comid.triples / 4 : { / comid.conditional-endorsement-triple / 9 : [ [ / stateful-environment-record / [ / environment-map / { / comid.class / 0 : { / comid.class-id / 0 : / tagged-impl-id-type / 600( h'61636d652d696d706c656d656e746174 696f6e2d69642d303030303030303031' ), / comid.vendor / 1 : "ACME Ltd.", / comid.model / 2 : "Roadrunner 1.0" } }, / measurement-map / { / comid.mval / 1 : { / comid.version / 0 : { / version / 0: "1.3.0" }, / comid.digests / 2 : [ [ / hash-alg-id / "sha-256", / hash-value / h'44aa336af4cb14a8 79432e53dd6571c7 fa9bccafb75f4882 59262d6ea3a4d91b' ] ], / comid.name / 11 : "PRoT" }, / authorized-by / 2 : [ 557([ / hash-alg-id / "sha-256", / hash-value / h'acbb11c7e4da2172 05523ce4ce1a245a e1a239ae3c6bfd9e 7871f7e5d8bae86b' ]) ] } ], / measurement-values-map / { / psa.cert-num / 100 : "1234567890123 - 12345" Fossati, et al. Expires 11 September 2023 [Page 11] Internet-Draft CoRIM PSA Profile March 2023 } ] ] } } Figure 5: Example Certification Claim 3.6. Software Upgrades and Patches In order to model software lifecycle events such as updates and patches, this profile defines a new triple that conveys the following semantics: * SUBJECT: a software component * PREDICATE: (non-critically / critically) (updates / patches) * OBJECT: another software component The triple is reified and used as the object of another triple, psa- swrel-triple-record, whose subject is the embedding environment. comid.psa-swrel-triples = TBD2 $$triples-map-extension //= ( comid.psa-swrel-triples => [ + psa-swrel-triple-record ] ) psa.updates = 1 psa.patches = 2 psa-swrel-rel = [ type: psa.updates / psa.patches security-critical: bool ; true means it's a fix for a security bug ] sw-rel = [ new: comid.measurement-map ; the "new" firmware rel: psa-swrel-rel ; patches/updates and the security flag old: comid.measurement-map ; the "old" firmware ] psa-swrel-triple-record = [ environment-map sw-rel ] Fossati, et al. Expires 11 September 2023 [Page 12] Internet-Draft CoRIM PSA Profile March 2023 An example of a security critical update involving versions "1.2.5" and "1.3.0" of software component "PRoT" within the target environment associated with Implementation ID acme-implementation- id-000000001 is shown in Figure 6. / concise-mid-tag / { / comid.tag-identity / 1 : { / comid.tag-id / 0 : h'3f06af63a93c11e4979700505690773f' }, / comid.triples / 4 : { / comid.psa-swrel-triples / 5 : [ [ / environment-map / { / comid.class-id / 0 : / tagged-impl-id-type / 600( h'61636d652d696d706c656d656e746174 696f6e2d69642d303030303030303031' ), / comid.vendor / 1 : "ACME Ltd.", / comid.model / 2 : "Roadrunner 1.0" }, / sw-rel / [ / new / { / comid.mval / 1 : { / comid.version / 0 : { / version / 0: "1.3.0" }, / comid.digests / 2 : [ [ / hash-alg-id / "sha-256", / hash-value / h'44aa336af4cb14a8 79432e53dd6571c7 fa9bccafb75f4882 59262d6ea3a4d91b' ] ], / comid.name / 11 : "PRoT" }, / authorized-by / 2 : [ 557([ / hash-alg-id / "sha-256", / hash-value / h'acbb11c7e4da2172 05523ce4ce1a245a e1a239ae3c6bfd9e 7871f7e5d8bae86b' ]) ] Fossati, et al. Expires 11 September 2023 [Page 13] Internet-Draft CoRIM PSA Profile March 2023 }, / rel / [ / type / 1, / psa.updates / / security-critical / true ], / old / { / comid.mval / 1 : { / comid.version / 0 : { / version / 0: "1.2.5" }, / comid.digests / 2 : [ [ / hash-alg-id / "sha-256", / hash-value / h'98b06c3f4bfeb294 f69dae2bbe7d4be0 750e258a86414d90 a17cda9e2e775337' ] ], / comid.name / 11 : "PRoT" }, / authorized-by / 2 : [ 