SCITT Reference APIs

Internet-Draft	SCRAPI	November 2024
Birkholz & Geater	Expires 23 May 2025	[Page]

Status of This Memo

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Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶

This Internet-Draft will expire on 23 May 2025.¶

Copyright Notice

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

1. Introduction

The SCITT Architecture [I-D.draft-ietf-scitt-architecture] defines the core operations necessary to support supply chain transparency using COSE (CBOR Object Signing and Encryption).¶

Issuance of Signed Statements¶
Verification of Signed Statements¶
Registration of Signed Statements¶
Issuance of Receipts¶
Verification of Receipts¶
Production of Transparent Statements¶
Verification of Transparent Statements¶

In addition to defining concrete HTTP endpoints for these operations, this specification defines support for the following endpoints which support these operations:¶

Resolving Verification Keys for Issuers¶
Retrieving Receipts Asynchronously¶
Retrieving Signed Statements from an Artifact Repository¶
Retrieving Statements from an Artifact Repository¶

1.1. Terminology

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.¶

This specification uses the terms "Signed Statement", "Receipt", "Transparent Statement", "Artifact Repositories", "Transparency Service", "Append-Only Log" and "Registration Policy" as defined in [I-D.draft-ietf-scitt-architecture].¶

This specification uses "payload" as defined in [RFC9052].¶

2. Endpoints

Authentication is out of scope for this document. If Authentication is not implemented, rate limiting or other denial of service mitigation MUST be applied to enable anonymous access.¶

NOTE: '' line wrapping per [RFC8792] in HTTP examples.¶

All messages are sent as HTTP GET or POST requests.¶

If the Transparency Service cannot process a client's request, it MUST return an HTTP 4xx or 5xx status code, and the body SHOULD be a Concise Problem Details object ([RFC9290]) containing:¶

title: A human-readable string identifying the error that prevented the Transparency Service from processing the request, ideally short and suitable for inclusion in log messages.¶
detail: A human-readable string describing the error in more depth, ideally with sufficient detail to enable the error to be rectified.¶
instance: A URN reference identifying the problem. To facilitate automated response to errors, this document defines a set of standard tokens for use in the type field within the URN namespace of: "urn:ietf:params:scitt:error:".¶
response-code: The HTTP error response code relating to this error.¶

application/concise-problem-details+cbor¶

NOTE: SCRAPI is not a CoAP API. Nonetheless Constrained Problem Details objects ([RFC9290]) provide a useful CBOR encoding for problem details and avoids the need for mixing CBOR and JSON in endpoint implementations.¶

As an example, submitting a Signed Statement with an unsupported signature algorithm would return a 400 Bad Request status code and the following body:¶

{
  / title /         -1: "Bad Signature Algorithm",
  / detail /        -2: "Signing algorithm 'WalnutDSA' not supported.",
  / instance /      -3: "urn:ietf:params:scitt:error:badSignatureAlgorithm",
  / response-code / -4: 400,
}

Most error types are specific to the type of request and are defined in the respective subsections below. The one exception is the "malformed" error type, which indicates that the Transparency Service could not parse the client's request because it did not comply with this document:¶

Error code: malformed (The request could not be parsed).¶

Clients SHOULD treat 500 and 503 HTTP status code responses as transient failures and MAY retry the same request without modification at a later date.¶

Note that in the case of any error response, the Transparency Service MAY include a Retry-After header field per [RFC9110] in order to request a minimum time for the client to wait before retrying the request. In the absence of this header field, this document does not specify a minimum.¶

2.1. Mandatory

The following HTTP endpoints are mandatory to implement to enable conformance to this specification.¶

2.1.1. Transparency Configuration

Authentication SHOULD NOT be implemented for this endpoint.¶

This endpoint is used to discover the capabilities and current configuration of a transparency service implementing this specification.¶

The Transparency Service responds with a dictionary of configuration elements. These elements are Transparency-Service specific.¶

Contents of bodies are informative examples only.¶

Request:¶

GET /.well-known/transparency-configuration HTTP/1.1
Host: transparency.example
Accept: application/cose

Response:¶

HTTP/1.1 200 Ok
Content-Type: application/cose

Payload (in CBOR diagnostic notation)

