RFC 9783

Arm's Platform Security Architecture (PSA) Attestation Token

📅 published June 2025, from ietf

RFC 9783: Arm's Platform Security Architecture (PSA) Attestation Token ✨

okay bestie, this one is an Informational doc from June 2025 (ISSN 2070-1721) 🌸. It's an Independent Submission, so it's not an IETF standard. The authors are H. Tschofenig (H-BRS), S. Frost and M. Brossard (Arm Limited), A. Shaw (HP Labs), and T. Fossati (Linaro) 🫶. The title block doesn't list anything it obsoletes or updates, so it's a fresh spec, no drama 💅.

Abstract 🦋

okay so Arm's Platform Security Architecture (PSA) is a whole family of hardware and firmware security specs, plus open-source reference implementations 🔥. The goal is helping device makers and chip manufacturers bake best-practice security into their products ✨. Devices that comply with PSA can generate attestation tokens described in this doc, and those tokens are the foundation for stuff like secure provisioning and network access control 🧚. This document spells out the structure and semantics of the PSA attestation token.

The PSA attestation token is a profile of the Entity Attestation Token (EAT) 💜. This spec covers the claims in a token made by PSA-compliant systems, how those claims get serialized for transmission, and how they're cryptographically protected 🔐.

This Informational doc is published as an Independent Submission to improve interoperability with Arm's architecture 🎀. It is not a standard nor a product of the IETF 🙈.

Status of This Memo 📜

This document is not an Internet Standards Track specification. It's published for informational purposes 🌈.

This is a contribution to the RFC Series, independent of any other RFC stream. The RFC Editor chose to publish it at their discretion, and they make no statement about its value for implementation or deployment 💀. Documents approved for publication by the RFC Editor aren't candidates for any level of Internet Standard, see Section 2 of RFC 7841 ✨.

Info about the current status of this document, any errata, and how to give feedback is at https://www.rfc-editor.org/info/rfc9783 🍓.

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/license-info) in effect on the date of publication. Please review those documents carefully, because they describe your rights and restrictions with respect to this document 📖.

Table of Contents 🗂️

   1.  Introduction
   2.  Conventions and Definitions
   3.  PSA Attester Model
   4.  PSA Claims
     4.1.  Caller Claims
       4.1.1.  Nonce
       4.1.2.  Client ID
     4.2.  Target Identification Claims
       4.2.1.  Instance ID
       4.2.2.  Implementation ID
       4.2.3.  Certification Reference
     4.3.  Target State Claims
       4.3.1.  Security Lifecycle
       4.3.2.  Boot Seed
     4.4.  Software Inventory Claims
       4.4.1.  Software Components
     4.5.  Verification Claims
       4.5.1.  Verification Service Indicator
       4.5.2.  Profile Definition
     4.6.  Backwards Compatibility Considerations
   5.  Profiles
     5.1.  Baseline Profile
       5.1.1.  Token Encoding and Signing
       5.1.2.  Freshness Model
       5.1.3.  Synopsis
     5.2.  Profile TFM
   6.  Collated CDDL
   7.  Scalability Considerations
   8.  PSA Token Verification
     8.1.  AR4SI Trustworthiness Claims Mappings
     8.2.  Endorsements, Reference Values, and Verification Key
           Material
   9.  Security and Privacy Considerations
   10. IANA Considerations
     10.1.  CBOR Web Token Claims Registration
       10.1.1.  Client ID Claim
       10.1.2.  Security Lifecycle Claim
       10.1.3.  Implementation ID Claim
       10.1.4.  Certification Reference Claim
       10.1.5.  Software Components Claim
       10.1.6.  Verification Service Indicator Claim
     10.2.  Media Types
     10.3.  CoAP Content-Formats Registration
       10.3.1.  Registry Contents
   11. References
     11.1.  Normative References
     11.2.  Informative References
   Appendix A.  Examples
     A.1.  COSE Sign1 Token
     A.2.  COSE Mac0 Token
   Acknowledgments
   Contributors
   Authors' Addresses

1. Introduction ✨

okay so the Platform Security Architecture (PSA) [PSA] is a set of hardware and firmware specifications, backed by reference implementations and a security certification program [PSACertified] 💅. Arm published the security specs, but the certification program and reference implementations came out of a collaborative effort by companies from multiple sectors, including evaluation laboratories, IP semiconductor vendors, and security consultancies 🫶. The main goal of PSA is helping device manufacturers and chip makers build best-practice security measures into their products 🎀.

Many devices now have Trusted Execution Environments (TEEs) 🔥. They're basically a safe space for security-sensitive code, like cryptography, secure boot, secure storage, and other essential security functions 🔐. These functions are usually exposed through a narrow and well-defined interface, and operating system libraries and applications can use them 🧚.

As outlined in the Remote ATtestation procedureS (RATS) Architecture [RFC9334], an Attester produces a signed collection of Claims that makes up Evidence about its Target Environment 🦋. This doc focuses on the output from PSA's Initial Attestation API [PSA-API]. That output corresponds to Evidence in [RFC9334], and as a design decision, the PSA attestation token is a profile of the Entity Attestation Token (EAT) [EAT] 💜. Note that there are other EAT profiles for different use cases and different attestation technologies, such as [RATS-TDX] and [RATS-QWESTOKEN] 🌈.

Here's the thing: PSA tokens get consumed by services outside the device too, so interoperability is a real need 🙈. This doc handles that by describing the exact syntax and semantics of the attestation claims, and defining how those claims are encoded and cryptographically protected 💖.

For more on the concepts below, check the PSA Security Model documentation [PSA-SM] 📖.

As mentioned in the abstract, this memo documents a vendor extension to the RATS architecture, and it is not a standard 🌸.

