draft-ietf-httpbis-digest-headers-13.txt   draft-ietf-httpbis-digest-headers-latest.txt 
HTTP Working Group R. Polli Internet Engineering Task Force (IETF) R. Polli
Internet-Draft Team Digitale, Italian Government Request for Comments: 9530 Team Digitale, Italian Government
Obsoletes: 3230 (if approved) L. Pardue Obsoletes: 3230 L. Pardue
Intended status: Standards Track Cloudflare Category: Standards Track Cloudflare
Expires: January 11, 2024 July 10, 2023 ISSN: 2070-1721 May 18, 2025
Digest Fields Digest Fields
draft-ietf-httpbis-digest-headers-13
Abstract Abstract
This document defines HTTP fields that support integrity digests. This document defines HTTP fields that support integrity digests.
The Content-Digest field can be used for the integrity of HTTP The Content-Digest field can be used for the integrity of HTTP
message content. The Repr-Digest field can be used for the integrity message content. The Repr-Digest field can be used for the integrity
of HTTP representations. Want-Content-Digest and Want-Repr-Digest of HTTP representations. Want-Content-Digest and Want-Repr-Digest
can be used to indicate a sender's interest and preferences for can be used to indicate a sender's interest and preferences for
receiving the respective Integrity fields. receiving the respective Integrity fields.
skipping to change at page 1, line 42 skipping to change at page 1, line 41
Discussion of this document takes place on the HTTP Working Group Discussion of this document takes place on the HTTP Working Group
mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>. Working Group <https://lists.w3.org/Archives/Public/ietf-http-wg/>. Working Group
information can be found at <https://httpwg.org/>. information can be found at <https://httpwg.org/>.
Source for this draft and an issue tracker can be found at Source for this draft and an issue tracker can be found at
<https://github.com/httpwg/http-extensions/labels/digest-headers>. <https://github.com/httpwg/http-extensions/labels/digest-headers>.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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-
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on January 11, 2024. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9530.
Copyright Notice Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Structure . . . . . . . . . . . . . . . . . . . 4 1.1. Document Structure . . . . . . . . . . . . . . . . . . . 4
1.2. Concept Overview . . . . . . . . . . . . . . . . . . . . 5 1.2. Concept Overview . . . . . . . . . . . . . . . . . . . . 4
1.3. Obsoleting RFC 3230 . . . . . . . . . . . . . . . . . . . 6 1.3. Obsoleting RFC 3230 . . . . . . . . . . . . . . . . . . . 5
1.4. Notational Conventions . . . . . . . . . . . . . . . . . 6 1.4. Notational Conventions . . . . . . . . . . . . . . . . . 6
2. The Content-Digest Field . . . . . . . . . . . . . . . . . . 7 2. The Content-Digest Field . . . . . . . . . . . . . . . . . . 7
3. The Repr-Digest Field . . . . . . . . . . . . . . . . . . . . 8 3. The Repr-Digest Field . . . . . . . . . . . . . . . . . . . . 8
3.1. Using Repr-Digest in State-Changing Requests . . . . . . 10 3.1. Using Repr-Digest in State-Changing Requests . . . . . . 9
3.2. Repr-Digest and Content-Location in Responses . . . . . . 10 3.2. Repr-Digest and Content-Location in Responses . . . . . . 10
4. Integrity preference fields . . . . . . . . . . . . . . . . . 11 4. Integrity Preference Fields . . . . . . . . . . . . . . . . . 10
5. Hash Algorithm Considerations and Registration . . . . . . . 11 5. Hash Algorithm Considerations and Registration . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6.1. HTTP Messages Are Not Protected In Full . . . . . . . . . 13 6.1. HTTP Messages Are Not Protected in Full . . . . . . . . . 13
6.2. End-to-End Integrity . . . . . . . . . . . . . . . . . . 14 6.2. End-to-End Integrity . . . . . . . . . . . . . . . . . . 13
6.3. Usage in Signatures . . . . . . . . . . . . . . . . . . . 14 6.3. Usage in Signatures . . . . . . . . . . . . . . . . . . . 13
6.4. Usage in Trailer Fields . . . . . . . . . . . . . . . . . 15 6.4. Usage in Trailer Fields . . . . . . . . . . . . . . . . . 14
6.5. Variations Within Content Encoding . . . . . . . . . . . 15 6.5. Variations within Content-Encoding . . . . . . . . . . . 14
6.6. Algorithm Agility . . . . . . . . . . . . . . . . . . . . 15 6.6. Algorithm Agility . . . . . . . . . . . . . . . . . . . . 15
6.7. Resource exhaustion . . . . . . . . . . . . . . . . . . . 16 6.7. Resource Exhaustion . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. HTTP Field Name Registration . . . . . . . . . . . . . . 16 7.1. HTTP Field Name Registration . . . . . . . . . . . . . . 16
7.2. Establish the Hash Algorithms for HTTP Digest Fields 7.2. Creation of the Hash Algorithms for HTTP Digest Fields
Registry . . . . . . . . . . . . . . . . . . . . . . . . 17 Registry . . . . . . . . . . . . . . . . . . . . . . . . 16
7.3. Deprecate the Hypertext Transfer Protocol (HTTP) Digest 7.3. Deprecate the Hypertext Transfer Protocol (HTTP) Digest
Algorithm Values Registry . . . . . . . . . . . . . . . . 18 Algorithm Values Registry . . . . . . . . . . . . . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18 8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 19 8.2. Informative References . . . . . . . . . . . . . . . . . 19
8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Resource Representation and Representation Data . . 21 Appendix A. Resource Representation and Representation Data . . 21
Appendix B. Examples of Unsolicited Digest . . . . . . . . . . . 24 Appendix B. Examples of Unsolicited Digest . . . . . . . . . . . 24
B.1. Server Returns Full Representation Data . . . . . . . . . 25 B.1. Server Returns Full Representation Data . . . . . . . . . 24
B.2. Server Returns No Representation Data . . . . . . . . . . 25 B.2. Server Returns No Representation Data . . . . . . . . . . 25
B.3. Server Returns Partial Representation Data . . . . . . . 26 B.3. Server Returns Partial Representation Data . . . . . . . 26
B.4. Client and Server Provide Full Representation Data . . . 27 B.4. Client and Server Provide Full Representation Data . . . 27
B.5. Client Provides Full Representation Data, Server Provides B.5. Client Provides Full Representation Data and Server
No Representation Data . . . . . . . . . . . . . . . . . 28 Provides No Representation Data . . . . . . . . . . . . . 28
B.6. Client and Server Provide Full Representation Data . . . 29 B.6. Client and Server Provide Full Representation Data . . . 29
B.7. POST Response does not Reference the Request URI . . . . 29 B.7. POST Response Does Not Reference the Request URI . . . . 29
B.8. POST Response Describes the Request Status . . . . . . . 30 B.8. POST Response Describes the Request Status . . . . . . . 30
B.9. Digest with PATCH . . . . . . . . . . . . . . . . . . . . 31 B.9. Digest with PATCH . . . . . . . . . . . . . . . . . . . . 31
B.10. Error responses . . . . . . . . . . . . . . . . . . . . . 32 B.10. Error Responses . . . . . . . . . . . . . . . . . . . . . 32
B.11. Use with Trailer Fields and Transfer Coding . . . . . . . 33 B.11. Use with Trailer Fields and Transfer Coding . . . . . . . 33
Appendix C. Examples of Want-Repr-Digest Solicited Digest . . . 34 Appendix C. Examples of Want-Repr-Digest Solicited Digest . . . 34
C.1. Server Selects Client's Least Preferred Algorithm . . . . 34 C.1. Server Selects Client's Least Preferred Algorithm . . . . 34
C.2. Server Selects Algorithm Unsupported by Client . . . . . 35 C.2. Server Selects Algorithm Unsupported by Client . . . . . 35
C.3. Server Does Not Support Client Algorithm and Returns an C.3. Server Does Not Support Client Algorithm and Returns an
Error . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Error . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Appendix D. Sample Digest Values . . . . . . . . . . . . . . . . 36 Appendix D. Sample Digest Values . . . . . . . . . . . . . . . . 36
Appendix E. Migrating from RFC 3230 . . . . . . . . . . . . . . 37 Appendix E. Migrating from RFC 3230 . . . . . . . . . . . . . . 37
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 38 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 38
Code Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
H.1. Since draft-ietf-httpbis-digest-headers-12 . . . . . . . 39
H.2. Since draft-ietf-httpbis-digest-headers-11 . . . . . . . 40
H.3. Since draft-ietf-httpbis-digest-headers-10 . . . . . . . 40
H.4. Since draft-ietf-httpbis-digest-headers-09 . . . . . . . 40
H.5. Since draft-ietf-httpbis-digest-headers-08 . . . . . . . 40
H.6. Since draft-ietf-httpbis-digest-headers-07 . . . . . . . 40
H.7. Since draft-ietf-httpbis-digest-headers-06 . . . . . . . 40
H.8. Since draft-ietf-httpbis-digest-headers-05 . . . . . . . 40
H.9. Since draft-ietf-httpbis-digest-headers-04 . . . . . . . 41
H.10. Since draft-ietf-httpbis-digest-headers-03 . . . . . . . 41
H.11. Since draft-ietf-httpbis-digest-headers-02 . . . . . . . 41
H.12. Since draft-ietf-httpbis-digest-headers-01 . . . . . . . 42
H.13. Since draft-ietf-httpbis-digest-headers-00 . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction 1. Introduction
HTTP does not define the means to protect the data integrity of HTTP does not define the means to protect the data integrity of
content or representations. When HTTP messages are transferred content or representations. When HTTP messages are transferred
between endpoints, lower layer features or properties such as TCP between endpoints, lower-layer features or properties such as TCP
checksums or TLS records [TLS] can provide some integrity protection. checksums or TLS records [TLS] can provide some integrity protection.
However, transport-oriented integrity provides a limited utility However, transport-oriented integrity provides a limited utility
because it is opaque to the application layer and only covers the because it is opaque to the application layer and only covers the
extent of a single connection. HTTP messages often travel over a extent of a single connection. HTTP messages often travel over a
chain of separate connections. In between connections there is a chain of separate connections. In between connections, there is a
possibility for data corruption. An HTTP integrity mechanism can possibility for data corruption. An HTTP integrity mechanism can
provide the means for endpoints, or applications using HTTP, to provide the means for endpoints, or applications using HTTP, to
detect data corruption and make a choice about how to act on it. An detect data corruption and make a choice about how to act on it. An
example use case is to aid fault detection and diagnosis across example use case is to aid fault detection and diagnosis across
system boundaries. system boundaries.
This document defines two digest integrity mechanisms for HTTP. This document defines two digest integrity mechanisms for HTTP.
First, content integrity, which acts on conveyed content (Section 6.4 First, content integrity, which acts on conveyed content (Section 6.4
of [HTTP]). Second, representation data integrity, which acts on of [HTTP]). Second, representation data integrity, which acts on
representation data (Section 8.1 of [HTTP]). This supports advanced representation data (Section 8.1 of [HTTP]). This supports advanced
use cases such as validating the integrity of a resource that was use cases, such as validating the integrity of a resource that was
reconstructed from parts retrieved using multiple requests or reconstructed from parts retrieved using multiple requests or
connections. connections.
This document obsoletes RFC 3230 and therefore the Digest and Want- This document obsoletes [RFC3230] and therefore the Digest and Want-
Digest HTTP fields; see Section 1.3. Digest HTTP fields; see Section 1.3.
1.1. Document Structure 1.1. Document Structure
This document is structured as follows: This document is structured as follows:
o New request and response header and trailer field definitions. o New request and response header and trailer field definitions.