18([                   ; COSE_Sign1 structure with tag 18
    h'44A123BEEFFACE', ; Protected header (example bytes)
    {},                ; Unprotected header
    {                  ; Payload - CBOR dict
        "issuer": "https://transparency.example",
        "base_url": "https://transparency.example/v1/scrapi",
        "oidc_auth_endpoint": "https://transparency.example/auth",
        "registration_policy": "https://transparency.example/statements/\
urn:ietf:params:scitt:statement:sha-256:base64url:5i6UeRzg1...qnGmr1o"
    },
    h'ABCDEF1234567890ABCDEF1234567890'  ; Signature placeholder
])

Responses to this message are vendor-specific. Fields that are not understood MUST be ignored.¶

2.1.2. Register Signed Statement

Authentication MAY be implemented for this endpoint. See notes on detached payloads below.¶

This endpoint is used to register a Signed Statement with a Transparency Service.¶

The following is a non-normative example of a HTTP request to register a Signed Statement:¶

Request:¶

POST /entries HTTP/1.1
Host: transparency.example
Accept: application/json
Content-Type: application/cose
Payload (in CBOR diagnostic notation)

18([                            / COSE Sign1         /
  h'a1013822',                  / Protected Header   /
  {},                           / Unprotected Header /
  null,                         / Detached Payload   /
  h'269cd68f4211dffc...0dcb29c' / Signature          /
])

The Registration Policy for the Transparency Service MUST be applied to the payload bytes, before any additional processing is performed.¶

If the payload is detached, the Transparency Service depends on the authentication context of the client in the Registration Policy. If the payload is attached, the Transparency Service depends on both the authentication context of the client (if present), and the verification of the Signed Statement in the Registration Policy. The details of Registration Policy are out of scope for this document.¶

If registration succeeds the following identifier MAY be used to refer to the Signed Statement that was accepted:¶

urn:ietf:params:scitt:signed-statement:sha-256:base64url:5i6UeRzg1...qnGmr1o¶

If the payload was attached, or otherwise communicated to the Transparency Service, the following identifier MAY be used to refer to the payload of the Signed Statement:¶

urn:ietf:params:scitt:statement:sha-256:base64url:5i6UeRzg1...qnGmr1o¶

Response:¶

One of the following:¶

2.1.2.1. Status 201 - Registration is successful

HTTP/1.1 201 Ok

Location: https://transparency.example/receipts\
/urn:ietf:params:scitt:signed-statement\
:sha-256:base64url:5i6UeRzg1...qnGmr1o

Content-Type: application/cose

Payload (in CBOR diagnostic notation)

18([                            / COSE Sign1         /
  h'a1013822',                  / Protected Header   /
  {},                           / Unprotected Header /
  null,                         / Detached Payload   /
  h'269cd68f4211dffc...0dcb29c' / Signature          /
])

The response contains the Receipt for the Signed Statement. Fresh receipts may be requested through the resource identified in the Location header.¶

2.1.2.2. Status 202 - Registration is running

HTTP/1.1 202 Accepted

Location: https://transparency.example/receipts\
/urn:ietf:params:scitt:signed-statement\
:sha-256:base64url:5i6UeRzg1...qnGmr1o

Content-Type: application/cbor
Retry-After: <seconds>

{

  "identifier": "urn:ietf:params:scitt:receipt\
:sha-256:base64url:5i6UeRzg1...qnGmr1o",

}

The response contains a reference to the receipt which will eventually be available for the Signed Statement.¶

If 202 is returned, then clients should wait until Registration succeeded or failed by polling the Resolve Receipt endpoint using the identifier returned in the response.¶

2.1.2.3. Status 400 - Invalid Client Request

The following expected errors are defined. Implementations MAY return other errors, so long as they are valid [RFC9290] objects.¶

HTTP/1.1 400 Bad Request
application/concise-problem-details+cbor

{
  / title /         -1: "Bad Signature Algorithm",
  / detail /        -2: "Signed Statement contained an algorithm that is not supported",
  / instance /      -3: "urn:ietf:params:scitt:error:badSignatureAlgorithm",
  / response-code / -4: 400,
}

HTTP/1.1 400 Bad Request
application/concise-problem-details+cbor

{
  / title /         -1: "Confirmation Missing",
  / detail /        -2: "Signed Statement did not contain proof of possession",
  / instance /      -3: "urn:ietf:params:scitt:error:signed-statement:confirmation-missing",
  / response-code / -4: 400,
}