557([ / hash-alg-id / "sha-256", / hash-value / h'acbb11c7e4da2172 05523ce4ce1a245a e1a239ae3c6bfd9e 7871f7e5d8bae86b' ]) ] } ] ] ] } } Figure 6: Example Critical Software Upgrade 4. Security Considerations // TODO 5. IANA Considerations Fossati, et al. Expires 11 September 2023 [Page 14] Internet-Draft CoRIM PSA Profile March 2023 5.1. CBOR Tag Registrations IANA is requested to allocate the following tag in the "CBOR Tags" registry [IANA.cbor-tags], preferably with the specified value: +=====+==============+==========================+ | Tag | Data Item | Semantics | +=====+==============+==========================+ | 600 | tagged bytes | PSA Implementation ID | | | | (Section 3.2 of RFCthis) | +-----+--------------+--------------------------+ Table 2: CoRIM CBOR Tags 5.2. CoRIM Profile Registration IANA is requested to register the following profile value in the // TODO CoRIM registry. +==========================+======+============================+ | Profile Value | Type | Semantics | +==========================+======+============================+ | http://arm.com/psa/iot/1 | uri | The CoRIM profile | | | | specified by this document | +--------------------------+------+----------------------------+ Table 3: PSA profile for CoRIM 5.3. CoMID Codepoints 5.3.1. CoMID Triples Map Extension IANA is requested to register the following codepoints to the "CoMID Triples Map" registry. +=======+=========================+===============+ | Index | Item Name | Specification | +=======+=========================+===============+ | 50 | comid.psa-swrel-triples | RFCthis | +-------+-------------------------+---------------+ Table 4: PSA CoMID Triples Fossati, et al. Expires 11 September 2023 [Page 15] Internet-Draft CoRIM PSA Profile March 2023 5.3.2. CoMID Measurement Values Map Extension +=====+====================+==============+========================+ | Key | Item Name | Item Type | Specification | +=====+====================+==============+========================+ | 100 | comid.psa-cert-num | psa-cert-num | Section 3.5 of RFCthis | +-----+--------------------+--------------+------------------------+ Table 5: Measurement Values Map Extensions Acknowledgements // TODO References Normative References [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-01, 9 March 2023, . [IANA.cbor-tags] IANA, "Concise Binary Object Representation (CBOR) Tags", . [PSA-TOKEN] Tschofenig, H., Frost, S., Brossard, M., Shaw, A. L., and T. Fossati, "Arm's Platform Security Architecture (PSA) Attestation Token", Work in Progress, Internet-Draft, draft-tschofenig-rats-psa-token-11, 28 February 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . Fossati, et al. Expires 11 September 2023 [Page 16] Internet-Draft CoRIM PSA Profile March 2023 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Informative References [PSA-CERTIFIED] "PSA Certified", 2021, . [RATS-ARCH] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote ATtestation procedureS (RATS) Architecture", RFC 9334, DOI 10.17487/RFC9334, January 2023, . [TEEP] Pei, M., Tschofenig, H., Thaler, D., and D. M. Wheeler, "Trusted Execution Environment Provisioning (TEEP) Architecture", Work in Progress, Internet-Draft, draft- ietf-teep-architecture-19, 24 October 2022, . Authors' Addresses Thomas Fossati Arm Ltd Email: thomas.fossati@arm.com Yogesh Deshpande Arm Ltd Email: yogesh.deshpande@arm.com Henk Birkholz Fraunhofer SIT Email: henk.birkholz@sit.fraunhofer.de Fossati, et al. Expires 11 September 2023 [Page 17]