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 🔥. Lowercase versions don't count, so no stress 💅.

The terms Attester, Relying Party, Verifier, Attestation Result, Target Environment, Attesting Environment, and Evidence are defined in [RFC9334] ✨. We use the term "receiver" to refer to Relying Parties and Verifiers 🫶.

We use the terms Evidence, "PSA attestation token", and "PSA token" interchangeably 🦋. The terms "sender" and Attester are used interchangeably too. Likewise, Verifier and "verification service" are interchangeable 🧚.

Root of Trust (RoT): The minimal set of software, hardware, and data that has to be implicitly trusted in the platform. There's no software or hardware at a deeper level that can verify that the RoT 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 🔐.

Secure Processing Environment (SPE): A platform's processing environment for software that provides confidentiality and integrity for its runtime state, from software and hardware outside of the SPE 👑. It contains trusted code and trusted hardware. (Equivalent to a TEE, "secure world", or "secure enclave".) 🌸

Non-Secure Processing Environment (NSPE): The security domain (Application domain) outside of the SPE. It typically contains the application firmware, real-time operating systems, applications, and general hardware 🍓. (Equivalent to Rich Execution Environment (REE), or "normal world".) 💜

In this document, the structure of data is specified in Concise Data Definition Language (CDDL) [RFC8610] 🎀.

Part 1 of 8 done, bestie 💖 more parts are coming, so stay tuned ✨

3. PSA Attester Model ✨

Okay bestie, the PSA Attester is the star of the show 🎀 Figure 1 shows how it's built, following the conceptual model from Section 3.1 of [RFC9334].

                                                       .----------.
                                                       | Verifier |
                                                       '----------'
                                                            ^
                                                            |
                                                  PSA Token |
                                                            |
   .--------------------------------------------------------|----------.
   | .------------------------------------------------------|--------. |
   | | Attesting Environment                                |        | |
   | |                .------------.     .-----.     .------+------. | |
   | |                | Main       |    | Main  |    | Initial     | | |
   | |                | Bootloader +--->| Boot  |<---+ Attestation | | |
   | |                |            | W  | State |  R | Service     | | |
   | |                '-----+------'     '-----'     '-------------' | |
   | '----------------------|----------------------------------------' |
   |           .------------+--------------+---------------.           |
   | .--------|-------------|--------------|----------------|--------. |
   | |        |             |              |                |        | |
   | | .------o-----. .-----o-------. .----o--------. .-----o------. | |
   | | | Updateable | | Application | | Application | | PSA RoT    | | |
   | | | PSA RoT    | | RoT         | | Loader      | | Parameters | | |
   | | '------------' '-------------' '-------------' '------------' | |
   | | Target Environment                                            | |
   | '---------------------------------------------------------------' |
   '-------------------------------------------------------------------'
   Legend:
                ---> read    ---> write    ---o measure
                 R            W

Figure 1: PSA Attester

The PSA Attester is a relatively straightforward embodiment of the RATS Attester 🦋, with exactly one Attesting Environment and one or more Target Environments.

The Attesting Environment is the part that gathers up the info that goes into PSA claims and assembles it all into Evidence 💅. It's made of two cooperating components:

  • Executing at boot-time, the Main Bootloader measures the Target Environments (i.e., loaded software components and all the relevant PSA RoT parameters) and stores the recorded information in secure memory (Main Boot State). See Figure 2.
      i-th Target    Main Boot     Main Boot
        Environment      Loader        State
             |             |             |
    .--------|-------------|-------------|----.
    | loop i |             |             |    |
    |        | measure     |             |    |
    |        |o------------+             |    |
    |        |             | write       |    |
    |        |             | measurement |    |
    |        |             +------------>|    |
    '--------|-------------|-------------|----'
             |             |             |

Figure 2: PSA Attester Boot Phase

  • The Initial Attestation Service (executing at run-time in SPE) answers requests coming from NSPE via the PSA attestation API [PSA-API] 🔥, collects and formats the claims from Main Boot State, and uses the Initial Attestation Key (IAK) to sign them and produce Evidence. See Figure 3.

The word "Initial" in "Initial Attestation Service" refers to a limited set of Target Environments, namely those representing the first foundational stages establishing the chain of trust of a PSA device 🧚. Collecting measurements from Target Environments after this initial phase is outside the scope of this specification. Extensions of this specification could collect up-to-date measurements from additional Target Environments and define additional claims for use within those environments, but these are, by definition, custom.

                        Initial
      Main Boot       Attestation
        State           Service     Verifier
          |                |           |
 .--------|----------------|-----------|----.
 | loop i | read           |           |    |
 |        | measurement of |           |    |
 |        | i-th Target    |           |    |
 |        | Environment    |           |    |
 |        |<---------------+           |    |
 '--------|----------------|-----------|----'
          |            .---+           |
          |       sign |   |           |
          |            '-->|           |
          |                | PSA Token |
          |                +---------->|
          |                |           |

Figure 3: PSA Attester Run-Time Phase

The Target Environments can be of four types 🌈, 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 [TF-M] ✨.

4. PSA Claims

This section is where the claims live 💖. It describes the claims to be used in a PSA attestation token. A more comprehensive treatment of the EAT profiles defined by PSA is found in Section 5.

CDDL [RFC8610] along with text descriptions is used to define each claim independent of encoding. The following CDDL types are reused by different claims:

psa-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64

Two conventions are used to encode the Right-Hand-Side (RHS) of a claim. The postfix -label is used for EAT-defined claims and the postfix -key is used for PSA-originated claims 🍓.

4.1. Caller Claims

4.1.1. Nonce

The EAT [EAT] "nonce" (claim key 10) is used to carry the challenge provided by the caller to demonstrate freshness of the generated token.