HTTP/1.1 400 Bad Request
application/concise-problem-details+cbor

{
  / title /         -1: "Payload Missing",
  / detail /        -2: "Signed Statement payload must be must be attached (must be present)",
  / instance /      -3: "urn:ietf:params:scitt:error:signed-statement:payload-missing",
  / response-code / -4: 400,
}

HTTP/1.1 400 Bad Request
application/concise-problem-details+cbor

{
  / title /         -1: "Payload Forbidden",
  / detail /        -2: "Signed Statement payload must be detached (must not be present)",
  / instance /      -3: "urn:ietf:params:scitt:error:signed-statement:payload-forbidden",
  / response-code / -4: 400,
}

HTTP/1.1 400 Bad Request
application/concise-problem-details+cbor

{
  / title /         -1: "Rejected",
  / detail /        -2: "Signed Statement not accepted by the current Registration Policy",
  / instance /      -3: "urn:ietf:params:scitt:error:signed-statement:rejected-by-registration-policy",
  / response-code / -4: 400,
}

2.2. Optional Endpoints

The following HTTP endpoints are optional to implement.¶

2.2.1. Issue Signed Statement

Authentication MUST be implemented for this endpoint.¶

This endpoint enables a Transparency Service to be an issuer of Signed Statements on behalf of authenticated clients. This supports cases where a client lacks the ability to perform complex cryptographic operations, but can be authenticated and report statements and measurements.¶

Request:¶

POST /signed-statements/issue HTTP/1.1
Host: transparency.example
Accept: application/json
Content-Type: application/spdx+json
Payload

{
  "spdxVersion": "SPDX-2.2",
  "dataLicense": "CC0-1.0",
  "SPDXID": "SPDXRef-DOCUMENT",
  "name": "cli-app 0.1.2",
  "documentNamespace": "https://spdx.org/spdxdocs/sbom-tool-2.2.7-38f61e97-e53c-46ef-a37d-62.../cli-app/0.1.2/0d06adf8a36...",
  "creationInfo": {
    "created": "2024-08-16T21:44:54Z",
    "creators": [
      "Organization: contoso"
    ]
  },
  "files": [
    {
      "name": "cli-app",
      "SPDXID": "SPDXRef-RootPackage",
      "downloadLocation": "NOASSERTION",
      "packageVerificationCode": {
        "packageVerificationCodeValue": "ecf0aae2a849cc51..."
      },
      "filesAnalyzed": true,
      "licenseConcluded": "NOASSERTION",
      "licenseInfoFromFiles": [
        "NOASSERTION"
      ],
      "licenseDeclared": "NOASSERTION",
      "copyrightText": "NOASSERTION",
      "versionInfo": "0.1.2",
      "externalRefs": [
        {
          "referenceCategory": "PACKAGE-MANAGER",
          "referenceType": "purl",
          "referenceLocator": "pkg:swid/contoso/spdx.org/cli-app@0.1.2?tag_id=ac073d0f-0aa7-4d27-87fa-7f..."
        }
      ],
      "supplier": "Organization: contoso",
      "hasFiles": [
        "SPDXRef-File--..."
      ]
    }
  ],
  "relationships": [
    {
      "relationshipType": "DESCRIBES",
      "relatedSpdxElement": "SPDXRef-RootPackage",
      "spdxElementId": "SPDXRef-DOCUMENT"
    },
    {
      "relationshipType": "DEPENDS_ON",
      "relatedSpdxElement": "SPDXRef-Package-FF36801C1982452...",
      "spdxElementId": "SPDXRef-RootPackage"
    }
  ],
  "documentDescribes": [
    "SPDXRef-RootPackage"
  ],
  "externalDocumentRefs": []
}

Response:¶

HTTP/1.1 200 Ok
Content-Type: application/cose

Payload (in CBOR diagnostic notation)

18([                            / COSE Sign1         /
  h'a1013822',                  / Protected Header   /
  {},                           / Unprotected Header /
  null,                         / Detached Payload   /
  h'269cd68f4211dffc...0dcb29c' / Signature          /
])

