SCITT H. Birkholz Internet-Draft Fraunhofer SIT Intended status: Standards Track O. Steele Expires: 28 July 2024 Transmute J. Geater DataTrails Inc. 25 January 2024 SCITT Reference APIs draft-ietf-scitt-scrapi-00 Abstract This document defines the SCITT REST API, an http interface to transparency services, supporting the primary operations needed to implement the SCITT Architecture [I-D.draft-ietf-scitt-architecture]. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-scitt-scrapi/. Discussion of this document takes place on the SCITT Working Group mailing list (mailto:scitt@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/scitt/. Subscribe at https://www.ietf.org/mailman/listinfo/scitt/. Source for this draft and an issue tracker can be found at https://github.com/ietf-wg-scitt/draft-ietf-scitt-scrapi. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at 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." Birkholz, et al. Expires 28 July 2024 [Page 1] Internet-Draft SCRAPI January 2024 This Internet-Draft will expire on 28 July 2024. Copyright Notice Copyright (c) 2024 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 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3 2. Relation to Identity . . . . . . . . . . . . . . . . . . . . 3 2.1. Authenticating Clients . . . . . . . . . . . . . . . . . 3 2.2. Discovering Federation . . . . . . . . . . . . . . . . . 3 2.3. Discovering Feeds . . . . . . . . . . . . . . . . . . . . 3 3. SCITT Reference REST API . . . . . . . . . . . . . . . . . . 3 3.1. Key Binding Confirmation . . . . . . . . . . . . . . . . 3 3.1.1. Challenge Endpoint . . . . . . . . . . . . . . . . . 5 3.1.2. Registration Endpoint . . . . . . . . . . . . . . . . 5 3.2. Messages . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2.1. Register Signed Statement . . . . . . . . . . . . . . 7 3.2.2. Retrieve Operation Status . . . . . . . . . . . . . . 8 3.2.3. Retrieve Signed Statement . . . . . . . . . . . . . . 9 3.2.4. Retrieve Registration Receipt . . . . . . . . . . . . 9 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6.1. URN Sub-namespace for SCITT (urn:ietf:params:scitt) . . . 10 6.2. Media Types . . . . . . . . . . . . . . . . . . . . . . . 10 6.3. Well Known URIs . . . . . . . . . . . . . . . . . . . . . 10 6.4. Media Type Registration . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.1. Normative References . . . . . . . . . . . . . . . . . . 12 7.2. Informative References . . . . . . . . . . . . . . . . . 12 Appendix A. Attic . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 Birkholz, et al. Expires 28 July 2024 [Page 2] Internet-Draft SCRAPI January 2024 1. Introduction This API definition MAY be exposed externally as part of a suite of APIs, or be encapsulated internally and exposed indirectly via proprietary APIs. 1.1. Requirements Notation 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. 2. 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. 2.1. Authenticating Clients TBD (comments on OAuth / Client Attestation). 2.2. Discovering Federation TBD (comments on GAIN / OIDC). 2.3. Discovering Feeds TBD (comments on URLs / QR Codes). 3. SCITT Reference REST API 3.1. Key Binding Confirmation In cases where a signed statement is issued by one party and registered by another, there is a need to prove possession of key material and detect tampering while authenticating both parties. Birkholz, et al. Expires 28 July 2024 [Page 3] Internet-Draft SCRAPI January 2024 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, Birkholz, et al. Expires 28 July 2024 [Page 4] Internet-Draft SCRAPI January 2024 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 parameters, and issuer a challenge token, that future registrations can use to bind to the original request. This interaction model works well for scenarios where requirements for a given registration 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. 3.1.1. Challenge Endpoint 3.1.1.1. Request GET https://transparency.example/registration/challenge 3.1.1.2. Response * Header: Content-Type: application/json * (Optional) Header: Retry-After: * Query: ?intention={todo} * Body: { "token": "JWT | SD-JWT | base64url( CWT | SD-CWT )>" } 3.1.2. Registration Endpoint 3.1.2.1. Request POST https://transparency.example/registration Headers: * Content-Type: application/cose Body: SCITT COSE_Sign1 message Birkholz, et al. Expires 28 July 2024 [Page 5] Internet-Draft SCRAPI January 2024 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 3.2. 