Since the EAT nonce claim offers flexibility for different attestation technologies, this specification applies the following constraints to the nonce-type:

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

This claim MUST be present in a PSA attestation token.

psa-nonce = (
    nonce-label => psa-hash-type
)

4.1.2. 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 [PSA-FF].

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
)

4.2. Target Identification Claims

4.2.1. Instance ID

The Instance ID claim represents the unique identifier of the IAK 🦋. The full definition is in [PSA-SM].

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-byte unique identifier of the IAK. [PSA-API] provides implementation options for deriving the IAK unique identifier from the IAK itself.

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
)

4.2.2. Implementation ID

The Implementation ID claim uniquely identifies the hardware assembly 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 Section 4.2.1.

psa-implementation-id-type = bytes .size 32

psa-implementation-id = (
    psa-implementation-id-key => psa-implementation-id-type
)

4.2.3. 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 🎀. The Certification Reference claim MUST be represented as a string made of nineteen numeric characters: a thirteen-digit EAN-13 [EAN-13] followed by a dash "-" and the five-digit versioning information described in [PSA-Cert-Guide].

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.

This claim MAY be present in a PSA attestation token.

psa-certification-reference-type = text .regexp "[0-9]{13}-[0-9]{5}"

psa-certification-reference = (
    ? psa-certification-reference-key =>
        psa-certification-reference-type
)

4.3. Target State Claims ✨

4.3.1. Security Lifecycle 🦋

okay so the Security Lifecycle claim tells you what stage the PSA RoT is in right now 🔄✨ the state is one integer that's split into two parts: a major state and a minor state 💅 the major state is mandatory and defined by [PSA-SM], and the minor state is optional and totally 'IMPLEMENTATION DEFINED' 🛠️ so here's the bit split:

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

the lifecycle states are shown in Figure 4 🌸 and here's the key tea: a Verifier can only trust reports from the PSA RoT when it's in the SECURED or NON_PSA_ROT_DEBUG major states 🔐 no cap, that's the whole game

this claim MUST be present in a PSA attestation token 💖

             .-------------------------.
            | Device Assembly and Test |
            '------------+------------'
                         | Device
                         | Lockdown
                         v
              .----------------------.
             | PSA RoT Provisioning  |
             '-----------+----------'
                         |
            Provisioning |   .------------------.
              Lockdown   |  |                    |
                         v  v                    |
                 .----------------.              |
   .-------------+    Secured     +-------.      |
  |              '-+--------------'        |     |
  |                |            ^        Debug   |
  |              Debug          |          |     |
  |                |        Recoverable    |  Recoverable
  |                v            |          v     |
  |            .----------------+--.  .----------+----.
  |            | (Non-Recoverable) |  | Recoverable   |
  |            | Non-PSA RoT Debug |  | PSA RoT Debug |
  |            '---------+---------'  '------+--------'
  |                      |                   |
Terminate         Non-Recoverable      PSA RoT Compromised
  |                      |                   |
  |                      v                   |
  |              .----------------.          |
   '------------>| Decommissioned |<--------'
                 '----------------'

                    Figure 4: PSA Lifecycle States

the CDDL is shown below 📜 and Table 1 maps Figure 4 onto the data model for you 🗺️

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-lifecycle-unknown-type doesn't show up in Figure 4 🙈 it stands for an invalid state that must not occur in a system, so it's the villain of this story 💀

+==============================================+===================+
| CDDL                                         | Lifecycle States  |
+==============================================+===================+
| psa-lifecycle-unknown-type                   |                   |
+----------------------------------------------+-------------------+
| psa-lifecycle-assembly-and-test-type         | Assembly and Test |
+----------------------------------------------+-------------------+
| psa-lifecycle-psa-rot-provisioning-type      | PSA RoT           |
|                                              | Provisioning      |
+----------------------------------------------+-------------------+
| psa-lifecycle-secured-type                   | Secured           |
+----------------------------------------------+-------------------+
| psa-lifecycle-non-psa-rot-debug-type         | Non-Recoverable   |
|                                              | PSA RoT Debug     |
+----------------------------------------------+-------------------+
| psa-lifecycle-recoverable-psa-rot-debug-type | Recoverable PSA   |
|                                              | RoT Debug         |
+----------------------------------------------+-------------------+
| psa-lifecycle-decommissioned-type            | Decommissioned    |
+----------------------------------------------+-------------------+

Table 1: Lifecycle States Mappings

4.3.2. Boot Seed 🌱

the "bootseed" claim holds a value that gets created at system boot time 🥾 it lets you tell apart attestation reports from different boot sessions of one particular entity (aka a certain Instance ID) 🧚

the EAT "bootseed" (claim key 268) is what gets used here 🔑 and the binary-data type comes with a constraint:

  • The length MUST be between 8 and 32 bytes.

this claim MAY be present in a PSA attestation token 🍓

psa-boot-seed-type = bytes .size (8..32)

psa-boot-seed = (
    boot-seed-label => psa-boot-seed-type
)

4.4. Software Inventory Claims 📦

4.4.1. Software Components 🧩

the Software Components claim is a list of software components 💜 it covers all the software (both code and configuration) that the PSA RoT loads 🫶 this claim MUST be included in attestation tokens produced by an implementation conformant with [PSA-SM]

each entry in the Software Components list describes one software component, using the attributes in the subsections below 📝 unless it's explicitly stated otherwise, the presence of an attribute is OPTIONAL 🌈

okay, important ngl: a Relying Party will usually see the result of the appraisal from the Verifier as an Attestation Result, not the PSA token from the attesting endpoint described in [RFC9334] 👀 so a Relying Party is not expected to understand the Software Components claim 🙅‍♀️ instead, it's the Verifier's job to check this claim against the available Reference Values and give back a "high-level" Attestation Result, which may or may not include the original Software Components claim ✨