2.2.2. Resolve Signed Statement

Authentication SHOULD be implemented for this endpoint.¶

This endpoint enables Transparency Service APIs to act like Artifact Repositories, and serve Signed Statements directly, instead of indirectly through Receipts.¶

Request:¶

GET /signed-statements/urn...qnGmr1o HTTP/1.1
Host: transparency.example
Accept: application/cose

Response:¶

One of the following:¶

2.2.2.1. Status 200 - Success

HTTP/1.1 200 Ok
Content-Type: application/cose

Payload (in CBOR diagnostic notation)

18([                            / COSE Sign1         /
  h'a1013822',                  / Protected Header   /
  {},                           / Unprotected Header /
  null,                         / Detached Payload   /
  h'269cd68f4211dffc...0dcb29c' / Signature          /
])

2.2.2.2. Status 404 - Not Found

The following expected errors are defined. Implementations MAY return other errors, so long as they are valid [RFC9290] objects.¶

HTTP/1.1 404 Not Found
application/concise-problem-details+cbor

{
  / title /         -1: "Not Found",
  / detail /        -2: "No Signed Statement found with the specified ID",
  / instance /      -3: "urn:ietf:params:scitt:error:notFound",
  / response-code / -4: 404,
}

2.2.3. Resolve Receipt

Authentication SHOULD be implemented for this endpoint.¶

Request:¶

GET /receipts/urn...qnGmr1o HTTP/1.1
Host: transparency.example
Accept: application/cose

Response:¶

2.2.3.1. Status 200

If the Signed Statement requested is already included in the Append-Only Log:¶

HTTP/1.1 200 Ok
Location: https://transparency.example/receipts/urn...qnGmr1o
Content-Type: application/cose

Payload (in CBOR diagnostic notation)

18([                            / COSE Sign1         /
  h'a1013822',                  / Protected Header   /
  {},                           / Unprotected Header /
  null,                         / Detached Payload   /
  h'269cd68f4211dffc...0dcb29c' / Signature          /
])

2.2.3.2. Status 202

If registration of the Signed Statement requested is in progress but not yet included in the Append-Only Log:¶

HTTP/1.1 202 Ok
Location: https://transparency.example/receipts/urn...qnGmr1o
Content-Type: application/json
Retry-After: <seconds>

{
  "receipt": "urn:ietf:params:scitt:receipt\
    :sha-256:base64url:5i6UeRzg1...qnGmr1o",
}

2.2.3.3. Status 404

If the Signed Statement requested is neither registered in the log nor subject to an in-progress registration:¶

HTTP/1.1 404 Not Found
application/concise-problem-details+cbor

{
  / title /         -1: "Not Found",
  / detail /        -2: "Signed Statement not known to this Transparency Service",
  / instance /      -3: "urn:ietf:params:scitt:error:receipt:not-found",
  / response-code / -4: 400,
}

2.2.3.4. Status 429

If a client is polling for an in-progress registration too frequently then the Transparency Service MAY, in addition to implementing rate-limiting, return a 429 response:¶

HTTP/1.1 429 Too Many Requests
Content-Type: application/json
Retry-After: <seconds>

{
  "type": "urn:ietf:params:scitt:error\
    :receipt:too-many-requests",
  "detail": \
    "Too Many Requests. Only <number> requests per <period> are allowed."
}

2.2.3.5. Eventual Consistency

For all responses additional eventually consistent operation details MAY be present. Support for eventually consistent Receipts is implementation specific, and out of scope for this specification.¶

2.2.4. Exchange Receipt

This endpoint is used to exchange old or expiring receipts for fresh ones.¶

The iat, exp and kid claims can change each time a receipt is exchanged.¶

This means that fresh receipts can have more recent issued at times, further in the future expiration times, and be signed with new signature algorithms.¶

Authentication SHOULD be implemented for this endpoint.¶

Request:¶

POST /exchange/receipt HTTP/1.1
Host: transparency.example
Accept: application/cose
Content-Type: application/cose
Payload (in CBOR diagnostic notation)

18([                            / COSE Sign1         /
  h'a1013822',                  / Protected Header   /
  {},                           / Unprotected Header /
  null,                         / Detached Payload   /
  h'269cd68f4211dffc...0dcb29c' / Signature          /
])

2.2.4.1. Status 200

A new receipt:¶

HTTP/1.1 200 Ok
Location: https://transparency.example/receipts/urn...qnGmr1o
Content-Type: application/cose

