Arm Limited

Hannes.Tschofenig@arm.com

Arm Limited

Simon.Frost@arm.com

Arm Limited

Mathias.Brossard@arm.com

HP Labs

Adrian.Shaw@hp.com

Arm Limited

Thomas.Fossati@arm.com

Security RATS Internet-Draft The Platform Security Architecture (PSA) is a family of hardware and firmware security specifications, as well as open-source reference implementations, to help device makers and chip manufacturers build best-practice security into products. Devices that are PSA compliant are able to produce attestation tokens as described in this memo, which are the basis for a number of different protocols, including secure provisioning and network access control. This document specifies the PSA attestation token structure and semantics. The PSA attestation token is a profiled Entity Attestation Token (EAT). This specification describes what claims are used in an attestation token generated by PSA compliant systems, how these claims get serialized to the wire, and how they are cryptographically protected. Note to Readers Source for this draft and an issue tracker can be found at https://github.com/thomas-fossati/draft-psa-token.

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 . 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 8 September 2022.

Copyright Notice Copyright (c) 2022 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 () 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.

Table of Contents

• .  Introduction
• .  Conventions and Definitions
  • .  Glossary
• .  PSA Claims
  • .  Caller Claims
    • .  Nonce
    • .  Client ID
  • .  Target Identification Claims
    • .   Instance ID
    • .  Implementation ID
    • .  Certification Reference
  • .  Target State Claims
    • .  Security Lifecycle
    • .  Boot Seed
  • .  Software Inventory Claims
    • .  Software Components
  • .  Verification Claims
    • .  Verification Service Indicator
    • .  Profile Definition
• .  Backwards Compatibility Considerations
• .   Token Encoding and Signing
• .  Freshness Model
• .  Collated CDDL
• .  Implementation Status
• .  Security and Privacy Considerations
• . Verification
• . IANA Considerations
  • .  CBOR Web Token Claims Registration
    • .   Client ID Claim
    • .   Security Lifecycle Claim
    • .   Implementation ID Claim
    • .   Boot Seed Claim
    • .   Certification Reference Claim
    • .   Software Components Claim
    • .   Verification Service Indicator Claim
  • .  Media Type Registration
  • .  CoAP Content-Formats Registration
    • .  Registry Contents
• . References
  • .  Normative References
  • .  Informative References
• .  Example
• Contributors
• Acknowledgments
• Authors' Addresses

Introduction Trusted execution environments are now present in many devices, which provide a safe environment to place security sensitive code such as cryptography, secure boot, secure storage, and other essential security functions. These security functions are typically exposed through a narrow and well-defined interface, and can be used by operating system libraries and applications. Various APIs have been developed by Arm as part of the Platform Security Architecture framework. This document focuses on the output provided by PSA's Initial Attestation API. Since the tokens are also consumed by services outside the device, there is an actual need to ensure interoperability. Interoperability needs are addressed here by describing the exact syntax and semantics of the attestation claims, and defining the way these claims are encoded and cryptographically protected. Further details on concepts expressed below can be found in the PSA Security Model documentation .

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 when, and only when, they appear in all capitals, as shown here.

Glossary

RoT

Root of Trust, the minimal set of software, hardware and data that has to be implicitly trusted in the platform - there is no software or hardware at a deeper level that can verify that the Root of Trust is authentic and unmodified. An example of RoT is an initial bootloader in ROM, which contains cryptographic functions and credentials, running on a specific hardware platform.

SPE

Secure Processing Environment, a platform's processing environment for software that provides confidentiality and integrity for its runtime state, from software and hardware, outside of the SPE. Contains trusted code and trusted hardware. (Equivalent to Trusted Execution Environment (TEE), or "secure world".)

NSPE

Non Secure Processing Environment, the security domain outside of the SPE, the Application domain, typically containing the application firmware, operating systems, and general hardware. (Equivalent to Rich Execution Environment (REE), or "normal world".)