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 ]
)

4.4.1.1. Measurement Type 🏷️

the Measurement Type attribute (key=1) is a short string that says what role this software component plays 🎭

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 ⚙️

this attribute SHOULD be present in a PSA software component unless there is a very good reason to leave it out ✨ like, for example, in networks with severely constrained bandwidth where sparing a few bytes really makes a difference 🦋

4.4.1.2. 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 🫶

4.4.1.3. Version 🔢

the Version attribute (key=4) is the issued software version, written as a text string 📄 the value of this attribute corresponds to the entry in the original signed manifest of the component 🗂️

4.4.1.4. Signer ID 🖋️

the Signer ID attribute (key=5) uniquely identifies the signer of the software component 🪪 this is typically done by hashing the signer's public key 🔑 the value of this attribute corresponds to the entry in the original manifest for the component 📜 a Verifier can use this to make sure the components were signed by an expected trusted source 🛡️

this attribute MUST be present in a PSA software component to be compliant with [PSA-SM] 💖

4.4.1.5. Measurement Description 📚

the Measurement Description attribute (key=6) is a string that names the hash algorithm used to compute the corresponding Measurement Value 🧮 the string SHOULD be encoded according to "Hash Name String" in the "Named Information Hash Algorithm Registry" [NAMED-INFO] 🌸

4.5. Verification Claims 🕵️‍♀️

okay so these claims are part of Evidence, but they don't reflect the Attester's internal state 🙈 instead, they're there to help receivers, Relying Parties included, process the attestation Evidence they got 🫶

4.5.1. Verification Service Indicator 🔍

the Verification Service Indicator claim is a hint a Relying Party uses to find a verification service for the token 🗺️ the value is a text string that can be used to locate the service (usually a URL with 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 = text

psa-verification-service-indicator = (
    ? psa-verification-service-indicator-key =>
        psa-verification-service-indicator-type
)

it's assumed that the Relying Party is pre-configured with a list of trusted verification services, and that the contents of this hint can be used to look up the correct one 📋 under no circumstances must the Relying Party be tricked into contacting an unknown and untrusted verification service, because the returned Attestation Result cannot be relied on 🚨 this is serious, bestie 😭

Note: This hint requires the Relying Party to parse the content of the PSA token 👀 since the Relying Party may not have a trust anchor to verify the digital signature, it uses the hint the same way it would treat any other information from an external party, which includes attacker-provided data 💀

4.5.2. Profile Definition 🎀

the Profile Definition claim holds the unique identifier for the EAT profile described by this document 🪄 that lets a receiver assign the intended meaning to the rest of the claims in the token 🧚

the EAT eat_profile (claim key 265) is used 🔑

the URI encoding MUST be used 🔗

the value MUST be tag:psacertified.org,2023:psa#tfm for the profile defined in Section 5.2 👑

future profiles derived from the baseline PSA profile SHALL create their unique value as described in Section 4.5.2.1 🌈

this claim MUST be present in a PSA attestation token 💖

for backwards compatibility considerations with previous versions of the PSA attestation token format, see Section 4.6 ✨

psa-profile-type = "tag:psacertified.org,2023:psa#tfm"

psa-profile = (
    profile-label => psa-profile-type
)

4.5.2.1. URI Structure for the Derived Profile Identifiers ✨

okay so every new profile gets its own unique string, bestie 🎀 that's its ID card.

That string MUST use the URI fragment syntax from Section 3.5 of [RFC3986], no exceptions 💅

Keep it short too! The string SHOULD be short so it doesn't add unnecessary overhead 🦋

To avoid name collisions, profile authors SHOULD tell everyone their plan upfront, using the inquiry form on the website [PSACertified]. Nobody wants two profiles fighting over the same string 😭

To work out the value for the eat_profile claim, you just stick the string on the end of the tag:psacertified.org,2023:psa tag URI [RFC4151] as a fragment 🧚

Example time 🌸 Say a hypothetical profile only uses COSE_Mac0 with the AES Message Authentication Code (AES-MAC). It might pick the string aes-mac, and then its eat_profile value would be:

tag:psacertified.org,2023:psa#aes-mac

4.6. Backwards Compatibility Considerations

Okay, real talk about the old stuff 🙈 An earlier draft of this document [PSA-OLD] was identified by the PSA_IOT_PROFILE_1 profile, and it used claim keys from the "private use range" of the CWT Claims registry. Those claim keys are now deprecated, so we're moving on 🫶

Table 2 shows how each deprecated key maps to its new replacement:

+==============+=================+=================================+
|              |PSA_IOT_PROFILE_1|tag:psacertified.org,2023:psa#tfm|
+==============+=================+=================================+
|Nonce         |-75008           |10 (EAT nonce)                   |
+--------------+-----------------+---------------------------------+
|Instance ID   |-75009           |256 (EAT euid)                   |
+--------------+-----------------+---------------------------------+
|Profile       |-75000           |265 (EAT eat_profile)            |
|Definition    |                 |                                 |
+--------------+-----------------+---------------------------------+
|Client ID     |-75001           |2394                             |
+--------------+-----------------+---------------------------------+
|Security      |-75002           |2395                             |
|Lifecycle     |                 |                                 |
+--------------+-----------------+---------------------------------+
|Implementation|-75003           |2396                             |
|ID            |                 |                                 |
+--------------+-----------------+---------------------------------+
|Boot Seed     |-75004           |268 (EAT bootseed)               |
+--------------+-----------------+---------------------------------+
|Certification |-75005           |2398                             |
|Reference     |                 |                                 |
+--------------+-----------------+---------------------------------+
|Software      |-75006           |2399                             |
|Components    |                 |                                 |
+--------------+-----------------+---------------------------------+
|Verification  |-75010           |2400                             |
|Service       |                 |                                 |
|Indicator     |                 |                                 |
+--------------+-----------------+---------------------------------+

                       Table 2: Claim Key Mappings

The new profile brings three more changes 👑

  • The "bootseed" claim is now optional and of variable length (see Section 4.3.2).
  • The "No Software Measurements" claim has been retired. Bye bye 👋
  • The "Certification Reference" claim syntax changed from EAN-13 to EAN-13+5 (see Section 4.2.3).

