Network Working Group M. Kleidl Internet-Draft Transloadit Intended status: Informational L. Pardue Expires: 24 April 2025 Cloudflare R. Polli Par-Tec 21 October 2024 HTTP Problem Types for Digest Fields draft-kleidl-digest-fields-problem-types-01 Abstract This document specifies problem types that servers can use in responses to problems encountered while dealing with a request carrying integrity fields and integrity preference fields. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://tus.github.io/draft-digest-fields-problem-types/draft-kleidl- digest-fields-problem-types.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft- kleidl-digest-fields-problem-types/. Source for this draft and an issue tracker can be found at https://github.com/tus/draft-digest-fields-problem-types. 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." This Internet-Draft will expire on 24 April 2025. Kleidl, et al. Expires 24 April 2025 [Page 1] Internet-Draft HTTP Problem Types for Digest Fields October 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Problem Types . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Unsupported Hashing Algorithm . . . . . . . . . . . . . . 3 3.2. Invalid Digest Value . . . . . . . . . . . . . . . . . . 5 3.3. Mismatching Digest Value . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5.1. Registration of "digest-unsupported-algorithm" Problem Type . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Registration of "digest-invalid-value" Problem Type . . . 7 5.3. Registration of "digest-mismatching-value" Problem Type . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Normative References . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction [DIGEST] by design does not define, require or recommend any specific behavior for error handling relating to integrity. The responsibility is instead delegated to applications. This draft defines a set of problem types ([PROBLEM]) that can be used by server applications to indicate that a problem was encountered while dealing with a request carrying integrity fields and integrity preference fields. For example, a request message may include content alongside Content- Digest and Repr-Digest fields that use a digest algorithm the server does not support. An application could decide to reject this request because it cannot validate the integrity. Using a problem type, the server can provide machine-readable error details to aid debugging or error reporting, as shown in the following example. Kleidl, et al. Expires 24 April 2025 [Page 2] Internet-Draft HTTP Problem Types for Digest Fields October 2024 HTTP/1.1 400 Bad Request Content-Type: application/problem+json Want-Content-Digest: sha-512=3, sha-256=10 { "type": "https://iana.org/assignments/http-problem-types#digest-unsupported-algorithm", "title": "hashing algorithm is not supported", "unsupported-algorithm": "foo" } 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. The terms "integrity fields" and "integrity preference fields" in this document are to be interpreted as described in [DIGEST]. The term "problem type" in this document is to be interpreted as described in [PROBLEM]. The term "request", "response", "intermediary", "sender", and "server" are from [HTTP]. 3. Problem Types 3.1. Unsupported Hashing Algorithm This section defines the "https://iana.org/assignments/http-problem- types#digest-unsupported-algorithm" problem type. A server MAY use this problem type if it wants to communicate to the client that one of the hashing algorithms referenced in the integrity or integrity preference fields present in the request is not supported. For this problem type, unsupported-algorithm is defined as the only extension member. It SHOULD be populated in a response using this problem type, with its value being the algorithm key of the unsupported algorithm from the request. The response can include the corresponding integrity preference field to indicate the server's algorithm support and preference. Example: Kleidl, et al. Expires 24 April 2025 [Page 3] Internet-Draft HTTP Problem Types for Digest Fields October 2024 POST /books HTTP/1.1 Host: foo.example Content-Type: application/json Accept: application/json Accept-Encoding: identity Repr-Digest: sha-256=:mEkdbO7Srd9LIOegftO0aBX+VPTVz7/CSHes2Z27gc4=: {"title": "New Title"} Figure 1: A request with a sha-256 integrity field, which is not supported by the server HTTP/1.1 400 Bad Request Content-Type: application/problem+json Want-Repr-Digest: sha-512=10, sha-256=0 { "type": "https://iana.org/assignments/http-problem-types#digest-unsupported-algorithm", "title": "Unsupported hashing algorithm", "unsupported-algorithm": "sha-256" } Figure 2: Response Advertising the Supported Algorithms This problem type is a hint to the client about algorithm support, which the client could use to retry the request with a different, supported, algorithm. Note that a request may contain more than one integrity field. This problem type can also be used when a request contains an integrity preference field. For example: GET /items/123 HTTP/1.1 Host: foo.example Want-Repr-Digest: sha=10 Figure 3: GET Request with Want-Repr-Digest HTTP/1.1 400 Bad Request Content-Type: application/problem+json { "type": "https://iana.org/assignments/http-problem-types#digest-unsupported-algorithm", "title": "Unsupported hashing algorithm", "unsupported-algorithm": "sha" } Figure 4: Response Advertising the Supported Algorithms Kleidl, et al. Expires 24 April 2025 [Page 4] Internet-Draft HTTP Problem Types for Digest Fields October 2024 3.2. Invalid Digest Value This section defines the "https://iana.org/assignments/http-problem- types#digest-invalid-value" problem type. A server MAY use this problem type when responding to a request, whose integrity fields include a digest value, that cannot be generated by the corresponding hashing algorithm. For