PSA Claims This section describes the claims to be used in a PSA attestation token. CDDL along with text descriptions is used to define each claim independent of encoding. The following CDDL type(s) are reused by different claims: psa-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64

Caller Claims

Nonce The Nonce claim is used to carry the challenge provided by the caller to demonstrate freshness of the generated token. The EAT nonce (claim key 10) is used. The following constraints apply to the nonce-type:

• The length MUST be either 32, 48, or 64 bytes.
• Only a single nonce value is conveyed. Per the array notation is not used for encoding the nonce value.

This claim MUST be present in a PSA attestation token. psa-nonce = ( nonce-label => psa-hash-type )

Client ID The Client ID claim represents the security domain of the caller. In PSA, a security domain is represented by a signed integer whereby negative values represent callers from the NSPE and where positive IDs represent callers from the SPE. The value 0 is not permitted. For an example definition of client IDs, see the PSA Firmware Framework . It is essential that this claim is checked in the verification process to ensure that a security domain, i.e., an attestation endpoint, cannot spoof a report from another security domain. This claim MUST be present in a PSA attestation token. psa-client-id-nspe-type = -2147483648...0 psa-client-id-spe-type = 1..2147483647 psa-client-id-type = psa-client-id-nspe-type / psa-client-id-spe-type psa-client-id = ( psa-client-id-key => psa-client-id-type )

Target Identification Claims

 Instance ID The Instance ID claim represents the unique identifier of the Initial Attestation Key (IAK). The full definition is in . The EAT ueid (claim key 256) of type RAND is used. The following constraints apply to the ueid-type:

• The length MUST be 33 bytes.
• The first byte MUST be 0x01 (RAND) followed by the 32-bytes key hash.

This claim MUST be present in a PSA attestation token. psa-instance-id-type = bytes .size 33 psa-instance-id = ( ueid-label => psa-instance-id-type )

Implementation ID The Implementation ID claim uniquely identifies the implementation of the immutable PSA RoT. A verification service uses this claim to locate the details of the PSA RoT implementation from an Endorser or manufacturer. Such details are used by a verification service to determine the security properties or certification status of the PSA RoT implementation. The value and format of the ID is decided by the manufacturer or a particular certification scheme. For example, the ID could take the form of a product serial number, database ID, or other appropriate identifier. This claim MUST be present in a PSA attestation token. Note that this identifies the PSA RoT implementation, not a particular instance. To uniquely identify an instance, see the Instance ID claim . psa-implementation-id-type = bytes .size 32 psa-implementation-id = ( psa-implementation-id-key => psa-implementation-id-type )

Certification Reference The Certification Reference claim is used to link the class of chip and PSA RoT of the attesting device to an associated entry in the PSA Certification database. It MUST be represented as a thirteen-digit . Linking to the PSA Certification entry can still be achieved if this claim is not present in the token by making an association at a Verifier between the reference value and other token claim values - for example, the Implementation ID. psa-certification-reference-type = text .regexp "[0-9]{13}" psa-certification-reference = ( ? psa-certification-reference-key => psa-certification-reference-type )

Target State Claims

Security Lifecycle The Security Lifecycle claim represents the current lifecycle state of the PSA RoT. The state is represented by an integer that is divided to convey a major state and a minor state. A major state is mandatory and defined by . A minor state is optional and 'IMPLEMENTATION DEFINED'. The PSA security lifecycle state and implementation state are encoded as follows:

• version[15:8] - PSA security lifecycle state, and
• version[7:0] - IMPLEMENTATION DEFINED state.

The PSA lifecycle states are illustrated in . For PSA, a Verifier can only trust reports from the PSA RoT when it is in SECURED or NON_PSA_ROT_DEBUG major states. This claim MUST be present in a PSA attestation token.

