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title: SCITT Reference APIs abbrev: SCRAPI docname: draft-birkholz-scitt-scrapi-latest stand_alone: true ipr: trust200902 area: Security submissionType: IETF wg: TBD kw: Internet-Draft cat: std pi: toc: yes sortrefs: yes symrefs: yes

author:

  • name: Henk Birkholz org: Fraunhofer SIT abbrev: Fraunhofer SIT email: [email protected] street: Rheinstrasse 75 code: '64295' city: Darmstadt country: Germany
  • ins: O. Steele name: Orie Steele organization: Transmute email: [email protected]
  • ins: J. Geater name: Jon Geater organization: DataTrails Inc. email: [email protected] country: UK country: United States

normative:

RFC7807: RFC7231: RFC3553:

IANA.params: I-D.draft-ietf-scitt-architecture: SCITT-ARCH

informative:

RFC2046: RFC6838:

--- abstract

This document defines the SCITT REST API, an http interface to transparency services, supporting the primary operations needed to implement the SCITT Architecture {{-SCITT-ARCH}}.

--- middle

Introduction

This API definition MAY be exposed externally as part of a suite of APIs, or be encapsulated internally and exposed indirectly via proprietart APIs.

Requirements Notation

{::boilerplate bcp14-tagged}

Relation to Identity

The SCITT REST API is designed to support identifier systems that are currently relevant to supply chains, including DID, x509 and PGP.

In order to support these systems, the API must be aware of specific header parameters, in particular, kid, x5u and x5c.

The API enables implementers to deploy interoperable URIs for disclosing information feeds related to supply chain actors, and artifacts accessible via transparency services.

Authenticating Clients

TBD (comments on OAuth / Client Attestation).

Discovering Federation

TBD (comments on GAIN / OIDC).

Discovering Feeds

TBD (comments on URLs / QR Codes).

SCITT Reference REST API

Key Binding Confirmation

In cases where a signed statement is issued by one party and registered by another, there is a need to prove posession of key material and detect tampering while authenticating both parties.

Typically a nonce would be chosen by the transparency service and the second party would sign over the nonce, when registering the first issuer's signed statement.

In order to avoid interactivity and improve interoperability, document describes a non-exclusive, but mandatory to support, confirmation scheme

In this scheme the verifier's challenge is a recent unix timestamp, the presenting party need not request this information from the transparency service.

Here is an example key binding token that can be paired with the confirmation claim in a signed statement:

{
  "iat": 1698077790,
  "aud": "https://transparency.example",
  "nonce": "1698077790"
}

When applying registration policies to signed statements with confirmation, the transparency service acts as a verifier, and performs the following checks:

  1. verify the integrity of the issuer's signed statement
  2. confirm the verified content meets the registration policy for the transparency service.
  3. verify the key binding token, using the confirmation claim in the verified issuer signed statement
  4. ensure the key binding token has a nonce that is a string representation of a recent unix timestamp

The exact window of validity for proving possession is a configuration detail of the transparency service. unix timestamps are used so that only a losely synchronised notion of time need be assumed and there is no requirement to account for timezones

If the confirmation key is stolen, the attacker can produce key binding tokens from that point forward in time. In an interactive confirmation schema, the transparency service can force the confirmation key holder to produce a signature over a nonce that is not guessable, and this prevents certain attacks related to the duration of access to a signing capability and other timing details. However, the cost of coordinating with the transparency service, coupled with the purpose of registering with a transparency service (to obtain a receipt, proving a signed statement was acceptable at a point in time) justify specifying the recent timestamp nonce as a mandatory to implement context binding.

In the case that a SCITT transparency service wants to support challenges (nonces) that are context binding, the transparency service can expose a "challenge token endpoint".

This endpoint can process request paramters, and issuer a challenge token, that future regsitrations can use to bind to the original request. This interaction model works well for scenarios where requirements for a given regsitration might change over time, but it is important for the registering party to commit to acceptable values at the time that a signed statement is registered. These endpoints are optional to implement.

Challenge Endpoint

Request

GET https://transparency.example/registration/challenge

Response

  • Header: Content-Type: application/json
  • (Optional) Header: Retry-After: <seconds>
  • Query: ?intention={todo}
  • Body: { "token": "JWT | SD-JWT | base64url( CWT | SD-CWT )>" }

Registration Endpoint

Request

POST https://transparency.example/registration

Headers:

  • Content-Type: application/cose

Body: SCITT COSE_Sign1 message

Note: that the challenge token MUST be present and integrity protected when submitting signed statements to this endpoint. Note: this endpoint is a duplicate of POST https://transparency.example/entries

Messages

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 JSON problem details object ({{RFC7807}}) containing:

  • type: A URI 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:".