* Section 2 (Content-Digest), * Section 2 (Content-Digest),
* Section 3 (Repr-Digest), and * Section 3 (Repr-Digest), and
* Section 4 (Want-Content-Digest and Want-Repr-Digest). * Section 4 (Want-Content-Digest and Want-Repr-Digest).
o Considerations specific to representation data integrity. o Considerations specific to representation data integrity.
* Section 3.1 (State-changing requests), * Section 3.1 (State-changing requests),
* Section 3.2 (Content-Location), * Section 3.2 (Content-Location),
* Appendix A contains worked examples of Representation data in * Appendix A contains worked examples of representation data in
message exchanges, and message exchanges, and
* Appendix B and Appendix C contain worked examples of Repr- * Appendixes B and C contain worked examples of Repr-Digest and
Digest and Want-Repr-Digest fields in message exchanges. Want-Repr-Digest fields in message exchanges.
o Section 5 presents hash algorithm considerations and defines o Section 5 presents hash algorithm considerations and defines
registration procedures for future entries. registration procedures for future entries.
1.2. Concept Overview 1.2. Concept Overview
The HTTP fields defined in this document can be used for HTTP The HTTP fields defined in this document can be used for HTTP
integrity. Senders choose a hashing algorithm and calculate a digest integrity. Senders choose a hashing algorithm and calculate a digest
from an input related to the HTTP message. The algorithm identifier from an input related to the HTTP message. The algorithm identifier
and digest are transmitted in an HTTP field. Receivers can validate and digest are transmitted in an HTTP field. Receivers can validate
skipping to change at page 5, line 37 skipping to change at page 5, line 12
trailer field is defined to support digests of content (Section 6.4 trailer field is defined to support digests of content (Section 6.4
of [HTTP]); see Section 2. of [HTTP]); see Section 2.
For more advanced use cases, the "Repr-Digest" request and response For more advanced use cases, the "Repr-Digest" request and response
header and trailer field (Section 3) is defined. It contains a header and trailer field (Section 3) is defined. It contains a
digest value computed by applying a hashing algorithm to selected digest value computed by applying a hashing algorithm to selected
representation data (Section 8.1 of [HTTP]). Basing "Repr-Digest" on representation data (Section 8.1 of [HTTP]). Basing "Repr-Digest" on
the selected representation makes it straightforward to apply it to the selected representation makes it straightforward to apply it to
use cases where the message content requires some sort of use cases where the message content requires some sort of
manipulation to be considered as representation of the resource or manipulation to be considered as representation of the resource or
content conveys a partial representation of a resource, such as Range the content conveys a partial representation of a resource, such as
Requests (see Section 14 of [HTTP]). range requests (see Section 14 of [HTTP]).
"Content-Digest" and "Repr-Digest" support hashing algorithm agility. "Content-Digest" and "Repr-Digest" support hashing algorithm agility.
The "Want-Content-Digest" and "Want-Repr-Digest" fields allow The "Want-Content-Digest" and "Want-Repr-Digest" fields allow
endpoints to express interest in "Content-Digest" and "Repr-Digest" endpoints to express interest in "Content-Digest" and "Repr-Digest",
respectively, and to express algorithm preferences in either. respectively, and to express algorithm preferences in either.
"Content-Digest" and "Repr-Digest" are collectively termed Integrity "Content-Digest" and "Repr-Digest" are collectively termed "Integrity
fields. "Want-Content-Digest" and "Want-Repr-Digest" are fields". "Want-Content-Digest" and "Want-Repr-Digest" are
collectively termed Integrity preference fields. collectively termed "Integrity preference fields".
Integrity fields are tied to the "Content-Encoding" and "Content- Integrity fields are tied to the "Content-Encoding" and "Content-
Type" header fields. Therefore, a given resource may have multiple Type" header fields. Therefore, a given resource may have multiple
different digest values when transferred with HTTP. different digest values when transferred with HTTP.
Integrity fields apply to HTTP message content or HTTP Integrity fields apply to HTTP message content or HTTP
representations. They do not apply to HTTP messages or fields. representations. They do not apply to HTTP messages or fields.
However, they can be combined with other mechanisms that protect However, they can be combined with other mechanisms that protect
metadata, such as digital signatures, in order to protect the phases metadata, such as digital signatures, in order to protect the phases
of an HTTP exchange in whole or in part. For example, HTTP Message of an HTTP exchange in whole or in part. For example, HTTP Message
Signatures [SIGNATURES] could be used to sign Integrity fields, thus Signatures [SIGNATURES] could be used to sign Integrity fields, thus
providing coverage for HTTP content or representation data. providing coverage for HTTP content or representation data.
This specification does not define means for authentication, This specification does not define means for authentication,
authorization, or privacy. authorization, or privacy.
1.3. Obsoleting RFC 3230 1.3. Obsoleting RFC 3230
[RFC3230] defined the "Digest" and "Want-Digest" HTTP fields for HTTP [RFC3230] defined the "Digest" and "Want-Digest" HTTP fields for HTTP
integrity. It also coined the term "instance" and "instance integrity. It also coined the terms "instance" and "instance
manipulation" in order to explain concepts that are now more manipulation" in order to explain concepts, such as selected
universally defined, and implemented, as HTTP semantics such as representation data (Section 8.1 of [HTTP]), that are now more
selected representation data (Section 8.1 of [HTTP]). universally defined and implemented as HTTP semantics.
Experience has shown that implementations of [RFC3230] have Experience has shown that implementations of [RFC3230] have
interpreted the meaning of "instance" inconsistently, leading to interpreted the meaning of "instance" inconsistently, leading to
interoperability issues. The most common issue relates to the interoperability issues. The most common issue relates to the
mistake of calculating the digest using (what we now call) message mistake of calculating the digest using (what we now call) message
content, rather than using (what we now call) representation data as content, rather than using (what we now call) representation data as
was originally intended. Interestingly, time has also shown that a was originally intended. Interestingly, time has also shown that a
digest of message content can be beneficial for some use cases. So digest of message content can be beneficial for some use cases, so it
it is difficult to detect if non-conformance to [RFC3230] is is difficult to detect if non-conformance to [RFC3230] is intentional
intentional or unintentional. or unintentional.
In order to address potential inconsistencies and ambiguity across In order to address potential inconsistencies and ambiguity across
implementations of "Digest" and "Want-Digest", this document implementations of "Digest" and "Want-Digest", this document
obsoletes [RFC3230]. The Integrity fields (Sections 2 and 3) and obsoletes [RFC3230]. The Integrity fields (Sections 2 and 3) and
Integrity preference fields (Section 4) defined in this document are Integrity preference fields (Section 4) defined in this document are
better aligned with current HTTP semantics and have names that more better aligned with current HTTP semantics and have names that more
clearly articulate the intended usages. clearly articulate the intended usages.
1.4. Notational Conventions 1.4. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This document uses the Augmented BNF defined in [RFC5234] and updated This document uses the Augmented BNF defined in [RFC5234] and updated
by [RFC7405]. This includes the rules: CR (carriage return), LF by [RFC7405]. This includes the rules CR (carriage return), LF (line
(line feed), and CRLF (CR LF). feed), and CRLF (CR LF).
This document uses the following terminology from Section 3 of This document uses the following terminology from Section 3 of
[STRUCTURED-FIELDS] to specify syntax and parsing: Boolean, Byte [STRUCTURED-FIELDS] to specify syntax and parsing: Boolean, Byte
Sequence, Dictionary, Integer, and List. Sequence, Dictionary, Integer, and List.
The definitions "representation", "selected representation", The definitions "representation", "selected representation",
"representation data", "representation metadata", "user agent", and "representation data", "representation metadata", "user agent", and
"content" in this document are to be interpreted as described in "content" in this document are to be interpreted as described in
[HTTP]. [HTTP].
This document uses the line folding strategies described in This document uses the line folding strategies described in
[FOLDING]. [FOLDING].
Hashing algorithm names respect the casing used in their definition Hashing algorithm names respect the casing used in their definition
document (e.g., SHA-1, CRC32c). document (e.g., SHA-1, CRC32c).
HTTP messages indicate hashing algorithms using an Algorithm Key HTTP messages indicate hashing algorithms using an Algorithm Key
(algorithms). Where the document refers to an Algorithm Key in (algorithms). Where the document refers to an Algorithm Key in
prose, it is quoted (e.g., "sha", "crc32c"). prose, it is quoted (e.g., "sha", "crc32c").
The term "checksum" describes the output of the application of an The term "checksum" describes the output of applying an algorithm to
algorithm to a sequence of bytes, whereas "digest" is only used in a sequence of bytes, whereas "digest" is only used in relation to the
relation to the value contained in the fields. value contained in the fields.
Integrity fields: collective term for "Content-Digest" and "Repr- "Integrity fields" is the collective term for "Content-Digest" and
Digest" "Repr-Digest".
Integrity preference fields: collective term for "Want-Repr-Digest" "Integrity preference fields" is the collective term for "Want-Repr-
and "Want-Content-Digest" Digest" and "Want-Content-Digest".
2. The Content-Digest Field 2. The Content-Digest Field
The "Content-Digest" HTTP field can be used in requests and responses The "Content-Digest" HTTP field can be used in requests and responses
to communicate digests that are calculated using a hashing algorithm to communicate digests that are calculated using a hashing algorithm
applied to the actual message content (see Section 6.4 of [HTTP]). applied to the actual message content (see Section 6.4 of [HTTP]).
It is a "Dictionary" (see Section 3.2 of [STRUCTURED-FIELDS]) where It is a "Dictionary" (see Section 3.2 of [STRUCTURED-FIELDS]), where
each: each:
o key conveys the hashing algorithm (see Section 5) used to compute o key conveys the hashing algorithm (see Section 5) used to compute
the digest; the digest;
o value is a "Byte Sequence" (Section 3.3.5 of [STRUCTURED-FIELDS]), o value is a "Byte Sequence" (Section 3.3.5 of [STRUCTURED-FIELDS])
that conveys an encoded version of the byte output produced by the that conveys an encoded version of the byte output produced by the
digest calculation. digest calculation.
For example: For example:
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
Content-Digest: \ Content-Digest: \
sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\ sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\
yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==: yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:
skipping to change at page 8, line 27 skipping to change at page 7, line 47
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
Content-Digest: \ Content-Digest: \
sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:,\ sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:,\
sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\ sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\
yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==: yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:
A recipient MAY ignore any or all digests. Application-specific A recipient MAY ignore any or all digests. Application-specific
behavior or local policy MAY set additional constraints on the behavior or local policy MAY set additional constraints on the
processing and validation practices of the conveyed digests. The processing and validation practices of the conveyed digests. The
security considerations covers some of the issues related to ignoring security considerations cover some of the issues related to ignoring
digests (see Section 6.6) and validating multiple digests (see digests (see Section 6.6) and validating multiple digests (see
Section 6.7). Section 6.7).
A sender MAY send a digest without knowing whether the recipient A sender MAY send a digest without knowing whether the recipient
supports a given hashing algorithm, or even knowing that the supports a given hashing algorithm. A sender MAY send a digest if it
recipient will ignore it. knows the recipient will ignore it.
"Content-Digest" can be sent in a trailer section. In this case, "Content-Digest" can be sent in a trailer section. In this case,
"Content-Digest" MAY be merged into the header section; see "Content-Digest" MAY be merged into the header section; see
Section 6.5.1 of [HTTP]. Section 6.5.1 of [HTTP].
3. The Repr-Digest Field 3. The Repr-Digest Field
The "Repr-Digest" HTTP field can be used in requests and responses to The "Repr-Digest" HTTP field can be used in requests and responses to
communicate digests that are calculated using a hashing algorithm communicate digests that are calculated using a hashing algorithm
applied to the entire selected representation data (see Section 8.1 applied to the entire selected representation data (see Section 8.1
of [HTTP]). of [HTTP]).