PSA Lifecycle States .----------------------. .--- Enrol ---+ Provisioning Lockdown | | '-----------+----------' | | .------------------. | | | | * v v | .--------------. .---------. | | Verifier | .---------+ Secured +-----------. | '--------------' | '-+-------' | | * | | ^ | | | | v | v | Blocklist | .------------+------. .----------+----. | | | Non-PSA RoT Debug | | Recoverable | | | '---------+---------' | PSA RoT Debug | .-+-----------+-. | '------+--------' | Terminate +------------+-------------------' '------+--------' | .----------------. '------------>| Decommissioned | '----------------'

psa-lifecycle-unknown-type = 0x0000..0x00ff psa-lifecycle-assembly-and-test-type = 0x1000..0x10ff psa-lifecycle-psa-rot-provisioning-type = 0x2000..0x20ff psa-lifecycle-secured-type = 0x3000..0x30ff psa-lifecycle-non-psa-rot-debug-type = 0x4000..0x40ff psa-lifecycle-recoverable-psa-rot-debug-type = 0x5000..0x50ff psa-lifecycle-decommissioned-type = 0x6000..0x60ff psa-lifecycle-type = psa-lifecycle-unknown-type / psa-lifecycle-assembly-and-test-type / psa-lifecycle-psa-rot-provisioning-type / psa-lifecycle-secured-type / psa-lifecycle-non-psa-rot-debug-type / psa-lifecycle-recoverable-psa-rot-debug-type / psa-lifecycle-decommissioned-type psa-lifecycle = ( psa-lifecycle-key => psa-lifecycle-type )

Boot Seed The Boot Seed claim represents a random value created at system boot time that will allow differentiation of reports from different boot sessions. This claim MUST be present in a PSA attestation token. psa-boot-seed-type = bytes .size 32 psa-boot-seed = ( psa-boot-seed-key => psa-boot-seed-type )

Software Inventory Claims

Software Components The Software Components claim is a list of software components that includes all the software loaded by the PSA RoT. This claim SHALL be included in attestation tokens produced by an implementation conformant with . Each entry in the Software Components list describes one software component using the attributes described in the following subsections. Unless explicitly stated, the presence of an attribute is OPTIONAL. Note that, as described in , a relying party will typically see the result of the verification process from the Verifier in form of an attestation result, rather than the "naked" PSA token from the attesting endpoint. Therefore, a relying party is not expected to understand the Software Components claim. Instead, it is for the Verifier to check this claim against the available endorsements and provide an answer in form of an "high level" attestation result, which may or may not include the original Software Components claim. psa-software-component = { ? 1 => text, ; measurement type 2 => psa-hash-type, ; measurement value ? 4 => text, ; version 5 => psa-hash-type, ; signer id ? 6 => text, ; measurement description } psa-software-components = ( psa-software-components-key => [ + psa-software-component ] )

Measurement Type The Measurement Type attribute (key=1) is short string representing the role of this software component. The following measurement types MAY be used:

• "BL": a Boot Loader
• "PRoT": a component of the PSA Root of Trust
• "ARoT": a component of the Application Root of Trust
• "App": a component of the NSPE application
• "TS": a component of a Trusted Subsystem

 Measurement Value The Measurement Value attribute (key=2) represents a hash of the invariant software component in memory at startup time. The value MUST be a cryptographic hash of 256 bits or stronger. This attribute MUST be present in a PSA software component.

Version The Version attribute (key=4) is the issued software version in the form of a text string. The value of this attribute will correspond to the entry in the original signed manifest of the component.

Signer ID The Signer ID attribute (key=5) is the hash of a signing authority public key for the software component. The value of this attribute will correspond to the entry in the original manifest for the component. This can be used by a Verifier to ensure the components were signed by an expected trusted source. This attribute MUST be present in a PSA software component to be compliant with .

Measurement Description The Measurement Description attribute (key=6) contains a string identifying the hash algorithm used to compute the corresponding Measurement Value. The string SHOULD be encoded according to .

Verification Claims

Verification Service Indicator The Verification Service Indicator claim is a hint used by a relying party to locate a validation service for the token. The value is a text string that can be used to locate the service or a URL specifying the address of the service. A Verifier may choose to ignore this claim in favor of other information. psa-verification-service-indicator-type = text psa-verification-service-indicator = ( ? psa-verification-service-indicator-key => psa-verification-service-indicator-type )

Profile Definition The Profile Definition claim encodes the unique identifier that corresponds to the EAT profile described by this document. This allows a receiver to assign the intended semantics to the rest of the claims found in the token. The EAT profile (claim key 265) is used. The following constraints apply to its type:

• The URI encoding MUST be used.
• The value MUST be http://arm.com/psa/2.0.0.

