]>

Hannes.Tschofenig@gmx.net

Arm Limited

Simon.Frost@arm.com

Arm Limited

Mathias.Brossard@arm.com

HP Labs

adrianlshaw@acm.org

Arm Limited

Thomas.Fossati@arm.com

Security Remote ATtestation ProcedureS 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.

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 Attester Model outlines the structure of the PSA Attester according to the conceptual model described in .

PSA Attester | Boot o-----+ Attestation | | | | | | | | State | | Service | | | | | '-----+------' '-----' '-------------' | | | '----------------------|----------------------------------------' | | .------------+--------------+---------------. | | .--------|-------------|--------------|----------------|--------. | | | | | | | | | | | .------o-----. .-----o-------. .----o--------. .-----o------. | | | | | Updateable | | Application | | Application | | PSA RoT | | | | | | PSA RoT | | RoT | | Loader | | Parameters | | | | | '------------' '-------------' '-------------' '------------' | | | | Target Environment | | | '---------------------------------------------------------------' | '-------------------------------------------------------------------' ]]>

The PSA Attester is a relatively straightforward embodiment of the RATS Attester with exactly one Attesting Environment and one Target Environment. The Attesting Environment is responsible for collecting the information to be represented in PSA claims and to assemble them into Evidence. It is made of two cooperating components:

• The Main Bootloader (executing at boot-time) measures the loaded software components, collects the relevant PSA RoT parameters, and stores the recorded information in secure memory (Main Boot State) from where the Initial Attestation Service will, when asked for a platform attestation report, retrieve them.
• The Initial Attestation Service (executing at run-time in SPE) answers requests coming from NSPE via the PSA attestation API , collects and formats the claims from Main Boot State, and uses the Initial Attestation Key (IAK) to sign the attestation report.

The Target Environment can be broken down into four macro "objects", some of which may or may not be present depending on the device architecture:

• (A subset of) the PSA RoT parameters, including Instance and Implementation IDs.
• The updateable PSA RoT, including the Secure Partition Manager and all PSA RoT services.
• The (optional) Application RoT, that is any application-defined security service, possibly making use of the PSA RoT services.
• The loader of the application software running in NSPE.

A reference implementation of the PSA Attester is provided by .

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:

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-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-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 ) ]]>

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 ) ]]>

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 string made of nineteen numeric characters: a thirteen-digit , followed by a dash "-", followed by the five-digit versioning information described in . 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 ) ]]>

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 | Decommissioned | '----------------' ]]>

psa-lifecycle-type ) ]]>

Boot Seed The Boot Seed claim represents a value created at system boot time that will allow differentiation of reports from different boot sessions. This claim MAY be present in a PSA attestation token. If present, it MUST be between 8 and 32 bytes. psa-boot-seed-type ) ]]>

Software Inventory Claims

Software Components The Software Components claim is a list of software components that includes all the software (both code and configuration) loaded by the PSA RoT. This claim MUST 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 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. text &(measurement-value: 2) => psa-hash-type ? &(version: 4) => text &(signer-id: 5) => psa-hash-type ? &(measurement-desc: 6) => text } 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 for code measurements:

• "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

The same labels with a "-config" postfix (e.g., "PRoT-config") MAY be used for configuration measurements.

 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 verification service for the token. The value is a text string that can be used to locate the service (typically, a URL specifying the address of the verification service API). A Relying Party may choose to ignore this claim in favor of other information. 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 ) ]]>

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

The new profile introduces three further changes:

• the "Boot Seed" claim is now optional and variable length (see ),
• the "No Software Measurements" claim has been retired,
• the "Certification Reference" syntax changed from EAN-13 to EAN-13+5 (see ).

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 the flexibility provided by the COSE format is sufficient to deal with the level of cryptographic agility needed to adapt to specific use cases. For interoperability considerations, it is RECOMMENDED that commonly adopted algorithms are used, such as those discussed in ). It is expected that receivers (Verifiers and Relying Parties) will accept a wider range of algorithms, while Attesters would produce PSA tokens using only one such algorithm. 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 and Section 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-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}-[0-9]{5}" 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 = { ? &(measurement-type: 1) => text &(measurement-value: 2) => psa-hash-type ? &(version: 4) => text &(signer-id: 5) => psa-hash-type ? &(measurement-desc: 6) => text } 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 Implementations of this specification are provided by the Trusted Firmware-M project , the Veraison project , and the Xclaim library. All three implementations are released as open-source software.