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). Birkholz, et al. Expires 28 July 2024 [Page 6] Internet-Draft SCRAPI January 2024 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. 3.2.1. Register Signed Statement 3.2.1.1. Request POST https://transparency.example/entries Headers: * Content-Type: application/cose Body: SCITT COSE_Sign1 message 3.2.1.2. Response One of the following: * Status 201 - Registration is successful. - Header Location: /entries/ - Header Content-Type: application/json - Body { "entryId": " } * Status 202 - Registration is running. - Header Location: /operations/ - Header Content-Type: application/json - (Optional) Header: Retry-After: - Body { "operationId": "", "status": "running" } * Status 400 - Registration was unsuccessful due to invalid input. - Error code badSignatureAlgorithm - TBD: more error codes to be defined Birkholz, et al. Expires 28 July 2024 [Page 7] Internet-Draft SCRAPI January 2024 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. 3.2.2. Retrieve Operation Status 3.2.2.1. Request GET https://transparency.example/operations/{operation_id} 3.2.2.2. Response One of the following: * Status 200 - Registration is running - Header: Content-Type: application/json - (Optional) Header: Retry-After: - Body: { "operationId": "", "status": "running" } * Status 200 - Registration was successful - Header: Location: /entries/ - Header: Content-Type: application/json - Body: { "operationId": "", "status": "succeeded", "entryId": "" } * Status 200 - Registration failed - Header Content-Type: application/json - Body: { "operationId": "", "status": "failed", "error": { "type": "", "detail": "" } } - Error code: badSignatureAlgorithm * Status 404 - Unknown Operation ID - Error code: operationNotFound - This can happen if the operation ID has expired and been deleted. Birkholz, et al. Expires 28 July 2024 [Page 8] Internet-Draft SCRAPI January 2024 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. 3.2.3. Retrieve Signed Statement 3.2.3.1. 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. 3.2.3.2. Response One of the following: * Status 200. - Header: Content-Type: application/cose - Body: COSE_Sign1 * Status 404 - Entry not found. - Error code: entryNotFound 3.2.4. Retrieve Registration Receipt 3.2.4.1. Request GET https://transparency.example/entries/{entry_id}/receipt 3.2.4.2. Response One of the following: * Status 200. Birkholz, et al. Expires 28 July 2024 [Page 9] Internet-Draft SCRAPI January 2024 - 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. 4. Privacy Considerations TODO 5. Security Considerations TODO 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. Media Types TODO: Register them from here. 6.3. Well Known URIs For discovering scitt configuration. TODO: Register them from here. Birkholz, et al. Expires 28 July 2024 [Page 10] Internet-Draft SCRAPI January 2024 6.4. 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 Birkholz, et al. Expires 28 July 2024 [Page 11] Internet-Draft SCRAPI January 2024 * 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-04, 23 October 2023, . [IANA.params] IANA, "Uniform Resource Name (URN) Namespace for IETF Use", . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014, . [RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 7.2. Informative References [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, DOI 10.17487/RFC2046, November 1996, . Birkholz, et al. Expires 28 July 2024 [Page 12] Internet-Draft SCRAPI January 2024 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, . Appendix A. Attic Not ready to throw texts blocks here into the trash bin yet. Authors' Addresses Henk Birkholz Fraunhofer SIT Rheinstrasse 75 64295 Darmstadt Germany Email: henk.birkholz@sit.fraunhofer.de Orie Steele Transmute Email: orie@transmute.industries Jon Geater DataTrails Inc. United States Email: jon.geater@datatrails.ai Birkholz, et al. Expires 28 July 2024 [Page 13]