This claim MUST be present in a PSA attestation token. See , for considerations about backwards compatibility with previous versions of the PSA attestation token format. psa-profile-type = "http://arm.com/psa/2.0.0" psa-profile = ( profile-label => psa-profile-type )

Backwards Compatibility Considerations A previous version of this specification (identified by the PSA_IOT_PROFILE_1 profile) used claim key values from the "private use range" of the CWT Claims registry. These claim keys have now been retired and their use is deprecated. provides the mappings between the deprecated and new claim keys. Claim key mappings

	PSA_IOT_PROFILE_1	http://arm.com/psa/2.0.0
Nonce	-75008	10 (EAT nonce)
Instance ID	-75009	256 (EAT euid)
Profile Definition	-75000	265 (EAT eat_profile)
Client ID	-75001	2394
Security Lifecycle	-75002	2395
Implementation ID	-75003	2396
Boot Seed	-75004	2397
Certification Reference	-75005	2398
Software Components	-75006	2399
Verification Service Indicator	-75010	2400

Unless compatibility with existing infrastructure is a concern, emitters (e.g., devices that implement the PSA Attestation API) SHOULD produce tokens with the claim keys specified in this document. To simplify the transition to the token format described in this document it is RECOMMENDED that receivers (e.g., PSA Attestation Verifiers) accept tokens encoded according to the old profile (PSA_IOT_PROFILE_1) as well as to the new profile (http://arm.com/psa/2.0.0), at least for the time needed to their clients to upgrade.

 Token Encoding and Signing The PSA attestation token is encoded in CBOR format. Only definite-length string, arrays, and maps are allowed. Cryptographic protection is obtained by wrapping the psa-token map in a COSE Web Token (CWT) . For asymmetric key algorithms, the signature structure MUST be COSE_Sign1. For symmetric key algorithms, the signature structure MUST be COSE_Mac0. Acknowledging the variety of markets, regulations and use cases in which the PSA attestation token can be used, this specification does not impose any strong requirement on the cryptographic algorithms that need to be supported by Attesters and Verifiers. It is assumed that some form of out-of-band discovery and negotiation is in place to allow interoperability between the involved parties, and that the flexibility provided by the COSE format is sufficient to deal with the level of cryptographic agility needed to adapt to specific use cases. The CWT CBOR tag (61) is not used. An application that needs to exchange PSA attestation tokens can wrap the serialised COSE_Sign1 or COSE_Mac0 in the media type defined in or the CoAP Content-Format defined in .

Freshness Model The PSA Token supports the freshness models for attestation Evidence based on nonces and epoch handles (Section 10.2 and 10.3 of ) using the nonce claim to convey the nonce or epoch handle supplied by the Verifier. No further assumption on the specific remote attestation protocol is made.