Security and Privacy Considerations This specification re-uses the EAT specification and therefore the CWT 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 using public key cryptography as well as message authentication codes (MACs). COSE_Sign1 is used for digital signatures and COSE_Mac0 for MACs, as defined in the COSE specification . Note, however, that the use of MAC authentication is NOT RECOMMENDED due to the associated infrastructure costs for key management and protocol complexities. 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. Deployments 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.

 AR4SI Trustworthiness Claims Mappings defines an information model that Verifiers can employ to produce Attestation Results. AR4SI provides a set of standardized appraisal categories and tiers that greatly simplifies the task of writing Relying Party policies in multi-attester environments. The contents of are intended as guidance for implementing a PSA Verifier that computes its results using AR4SI. The table describes which PSA Evidence claims (if any) are related to which AR4SI trustworthiness claim, and therefore what the Verifier must consider when deciding if and how to appraise a certain feature associated with the PSA Attester. AR4SI Claims mappings

Trustworthiness Vector claims	Related PSA claims
configuration	Software Components ()
executables	ditto
file-system	N/A
hardware	Implementation ID ()
instance-identity	Instance ID (). The Security Lifecycle () can also impact the derived identity.
runtime-opaque	Indirectly derived from executables, hardware, and instance-identity. The Security Lifecycle () can also be relevant: for example, any debug state will expose otherwise protected memory.
sourced-data	N/A
storage-opaque	Indirectly derived from executables, hardware, and instance-identity.

This document does not prescribe what value must be chosen based on each possible situation: when assigning specific Trustworthiness Claim values, an implementation is expected to follow the algorithm described in .

Endorsements, Reference Values and Verification Key Material defines a protocol based on the data model that can be used to convey PSA Endorsements, Reference Values and verification key material to the Verifier.

IANA Considerations

CBOR Web Token Claims Registration IANA is requested to make permanent the following claims that have been assigned via early allocation 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: 2394
• Claim Value Type(s): signed integer
• Change Controller: Hannes Tschofenig
• Specification Document(s): of RFCthis

 Security Lifecycle Claim

• Claim Name: psa-security-lifecycle
• Claim Description: PSA Security Lifecycle
• JWT Claim Name: N/A
• Claim Key: 2395
• Claim Value Type(s): unsigned integer
• Change Controller: Hannes Tschofenig
• Specification Document(s): of RFCthis

 Implementation ID Claim

• Claim Name: psa-implementation-id
• Claim Description: PSA Implementation ID
• JWT Claim Name: N/A
• Claim Key: 2396
• Claim Value Type(s): byte string
• Change Controller: Hannes Tschofenig
• Specification Document(s): of RFCthis

 Boot Seed Claim

• Claim Name: psa-boot-seed
• Claim Description: PSA Boot Seed
• JWT Claim Name: N/A
• Claim Key: 2397
• Claim Value Type(s): byte string
• Change Controller: Hannes Tschofenig
• Specification Document(s): of RFCthis

 Certification Reference Claim

• Claim Name: psa-certification-reference
• Claim Description: PSA Certification Reference
• JWT Claim Name: N/A
• Claim Key: 2398
• Claim Value Type(s): text string
• Change Controller: Hannes Tschofenig
• Specification Document(s): of RFCthis

 Software Components Claim

• Claim Name: psa-software-components
• Claim Description: PSA Software Components
• JWT Claim Name: N/A
• Claim Key: 2399
• Claim Value Type(s): array
• Change Controller: Hannes Tschofenig
• Specification Document(s): of RFCthis

 Verification Service Indicator Claim

• Claim Name: psa-verification-service-indicator
• Claim Description: PSA Verification Service Indicator
• JWT Claim Name: N/A
• Claim Key: 2400
• Claim Value Type(s): text string
• Change Controller: Hannes Tschofenig
• Specification Document(s): of RFCthis

Media Type Registration To indicate that the transmitted content is a PSA Attestation Token, applications can use the application/eat-cwt media type defined in with the eat_profile parameter set to http://arm.com/psa/2.0.0 (or PSA_IOT_PROFILE_1 if the token is encoded according to the old profile, see ).