example, if the digest value of the sha-512 hashing algorithm is not 64 bytes long, it cannot be a valid digest value and the server can skip computing the digest value. This problem type MUST NOT be used if the server is not able to parse the integrity fields according to Section 4.5 of [STRUCTURED-FIELDS], for example because of a syntax error in the field value. The server SHOULD include a human-readable description why the value is considered invalid in the title member. The following example shows a request with the content {"hello": "world"} (plus LF), but the digest has been truncated. The subsequent response indicates the invalid SHA-512 digest. PUT /items/123 HTTP/1.1 Host: foo.example Content-Type: application/json Repr-Digest: sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4: {"hello": "world"} Figure 5: A request with a sha-512 integrity field, whose digest has been truncated HTTP/1.1 400 Bad Request Content-Type: application/problem+json { "type": "https://iana.org/assignments/http-problem-types#digest-invalid-value", "title": "digest value for sha-512 is not 64 bytes long" } Figure 6: Response indicating that the provided digest is too short This problem type indicates a fault in the sender's calculation or encoding of the digest value. A retry of the same request without modification will likely not yield a successful response. Kleidl, et al. Expires 24 April 2025 [Page 5] Internet-Draft HTTP Problem Types for Digest Fields October 2024 3.3. Mismatching Digest Value This section defines the "https://iana.org/assignments/http-problem- types#digest-mismatching-value" problem type. A server MAY use this problem type when responding to a request, whose integrity fields include a digest value that does not match the digest value that the server calculated for the request content or representation. Three problem type extension members are defined: the algorithm, provided-digest, and calculated-digest members. A response using this problem type SHOULD populate all members, with the value of algorithm being the algorithm key of the used hashing algorithm, with the value of provided-digest being the digest value taken from the request's integrity fields, and the value of calculated-digest being the calculated digest. The digest values MUST BE serialized as byte sequences as described in Section 4.1.8 of [STRUCTURED-FIELDS]. The following example shows a request with the content {"hello": "woXYZ"} (plus LF), but the representation digest for {"hello": "world"} (plus LF). The subsequent response indicates the mismatching SHA-256 digest values. PUT /items/123 HTTP/1.1 Host: foo.example Content-Type: application/json Repr-Digest: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=: {"hello": "woXYZ"} Figure 7: A request with a sha-256 integrity field, which does not match the representation HTTP/1.1 400 Bad Request Content-Type: application/problem+json { "type": "https://iana.org/assignments/http-problem-types#digest-mismatching-value", "title": "digest value fromr request does not match expected value", "algorithm": "sha-256", "provided-digest": ":RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=:", "calculated-digest": ":8vXo+0QVwf2woEblm4hTAftp0/K5fWSMZG4CKtplwjc=:" } Figure 8: Response indicating the mismatching digests Kleidl, et al. Expires 24 April 2025 [Page 6] Internet-Draft HTTP Problem Types for Digest Fields October 2024 If the sender receives this problem type, the request might be modified unintentionally by an intermediary. The sender could use this information to retry the request without modification to address temporary transmission issues. 4. Security Considerations Disclosing error details could leak information such as the presence of intermediaries or the server's implementation details. Moreover, they can be used to fingerprint the server. To mitigate these risks, a server could assess the risk of disclosing error details and prefer a general problem type over a more specific one. 5. IANA Considerations IANA is asked to register the following entries in the "HTTP Problem Types" registry at https://www.iana.org/assignments/http-problem- types (https://www.iana.org/assignments/http-problem-types). 5.1. Registration of "digest-unsupported-algorithm" Problem Type Type URI: https://iana.org/assignments/http-problem-types#digest- unsupported-algorithm Title: Unsupported Hashing Algorithm Recommended HTTP status code: 400 Reference: Section 3.1 of this document 5.2. Registration of "digest-invalid-value" Problem Type Type URI: https://iana.org/assignments/http-problem-types#digest- invalid-value Title: Invalid Digest Value Recommended HTTP status code: 400 Reference: Section 3.2 of this document 5.3. Registration of "digest-mismatching-value" Problem Type Type URI: https://iana.org/assignments/http-problem-types#digest- mismatching-value Kleidl, et al. Expires 24 April 2025 [Page 7] Internet-Draft HTTP Problem Types for Digest Fields October 2024 Title: Mismatching Digest Value Recommended HTTP status code: 400 Reference: Section 3.3 of this document 6. Normative References [DIGEST] Polli, R. and L. Pardue, "Digest Fields", RFC 9530, DOI 10.17487/RFC9530, February 2024, . [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, . [PROBLEM] Nottingham, M., Wilde, E., and S. Dalal, "Problem Details for HTTP APIs", RFC 9457, DOI 10.17487/RFC9457, July 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [STRUCTURED-FIELDS] Nottingham, M. and P. Kamp, "Structured Field Values for HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, . Authors' Addresses Marius Kleidl Transloadit Email: marius@transloadit.com Lucas Pardue Cloudflare Email: lucas@lucaspardue.com Kleidl, et al. Expires 24 April 2025 [Page 8] Internet-Draft HTTP Problem Types for Digest Fields October 2024 Roberto Polli Par-Tec Italy Email: robipolli@gmail.com Kleidl, et al. Expires 24 April 2025 [Page 9]