Collated CDDL psa-token = { psa-nonce, psa-instance-id, psa-verification-service-indicator, psa-profile, psa-implementation-id, psa-client-id, psa-lifecycle, psa-certification-reference, psa-boot-seed, psa-software-components, } psa-client-id-key = 2394 psa-lifecycle-key = 2395 psa-implementation-id-key = 2396 psa-boot-seed-key = 2397 psa-certification-reference-key = 2398 psa-software-components-key = 2399 psa-verification-service-indicator-key = 2400 ; from EAT nonce-label = 10 ueid-label = 256 profile-label = 265 psa-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64 psa-boot-seed-type = bytes .size 32 psa-boot-seed = ( psa-boot-seed-key => psa-boot-seed-type ) psa-client-id-nspe-type = -2147483648...0 psa-client-id-spe-type = 1..2147483647 psa-client-id-type = psa-client-id-nspe-type / psa-client-id-spe-type psa-client-id = ( psa-client-id-key => psa-client-id-type ) psa-certification-reference-type = text .regexp "[0-9]{13}" psa-certification-reference = ( ? psa-certification-reference-key => psa-certification-reference-type ) psa-implementation-id-type = bytes .size 32 psa-implementation-id = ( psa-implementation-id-key => psa-implementation-id-type ) psa-instance-id-type = bytes .size 33 psa-instance-id = ( ueid-label => psa-instance-id-type ) psa-nonce = ( nonce-label => psa-hash-type ) psa-profile-type = "http://arm.com/psa/2.0.0" psa-profile = ( profile-label => psa-profile-type ) psa-lifecycle-unknown-type = 0x0000..0x00ff psa-lifecycle-assembly-and-test-type = 0x1000..0x10ff psa-lifecycle-psa-rot-provisioning-type = 0x2000..0x20ff psa-lifecycle-secured-type = 0x3000..0x30ff psa-lifecycle-non-psa-rot-debug-type = 0x4000..0x40ff psa-lifecycle-recoverable-psa-rot-debug-type = 0x5000..0x50ff psa-lifecycle-decommissioned-type = 0x6000..0x60ff psa-lifecycle-type = psa-lifecycle-unknown-type / psa-lifecycle-assembly-and-test-type / psa-lifecycle-psa-rot-provisioning-type / psa-lifecycle-secured-type / psa-lifecycle-non-psa-rot-debug-type / psa-lifecycle-recoverable-psa-rot-debug-type / psa-lifecycle-decommissioned-type psa-lifecycle = ( psa-lifecycle-key => psa-lifecycle-type ) psa-software-component = { ? 1 => text, ; measurement type 2 => psa-hash-type, ; measurement value ? 4 => text, ; version 5 => psa-hash-type, ; signer id ? 6 => text, ; measurement description } psa-software-components = ( psa-software-components-key => [ + psa-software-component ] ) psa-verification-service-indicator-type = text psa-verification-service-indicator = ( ? psa-verification-service-indicator-key => psa-verification-service-indicator-type )

Implementation Status Independent implementations of this specification are provided by the Trusted Firmware project , the Veraison project , and Xclaim . All three implementations are released as open-source software.

Security and Privacy Considerations This specification re-uses the CWT and the EAT specification. Hence, the security and privacy considerations of those specifications apply here as well. Since CWTs offer different ways to protect the token, this specification profiles those options and allows signatures based on use of public key cryptography as well as MAC authentication. The token MUST be signed following the structure of the COSE specification . The COSE type MUST be COSE_Sign1 for public key signatures or COSE_Mac0 for MAC authentication. Note however that use of MAC authentication is NOT RECOMMENDED due to the associated infrastructure costs for key management and protocol complexities. It may also restrict the ability to interoperate with third parties. Attestation tokens contain information that may be unique to a device and therefore they may allow to single out an individual device for tracking purposes. Implementations that have privacy requirements must take appropriate measures to ensure that the token is only used to provision anonymous/pseudonym keys.

Verification To verify the token, the primary need is to check correct encoding and signing as detailed in . In particular, the Instance ID claim is used (together with the kid in the COSE header, if present) to assist in locating the public key used to verify the signature covering the CWT token. The key used for verification is supplied to the Verifier by an authorized Endorser along with the corresponding Attester's Instance ID. In addition, the Verifier will typically operate a policy where values of some of the claims in this profile can be compared to reference values, registered with the Verifier for a given deployment, in order to confirm that the device is endorsed by the manufacturer supply chain. The policy may require that the relevant claims must have a match to a registered reference value. All claims may be worthy of additional appraisal. It is likely that most deployments would include a policy with appraisal for the following claims:

• Implementation ID - the value of the Implementation ID can be used to identify the verification requirements of the deployment.
• Software Component, Measurement Value - this value can uniquely identify a firmware release from the supply chain. In some cases, a Verifier may maintain a record for a series of firmware releases, being patches to an original baseline release. A verification policy may then allow this value to match any point on that release sequence or expect some minimum level of maturity related to the sequence.
• Software Component, Signer ID - where present in a deployment, this could allow a Verifier to operate a more general policy than that for Measurement Value as above, by allowing a token to contain any firmware entries signed by a known Signer ID, without checking for a uniquely registered version.
• Certification Reference - if present, this value could be used as a hint to locate security certification information associated with the attesting device. An example could be a reference to a certificate.