Representations take into account the effect of the HTTP semantics on Representations take into account the effect of the HTTP semantics on
messages. For example, the content can be affected by Range Requests messages. For example, the content can be affected by range requests
or methods such as HEAD, while the way the content is transferred "on or methods, such as HEAD, while the way the content is transferred
the wire" is dependent on other transformations (e.g., transfer "on the wire" is dependent on other transformations (e.g., transfer
codings for HTTP/1.1 - see Section 6.1 of [RFC9112]). To help codings for HTTP/1.1; see Section 6.1 of [RFC9112]). To help
illustrate HTTP representation concepts, several examples are illustrate HTTP representation concepts, several examples are
provided in Appendix A. provided in Appendix A.
When a message has no representation data it is still possible to When a message has no representation data, it is still possible to
assert that no representation data was sent by computing the digest assert that no representation data was sent by computing the digest
on an empty string (see Section 6.3). on an empty string (see Section 6.3).
"Repr-Digest" is a "Dictionary" (see Section 3.2 of "Repr-Digest" is a "Dictionary" (see Section 3.2 of
[STRUCTURED-FIELDS]) where each: [STRUCTURED-FIELDS]), where each:
o key conveys the hashing algorithm (see Section 5) used to compute o key conveys the hashing algorithm (see Section 5) used to compute
the digest; the digest;
o value is a "Byte Sequence", that conveys an encoded version of the o value is a "Byte Sequence" that conveys an encoded version of the
byte output produced by the digest calculation. byte output produced by the digest calculation.
For example: For example:
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
Repr-Digest: \ Repr-Digest: \
sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\ sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\
yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==: yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:
The "Dictionary" type can be used, for example, to attach multiple The "Dictionary" type can be used to attach multiple digests
digests calculated using different hashing algorithms in order to calculated using different hashing algorithms in order to support a
support a population of endpoints with different or evolving population of endpoints with different or evolving capabilities.
capabilities. Such an approach could support transitions away from
weaker algorithms (see Section 6.6). Such an approach could support transitions away from weaker
algorithms (see Section 6.6).
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
Repr-Digest: \ Repr-Digest: \
sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:,\ sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:,\
sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\ sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\
yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==: yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:
A recipient MAY ignore any or all digests. Application-specific A recipient MAY ignore any or all digests. Application-specific
behavior or local policy MAY set additional constraints on the behavior or local policy MAY set additional constraints on the
processing and validation practices of the conveyed digests. The processing and validation practices of the conveyed digests. The
security considerations covers some of the issues related to ignoring security considerations cover some of the issues related to ignoring
digests (see Section 6.6) and validating multiple digests (see digests (see Section 6.6) and validating multiple digests (see
Section 6.7). Section 6.7).
A sender MAY send a digest without knowing whether the recipient A sender MAY send a digest without knowing whether the recipient
supports a given hashing algorithm, or even knowing that the supports a given hashing algorithm. A sender MAY send a digest if it
recipient will ignore it. knows the recipient will ignore it.
"Repr-Digest" can be sent in a trailer section. In this case, "Repr- "Repr-Digest" can be sent in a trailer section. In this case, "Repr-
Digest" MAY be merged into the header section; see Section 6.5.1 of Digest" MAY be merged into the header section; see Section 6.5.1 of
[HTTP]. [HTTP].
3.1. Using Repr-Digest in State-Changing Requests 3.1. Using Repr-Digest in State-Changing Requests
When the representation enclosed in a state-changing request does not When the representation enclosed in a state-changing request does not
describe the target resource, the representation digest MUST be describe the target resource, the representation digest MUST be
computed on the representation data. This is the only possible computed on the representation data. This is the only possible
choice because representation digest requires complete representation choice because representation digest requires complete representation
metadata (see Section 3). metadata (see Section 3).
In responses, In responses,
o if the representation describes the status of the request, "Repr- o if the representation describes the status of the request, "Repr-
Digest" MUST be computed on the enclosed representation (see Digest" MUST be computed on the enclosed representation (see
Appendix B.8); Appendix B.8);
o if there is a referenced resource "Repr-Digest" MUST be computed o if there is a referenced resource, "Repr-Digest" MUST be computed
on the selected representation of the referenced resource even if on the selected representation of the referenced resource even if
that is different from the target resource. That might or might that is different from the target resource. This might or might
not result in computing "Repr-Digest" on the enclosed not result in computing "Repr-Digest" on the enclosed
representation. representation.
The latter case is done according to the HTTP semantics of the given The latter case is done according to the HTTP semantics of the given
method, for example using the "Content-Location" header field (see method, for example, using the "Content-Location" header field (see
Section 8.7 of [HTTP]). In contrast, the "Location" header field Section 8.7 of [HTTP]). In contrast, the "Location" header field
does not affect "Repr-Digest" because it is not representation does not affect "Repr-Digest" because it is not representation
metadata. metadata.
For example, in "PATCH" requests, the representation digest will be For example, in "PATCH" requests, the representation digest will be
computed on the patch document because the representation metadata computed on the patch document because the representation metadata
refers to the patch document and not to the target resource (see refers to the patch document and not the target resource (see
Section 2 of [PATCH]). In responses, instead, the representation Section 2 of [PATCH]). In responses, instead, the representation
digest will be computed on the selected representation of the patched digest will be computed on the selected representation of the patched
resource. resource.
3.2. Repr-Digest and Content-Location in Responses 3.2. Repr-Digest and Content-Location in Responses
When a state-changing method returns the "Content-Location" header When a state-changing method returns the "Content-Location" header
field, the enclosed representation refers to the resource identified field, the enclosed representation refers to the resource identified
by its value and "Repr-Digest" is computed accordingly. An example by its value and "Repr-Digest" is computed accordingly. An example
is given in Appendix B.7. is given in Appendix B.7.
4. Integrity preference fields 4. Integrity Preference Fields
Senders can indicate their interest in Integrity fields and hashing Senders can indicate their interest in Integrity fields and hashing
algorithm preferences using the "Want-Content-Digest" or "Want-Repr- algorithm preferences using the "Want-Content-Digest" or "Want-Repr-
Digest" fields. These can be used in both requests and responses. Digest" HTTP fields. These can be used in both requests and
responses.
"Want-Content-Digest" indicates that the sender would like to receive "Want-Content-Digest" indicates that the sender would like to receive
a content digest on messages associated with the request URI and (via the Content-Digest field) a content digest on messages
representation metadata, using the "Content-Digest" field. associated with the request URI and representation metadata. "Want-
Repr-Digest" indicates that the sender would like to receive (via the
"Want-Repr-Digest" indicates that the sender would like to receive a Repr-Digest field) a representation digest on messages associated
representation digest on messages associated with the request URI and with the request URI and representation metadata.
representation metadata, using the "Repr-Digest" field.
If "Want-Content-Digest" or "Want-Repr-Digest" are used in a If "Want-Content-Digest" or "Want-Repr-Digest" are used in a
response, it indicates that the server would like the client to response, it indicates that the server would like the client to
provide the respective Integrity field on future requests. provide the respective Integrity field on future requests.
Integrity preference fields are only a hint. The receiver of the Integrity preference fields are only a hint. The receiver of the
field can ignore it and send an Integrity field using any algorithm field can ignore it and send an Integrity field using any algorithm
or omit the field entirely, for example see Appendix C.2. It is not or omit the field entirely; for example, see Appendix C.2. It is not
a protocol error if preferences are ignored. Applications that use a protocol error if preferences are ignored. Applications that use
Integrity fields and Integrity preferences can define expectations or Integrity fields and Integrity preferences can define expectations or
constraints that operate in addition to this specification. Ignored constraints that operate in addition to this specification. Ignored
preferences are an application-specific concern. preferences are an application-specific concern.
"Want-Content-Digest" and "Want-Repr-Digest" are of type "Dictionary" "Want-Content-Digest" and "Want-Repr-Digest" are of type "Dictionary"
where each: where each:
o key conveys the hashing algorithm (see Section 5); o key conveys the hashing algorithm (see Section 5);
o value is an "Integer" (Section 3.3.1 of [STRUCTURED-FIELDS]) that o value is an "Integer" (Section 3.3.1 of [STRUCTURED-FIELDS]) that
conveys an ascending, relative, weighted preference. It must be conveys an ascending, relative, weighted preference. It must be
in the range 0 to 10 inclusive. 1 is the least preferred, 10 is in the range 0 to 10 inclusive. 1 is the least preferred, 10 is
the most preferred, and a value of 0 means "not acceptable". the most preferred, and a value of 0 means "not acceptable".
Examples: Examples:
Want-Repr-Digest: sha-256=1 Want-Repr-Digest: sha-256=1
Want-Repr-Digest: sha-512=3, sha-256=10, unixsum=0 Want-Repr-Digest: sha-512=3, sha-256=10, unixsum=0
Want-Content-Digest: sha-256=1 Want-Content-Digest: sha-256=1
skipping to change at page 12, line 12 skipping to change at page 11, line 28
There are a wide variety of hashing algorithms that can be used for There are a wide variety of hashing algorithms that can be used for
the purposes of integrity. The choice of algorithm depends on the purposes of integrity. The choice of algorithm depends on
several factors such as the integrity use case, implementation needs several factors such as the integrity use case, implementation needs
or constraints, or application design and workflows. or constraints, or application design and workflows.
An initial set of algorithms will be registered with IANA in the An initial set of algorithms will be registered with IANA in the
"Hash Algorithms for HTTP Digest Fields" registry; see Section 7.2. "Hash Algorithms for HTTP Digest Fields" registry; see Section 7.2.
Additional algorithms can be registered in accordance with the Additional algorithms can be registered in accordance with the
policies set out in this section. policies set out in this section.
Each algorithm has a status field, which is intended to provide an Each algorithm has a status field that is intended to provide an aid
aid to implementation selection. to implementation selection.
Algorithms with a status value of "Active" are suitable for many Algorithms with a status value of "Active" are suitable for many
purposes and it is RECOMMENDED that applications use these purposes and it is RECOMMENDED that applications use these
algorithms. These can be used in adversarial situations where hash algorithms. These can be used in adversarial situations where hash
functions might need to provide resistance to collision, first- functions might need to provide resistance to collision, first-
preimage and second-preimage attacks. For adversarial situations, preimage, and second-preimage attacks. For adversarial situations,
selecting which of the "Active" algorithms are acceptable will depend selection of the acceptable "Active" algorithms will depend on the
on the level of protection the circumstances demand. More level of protection the circumstances demand. More considerations
considerations are presented in Section 6.6. are presented in Section 6.6.
Algorithms with a status value of "Deprecated" either provide none of Algorithms with a status value of "Deprecated" either provide none of
these properties, or are known to be weak (see [NO-MD5] and these properties or are known to be weak (see [NO-MD5] and [NO-SHA]).
[NO-SHA]). These algorithms MAY be used to preserve integrity These algorithms MAY be used to preserve integrity against
against corruption, but MUST NOT be used in a potentially adversarial corruption, but MUST NOT be used in a potentially adversarial
setting; for example, when signing Integrity fields' values for setting, for example, when signing Integrity fields' values for
authenticity. Permitting the use of these algorithms can help some authenticity. Permitting the use of these algorithms can help some
applications, for example, those that previously used [RFC3230], are applications (such as those that previously used [RFC3230], are
migrating to this specification (Appendix E), and have existing migrating to this specification (Appendix E), and have existing
stored collections of computed digest values avoid undue operational stored collections of computed digest values) avoid undue operational
overhead caused by recomputation using other more-secure algorithms. overhead caused by recomputation using other more-secure algorithms.
Such applications are not exempt from the requirements in this Such applications are not exempt from the requirements in this
section. Furthermore, applications without such legacy or history section. Furthermore, applications without such legacy or history
ought to follow the guidance for using algorithms with the status ought to follow the guidance for using algorithms with the status
value "Active". value "Active".