To make the move to the token format in this document smoother, it is RECOMMENDED that Verifiers accept tokens encoded under the old profile (PSA_IOT_PROFILE_1) as well as under the profile defined here (tag:psacertified.org,2023:psa#tfm). Keep that support going at least until devices have had time to upgrade 🌈

5. Profiles 👑

This document sets up a baseline with common requirements that all PSA profiles must satisfy. (Quick note: this doesn't apply to [PSA-OLD].) 💅

It also defines a "TFM" profile (Section 5.2). That one builds on the baseline and constrains how COSE algorithms are used, so Attesters and Verifiers play nicely together 🫶

Baseline and TFM are what the EAT calls a "partial" and "full" profile, respectively. Check out Section 6.2 of [EAT] for more on profiles 🦋

5.1. Baseline Profile

5.1.1. Token Encoding and Signing

The PSA attestation token is encoded in CBOR [STD94] format. The CBOR representation of a PSA token MUST be "valid" according to the definition in Section 1.2 of RFC 8949 [STD94]. Besides, only definite-length strings, arrays, and maps are allowed. A PSA Attester usually lives in a constrained device, so it MAY NOT emit CBOR preferred serializations (Section 4.1 of RFC 8949 [STD94]). That means the Verifier MUST be a variation-tolerant CBOR decoder 🧠✨

Cryptographic protection comes from wrapping the psa-token claims set in a COSE Web Token (CWT) [RFC8392]. For asymmetric key algorithms, the signature structure MUST be a tagged (18) COSE_Sign1. For symmetric key algorithms, the signature structure MUST be a tagged (17) COSE_Mac0 🔥

There are so many markets, regulations, and use cases for the PSA attestation token, so the baseline profile doesn't force any strong requirement on which cryptographic algorithms Attesters and Verifiers have to support. The flexibility of the COSE format should be enough to handle the cryptographic agility each use case needs 💜 It is RECOMMENDED that commonly adopted algorithms are used, like the ones discussed in [COSE-ALGS]. It's expected that receivers 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. If an application needs to exchange PSA attestation tokens, it can wrap the serialized COSE_Sign1 or COSE_Mac0 in the media type defined in Section 10.2, or in the CoAP Content-Format defined in Section 10.3 📦

A PSA token is always signed directly by the PSA RoT. So a PSA-token claims set (Section 4) is never carried in a Detached EAT bundle (Section 5 of [EAT]). No detours, periodt 💅

5.1.2. Freshness Model

The PSA token supports the freshness models for attestation Evidence that are based on nonces and epoch handles (Section 10.2 and Section 10.3 of [RFC9334]). It does this with the "nonce" claim, which carries the nonce or epoch handle the Verifier supplied. No further assumptions are made about the specific remote attestation protocol, so you're free to pick your own 🦋

Heads up though: using epoch handles is limited by the type restrictions in the eat_nonce syntax. For PSA tokens, the epoch handle has to be encodable as an opaque binary string between 8 and 64 octets 👀

5.1.3. Synopsis

Table 3 is the cheat sheet 📝 It's a quick, concise view of everything we just went over in the sections above, so bookmark it bestie 🍓

 +==================+=============================================+
 | Issue            | Profile Definition                          |
 +==================+=============================================+
 | CBOR/JSON        | CBOR MUST be used.                          |
 +------------------+---------------------------------------------+
 | CBOR Encoding    | Definite length maps and arrays MUST be     |
 |                  | used.                                       |
 +------------------+---------------------------------------------+
 | CBOR Encoding    | Definite length strings MUST be used.       |
 +------------------+---------------------------------------------+
 | CBOR             | Variant serialization MAY be used.          |
 | Serialization    |                                             |
 +------------------+---------------------------------------------+
 | COSE Protection  | COSE_Sign1 and/or COSE_Mac0 MUST be used.   |
 +------------------+---------------------------------------------+
 | Algorithms       | [COSE-ALGS] SHOULD be used.                 |
 +------------------+---------------------------------------------+
 | Detached EAT     | Detached EAT bundles MUST NOT be sent.      |
 | Bundle Usage     |                                             |
 +------------------+---------------------------------------------+
 | Verification Key | Any identification method listed in         |
 | Identification   | Appendix F.1 of [EAT].                      |
 +------------------+---------------------------------------------+
 | Endorsements     | See Section 8.2.                            |
 +------------------+---------------------------------------------+
 | Freshness        | Nonce or epoch ID-based.                    |
 +------------------+---------------------------------------------+
 | Claims           | Those defined in Section 4.  As per general |
 |                  | EAT rules, the receiver MUST NOT error out  |
 |                  | on claims it does not understand.           |
 +------------------+---------------------------------------------+

                    Table 3: Baseline Profile

5.2. Profile TFM 🎀

okay so the TFM profile is the one for the code base in [TF-M], and it should apply for most derivative implementations 💅 if your implementation changes the requirements below, you should use a different profile value (Section 4.5.2.1) so everyone stays interoperable 🫶 that includes restricting the profile to a subset of the COSE Protection scheme requirements ✨