  • detail: A human-readable string describing the error that prevented the Transparency Service from processing the request, ideally with sufficient detail to enable the error to be rectified.

Error responses SHOULD be sent with the Content-Type: application/problem+json HTTP header.

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

{
  "type": "urn:ietf:params:scitt:error:badSignatureAlgorithm",
  "detail": "Signing algorithm not support"
}

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 a 503 response, the Transparency Service MAY include a Retry-After header field per {{RFC7231}} 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.

Register Signed Statement

Request

POST https://transparency.example/entries

Headers:

  • Content-Type: application/cose

Body: SCITT COSE_Sign1 message

Response

One of the following:

  • Status 201 - Registration is successful.

    • Header Location: <Base URL>/entries/<Entry ID>
    • Header Content-Type: application/json
    • Body { "entryId": "<Entry ID"> }

  • Status 202 - Registration is running.

    • Header Location: <Base URL>/operations/<Operation ID>
    • Header Content-Type: application/json
    • (Optional) Header: Retry-After: <seconds>
    • Body { "operationId": "<Operation ID>", "status": "running" }

  • Status 400 - Registration was unsuccessful due to invalid input.

    • Error code badSignatureAlgorithm
    • TBD: more error codes to be defined

If 202 is returned, then clients should wait until Registration succeeded or failed by polling the Registration status using the Operation ID returned in the response. Clients should always obtain a Receipt as a proof that Registration has succeeded.

Retrieve Operation Status

Request

GET https://transparency.example/operations/{operation_id}

Response

One of the following:

  • Status 200 - Registration is running

    • Header: Content-Type: application/json
    • (Optional) Header: Retry-After: <seconds>
    • Body: { "operationId": "<Operation ID>", "status": "running" }

  • Status 200 - Registration was successful

    • Header: Location: <Base URL>/entries/<Entry ID>
    • Header: Content-Type: application/json
    • Body: { "operationId": "<Operation ID>", "status": "succeeded", "entryId": "<Entry ID>" }

  • Status 200 - Registration failed

    • Header Content-Type: application/json
    • Body: { "operationId": "<Operation ID>", "status": "failed", "error": { "type": "<type>", "detail": "<detail>" } }
    • Error code: badSignatureAlgorithm
    • [TODO]: more error codes to be defined, see #17

  • Status 404 - Unknown Operation ID

    • Error code: operationNotFound
    • This can happen if the operation ID has expired and been deleted.

If an operation failed, then error details SHOULD be embedded as a JSON problem details object in the "error" field.

If an operation ID is invalid (i.e., it does not correspond to any submit operation), a service may return either a 404 or a running status. This is because differentiating between the two may not be possible in an eventually consistent system.

Retrieve Signed Statement

Request

GET https://transparency.example/entries/{entry_id}

Query parameters:

  • (Optional) embedReceipt=true

If the query parameter embedReceipt=true is provided, then the Signed Statement is returned with the corresponding Registration Receipt embedded in the COSE unprotected header.

Response

One of the following:

  • Status 200.

    • Header: Content-Type: application/cose
    • Body: COSE_Sign1

  • Status 404 - Entry not found.

    • Error code: entryNotFound

Retrieve Registration Receipt

Request

GET https://transparency.example/entries/{entry_id}/receipt

Response

One of the following:

  • Status 200.
    • Header: Content-Type: application/cbor
    • Body: SCITT_Receipt
  • Status 404 - Entry not found.
    • Error code: entryNotFound

The retrieved Receipt may be embedded in the corresponding COSE_Sign1 document in the unprotected header.

Privacy Considerations

TODO

Security Considerations

TODO

IANA Considerations

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.

Media Types

TODO: Register them from here.

Well Known URIs

For discovering scitt configuration.

TODO: Register them from here.

Media Type Registration

This section requests registration of the "application/receipt+cose" media type {{RFC2046}} in the "Media Types" registry in the manner described in {{RFC6838}}.

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

To indicate that the content is a SCITT Receipt:

  • Type name: application
  • Subtype name: 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

--- back

Attic

Not ready to throw these texts into the trash bin yet.