Discussion of algorithm agility is presented in Section 6.6. Discussion of algorithm agility is presented in Section 6.6.
Registration requests for the "Hash Algorithms for HTTP Digest Registration requests for the "Hash Algorithms for HTTP Digest
Fields" registry use the Specification Required policy (Section 4.6 Fields" registry use the Specification Required policy (Section 4.6
of [RFC8126]). Requests should use the following template: of [RFC8126]). Requests should use the following template:
o Algorithm Key: the Structured Fields key value used in "Content- o Algorithm Key: The Structured Fields key value used in "Content-
Digest", "Repr-Digest", "Want-Content-Digest", or "Want-Repr- Digest", "Repr-Digest", "Want-Content-Digest", or "Want-Repr-
Digest" field Dictionary member keys Digest" field Dictionary member keys.
o Status: the status of the algorithm. The options are: o Status: The status of the algorithm. The options are:
* "Active" - for algorithms without known problems, * "Active" - Algorithms without known problems
* "Provisional" - for unproven algorithms,
* "Deprecated" - for deprecated or insecure algorithms, * "Provisional" - Unproven algorithms
o Description: a short description of the algorithm * "Deprecated" - Deprecated or insecure algorithms
o Reference(s): pointer(s) to the primary document(s) defining the o Description: A short description of the algorithm
Algorithm Key and technical details of the algorithm
o Reference(s): Pointer(s) to the primary document(s) defining the
Algorithm Key and technical details of the algorithm.
When reviewing registration requests, the designated expert(s) should When reviewing registration requests, the designated expert(s) should
pay attention to the requested status. The status value should pay attention to the requested status. The status value should
reflect standardization status and the broad opinion of relevant reflect standardization status and the broad opinion of relevant
interest groups such as the IETF or security-related SDOs. The interest groups such as the IETF or security-related Standards
"Active" status is not suitable for an algorithm that is known to be Development Organizations (SDOs). The "Active" status is not
weak, broken, or experimental. If a registration request attempts to suitable for an algorithm that is known to be weak, broken, or
register such an algorithm as "Active", the designated expert(s) experimental. If a registration request attempts to register such an
should suggest an alternative status of "Deprecated" or algorithm as "Active", the designated expert(s) should suggest an
"Provisional". alternative status of "Deprecated" or "Provisional".
When reviewing registration requests, the designated expert(s) cannot When reviewing registration requests, the designated expert(s) cannot
use a status of "Deprecated" or "Provisional" as grounds for use a status of "Deprecated" or "Provisional" as grounds for
rejection. rejection.
Requests to update or change the fields in an existing registration Requests to update or change the fields in an existing registration
are permitted. For example, this could allow for the transition of are permitted. For example, this could allow for the transition of
an algorithm status from "Active" to "Deprecated" as the security an algorithm status from "Active" to "Deprecated" as the security
environment evolves. environment evolves.
6. Security Considerations 6. Security Considerations
6.1. HTTP Messages Are Not Protected In Full 6.1. HTTP Messages Are Not Protected in Full
This document specifies a data integrity mechanism that protects HTTP This document specifies a data integrity mechanism that protects HTTP
representation data or content, but not HTTP header and trailer representation data or content, but not HTTP header and trailer
fields, from certain kinds of corruption. fields, from certain kinds of corruption.
Integrity fields are not intended to be a general protection against Integrity fields are not intended to be a general protection against
malicious tampering with HTTP messages. In the absence of additional malicious tampering with HTTP messages. In the absence of additional
security mechanisms, an on-path, malicious actor can remove or security mechanisms, an on-path malicious actor can either remove a
recalculate and substitute a digest value. This attack can be digest value entirely or substitute it with a new digest value
mitigated by combining mechanisms described in this document with computed over manipulated representation data or content. This
other approaches such as transport-layer security or digital attack can be mitigated by combining mechanisms described in this
signatures (for example, HTTP Message Signatures [SIGNATURES]). document with other approaches such as Transport Layer Security (TLS)
or digital signatures (for example, HTTP Message Signatures
[SIGNATURES]).
6.2. End-to-End Integrity 6.2. End-to-End Integrity
Integrity fields can help detect representation data or content Integrity fields can help detect representation data or content
modification due to implementation errors, undesired "transforming modification due to implementation errors, undesired "transforming
proxies" (see Section 7.7 of [HTTP]) or other actions as the data proxies" (see Section 7.7 of [HTTP]), or other actions as the data
passes across multiple hops or system boundaries. Even a simple passes across multiple hops or system boundaries. Even a simple
mechanism for end-to-end representation data integrity is valuable mechanism for end-to-end representation data integrity is valuable
because a user agent can validate that resource retrieval succeeded because a user agent can validate that resource retrieval succeeded
before handing off to an HTML parser, video player, etc. for parsing. before handing off to an HTML parser, video player, etc., for
parsing.
Note that using these mechanisms alone does not provide end-to-end Note that using these mechanisms alone does not provide end-to-end
integrity of HTTP messages over multiple hops, since metadata could integrity of HTTP messages over multiple hops since metadata could be
be manipulated at any stage. Methods to protect metadata are manipulated at any stage. Methods to protect metadata are discussed
discussed in Section 6.3. in Section 6.3.
6.3. Usage in Signatures 6.3. Usage in Signatures
Digital signatures are widely used together with checksums to provide Digital signatures are widely used together with checksums to provide
the certain identification of the origin of a message [NIST800-32]. the certain identification of the origin of a message [FIPS186-5].
Such signatures can protect one or more HTTP fields and there are Such signatures can protect one or more HTTP fields and there are
additional considerations when Integrity fields are included in this additional considerations when Integrity fields are included in this
set. set.
There are no restrictions placed on the type or format of digital There are no restrictions placed on the type or format of digital
signature that Integrity fields can be used with. One possible signature that Integrity fields can be used with. One possible
approach is to combine them with HTTP Message Signatures approach is to combine them with HTTP Message Signatures
[SIGNATURES]. [SIGNATURES].
Digests explicitly depend on the "representation metadata" (e.g., the Digests explicitly depend on the "representation metadata" (e.g., the
values of "Content-Type", "Content-Encoding" etc.). A signature that values of "Content-Type", "Content-Encoding", etc.). A signature
protects Integrity fields but not other "representation metadata" can that protects Integrity fields but not other "representation
expose the communication to tampering. For example, an actor could metadata" can expose the communication to tampering. For example, an
manipulate the "Content-Type" field-value and cause a digest actor could manipulate the "Content-Type" field-value and cause a
validation failure at the recipient, preventing the application from digest validation failure at the recipient, preventing the
accessing the representation. Such an attack consumes the resources application from accessing the representation. Such an attack
of both endpoints. See also Section 3.2. consumes the resources of both endpoints. See also Section 3.2.
Signatures are likely to be deemed an adversarial setting when Signatures are likely to be deemed an adversarial setting when
applying Integrity fields; see Section 5. "Repr-Digest" offers an applying Integrity fields; see Section 5. "Repr-Digest" offers an
interesting possibility when combined with signatures. In the interesting possibility when combined with signatures. In the
scenario where there is no content to send, the digest of an empty scenario where there is no content to send, the digest of an empty
string can be included in the message and, if signed, can help the string can be included in the message and, if signed, can help the
recipient detect if content was added either as a result of accident recipient detect if content was added either as a result of accident
or purposeful manipulation. The opposite scenario is also supported; or purposeful manipulation. The opposite scenario is also supported;
including an Integrity field for content, and signing it, can help a including an Integrity field for content and signing it can help a
recipient detect where the content was removed. recipient detect where the content was removed.
Any mangling of Integrity fields, including digests' de-duplication Any mangling of Integrity fields might affect signature validation.
or combining different field values (see Section 5.2 of [HTTP]) might Examples of such mangling include de-duplicating digests or combining
affect signature validation. different field values (see Section 5.2 of [HTTP]).
6.4. Usage in Trailer Fields 6.4. Usage in Trailer Fields
Before sending Integrity fields in a trailer section, the sender Before sending Integrity fields in a trailer section, the sender
should consider that intermediaries are explicitly allowed to drop should consider that intermediaries are explicitly allowed to drop
any trailer (see Section 6.5.2 of [HTTP]). any trailer (see Section 6.5.2 of [HTTP]).
When Integrity fields are used in a trailer section, the field-values When Integrity fields are used in a trailer section, the field-values
are received after the content. Eager processing of content before are received after the content. Eager processing of content before
the trailer section prevents digest validation, possibly leading to the trailer section prevents digest validation, possibly leading to
processing of invalid data. processing of invalid data.
One of the benefits of using Integrity fields in a trailer section is One of the benefits of using Integrity fields in a trailer section is
that it allows hashing of bytes as they are sent. However, it is that it allows hashing of bytes as they are sent. However, it is
possible to design a hashing algorithm that requires processing of possible to design a hashing algorithm that requires processing of
content in such a way that would negate these benefits. For example, content in such a way that would negate these benefits. For example,
Merkle Integrity Content Encoding [I-D.thomson-http-mice] requires Merkle Integrity Content Encoding [MICE] requires content to be
content to be processed in reverse order. This means the complete processed in reverse order. This means the complete data needs to be
data needs to be available, which means there is negligible available, which means there is negligible processing difference in
processing difference in sending an Integrity field in a header or sending an Integrity field in a header versus a trailer section.
trailer section.
6.5. Variations Within Content Encoding 6.5. Variations within Content-Encoding
Content coding mechanisms can support different encoding parameters, Content coding mechanisms can support different encoding parameters,
meaning that the same input content can produce different outputs. meaning that the same input content can produce different outputs.
For example, GZIP supports multiple compression levels. Such For example, GZIP supports multiple compression levels. Such
encoding parameters are generally not communicated as representation encoding parameters are generally not communicated as representation
metadata. For instance, different compression levels would all use metadata. For instance, different compression levels would all use
the same "Content-Encoding: gzip" field. Other examples include the same "Content-Encoding: gzip" field. Other examples include
where encoding relies on nonces or timestamps, such as the aes128gcm where encoding relies on nonces or timestamps, such as the aes128gcm
content coding defined in [RFC8188]. content coding defined in [RFC8188].
Since it is possible for there to be variation within content coding, Since it is possible for there to be variation within content coding,
the checksum conveyed by the integrity fields cannot be used to the checksum conveyed by the Integrity fields cannot be used to
provide a proof of integrity "at rest" unless the whole content is provide a proof of integrity "at rest" unless the whole content is
persisted. persisted.
6.6. Algorithm Agility 6.6. Algorithm Agility
The security properties of hashing algorithms are not fixed. The security properties of hashing algorithms are not fixed.
Algorithm Agility (see [RFC7696]) is achieved by providing Algorithm agility (see [RFC7696]) is achieved by providing
implementations with flexibility to choose hashing algorithms from implementations with flexibility to choose hashing algorithms from
the IANA Hash Algorithms for HTTP Digest Fields registry; see the IANA Hash Algorithms for HTTP Digest Fields registry; see
Section 7.2. Section 7.2.
Transition from weak algorithms is supported by negotiation of Transition from weak algorithms is supported by negotiation of
hashing algorithm using "Want-Content-Digest" or "Want-Repr-Digest" hashing algorithm using "Want-Content-Digest" or "Want-Repr-Digest"
(see Section 4) or by sending multiple digests from which the (see Section 4) or by sending multiple digests from which the
receiver chooses. A receiver that depends on a digest for security receiver chooses. A receiver that depends on a digest for security
will be vulnerable to attacks on the weakest algorithm it is willing will be vulnerable to attacks on the weakest algorithm it is willing
to accept. Endpoints are advised that sending multiple values to accept. Endpoints are advised that sending multiple values
consumes resources, which may be wasted if the receiver ignores them consumes resources that may be wasted if the receiver ignores them
(see Section 3). (see Section 3).