Table 4 is the quick-glance version of everything 👀

The value of the eat_profile MUST be tag:psacertified.org,2023:psa#tfm 🌸

  +================+==============================================+
  | Issue          | Profile Definition                           |
  +================+==============================================+
  | CBOR/JSON      | See Section 5.1.                             |
  +----------------+----------------------------------------------+
  | CBOR Encoding  | See Section 5.1.                             |
  +----------------+----------------------------------------------+
  | CBOR Encoding  | See Section 5.1.                             |
  +----------------+----------------------------------------------+
  | CBOR           | See Section 5.1.                             |
  | Serialization  |                                              |
  +----------------+----------------------------------------------+
  | COSE           | COSE_Sign1 or COSE_Mac0 MUST be used.        |
  | Protection     |                                              |
  +----------------+----------------------------------------------+
  | Algorithms     | The receiver MUST accept ES256, ES384, and   |
  |                | ES512 with COSE_Sign1 and HMAC256/256,       |
  |                | HMAC384/384, and HMAC512/512 with COSE_Mac0; |
  |                | the sender MUST send one of these.           |
  +----------------+----------------------------------------------+
  | Detached EAT   | See Section 5.1.                             |
  | Bundle Usage   |                                              |
  +----------------+----------------------------------------------+
  | Verification   | Claim-Based Key Identification               |
  | Key            | (Appendix F.1.4 of [EAT]) using Instance ID. |
  | Identification |                                              |
  +----------------+----------------------------------------------+
  | Endorsements   | See Section 8.2.                             |
  +----------------+----------------------------------------------+
  | Freshness      | See Section 5.1.                             |
  +----------------+----------------------------------------------+
  | Claims         | See Section 5.1.                             |
  +----------------+----------------------------------------------+

                       Table 4: TF-M Profile

6. Collated CDDL 🧚

okay this bit is the big CDDL roundup, all the pieces in one place so you don't have to hunt for them 🔍 copy it exactly, no vibes-based edits 😭

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-certification-reference-key = 2398
psa-software-components-key = 2399
psa-verification-service-indicator-key = 2400

nonce-label = 10
ueid-label = 256
boot-seed-label = 268
profile-label = 265

psa-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64

psa-boot-seed-type = bytes .size (8..32)

psa-boot-seed = (
    boot-seed-label => 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 = "tag:psacertified.org,2023:psa#tfm"

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
)

7. Scalability Considerations 🦋

so IAKs (see Section 3) can be raw public keys or certified public keys 🔑

certified public keys mean the manufacturer has to run the certification authority (CA) that issues X.509 certificates for the IAKs 🏛️ (fair warning: running a CA is complex and expensive, and it may be unaffordable for some manufacturers 💀)

using certified public keys is more scalable than raw public keys, and here's why 👑

  • storage for the Verifier stays minimal, because the same manufacturer's trust anchor covers any number of devices 📦
  • the provisioning model is simpler and more robust, since nobody has to tell the Verifier about each newly manufactured device 🙌

and on top of that, existing, well-understood revocation mechanisms can be readily used 🔒

the IAK's X.509 certificates can be inlined in the PSA token with the x5chain COSE header parameter [COSE-X509], but the token gets bigger as a result 📏 [TLS12-IoT] (Section 4.4) and [TLS13-IoT] (Section 15) give guidance on profiling X.509 certificates for IoT deployments 📚 the exact split between pre-provisioned and inlined certificates may vary depending on the deployment, and x5chain is super flexible about it 🧩 it can hold the end entity (EE) certification only, the EE and a partial chain, or the EE and the full chain up to the trust anchor (see Section 2 of [COSE-X509] for the details) 🔗 network bandwidth and the computing resources available to endpoints (like network buffers) may dictate a reasonable split point ⚖️

8. PSA Token Verification 🔍

okay the main thing for verifying the token is checking correct encoding and signing, as detailed in Section 5.1.1 ✅ the key used for verification is either supplied to the Verifier by an authorized Endorser along with the corresponding Attester's Instance ID, or inlined in the token with the x5chain header parameter as described in Section 7 🗝️ if the IAK is a raw public key, the Instance ID claim is used to assist in locating the key used to verify the signature covering the CWT token 🧭 if the IAK is a certified public key, X.509 path construction and validation (Section 6 of [X509]) up to a trusted CA MUST be successful before the key is used to verify the token signature 🛡️ this also includes revocation checking 🚨

the Verifier typically has a policy that compares some claims in this profile to reference values registered with it for a given deployment 📋 this verification process helps confirm that the device is endorsed by the manufacturer supply chain 🏭 the policy may require that the relevant claims have a match to a registered reference value, and all claims may be worthy of additional appraisal 💜 most deployments would likely include a policy with appraisal for these 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 🔐 sometimes a Verifier keeps a record for a series of firmware releases that are patches to an original baseline release, so a verification policy may let this value 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 let a Verifier run a more general policy than the Measurement Value one, 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 for the attesting device 🏅 for example, it could be a reference to a [PSACertified] certificate 🎓

Okay bestie, picking up right where we left off. Let's get into the AR4SI mapping table, the crypto checks, and all the IANA registrations 💅🦋

8. Verifiers

Hmm, wait. This part actually starts at Section 8.1, so the heading goes like this:

8.1. AR4SI Trustworthiness Claims Mappings ✨

okay so [RATS-AR4SI] defines an information model that Verifiers can employ to produce Attestation Results 🧚 AR4SI gives you a set of standardized appraisal categories and tiers, and honestly it's giving simplicity when you're writing Relying Party policies in Multi-Attester environments 💖

The contents of Table 5 are intended as guidance for implementing a PSA Verifier that computes its results using AR4SI 🌸 The table shows which PSA Evidence claims (if any) relate to which AR4SI trustworthiness claim, so you know what the Verifier has to consider when deciding if and how to appraise a certain feature linked to the PSA Attester 👑