Payload (in CBOR diagnostic notation)

18([                            / COSE Sign1         /
  h'a1013822',                  / Protected Header   /
  {},                           / Unprotected Header /
  null,                         / Detached Payload   /
  h'269cd68f4211dffc...0dcb29c' / Signature          /
])

2.2.5. Resolve Issuer

This endpoint is inspired by [I-D.draft-ietf-oauth-sd-jwt-vc]. Authentication SHOULD NOT be implemented for this endpoint. This endpoint is used to discover verification keys, which is the reason that authentication is not required.¶

The following is a non-normative example of a HTTP request for the Issuer Metadata configuration when iss is set to https://transparency.example/tenant/1234:¶

Request:¶

GET /.well-known/issuer/tenant/1234 HTTP/1.1
Host: transparency.example
Accept: application/json

Response:¶

HTTP/1.1 200 Ok
Content-Type: application/json

{
  "issuer": "https://transparency.example/tenant/1234",
  "jwks": {
    "keys": [
      {
        "kid": "urn:ietf:params:oauth\
:jwk-thumbprint:sha-256:DgyowWs04gfVRim5i1WlQ-HFFFKI6Ltqulj1rXPagRo",
        "alg": "ES256",
        "use": "sig",
        "kty": "EC",
        "crv": "P-256",
        "x": "p-kZ4uOASt9IjQRTrWikGnlbGb-z3LU1ltwRjZaOS9w",
        "y": "ymXE1yltJPXgjQSRe9NweN3TLlSUALYZTzy83NVfdg0"
      },
      {
        "kid": "urn:ietf:params:oauth\
:jwk-thumbprint:sha-256:4Fzx5HO1W0ob9CZNc3RJx28Ixpgy9JAFM8jyXKW0ClE",
        "alg": "HPKE-Base-P256-SHA256-AES128GCM",
        "use": "enc",
        "kty": "EC",
        "crv": "P-256",
        "x": "Vreuil95vzR6ixutgBBf2ota-rj97MvKfuJWB4qqp5w",
        "y": "NkUTeaoNlLRRsVRxHGDA-RsA0ex2tSpcd3G-4SmKXbs"
      }
    ]
  }
}

2.2.6. Request Nonce

This endpoint in inspired by [I-D.draft-demarco-oauth-nonce-endpoint].¶

Authentication SHOULD NOT be implemented for this endpoint. This endpoint is used to demonstrate proof of possession, which is the reason that authentication is not required. Client holding signed statements that require demonstrating proof of possession MUST use this endpoint to obtain a nonce.¶

Request:¶

GET /nonce HTTP/1.1
Host: transparency.example
Accept: application/json

Response:¶

HTTP/1.1 200 OK
Content-Type: application/json

{
  "nonce": "d2JhY2NhbG91cmVqdWFuZGFt"
}

4. Security Considerations

4.1. General scope

This document describes the interoperable API for client calls to, and implementations of, a Transparency Service as specified in [I-D.draft-ietf-scitt-architecture]. As such the security considerations in this section are concerned only with security considerations that are relevant at that implementation layer. All questions of security of the related COSE formats, algorithm choices, cryptographic envelopes,verifiable data structures and the like are handled elsewhere and out of scope of this document.¶

4.2. Applicable Environment

SCITT is concerned with issues of cross-boundary supply-chain-wide data integrity and as such must assume a very wide range of deployment environments. Thus, no assumptions can be made about the security of the computing environment in which any client implementation of this specification runs.¶

4.3. User-host authentication

[I-D.draft-ietf-scitt-architecture] defines 2 distinct roles that require authentication: Issuers who sign Statements, and clients that submit API calls on behalf of Issuers. While Issuer authentication and signing of Statements is very important for the trustworthiness of systems implementing the SCITT building blocks, it is out of scope of this document. This document is only concerned with authentication of API clients.¶

For those endpoints that require client authentication, Transparency Services MUST support at least one of the following options:¶

HTTP Authorization header with a JWT¶
domain-bound API key¶
TLS client authentication¶

Where authentication methods rely on long term secrets, both clients and Transparency Services implementing this specification SHOULD allow for the revocation and rolling of authentication secrets.¶