While algorithm agility allows the migration to stronger algorithms While algorithm agility allows the migration to stronger algorithms,
it does not prevent the use of weaker algorithms. Integrity fields it does not prevent the use of weaker algorithms. Integrity fields
do not provide any mitigations for downgrade or substitution attacks do not provide any mitigations for downgrade or substitution attacks
(see Section 1 of [RFC6211]) of the hashing algorithm. To protect (see Section 1 of [RFC6211]) of the hashing algorithm. To protect
against such attacks, endpoints could restrict their set of supported against such attacks, endpoints could restrict their set of supported
algorithms to stronger ones and protect the fields value by using TLS algorithms to stronger ones and protect the fields' values by using
and/or digital signatures. TLS and/or digital signatures.
6.7. Resource exhaustion 6.7. Resource Exhaustion
Integrity fields validation consumes computational resources. In Integrity field validation consumes computational resources. In
order to avoid resource exhaustion, implementations can restrict order to avoid resource exhaustion, implementations can restrict
validation of the algorithm types, number of validations, or the size validation of the algorithm types, the number of validations, or the
of content. In these cases, skipping validation entirely or ignoring size of content. In these cases, skipping validation entirely or
validation failure of a more-preferred algorithm leaves the ignoring validation failure of a more-preferred algorithm leaves the
possibility of a downgrade attack (see Section 6.6). possibility of a downgrade attack (see Section 6.6).
7. IANA Considerations 7. IANA Considerations
7.1. HTTP Field Name Registration 7.1. HTTP Field Name Registration
IANA is asked to update the "Hypertext Transfer Protocol (HTTP) Field IANA has updated the "Hypertext Transfer Protocol (HTTP) Field Name
Name Registry" registry ([HTTP]) according to the table below: Registry" [HTTP] as shown in the table below:
+---------------------+-----------+---------------------------------+ +---------------------+-----------+---------------------------------+
| Field Name | Status | Reference | | Field Name | Status | Reference |
+---------------------+-----------+---------------------------------+ +---------------------+-----------+---------------------------------+
| Content-Digest | permanent | Section 2 of this document | | Content-Digest | permanent | Section 2 of RFC 9530 |
| Repr-Digest | permanent | Section 3 of this document | | Repr-Digest | permanent | Section 3 of RFC 9530 |
| Want-Content-Digest | permanent | Section 4 of this document | | Want-Content-Digest | permanent | Section 4 of RFC 9530 |
| Want-Repr-Digest | permanent | Section 4 of this document | | Want-Repr-Digest | permanent | Section 4 of RFC 9530 |
| Digest | obsoleted | [RFC3230], Section 1.3 of this | | Digest | obsoleted | [RFC3230], Section 1.3 of RFC |
| | | document | | | | 9530 |
| Want-Digest | obsoleted | [RFC3230], Section 1.3 of this | | Want-Digest | obsoleted | [RFC3230], Section 1.3 of RFC |
| | | document | | | | 9530 |
+---------------------+-----------+---------------------------------+ +---------------------+-----------+---------------------------------+
7.2. Establish the Hash Algorithms for HTTP Digest Fields Registry Table 1: Hypertext Transfer Protocol (HTTP) Field Name Registry
Update
IANA is requested to create the new "Hash Algorithms for HTTP Digest 7.2. Creation of the Hash Algorithms for HTTP Digest Fields Registry
Fields" registry at https://www.iana.org/assignments/http-digest-
hash-alg/ [1] and populate it with the entries in Table 1. The
procedure for new registrations is provided in Section 5.
+-----------+------------+-------------------------+----------------+ IANA has created the new "Hash Algorithms for HTTP Digest Fields"
| Algorithm | Status | Description | Reference(s) | registry at <https://www.iana.org/assignments/http-digest-hash-alg/>
| Key | | | | and populated it with the entries in Table 2. The procedure for new
+-----------+------------+-------------------------+----------------+ registrations is provided in Section 5.
| sha-512 | Active | The SHA-512 algorithm. | [RFC6234], |
| | | | [RFC4648], |
| | | | this document. |
| sha-256 | Active | The SHA-256 algorithm. | [RFC6234], |
| | | | [RFC4648], |
| | | | this document. |
| md5 | Deprecated | The MD5 algorithm. It | [RFC1321], |
| | | is vulnerable to | [RFC4648], |
| | | collision attacks; see | this document. |
| | | [NO-MD5] and | |
| | | [CMU-836068] | |
| sha | Deprecated | The SHA-1 algorithm. It | [RFC3174], |
| | | is vulnerable to | [RFC4648], |
| | | collision attacks; see | [RFC6234] this |
| | | [NO-SHA] and | document. |
| | | [IACR-2020-014] | |
| unixsum | Deprecated | The algorithm used by | [RFC4648], |
| | | the UNIX "sum" command. | [RFC6234], |
| | | | [UNIX], this |
| | | | document. |
| unixcksum | Deprecated | The algorithm used by | [RFC4648], |
| | | the UNIX "cksum" | [RFC6234], |
| | | command. | [UNIX], this |
| | | | document. |
| adler | Deprecated | The ADLER32 algorithm. | [RFC1950], |
| | | | this document. |
| crc32c | Deprecated | The CRC32c algorithm. | [RFC9260] |
| | | | appendix A, |
| | | | this document. |
+-----------+------------+-------------------------+----------------+
Table 1: Initial Hash Algorithms +-----------+------------+--------------------------+---------------+
| Algorithm | Status | Description | Reference |
| Key | | | |
+-----------+------------+--------------------------+---------------+
| sha-512 | Active | The SHA-512 algorithm. | [RFC6234], |
| | | | [RFC4648], |
| | | | RFC 9530 |
| sha-256 | Active | The SHA-256 algorithm. | [RFC6234], |
| | | | [RFC4648], |
| | | | RFC 9530 |
| md5 | Deprecated | The MD5 algorithm. It is | [RFC1321], |
| | | vulnerable to collision | [RFC4648], |
| | | attacks; see [NO-MD5] | RFC 9530 |
| | | and [CMU-836068] | |
| sha | Deprecated | The SHA-1 algorithm. It | [RFC3174], |
| | | is vulnerable to | [RFC4648], |
| | | collision attacks; see | [RFC6234], |
| | | [NO-SHA] and | RFC 9530 |
| | | [IACR-2020-014] | |
| unixsum | Deprecated | The algorithm used by | [RFC4648], |
| | | the UNIX "sum" command. | [RFC6234], |
| | | | [UNIX], RFC |
| | | | 9530 |
| unixcksum | Deprecated | The algorithm used by | [RFC4648], |
| | | the UNIX "cksum" | [RFC6234], |
| | | command. | [UNIX], RFC |
| | | | 9530 |
| adler | Deprecated | The ADLER32 algorithm. | [RFC1950], |
| | | | RFC 9530 |
| crc32c | Deprecated | The CRC32c algorithm. | Appendix A of |
| | | | [RFC9260], |
| | | | RFC 9530 |
+-----------+------------+--------------------------+---------------+
Table 2: Initial Hash Algorithms
7.3. Deprecate the Hypertext Transfer Protocol (HTTP) Digest Algorithm 7.3. Deprecate the Hypertext Transfer Protocol (HTTP) Digest Algorithm
Values Registry Values Registry
IANA is requested to deprecate the "Hypertext Transfer Protocol IANA has deprecated the "Hypertext Transfer Protocol (HTTP) Digest
(HTTP) Digest Algorithm Values" registry at Algorithm Values" registry at <https://www.iana.org/assignments/http-
https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml [2] dig-alg/> and replaced the note on that registry with the following
and replace the note on this registry with the following text: text:
"This registry is deprecated since it lists the algorithms that This registry is deprecated since it lists the algorithms that can
can be used with the Digest and Want-Digest fields defined in be used with the Digest and Want-Digest fields defined in
[RFC3230] https://www.iana.org/ [3], which has been obsoleted by [RFC3230], which has been obsoleted by RFC 9530. While
[rfc-to-be-this-document]. While registration is not closed, new registration is not closed, new registrations are encouraged to
registrations are encouraged to use the [Hash Algorithms for HTTP use the Hash Algorithms for HTTP Digest Fields
Digest Fields]https://www.iana.org/assignments/http-digest-hash- (https://www.iana.org/assignments/http-digest-hash-alg/) registry
alg/ [4] registry instead. instead.
8. References 8. References
8.1. Normative References 8.1. Normative References
[FOLDING] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu, [FOLDING] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and "Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020, RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>. <https://www.rfc-editor.org/info/rfc8792>.
skipping to change at page 19, line 45 skipping to change at page 19, line 32
[STRUCTURED-FIELDS] [STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/info/rfc8941>. <https://www.rfc-editor.org/info/rfc8941>.
8.2. Informative References 8.2. Informative References
[CMU-836068] [CMU-836068]
Carnegie Mellon University, Software Engineering Carnegie Mellon University, Software Engineering
Institute, "MD5 Vulnerable to collision attacks", December Institute, "MD5 vulnerable to collision attacks", December
2008, <https://www.kb.cert.org/vuls/id/836068/>. 2008, <https://www.kb.cert.org/vuls/id/836068/>.
[I-D.thomson-http-mice] [FIPS186-5]
Thomson, M. and J. Yasskin, "Merkle Integrity Content National Institute of Standards and Technology (NIST),
Encoding", draft-thomson-http-mice-03 (work in progress), "Digital Signature Standard (DSS)",
August 2018. DOI 10.6028/NIST.FIPS.186-5, FIPS PUB 186-5, February
2023, <https://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-5.pdf>.
[IACR-2020-014] [IACR-2020-014]
Leurent, G. and T. Peyrin, "SHA-1 is a Shambles", January Leurent, G. and T. Peyrin, "SHA-1 is a Shambles", January
2020, <https://eprint.iacr.org/2020/014.pdf>. 2020, <https://eprint.iacr.org/2020/014.pdf>.
[NIST800-32] [MICE] Thomson, M. and J. Yasskin, "Merkle Integrity Content
National Institute of Standards and Technology, U.S. Encoding", draft-thomson-http-mice-03 (work in progress),
Department of Commerce, "Introduction to Public Key August 2018.
Technology and the Federal PKI Infrastructure", February
2001, <https://nvlpubs.nist.gov/nistpubs/Legacy/SP/
nistspecialpublication800-32.pdf>.
[NO-MD5] Turner, S. and L. Chen, "Updated Security Considerations [NO-MD5] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms", for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011, RFC 6151, DOI 10.17487/RFC6151, March 2011,
<https://www.rfc-editor.org/info/rfc6151>. <https://www.rfc-editor.org/info/rfc6151>.
[NO-SHA] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security [NO-SHA] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<https://www.rfc-editor.org/info/rfc6194>. <https://www.rfc-editor.org/info/rfc6194>.
skipping to change at page 20, line 48 skipping to change at page 20, line 37
[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396, [RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014, DOI 10.17487/RFC7396, October 2014,
<https://www.rfc-editor.org/info/rfc7396>. <https://www.rfc-editor.org/info/rfc7396>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms", Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>. <https://www.rfc-editor.org/info/rfc7696>.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<https://www.rfc-editor.org/info/rfc7807>.
[RFC8188] Thomson, M., "Encrypted Content-Encoding for HTTP", [RFC8188] Thomson, M., "Encrypted Content-Encoding for HTTP",
RFC 8188, DOI 10.17487/RFC8188, June 2017, RFC 8188, DOI 10.17487/RFC8188, June 2017,
<https://www.rfc-editor.org/info/rfc8188>. <https://www.rfc-editor.org/info/rfc8188>.
[RFC9112] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [RFC9112] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112, Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
June 2022, <https://www.rfc-editor.org/info/rfc9112>. June 2022, <https://www.rfc-editor.org/info/rfc9112>.