+=====================+===========================================+
| Trustworthiness     | Related PSA claims                        |
| Vector claims       |                                           |
+=====================+===========================================+
| "configuration"     | Software Components (Section 4.4.1)       |
+---------------------+-------------------------------------------+
| "executables"       | ditto                                     |
+---------------------+-------------------------------------------+
| "file-system"       | N/A                                       |
+---------------------+-------------------------------------------+
| "hardware"          | Implementation ID (Section 4.2.2)         |
+---------------------+-------------------------------------------+
| "instance-identity" | Instance ID (Section 4.2.1).  The         |
|                     | Security Lifecycle (Section 4.3.1) can    |
|                     | also impact the derived identity.         |
+---------------------+-------------------------------------------+
| "runtime-opaque"    | Indirectly derived from "executables",    |
|                     | "hardware", and "instance-identity".  The |
|                     | Security Lifecycle (Section 4.3.1) can    |
|                     | also be relevant, e.g., any debug state   |
|                     | will expose otherwise protected memory.   |
+---------------------+-------------------------------------------+
| "sourced-data"      | N/A                                       |
+---------------------+-------------------------------------------+
| "storage-opaque"    | Indirectly derived from "executables",    |
|                     | "hardware", and "instance-identity".      |
+---------------------+-------------------------------------------+

                   Table 5: AR4SI Claims mappings

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 Section 2.3.3 of [RATS-AR4SI] 🍓

8.2. Endorsements, Reference Values, and Verification Key Material 🎀

[PSA-Endorsements] defines a protocol based on the [RATS-CoRIM] data model that can be used to convey PSA Endorsements, Reference Values, and verification key material to the Verifier 💜

9. Security and Privacy Considerations 🔐

Bestie, this part is SERIOUS 😭 This specification reuses the EAT specification and therefore the CWT specification, so 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 [STD96] 🦋 Note, however, that the use of MAC authentication is NOT RECOMMENDED, because of the infrastructure costs for key management and the protocol complexity 🙈

A PSA Attester MUST NOT provide Evidence to an untrusted challenger 🚨 It may allow attackers to interpose and trick the Verifier into believing the attacker is a legitimate Attester. This is especially relevant to protocols that use PSA attestation tokens to authenticate the attester to a Relying Party 😭

Attestation tokens contain information that may be unique to a device 🫶 So they may allow a single device to be singled out for tracking purposes 👀 Deployments with privacy requirements must take appropriate measures to ensure that the token is only used to provision anonymous/pseudonym keys 🌈

10. IANA Considerations 📋

10.1. CBOR Web Token Claims Registration 🧚

IANA has registered the following claims in the "CBOR Web Token (CWT) Claims" registry [CWT] 💖

10.1.1. 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):  Section 4.1.2 of RFC 9783

10.1.2. 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):  Section 4.3.1 of RFC 9783

10.1.3. 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):  Section 4.2.2 of RFC 9783

10.1.4. 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):  Section 4.2.3 of RFC 9783

10.1.5. 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):  Section 4.4.1 of RFC 9783

10.1.6. 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):  Section 4.5.1 of RFC 9783

10.2. Media Types 📱

This document does not register any new media types 🙅‍♀️ To say that the transmitted content is a PSA attestation token, applications can use the application/eat+cwt media type defined in [EAT-MEDIATYPES] with the eat_profile parameter set to tag:psacertified.org,2023:psa#tfm (or tag:psacertified.org,2019:psa#legacy if the token is encoded according to the old profile; see Section 4.6) 🌸

10.3. CoAP Content-Formats Registration 🦋

IANA has registered two CoAP Content-Format IDs in the First Come First Served range of the "CoAP Content-Formats" registry [Content-Formats] 🎀

  • One for the application/eat+cwt media type with the eat_profile parameter equal to tag:psacertified.org,2023:psa#tfm.
  • Another for the application/eat+cwt media type with the eat_profile parameter equal to tag:psacertified.org,2019:psa#legacy.

10.3.1. Registry Contents

Media Type:  application/eat+cwt;
   eat_profile="tag:psacertified.org,2023:psa#tfm"
Encoding:  -
ID:  10003
Reference:  RFC 9783

Media Type:  application/eat+cwt;
   eat_profile="tag:psacertified.org,2019:psa#legacy"
Encoding:  -
ID:  10004
Reference:  RFC 9783

11. References 📚

11.1. Normative References ✨

okay bestie, these are the sources the spec needs you to have read 📚💅 they're the must-reads, no cap

11.2. Informative References 🧠💖

these ones are the extra-credit reading, the "ooh, tell me more" pile 🌸

Appendix A. Examples 🎀

okay the examples are where it all clicks, the vibes are immaculate ✨

these show PSA attestation tokens for a made-up system with just one measured software component 🧚 the attesting device is in a lifecycle state (Section 4.3.1) of SECURED 🔒 and the attestation was requested from a client living in the SPE, so it's giving very secure, very main character 💅

Appendix A.1 covers the case where the IAK is an asymmetric key 🔑 there, a COSE Sign1 envelope wraps up the PSA-token claims set 🎁

Appendix A.2 covers the case where the IAK is a symmetric key 🗝️ so it uses a COSE Mac0 envelope instead 🦋

the claims sets are identical, except for the Instance ID, which is synthesized from the key material 🫶 (that's the only tea spilled between them, iykyk ☕)

the examples were made with the iat-verifier tool [IAT-VERIFIER] 🛠️✨

A.1. COSE Sign1 Token 🎀

Okay bestie, this is the COSE Sign1 token example, and it's giving full PSA attestation energy ✨. Here's the token's claims map 💅:

{
  / ueid /                     256: h'01020202020202020202020202
0202020202020202020202020202020202020202',
  / psa-implementation-id /   2396: h'00000000000000000000000000
00000000000000000000000000000000000000',
  / eat_nonce /                 10: h'01010101010101010101010101
01010101010101010101010101010101010101',
  / psa-client-id /           2394: 2147483647,
  / psa-security-lifecycle /  2395: 12288,
  / eat_profile /           265: "tag:psacertified.org,2023:psa#tfm",
  / bootseed /                 268: h'0000000000000000',
  / psa-software-components / 2399: [
    {
      / signer ID /         5: h'0404040404040404040404040404040
404040404040404040404040404040404',
      / measurement value / 2: h'0303030303030303030303030303030
303030303030303030303030303030303',
      / measurement type /  1: "PRoT"
    }
  ]
}

Next up is the JWK version of the IAK used to make the COSE Sign1 signature over the PSA token 🔑:

{
  "kty": "EC",
  "crv": "P-256",
  "alg": "ES256",
  "x": "Tl4iCZ47zrRbRG0TVf0dw7VFlHtv18HInYhnmMNybo8",
  "y": "gNcLhAslaqw0pi7eEEM2TwRAlfADR0uR4Bggkq-xPy4",
  "d": "Q__-y5X4CFp8QOHT6nkL7063jN131YUDpkwWAPkbM-c"
}

And the resulting COSE object is 🧚:

18([
  h'A10126',
  {},
  h'A81901005821010202020202020202020202020202020202020202020202
02020202020202020219095C5820000000000000000000000000000000000000
00000000000000000000000000000A5820010101010101010101010101010101
010101010101010101010101010101010119095A1A7FFFFFFF19095B19300019
010978217461673A7073616365727469666965642E6F72672C323032333A7073
612374666D19010C48000000000000000019095F81A305582004040404040404
0404040404040404040404040404040404040404040404040402582003030303
0303030303030303030303030303030303030303030303030303030301645052
6F54',
  h'786E937A4C42667AF3847399319CA95C7E7DBABDC9B50FDB8DE3F6BFF4AB
82FF80C42140E2A488000219E3E10663193DA69C75F52B798EA10B2F7041A90E
8E5A'
])

which has this base16 encoding 🦋:
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A.2. COSE Mac0 Token 🌸

Now we switch to a COSE Mac0 token, which is the same vibe but with a different wrapper 🍓. The claims map is basically the same, just with psa-boot-seed written out in full 💜:

{
  / ueid /                     256: h'01C557BD4FADC83F756FCA2CD5
EA2DCC8B82159BB4E7453D6A744D4EECD6D0AC60',
  / psa-implementation-id /   2396: h'00000000000000000000000000
00000000000000000000000000000000000000',
  / eat_nonce /                 10: h'01010101010101010101010101
01010101010101010101010101010101010101',
  / psa-client-id /           2394: 2147483647,
  / psa-security-lifecycle /  2395: 12288,
  / eat_profile /           265: "tag:psacertified.org,2023:psa#tfm",
  / psa-boot-seed /            268: h'0000000000000000',
  / psa-software-components / 2399: [
    {
      / signer ID /         5: h'0404040404040404040404040404040
404040404040404040404040404040404',
      / measurement value / 2: h'0303030303030303030303030303030
303030303030303030303030303030303',
      / measurement type /  1: "PRoT"
    }
  ]
}

The JWK representation of the IAK used to create the COSE Mac0 signature over the PSA token comes next 🔐. Heads up, this one is a symmetric key, so it's oct and not EC. The k value is wrapped with a backslash, per the note below 👀:

========== NOTE: '\\' line wrapping per RFC 8792 ==========

{
  "kty": "oct",
  "alg": "HS256",
  "k": "3gOLNKyhJXaMXjNXq40Gs2e5qw1-i-Ek7cpH_gM6W7epPTB_8imqNv8k\
       \bBKVlk-s9xq3qm7E_WECt7OYMlWtkg"
}

The resulting COSE object is 💖:

17([
  h'A10105',
  {},
  h'A8190100582101C557BD4FADC83F756FCA2CD5EA2DCC8B82159BB4E7453D
6A744D4EECD6D0AC6019095C5820000000000000000000000000000000000000
00000000000000000000000000000A5820010101010101010101010101010101
010101010101010101010101010101010119095A1A7FFFFFFF19095B19300019
010978217461673A7073616365727469666965642E6F72672C323032333A7073
612374666D19010C48000000000000000019095F81A305582004040404040404
0404040404040404040404040404040404040404040404040402582003030303
0303030303030303030303030303030303030303030303030303030301645052
6F54',
  h'CF88D330E7A5366A95CF744A4DBF0D50304D405EDD8B2530E243EDDBD317
7820'
])

which has this base16 encoding 🌈:
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Acknowledgments 🫶

Huge thank you to Carsten Bormann for helping out with the CDDL 💜. Thanks also to Nicholas Wood, Eliot Lear, Yaron Sheffer, Kathleen Moriarty, and Ned Smith for ideas, comments, and suggestions ✨. Y'all are iconic 👑.

Contributors 🌸

Laurence Lundblade Security Theory LLC Email: lgl@securitytheory.com

Tamas Ban Arm Limited Email: Tamas.Ban@arm.com

Sergei Trofimov Arm Limited Email: Sergei.Trofimov@arm.com

Authors' Addresses 💌

Hannes Tschofenig University of Applied Sciences Bonn-Rhein-Sieg Germany Email: Hannes.Tschofenig@gmx.net

Simon Frost Arm Limited Email: Simon.Frost@arm.com

Mathias Brossard Arm Limited Email: Mathias.Brossard@arm.com

Adrian Shaw HP Labs Email: adrianlshaw@acm.org

Thomas Fossati Linaro Email: thomas.fossati@linaro.org

📦 where this page comes from