The protocol used to convey Endorsements and Reference Values to the Verifier is not in scope for this document.

IANA Considerations

CBOR Web Token Claims Registration This specification requests IANA to register the following claims in the "CBOR Web Token (CWT) Claims" registry .

 Client ID Claim

• Claim Name: psa-client-id
• Claim Description: PSA Client ID
• JWT Claim Name: N/A
• Claim Key: TBD (requested value: 2394)
• Claim Value Type(s): signed integer
• Change Controller: [[Authors of this RFC]]
• Specification Document(s): of [[this RFC]]

 Security Lifecycle Claim

• Claim Name: psa-security-lifecycle
• Claim Description: PSA Security Lifecycle
• JWT Claim Name: N/A
• Claim Key: TBD (requested value: 2395)
• Claim Value Type(s): unsigned integer
• Change Controller: [[Authors of this RFC]]
• Specification Document(s): of [[this RFC]]

 Implementation ID Claim

• Claim Name: psa-implementation-id
• Claim Description: PSA Implementation ID
• JWT Claim Name: N/A
• Claim Key: TBD (requested value: 2396)
• Claim Value Type(s): byte string
• Change Controller: [[Authors of this RFC]]
• Specification Document(s): of [[this RFC]]

 Boot Seed Claim

• Claim Name: psa-boot-seed
• Claim Description: PSA Boot Seed
• JWT Claim Name: N/A
• Claim Key: TBD (requested value: 2397)
• Claim Value Type(s): byte string
• Change Controller: [[Authors of this RFC]]
• Specification Document(s): of [[this RFC]]

 Certification Reference Claim

• Claim Name: psa-certification-reference
• Claim Description: PSA Certification Reference
• JWT Claim Name: N/A
• Claim Key: TBD (requested value: 2398)
• Claim Value Type(s): text string
• Change Controller: [[Authors of this RFC]]
• Specification Document(s): of [[this RFC]]

 Software Components Claim

• Claim Name: psa-software-components
• Claim Description: PSA Software Components
• JWT Claim Name: N/A
• Claim Key: TBD (requested value: 2399)
• Claim Value Type(s): array
• Change Controller: [[Authors of this RFC]]
• Specification Document(s): of [[this RFC]]

 Verification Service Indicator Claim

• Claim Name: psa-verification-service-indicator
• Claim Description: PSA Verification Service Indicator
• JWT Claim Name: N/A
• Claim Key: TBD (requested value: 2400)
• Claim Value Type(s): text string
• Change Controller: [[Authors of this RFC]]
• Specification Document(s): of [[this RFC]]

Media Type Registration IANA is requested to register the "application/psa-attestation-token" media type in the "Media Types" registry in the manner described in RFC 6838 , which can be used to indicate that the content is a PSA Attestation Token.

• Type name: application
• Subtype name: psa-attestation-token
• Required parameters: n/a
• Optional parameters: n/a
• Encoding considerations: binary
• Security considerations: See the Security Considerations section of [[this RFC]]
• Interoperability considerations: n/a
• Published specification: [[this RFC]]
• Applications that use this media type: Attesters and Relying Parties sending PSA attestation tokens over HTTP(S), CoAP(S), and other transports.
• Fragment identifier considerations: n/a
• Additional information:
  • Magic number(s): n/a
  • File extension(s): n/a
  • Macintosh file type code(s): n/a
• Person & email address to contact for further information: Hannes Tschofenig, Hannes.Tschofenig@arm.com
• Intended usage: COMMON
• Restrictions on usage: none
• Author: Hannes Tschofenig, Hannes.Tschofenig@arm.com
• Change controller: IESG
• Provisional registration? No

CoAP Content-Formats Registration IANA is requested to register the CoAP Content-Format ID for the "application/psa-attestation-token" media type in the "CoAP Content-Formats" registry .