[RFC9260] Stewart, R., Tuexen, M., and K. Nielsen, "Stream Control [RFC9260] Stewart, R., Tuexen, M., and K. Nielsen, "Stream Control
Transmission Protocol", RFC 9260, DOI 10.17487/RFC9260, Transmission Protocol", RFC 9260, DOI 10.17487/RFC9260,
June 2022, <https://www.rfc-editor.org/info/rfc9260>. June 2022, <https://www.rfc-editor.org/info/rfc9260>.
[RFC9457] Nottingham, M., Wilde, E., and S. Dalal, "Problem Details
for HTTP APIs", RFC 9457, DOI 10.17487/RFC9457, July 2023,
<https://www.rfc-editor.org/info/rfc9457>.
[SIGNATURES] [SIGNATURES]
Backman, A., Richer, J., and M. Sporny, "HTTP Message Backman, A., Richer, J., and M. Sporny, "HTTP Message
Signatures", draft-ietf-httpbis-message-signatures-17 Signatures", draft-ietf-httpbis-message-signatures-19
(work in progress), May 2023. (work in progress), July 2023.
[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol [TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[UNIX] The Open Group, "The Single UNIX Specification, Version 2 [UNIX] The Open Group, "The Single UNIX Specification, Version 2
- 6 Vol Set for UNIX 98", February 1997. - 6 Vol Set for UNIX 98", January 1998.
8.3. URIs
[1] https://www.iana.org/assignments/http-digest-hash-alg/
[2] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[3] https://www.iana.org/
[4] https://www.iana.org/assignments/http-digest-hash-alg/
Appendix A. Resource Representation and Representation Data Appendix A. Resource Representation and Representation Data
This section following examples show how representation metadata, The following examples show how representation metadata, content
content transformations, and method impacts on the message and transformations, and methods impact the message and content. These
content. These examples a not exhaustive. examples a not exhaustive.
Unless otherwise indicated, the examples are based on the JSON object Unless otherwise indicated, the examples are based on the JSON object
"{"hello": "world"}" followed by an LF. When the content contains "{"hello": "world"}" followed by an LF. When the content contains
non-printable characters (e.g., when it is encoded) it is shown as a non-printable characters (e.g., when it is encoded), it is shown as a
sequence of hex-encoded bytes. sequence of hex-encoded bytes.
Consider a client that wishes to upload a JSON object using the PUT Consider a client that wishes to upload a JSON object using the PUT
method. It could do this using the application/json content type method. It could do this using the application/json Content-Type
without any content coding. without any content coding.
PUT /entries/1234 HTTP/1.1 PUT /entries/1234 HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
Content-Length: 19 Content-Length: 19
{"hello": "world"} {"hello": "world"}
Request containing a JSON object without any content coding Request Containing a JSON Object without Any Content Coding
However, the use of content coding is quite common. The client could However, the use of content coding is quite common. The client could
also upload the same data with a gzip coding (Section 8.4.1.3 of also upload the same data with a GZIP coding (Section 8.4.1.3 of
[HTTP]). Note that in this case, the "Content-Length" contains a [HTTP]). Note that in this case, the "Content-Length" contains a
larger value due to the coding overheads. larger value due to the coding overheads.
PUT /entries/1234 HTTP/1.1 PUT /entries/1234 HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
Content-Encoding: gzip Content-Encoding: gzip
Content-Length: 39 Content-Length: 39
1F 8B 08 00 88 41 37 64 00 FF 1F 8B 08 00 88 41 37 64 00 FF
AB 56 CA 48 CD C9 C9 57 B2 52 AB 56 CA 48 CD C9 C9 57 B2 52
50 2A CF 2F CA 49 51 AA E5 02 50 2A CF 2F CA 49 51 AA E5 02
00 D9 E4 31 E7 13 00 00 00 00 D9 E4 31 E7 13 00 00 00
Figure 1: Request containing a gzip-encoded JSON object Figure 1: Request Containing a GZIP-Encoded JSON Object
Sending the gzip coded data without indicating it via "Content- Sending the GZIP-coded data without indicating it via "Content-
Encoding" means that the content is malformed. In this case, the Encoding" means that the content is malformed. In this case, the
server can reply with an error. server can reply with an error.
PUT /entries/1234 HTTP/1.1 PUT /entries/1234 HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
Content-Length: 39 Content-Length: 39
1F 8B 08 00 88 41 37 64 00 FF 1F 8B 08 00 88 41 37 64 00 FF
AB 56 CA 48 CD C9 C9 57 B2 52 AB 56 CA 48 CD C9 C9 57 B2 52
50 2A CF 2F CA 49 51 AA E5 02 50 2A CF 2F CA 49 51 AA E5 02
00 D9 E4 31 E7 13 00 00 00 00 D9 E4 31 E7 13 00 00 00
Request containing malformed JSON Request Containing Malformed JSON
HTTP/1.1 400 Bad Request HTTP/1.1 400 Bad Request
An error response for a malformed content An Error Response for Malformed Content
A Range-Request affects the transferred message content. In this A Range-Request affects the transferred message content. In this
example, the client is accessing the resource at "/entries/1234", example, the client is accessing the resource at "/entries/1234",
which is the JSON object "{"hello": "world"}" followed by an LF. which is the JSON object "{"hello": "world"}" followed by an LF.
However, the client has indicated a preferred content coding and a However, the client has indicated a preferred content coding and a
specific byte range. specific byte range.
GET /entries/1234 HTTP/1.1 GET /entries/1234 HTTP/1.1
Host: foo.example Host: foo.example
Accept-Encoding: gzip Accept-Encoding: gzip
Range: bytes=1-7 Range: bytes=1-7
Request for partial content Request for Partial Content
The server satisfies the client request by responding with a partial The server satisfies the client request by responding with a partial
representation (equivalent to the first 10 of the JSON object representation (equivalent to the first 10 bytes of the JSON object
displayed in whole in Figure 1). displayed in whole in Figure 1).
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Content-Encoding: gzip Content-Encoding: gzip
Content-Type: application/json Content-Type: application/json
Content-Range: bytes 0-9/39 Content-Range: bytes 0-9/39
1F 8B 08 00 A5 B4 BD 62 02 FF 1F 8B 08 00 A5 B4 BD 62 02 FF
Partial response from a gzip-encoded representation Partial Response from a GZIP-Encoded Representation
Aside from content coding or range requests, the method can also Aside from content coding or range requests, the method can also
affect the transferred message content. For example, the response to affect the transferred message content. For example, the response to
a HEAD request does not carry content but in this example case does a HEAD request does not carry content, but this example case includes
include a Content-Length; see Section 8.6 of [HTTP]. Content-Length; see Section 8.6 of [HTTP].
HEAD /entries/1234 HTTP/1.1 HEAD /entries/1234 HTTP/1.1
Host: foo.example Host: foo.example
Accept: application/json Accept: application/json
Accept-Encoding: gzip Accept-Encoding: gzip
HEAD request HEAD Request
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Encoding: gzip Content-Encoding: gzip
Content-Length: 39 Content-Length: 39
Response to HEAD request (empty content) Response to HEAD Request (Empty Content)
Finally, the semantics of a response might decouple the target URI Finally, the semantics of a response might decouple the target URI
from the enclosed representation. In the example below, the client from the enclosed representation. In the example below, the client
issues a POST request directed to "/authors/" but the response issues a POST request directed to "/authors/", but the response
includes a "Content-Location" header field that indicates the includes a "Content-Location" header field indicating that the
enclosed representation refers to the resource available at enclosed representation refers to the resource available at
"/authors/123". Note that "Content-Length" is not sent in this "/authors/123". Note that "Content-Length" is not sent in this
example. example.
POST /authors/ HTTP/1.1 POST /authors/ HTTP/1.1
Host: foo.example Host: foo.example
Accept: application/json Accept: application/json
Content-Type: application/json Content-Type: application/json
{"author": "Camilleri"} {"author": "Camilleri"}
POST request POST Request
HTTP/1.1 201 Created HTTP/1.1 201 Created
Content-Type: application/json Content-Type: application/json
Content-Location: /authors/123 Content-Location: /authors/123
Location: /authors/123 Location: /authors/123
{"id": "123", "author": "Camilleri"} {"id": "123", "author": "Camilleri"}
Response with Content-Location header Response with Content-Location Header
Appendix B. Examples of Unsolicited Digest Appendix B. Examples of Unsolicited Digest
The following examples demonstrate interactions where a server The following examples demonstrate interactions where a server
responds with a "Content-Digest" or "Repr-Digest" fields even though responds with a "Content-Digest" or "Repr-Digest" field, even though
the client did not solicit one using "Want-Content-Digest" or "Want- the client did not solicit one using "Want-Content-Digest" or "Want-
Repr-Digest". Repr-Digest".
Some examples include JSON objects in the content. For presentation Some examples include JSON objects in the content. For presentation
purposes, objects that fit completely within the line-length limits purposes, objects that fit completely within the line-length limits
are presented on a single line using compact notation with no leading are presented on a single line using compact notation with no leading
space. Objects that would exceed line-length limits are presented space. Objects that would exceed line-length limits are presented
across multiple lines (one line per key-value pair) with 2 spaces of across multiple lines (one line per key-value pair) with two spaces
leading indentation. of leading indentation.
Checksum mechanisms defined in this document are media-type agnostic Checksum mechanisms defined in this document are media-type agnostic
and do not provide canonicalization algorithms for specific formats. and do not provide canonicalization algorithms for specific formats.
Examples are calculated inclusive of any space. While examples can Examples are calculated inclusive of any space. While examples can
include both fields, "Content-Digest" and "Repr-Digest" can be include both fields, "Content-Digest" and "Repr-Digest" can be
returned independently. returned independently.
B.1. Server Returns Full Representation Data B.1. Server Returns Full Representation Data
In this example, the message content conveys complete representation In this example, the message content conveys complete representation
data. This means that in the response, "Content-Digest" and "Repr- data. This means that in the response, "Content-Digest" and "Repr-
Digest" are both computed over the JSON object "{"hello": "world"}" Digest" are both computed over the JSON object "{"hello": "world"}"
followed by an LF, and thus have the same value. followed by an LF; thus, they have the same value.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
GET request for an item GET Request for an Item
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Length: 19 Content-Length: 19
Content-Digest: \ Content-Digest: \
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=:
Repr-Digest: \ Repr-Digest: \
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=:
{"hello": "world"} {"hello": "world"}
Response with identical Repr-Digest and Content-Digest Response with Identical Repr-Digest and Content-Digest
B.2. Server Returns No Representation Data B.2. Server Returns No Representation Data
In this example, a HEAD request is used to retrieve the checksum of a In this example, a HEAD request is used to retrieve the checksum of a
resource. resource.
The response "Content-Digest" field-value is computed on empty The response "Content-Digest" field-value is computed on empty
content. "Repr-Digest" is calculated over the JSON object "{"hello": content. "Repr-Digest" is calculated over the JSON object "{"hello":
"world"}" followed by an LF, which is not shown because there is no "world"}" followed by an LF, which is not shown because there is no
content. content.