4.4. Primary threats

4.4.1. In scope

The most serious threats to implementations on Transparency Services are ones that would cause the failure of their main promises, to wit:¶

Threats to strong identification, for example representing the Statements from one issuer as those of another¶
Threats to payload integrity, for example changing the contents of a Signed Statement before making it transparent¶
Threats to non-equivocation, for example attacks that would enable the presentation or verification of divergent proofs for the same Statement payload¶

4.4.1.1. Denial of service attacks

While denial of service attacks are very hard to defend against completely, and Transparency Services are unlikely to be in the critical path of any safety-liable operation, any attack which could cause the silent failure of Signed Statement registration, for example, should be considered in scope.¶

In principle DoS attacks are easily mitigated by the client checking that the Transparency Service has registered any submitted Signed Statement and returned a Receipt. Since verification of Receipts does not require the involvement of the Transparency Service DoS attacks are not a major issue.¶

Clients to Transparency Services SHOULD ensure that Receipts are available for their registered Statements, either on a periodic or needs-must basis, depending on the use case.¶

Beyond this, implementers of Transparency Services SHOULD implement general good practice around network attacks, flooding, rate limiting etc.¶

4.4.1.2. Eavesdropping

Since the purpose of this API is to ultimately put the message payloads on a Transparency Log there is limited risk to eavesdropping. Nonetheless transparency may mean 'within a limited community' rather than 'in full public', so implementers MUST add protections against man-in-the-middle and network eavesdropping, such as TLS.¶

4.4.1.3. Message modification attacks

While most relevant modification attacks are mitigated by the use of the Issuer signature on the Signed Statement, the Issue Statement endpoint presents an opportunity for manipulation of messages and misrepresentation of Issuer intent that could mislead later Verifiers.¶

Transparency Services offering the Issue Statement endpoint MUST require authentication and transport-level security for that endpoint, MUST NOT modify anything in the message to be signed, and MUST take steps to ensure that the party calling the endpoint is authorized to register statements on behalf of the specified Issuer.¶

4.4.1.4. Message insertion attacks

While most relevant insertion attacks are mitigated by the use of the Issuer signature on the Signed Statement, the Issue Statement endpoint presents an opportunity for insertion of messages and misrepresentation of Issuer intent that could mislead later Verifiers. There are 2 most likely avenues to this attack:¶

Stolen client endpoint authentication credentials¶
Stolen or misused Issuer keys held in the Transparency Service on behalf of clients¶

Clients relying on the Issue Statement endpoint SHOULD take steps to ensure their endpoint authentication credentials are securely stored and can be rotated and/or revoked in the case of a breach.¶

Transparency Services offering the Issue Statement endpoint MUST require authentication and transport-level security for that endpoint, and MUST enable the rotation and revocation of those credentials.¶

Transparency Services offering the Issue Statement endpoint MUST take careful steps in both design and operation of their software stack to prevent the theft or inappropriate use of the Issuer keys they use to sign Statements on behalf of Issuers, such as HSMs for storage and least-privilege, regularly refreshed access controls for use.¶

Transparency Services MAY also implement additional protections such as anomaly detection or rate limiting in order to mitigate the impact of any breach.¶

4.4.2. Out of scope

4.4.2.1. Replay attacks

Replay attacks are not particularly concerning for SCITT or SCRAPI: once a statement is made, it is intended to be immutable and non-repudiable, so making it twice should not lead to any particular issues. There could be issues at the payload level (for instance, the statement "it is raining" may true when first submitted but not when replayed), but being payload-agnostic implementations of SCITT services cannot be required to worry about that.¶

If the semantic content of the payload are time dependent and susceptible to replay attacks in this way then timestamps MAY be added to the protected header signed by the Issuer.¶

4.4.2.2. Message deletion attacks

Once registered with a Transparency Service, Registered Signed Statements cannot be deleted. Thus, any message deletion attack must occur prior to registration else it is indistinguishable from a man-in-the-middle or denial-of-service attack on this interface.¶

5. TODO

TODO: Consider negotiation for receipt as "JSON" or "YAML". TODO: Consider impact of media type on "Data URIs" and QR Codes.¶

6. IANA Considerations

6.1. URN Sub-namespace for SCITT (urn:ietf:params:scitt)

IANA is requested to register the URN sub-namespace urn:ietf:params:scitt in the "IETF URN Sub-namespace for Registered Protocol Parameter Identifiers" Registry [IANA.params], following the template in [RFC3553]:¶

   Registry name:  scitt
   Specification:  [RFCthis]
   Repository:  http://www.iana.org/assignments/scitt
   Index value:  No transformation needed.