Registry Contents

• Media Type: application/psa-attestation-token
• Encoding: -
• Id: [[To-be-assigned by IANA]]
• Reference: [[this RFC]]

References Normative References GS1 Security Theory LLC Qualcomm Technologies Inc. Qualcomm Technologies Inc. An Entity Attestation Token (EAT) provides an attested claims set that describes state and characteristics of an entity, a device like a phone, IoT device, network equipment or such. This claims set is used by a relying party, server or service to determine how much it wishes to trust the entity. An EAT is either a CBOR Web Token (CWT) or JSON Web Token (JWT) with attestation-oriented claims. To a large degree, all this document does is extend CWT and JWT. Work in Progress Arm Arm This second document defines the general structure of the MIME media typing system and defines an initial set of media types. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need for the ability to have basic security services defined for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR), and CBOR Object Signing and Encryption (COSE) is used for added application-layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/value pair consisting of a claim name and a claim value. CWT is derived from JSON Web Token (JWT) but uses CBOR rather than JSON. This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. Informative References Fraunhofer SIT Microsoft Sandelman Software Works Intel Corporation Huawei Technologies In network protocol exchanges it is often useful for one end of a communication to know whether the other end is in an intended operating state. This document provides an architectural overview of the entities involved that make such tests possible through the process of generating, conveying, and evaluating evidentiary claims. An attempt is made to provide for a model that is neutral toward processor architectures, the content of claims, and protocols. Work in Progress IANA IANA IANA IANA Arm PSA Certified Linaro The Veraison Project

Example The following example shows a PSA attestation token for an hypothetical system comprising two measured software components (a boot loader and a trusted RTOS). The attesting device is in a lifecycle state of SECURED. The attestation has been requested from a client residing in the SPE: { / eat_profile / 265: "http://arm.com/psa/2.0.0", / psa-client-id / 2394: 1, / psa-lifecycle / 2395: 12288, / psa-implementation-id / 2396: h'50515253545556575051 52535455565750515253545556575051525354555657', / psa-boot-seed / 2397: h'DEADBEEFDEADBEEFDEAD BEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEF', / psa-certification-reference / 2398: "1234567890123", / psa-software-components / 2399: [ { / measurement type / 1: "BL", / measurement value / 2: h'0001020400010204000102040001020 400010204000102040001020400010204', / signer ID / 5: h'519200FF519200FF519200FF519200F F519200FF519200FF519200FF519200FF' }, { / measurement type / 1: "PRoT", / measurement value / 2: h'0506070805060708050607080506070 805060708050607080506070805060708', / signer ID / 5: h'519200FF519200FF519200FF519200F F519200FF519200FF519200FF519200FF' } ], / nonce / 10: h'00010203000102030001020300010203 00010203000102030001020300010203', / ueid / 256: h'01A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2 A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3', / psa-verification-service-indicator / 2400: "https://psa-ve rifier.org" } The JWK representation of the IAK used for creating the COSE Sign1 signature over the PSA token is: { "kty": "EC", "crv": "P-256", "x": "MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4", "y": "4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM", "d": "870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE", "use": "enc", "kid": "1" } The resulting COSE object is: 18( [ / protected / h'A10126', / unprotected / {}, / payload / h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signature / h'E3B80C143403ECB744B1D6EF732872A1A3E682783E 939F72A3CEF6BF74EF4BC5E7065725FF5C948770B673C5896D3F796F55D144FC B456BEA832EB13E8258DB8' ] )

Contributors We would like to thank the following colleagues for their contributions: * Laurence Lundblade Security Theory LLC lgl@securitytheory.com * Tamas Ban Arm Limited Tamas.Ban@arm.com * Sergei Trofimov Arm Limited Sergei.Trofimov@arm.com

Acknowledgments Thanks to Carsten Bormann for help with the CDDL and Nicholas Wood for ideas and comments.

Authors' Addresses Arm Limited

Hannes.Tschofenig@arm.com

Arm Limited

Simon.Frost@arm.com

Arm Limited

Mathias.Brossard@arm.com

HP Labs

Adrian.Shaw@hp.com

Arm Limited

Thomas.Fossati@arm.com