HEAD /items/123 HTTP/1.1 HEAD /items/123 HTTP/1.1
Host: foo.example Host: foo.example
HEAD request for an item HEAD Request for an Item
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Digest: \ Content-Digest: \
sha-256=:47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=: sha-256=:47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=:
Repr-Digest: \ Repr-Digest: \
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=:
Response with both Content-Digest and Digest; empty content Response with Both Content-Digest and Digest (Empty Content)
B.3. Server Returns Partial Representation Data B.3. Server Returns Partial Representation Data
In this example, the client makes a range request and the server In this example, the client makes a range request and the server
responds with partial content. responds with partial content.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Range: bytes=10-18 Range: bytes=10-18
Request for partial content Request for Partial Content
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Content-Type: application/json Content-Type: application/json
Content-Range: bytes 10-18/19 Content-Range: bytes 10-18/19
Content-Digest: \ Content-Digest: \
sha-256=:jjcgBDWNAtbYUXI37CVG3gRuGOAjaaDRGpIUFsdyepQ=: sha-256=:jjcgBDWNAtbYUXI37CVG3gRuGOAjaaDRGpIUFsdyepQ=:
Repr-Digest: \ Repr-Digest: \
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=:
"world"} "world"}
Partial response with both Content-Digest and Repr-Digest Partial Response with Both Content-Digest and Repr-Digest
In the response message above, note that the "Repr-Digest" and In the response message above, note that the "Repr-Digest" and
"Content-Digests" are different. The "Repr-Digest" field-value is "Content-Digests" are different. The "Repr-Digest" field-value is
calculated across the entire JSON object "{"hello": "world"}" calculated across the entire JSON object "{"hello": "world"}"
followed by an LF, and the field is followed by an LF, and the field appears as follows:
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
Repr-Digest: \ Repr-Digest: \
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=:
However, since the message content is constrained to bytes 10-18, the However, since the message content is constrained to bytes 10-18, the
"Content-Digest" field-value is calculated over the sequence "Content-Digest" field-value is calculated over the sequence
""world"}" followed by an LF, thus resulting in ""world"}" followed by an LF, thus resulting in the following:
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
Content-Digest: \ Content-Digest: \
sha-256=:jjcgBDWNAtbYUXI37CVG3gRuGOAjaaDRGpIUFsdyepQ=: sha-256=:jjcgBDWNAtbYUXI37CVG3gRuGOAjaaDRGpIUFsdyepQ=:
B.4. Client and Server Provide Full Representation Data B.4. Client and Server Provide Full Representation Data
The request contains a "Repr-Digest" field-value calculated on the The request contains a "Repr-Digest" field-value calculated on the
enclosed representation. It also includes an "Accept-Encoding: br" enclosed representation. It also includes an "Accept-Encoding: br"
header field that advertises the client supports Brotli encoding. header field that advertises that the client supports Brotli
encoding.
The response includes a "Content-Encoding: br" that indicates the The response includes a "Content-Encoding: br" that indicates the
selected representation is Brotli-encoded. The "Repr-Digest" field- selected representation is Brotli-encoded. The "Repr-Digest" field-
value is therefore different compared to the request. value is therefore different compared to the request.
For presentation purposes, the response body is displayed as a For presentation purposes, the response body is displayed as a
sequence of hex-encoded bytes because it contains non-printable sequence of hex-encoded bytes because it contains non-printable
characters. characters.
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
skipping to change at page 28, line 19 skipping to change at page 28, line 19
Content-Location: /items/123 Content-Location: /items/123
Content-Encoding: br Content-Encoding: br
Content-Length: 23 Content-Length: 23
Repr-Digest: \ Repr-Digest: \
sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=: sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:
8B 08 80 7B 22 68 65 6C 6C 6F 8B 08 80 7B 22 68 65 6C 6C 6F
22 3A 20 22 77 6F 72 6C 64 22 22 3A 20 22 77 6F 72 6C 64 22
7D 0A 03 7D 0A 03
Response with Digest of encoded response Response with Digest of Encoded Response
B.5. Client Provides Full Representation Data, Server Provides No B.5. Client Provides Full Representation Data and Server Provides No
Representation Data Representation Data
The request "Repr-Digest" field-value is calculated on the enclosed The request "Repr-Digest" field-value is calculated on the enclosed
content, which is the JSON object "{"hello": "world"}" followed by an content, which is the JSON object "{"hello": "world"}" followed by an
LF LF.
The response "Repr-Digest" field-value depends on the representation The response "Repr-Digest" field-value depends on the representation
metadata header fields, including "Content-Encoding: br" even when metadata header fields, including "Content-Encoding: br", even when
the response does not contain content. the response does not contain content.
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
PUT /items/123 HTTP/1.1 PUT /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
Content-Length: 19 Content-Length: 19
Accept-Encoding: br Accept-Encoding: br
Repr-Digest: \ Repr-Digest: \
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg==: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg==:
{"hello": "world"} {"hello": "world"}
HTTP/1.1 204 No Content HTTP/1.1 204 No Content
Content-Type: application/json Content-Type: application/json
Content-Encoding: br Content-Encoding: br
Repr-Digest: sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=: Repr-Digest: sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:
Empty response with Digest Empty Response with Digest
B.6. Client and Server Provide Full Representation Data B.6. Client and Server Provide Full Representation Data
The response contains two digest values using different algorithms. The response contains two digest values using different algorithms.
For presentation purposes, the response body is displayed as a For presentation purposes, the response body is displayed as a
sequence of hex-encoded bytes because it contains non-printable sequence of hex-encoded bytes because it contains non-printable
characters. characters.
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
skipping to change at page 29, line 43 skipping to change at page 29, line 43
sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:,\ sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:,\
sha-512=:db7fdBbgZMgX1Wb2MjA8zZj+rSNgfmDCEEXM8qLWfpfoNY0sCpHAzZbj\ sha-512=:db7fdBbgZMgX1Wb2MjA8zZj+rSNgfmDCEEXM8qLWfpfoNY0sCpHAzZbj\
09X1/7HAb7Od5Qfto4QpuBsFbUO3dQ==: 09X1/7HAb7Od5Qfto4QpuBsFbUO3dQ==:
8B 08 80 7B 22 68 65 6C 6C 6F 8B 08 80 7B 22 68 65 6C 6C 6F
22 3A 20 22 77 6F 72 6C 64 22 22 3A 20 22 77 6F 72 6C 64 22
7D 0A 03 7D 0A 03
Response with Digest of Encoded Content Response with Digest of Encoded Content
B.7. POST Response does not Reference the Request URI B.7. POST Response Does Not Reference the Request URI
The request "Repr-Digest" field-value is computed on the enclosed The request "Repr-Digest" field-value is computed on the enclosed
representation (see Section 3.1), which is the JSON object "{"title": representation (see Section 3.1), which is the JSON object "{"title":
"New Title"}" followed by an LF. "New Title"}" followed by an LF.
The representation enclosed in the response is a multiline JSON The representation enclosed in the response is a multiline JSON
object followed by an LF. It refers to the resource identified by object followed by an LF. It refers to the resource identified by
"Content-Location" (see Section 6.4.2 of [HTTP]); an application can "Content-Location" (see Section 6.4.2 of [HTTP]); thus, an
thus use "Repr-Digest" in association with the resource referenced by application can use "Repr-Digest" in association with the resource
"Content-Location". referenced by "Content-Location".
POST /books HTTP/1.1 POST /books HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
Accept: application/json Accept: application/json
Accept-Encoding: identity Accept-Encoding: identity
Repr-Digest: sha-256=:mEkdbO7Srd9LIOegftO0aBX+VPTVz7/CSHes2Z27gc4=: Repr-Digest: sha-256=:mEkdbO7Srd9LIOegftO0aBX+VPTVz7/CSHes2Z27gc4=:
{"title": "New Title"} {"title": "New Title"}
skipping to change at page 31, line 36 skipping to change at page 31, line 36
} }
Response with Digest of Representation Response with Digest of Representation
B.9. Digest with PATCH B.9. Digest with PATCH
This case is analogous to a POST request where the target resource This case is analogous to a POST request where the target resource
reflects the target URI. reflects the target URI.
The PATCH request uses the "application/merge-patch+json" media type The PATCH request uses the "application/merge-patch+json" media type
defined in [RFC7396]. "Repr-Digest" is calculated on the content, defined in [RFC7396]. "Repr-Digest" is calculated on the content
which corresponds to the patch document and is the JSON object that corresponds to the patch document and is the JSON object
"{"title": "New Title"}" followed by an LF. "{"title": "New Title"}" followed by an LF.
The response "Repr-Digest" field-value is computed on the complete The response "Repr-Digest" field-value is computed on the complete
representation of the patched resource. It is a multiline JSON representation of the patched resource. It is a multiline JSON
object followed by an LF. object followed by an LF.
PATCH /books/123 HTTP/1.1 PATCH /books/123 HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/merge-patch+json Content-Type: application/merge-patch+json
Accept: application/json Accept: application/json
skipping to change at page 32, line 27 skipping to change at page 32, line 27
Content-Type: application/json Content-Type: application/json
Repr-Digest: sha-256=:uVSlinTTdQUwm2On4k8TJUikGN1bf/Ds8WPX4oe0h9I=: Repr-Digest: sha-256=:uVSlinTTdQUwm2On4k8TJUikGN1bf/Ds8WPX4oe0h9I=:
{ {
"id": "123", "id": "123",
"title": "New Title" "title": "New Title"
} }
Response with Digest of Representation Response with Digest of Representation
Note that a "204 No Content" response without content but with the Note that a "204 No Content" response without content, but with the
same "Repr-Digest" field-value would have been legitimate too. In same "Repr-Digest" field-value, would have been legitimate too. In
that case, "Content-Digest" would have been computed on an empty that case, "Content-Digest" would have been computed on an empty
content. content.
B.10. Error responses B.10. Error Responses
In error responses, the representation data does not necessarily In error responses, the representation data does not necessarily
refer to the target resource. Instead, it refers to the refer to the target resource. Instead, it refers to the
representation of the error. representation of the error.
In the following example, a client sends the same request from In the following example, a client sends the same request from
Figure 2 to patch the resource located at /books/123. However, the Figure 2 to patch the resource located at /books/123. However, the
resource does not exist and the server generates a 404 response with resource does not exist and the server generates a 404 response with
a body that describes the error in accordance with [RFC7807]. a body that describes the error in accordance with [RFC9457].
The response "Repr-Digest" field-value is computed on this enclosed The response "Repr-Digest" field-value is computed on this enclosed
representation. It is a multiline JSON object followed by an LF. representation. It is a multiline JSON object followed by an LF.
HTTP/1.1 404 Not Found HTTP/1.1 404 Not Found
Content-Type: application/problem+json Content-Type: application/problem+json
Repr-Digest: sha-256=:EXB0S2VF2H7ijkAVJkH1Sm0pBho0iDZcvVUHHXTTZSA=: Repr-Digest: sha-256=:EXB0S2VF2H7ijkAVJkH1Sm0pBho0iDZcvVUHHXTTZSA=:
{ {
"title": "Not Found", "title": "Not Found",
skipping to change at page 33, line 25 skipping to change at page 33, line 25
Response with Digest of Error Representation Response with Digest of Error Representation
B.11. Use with Trailer Fields and Transfer Coding B.11. Use with Trailer Fields and Transfer Coding
An origin server sends "Repr-Digest" as trailer field, so it can An origin server sends "Repr-Digest" as trailer field, so it can
calculate digest-value while streaming content and thus mitigate calculate digest-value while streaming content and thus mitigate
resource consumption. The "Repr-Digest" field-value is the same as resource consumption. The "Repr-Digest" field-value is the same as
in Appendix B.1 because "Repr-Digest" is designed to be independent in Appendix B.1 because "Repr-Digest" is designed to be independent
of the use of one or more transfer codings (see Section 3). of the use of one or more transfer codings (see Section 3).
In the response content below, the string "\r\n" represent the bytes In the response content below, the string "\r\n" represents the CRLF
CRLF. bytes.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
GET Request GET Request
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Transfer-Encoding: chunked Transfer-Encoding: chunked
Trailer: Digest Trailer: Repr-Digest
8\r\n 8\r\n
{"hello"\r\n {"hello"\r\n
8\r\n 8\r\n
: "world\r\n : "world\r\n
3\r\n 3\r\n
"}\n\r\n "}\n\r\n
0\r\n 0\r\n
Repr-Digest: \ Repr-Digest: \
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg==:\r\n sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg==:\r\n
skipping to change at page 34, line 34 skipping to change at page 34, line 34
Appendix C. Examples of Want-Repr-Digest Solicited Digest Appendix C. Examples of Want-Repr-Digest Solicited Digest
The following examples demonstrate interactions where a client The following examples demonstrate interactions where a client
solicits a "Repr-Digest" using "Want-Repr-Digest". The behavior of solicits a "Repr-Digest" using "Want-Repr-Digest". The behavior of
"Content-Digest" and "Want-Content-Digest" is identical. "Content-Digest" and "Want-Content-Digest" is identical.