6.2. Well-Known URI for Issuers

The following value is requested to be registered in the "Well-Known URIs" registry (using the template from [RFC8615]):¶

URI suffix: issuer Change controller: IETF Specification document(s): RFCthis. Related information: N/A¶

6.3. Well-Known URI for Transparency Configuration

The following value is requested to be registered in the "Well-Known URIs" registry (using the template from [RFC8615]):¶

URI suffix: transparency-configuration Change controller: IETF Specification document(s): RFCthis. Related information: N/A¶

TODO: Register them from here.¶

6.4. Media Type Registration

This section requests registration of the "application/scitt.receipt+cose" media type [RFC2046] in the "Media Types" registry in the manner described in [RFC6838].¶

To indicate that the content is a SCITT Receipt:¶

Type name: application¶
Subtype name: scitt.receipt+cose¶
Required parameters: n/a¶
Optional parameters: n/a¶
Encoding considerations: TODO¶
Security considerations: TODO¶
Interoperability considerations: n/a¶
Published specification: this specification¶
Applications that use this media type: TBD¶
Fragment identifier considerations: n/a¶
Additional information:¶
- Magic number(s): n/a¶
- File extension(s): n/a¶
- Macintosh file type code(s): n/a¶
Person & email address to contact for further information: TODO¶
Intended usage: COMMON¶
Restrictions on usage: none¶
Author: TODO¶
Change Controller: IESG¶
Provisional registration? No¶

7. References

7.1. Normative References

[I-D.draft-ietf-scitt-architecture]: Birkholz, H., Delignat-Lavaud, A., Fournet, C., Deshpande, Y., and S. Lasker, "An Architecture for Trustworthy and Transparent Digital Supply Chains", Work in Progress, Internet-Draft, draft-ietf-scitt-architecture-10, 13 November 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-scitt-architecture-10>.
[IANA.params]: IANA, "Uniform Resource Name (URN) Namespace for IETF Use", <https://www.iana.org/assignments/params>.
[RFC2119]: Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3553]: Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An IETF URN Sub-namespace for Registered Protocol Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June 2003, <https://www.rfc-editor.org/rfc/rfc3553>.
[RFC8174]: Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8615]: Nottingham, M., "Well-Known Uniform Resource Identifiers (URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019, <https://www.rfc-editor.org/rfc/rfc8615>.
[RFC9052]: Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", STD 96, RFC 9052, DOI 10.17487/RFC9052, August 2022, <https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9110]: Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, <https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9290]: Fossati, T. and C. Bormann, "Concise Problem Details for Constrained Application Protocol (CoAP) APIs", RFC 9290, DOI 10.17487/RFC9290, October 2022, <https://www.rfc-editor.org/rfc/rfc9290>.

7.2. Informative References

[I-D.draft-demarco-oauth-nonce-endpoint]: De Marco, G. and O. Steele, "OAuth 2.0 Nonce Endpoint", Work in Progress, Internet-Draft, draft-demarco-oauth-nonce-endpoint-00, 6 February 2024, <https://datatracker.ietf.org/doc/html/draft-demarco-oauth-nonce-endpoint-00>.
[I-D.draft-ietf-oauth-sd-jwt-vc]: Terbu, O., Fett, D., and B. Campbell, "SD-JWT-based Verifiable Credentials (SD-JWT VC)", Work in Progress, Internet-Draft, draft-ietf-oauth-sd-jwt-vc-06, 13 November 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-oauth-sd-jwt-vc-06>.
[RFC2046]: Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, DOI 10.17487/RFC2046, November 1996, <https://www.rfc-editor.org/rfc/rfc2046>.
[RFC6838]: Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, <https://www.rfc-editor.org/rfc/rfc6838>.
[RFC8792]: Watsen, K., Auerswald, E., Farrel, A., and Q. Wu, "Handling Long Lines in Content of Internet-Drafts and RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020, <https://www.rfc-editor.org/rfc/rfc8792>.