CoAP Content-Formats Registration IANA is requested to register two CoAP Content-Format IDs in the "CoAP Content-Formats" registry :

• One for the application/eat-cwt media type with the eat_profile parameter equal to http://arm.com/psa/2.0.0
• Another for the application/eat-cwt media type with the eat_profile parameter equal to PSA_IOT_PROFILE_1

Registry Contents

• Media Type: application/eat-cwt; eat_profile="http://arm.com/psa/2.0.0"
• Encoding: -
• Id: [[To-be-assigned by IANA]]
• Reference: RFCthis
• Media Type: application/eat-cwt; eat_profile="PSA_IOT_PROFILE_1"
• Encoding: -
• Id: [[To-be-assigned by IANA]]
• Reference: RFCthis

References Normative References Arm GS1 Arm PSA Certified Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services 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. This document, along with RFC 9053, obsoletes RFC 8152. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines a set of algorithms that can be used with the CBOR Object Signing and Encryption (COSE) protocol (RFC 9052). This document, along with RFC 9052, obsoletes RFC 8152. IANA 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. 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. 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. Security Theory LLC Qualcomm Technologies Inc. Qualcomm Technologies Inc. Red Hound Software, Inc. An Entity Attestation Token (EAT) provides an attested claims set that describes state and characteristics of an entity, a device like a smartphone, 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. 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. 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. Security Theory LLC Fraunhofer Institute for Secure Information Technology arm Payloads used in Remote Attestation Procedures may require an associated media type for their conveyance, for example when used in RESTful APIs. This memo defines media types to be used for Entity Attestation Tokens (EAT). Informative References 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. It provides a model that is neutral toward processor architectures, the content of Claims, and protocols. IANA IANA Linaro The Veraison Project Arm PSA Certified Arm Arm Ltd Arm Ltd Fraunhofer SIT PSA Endorsements include reference values, cryptographic key material and certification status information that a Verifier needs in order to appraise attestation Evidence produced by a PSA device. This memo defines such PSA Endorsements as a profile of the CoRIM data model. Fraunhofer SIT arm arm Intel Huawei Technologies Remote Attestation Procedures (RATS) enable Relying Parties to assess the trustworthiness of a remote Attester and therefore to decide whether to engage in secure interactions with it. Evidence about trustworthiness can be rather complex and it is deemed unrealistic that every Relying Party is capable of the appraisal of Evidence. Therefore that burden is typically offloaded to a Verifier. In order to conduct Evidence appraisal, a Verifier requires not only fresh Evidence from an Attester, but also trusted Endorsements and Reference Values from Endorsers and Reference Value Providers, such as manufacturers, distributors, or device owners. This document specifies Concise Reference Integrity Manifests (CoRIM) that represent Endorsements and Reference Values in CBOR format. Composite devices or systems are represented by a collection of Concise Module Identifiers (CoMID) and Concise Software Identifiers (CoSWID) bundled in a CoRIM document. Cisco Systems Fraunhofer SIT MIT Arm Limited Intel This document defines reusable Attestation Result information elements. When these elements are offered to Relying Parties as Evidence, different aspects of Attester trustworthiness can be evaluated. Additionally, where the Relying Party is interfacing with a heterogeneous mix of Attesting Environment and Verifier types, consistent policies can be applied to subsequent information exchange between each Attester and the Relying Party.

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: The JWK representation of the IAK used for creating the COSE Sign1 signature over the PSA token is: The resulting COSE object is:

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

Contributors Security Theory LLC

lgl@securitytheory.com

Arm Limited

Tamas.Ban@arm.com

Arm Limited

Sergei.Trofimov@arm.com