Some examples include JSON objects in the content. For presentation Some examples include JSON objects in the content. For presentation
purposes, objects that fit completely within the line-length limits purposes, objects that fit completely within the line-length limits
are presented on a single line using compact notation with no leading are presented on a single line using compact notation with no leading
space. Objects that would exceed line-length limits are presented space. Objects that would exceed line-length limits are presented
across multiple lines (one line per key-value pair) with 2 spaces of across multiple lines (one line per key-value pair) with two spaces
leading indentation. of leading indentation.
Checksum mechanisms described in this document are media-type Checksum mechanisms described in this document are media-type
agnostic and do not provide canonicalization algorithms for specific agnostic and do not provide canonicalization algorithms for specific
formats. Examples are calculated inclusive of any space. formats. Examples are calculated inclusive of any space.
C.1. Server Selects Client's Least Preferred Algorithm C.1. Server Selects Client's Least Preferred Algorithm
The client requests a digest, preferring "sha". The server is free The client requests a digest and prefers "sha". The server is free
to reply with "sha-256" anyway. to reply with "sha-256" anyway.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Want-Repr-Digest: sha-256=3, sha=10 Want-Repr-Digest: sha-256=3, sha=10
GET Request with Want-Repr-Digest GET Request with Want-Repr-Digest
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
skipping to change at page 35, line 26 skipping to change at page 35, line 26
sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg==: sha-256=:RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg==:
{"hello": "world"} {"hello": "world"}
Response with Different Algorithm Response with Different Algorithm
C.2. Server Selects Algorithm Unsupported by Client C.2. Server Selects Algorithm Unsupported by Client
The client requests a "sha" digest because that is the only algorithm The client requests a "sha" digest because that is the only algorithm
it supports. The server is not obliged to produce a response it supports. The server is not obliged to produce a response
containing a "sha" digest, it instead uses a different algorithm. containing a "sha" digest; it instead uses a different algorithm.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Want-Repr-Digest: sha=10 Want-Repr-Digest: sha=10
GET Request with Want-Repr-Digest GET Request with Want-Repr-Digest
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK HTTP/1.1 200 OK
skipping to change at page 36, line 8 skipping to change at page 36, line 8
sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\ sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\
yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==: yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:
{"hello": "world"} {"hello": "world"}
Response with Unsupported Algorithm Response with Unsupported Algorithm
C.3. Server Does Not Support Client Algorithm and Returns an Error C.3. Server Does Not Support Client Algorithm and Returns an Error
Appendix C.2 is an example where a server ignores the client's Appendix C.2 is an example where a server ignores the client's
preferred digest algorithm. Alternatively a server can also reject preferred digest algorithm. Alternatively, a server can also reject
the request and return a response with error status code such as 4xx the request and return a response with an error status code such as
or 5xx. This specification does not prescribe any requirement on 4xx or 5xx. This specification does not prescribe any requirement on
status code selection; the follow example illustrates one possible status code selection; the following example illustrates one possible
option. option.
In this example, the client requests a "sha" "Repr-Digest", and the In this example, the client requests a "sha" "Repr-Digest", and the
server returns an error with problem details [RFC7807] contained in server returns an error with problem details [RFC9457] contained in
the content. The problem details contain a list of the hashing the content. The problem details contain a list of the hashing
algorithms that the server supports. This is purely an example, this algorithms that the server supports. This is purely an example; this
specification does not define any format or requirements for such specification does not define any format or requirements for such
content. content.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Want-Repr-Digest: sha=10 Want-Repr-Digest: sha=10
GET Request with Want-Repr-Digest GET Request with Want-Repr-Digest
HTTP/1.1 400 Bad Request HTTP/1.1 400 Bad Request
Content-Type: application/problem+json Content-Type: application/problem+json
{ {
"title": "Bad Request", "title": "Bad Request",
"detail": "Supported hashing algorithms: sha-256, sha-512", "detail": "Supported hashing algorithms: sha-256, sha-512",
"status": 400 "status": 400
} }
Response advertising the supported algorithms Response Advertising the Supported Algorithms
Appendix D. Sample Digest Values Appendix D. Sample Digest Values
This section shows examples of digest values for different hashing This section shows examples of digest values for different hashing
algorithms. The input value is the JSON object "{"hello": "world"}". algorithms. The input value is the JSON object "{"hello": "world"}".
The digest values are each produced by running the relevant hashing The digest values are each produced by running the relevant hashing
algorithm over the input and running the output bytes through "Byte algorithm over the input and running the output bytes through "Byte
Sequence" serialization; see Section 4.1.8 of [STRUCTURED-FIELDS]. Sequence" serialization; see Section 4.1.8 of [STRUCTURED-FIELDS].
NOTE: '\' line wrapping per RFC 8792 NOTE: '\' line wrapping per RFC 8792
skipping to change at page 37, line 27 skipping to change at page 37, line 27
unixcksum - :7zsHAA==: unixcksum - :7zsHAA==:
adler - :OZkGFw==: adler - :OZkGFw==:
crc32c - :Q3lHIA==: crc32c - :Q3lHIA==:
Appendix E. Migrating from RFC 3230 Appendix E. Migrating from RFC 3230
HTTP digests are computed by applying a hashing algorithm to input HTTP digests are computed by applying a hashing algorithm to input
data. RFC 3230 defined the input data as an "instance", a term it data. [RFC3230] defined the input data as an "instance", a term it
also defined. The concept of instance has since been superseded by also defined. The concept of an instance has since been superseded
the HTTP semantic term "representation". It is understood that some by the HTTP semantic term "representation". It is understood that
implementations of RFC 3230 mistook "instance" to mean HTTP content. some implementations of [RFC3230] mistook "instance" to mean HTTP
Using content for the Digest field is an error that leads to content. Using content for the Digest field is an error that leads
interoperability problems between peers that implement RFC 3230. to interoperability problems between peers that implement [RFC3230].
RFC 3230 was only ever intended to use what HTTP now defines as [RFC3230] was only ever intended to use what HTTP now defines as
selected representation data. The semantic concept of digest and selected representation data. The semantic concept of digest and
representation are explained alongside the definition of the Repr- representation are explained alongside the definition of the Repr-
Digest field (Section 3). Digest field (Section 3).
While the syntax of Digest and Repr-Digest are different, the While the syntax of Digest and Repr-Digest are different, the
considerations and examples this document gives for Repr-Digest apply considerations and examples this document gives for Repr-Digest apply
equally to Digest because they operate on the same input data; see equally to Digest because they operate on the same input data; see
Sections 3.1, 6 and 6.3. Sections 3.1, 6 and 6.3.
RFC 3230 could never communicate the digest of HTTP message content [RFC3230] could never communicate the digest of HTTP message content
in the Digest field; Content-Digest now provides that capability. in the Digest field; Content-Digest now provides that capability.
RFC 3230 allowed algorithms to define their output encoding format [RFC3230] allowed algorithms to define their output encoding format
for use with the Digest field. This resulted in a mix of formats for use with the Digest field. This resulted in a mix of formats
such as base64, hex or decimal. By virtue of using Structured such as base64, hex, or decimal. By virtue of using Structured
fields, Content-Digest and Repr-Digest use only a single encoding Fields, Content-Digest, and Repr-Digest use only a single encoding
format. Further explanation and examples are provided in Appendix D. format. Further explanation and examples are provided in Appendix D.
Acknowledgements Acknowledgements
This document is based on ideas from [RFC3230], so thanks to Jeff This document is based on ideas from [RFC3230], so thanks to Jeff
Mogul and Arthur Van Hoff for their great work. The original idea of Mogul and Arthur Van Hoff for their great work. The original idea of
refreshing RFC3230 arose from an interesting discussion with Mark refreshing [RFC3230] arose from an interesting discussion with Mark
Nottingham, Jeffrey Yasskin, and Martin Thomson when reviewing the Nottingham, Jeffrey Yasskin, and Martin Thomson when reviewing the
MICE content coding. MICE content coding.
Thanks to Julian Reschke for his valuable contributions to this Thanks to Julian Reschke for his valuable contributions to this
document, and to the following contributors that have helped improve document, and to the following contributors that have helped improve
this specification by reporting bugs, asking smart questions, this specification by reporting bugs, asking smart questions,
drafting or reviewing text, and evaluating open issues: Mike Bishop, drafting or reviewing text, and evaluating open issues: Mike Bishop,
Brian Campbell, Matthew Kerwin, James Manger, Tommy Pauly, Sean Brian Campbell, Matthew Kerwin, James Manger, Tommy Pauly, Sean
Turner, Justin Richer, and Erik Wilde. Turner, Justin Richer, and Erik Wilde.
Code Samples
This section is to be removed before publishing as an RFC.
How can I generate and validate the digest values, computed over the
JSON object "{"hello": "world"}" followed by an LF, shown in the
examples throughout this document?
The following python3 code can be used to generate digests for JSON
objects using SHA algorithms for a range of encodings. Note that
these are formatted as base64. This function could be adapted to
other algorithms and should take into account their specific
formatting rules.
import base64, json, hashlib, brotli, logging
log = logging.getLogger()
def digest_bytes(bytes_, algorithm=hashlib.sha256):
checksum_bytes = algorithm(bytes_).digest()
log.warning("Log bytes: \n[%r]", bytes_)
return base64.encodebytes(checksum_bytes).strip()
def digest(bytes_, encoding=lambda x: x, algorithm=hashlib.sha256):
content_encoded = encoding(bytes_)
return digest_bytes(content_encoded, algorithm)
bytes_ = b'{"hello": "world"}\n'
print("Encoding | hashing algorithm | digest-value")
print("Identity | sha256 |", digest(bytes_))
# Encoding | hashing algorithm | digest-value
# Identity | sha256 | RK/0qy18MlBSVnWgjwz6lZEWjP/lF5HF9bvEF8FabDg=
print("Encoding | hashing algorithm | digest-value")
print("Brotli | sha256 |", digest(bytes_, encoding=brotli.compress))
# Encoding | hashing algorithm | digest-value
# Brotli | sha256 | d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=
print("Encoding | hashing algorithm | digest-value")
print("Identity | sha512 |", digest(bytes_, algorithm=hashlib.sha512))
print("Brotli | sha512 |", digest(bytes_, algorithm=hashlib.sha512,
encoding=brotli.compress))
# Encoding | hashing algorithm | digest-value
# Identity | sha512 |b'YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP'
# '+pgk4vf2aCsyRZOtw8MjkM7iw7yZ/WkppmM44T3qg=='
# Brotli | sha512 | b'db7fdBbgZMgX1Wb2MjA8zZj+rSNgfmDCEEXM8qLWfpfoNY'
# '0sCpHAzZbj09X1/7HAb7Od5Qfto4QpuBsFbUO3dQ=='
Changes
This section is to be removed before publishing as an RFC.
H.1. Since draft-ietf-httpbis-digest-headers-12
o Be clearer that applications can enforce additional requirements
wrt digest
o Change algorithm status names: s/standard/active, s/insecure/
deprecated
o Remove "reserved" algorithm status
o Provide clear guidance about the use of standard or deprecated
algorithms
o Editorial or minor changes
H.2. Since draft-ietf-httpbis-digest-headers-11
o Editorial or minor changes
H.3. Since draft-ietf-httpbis-digest-headers-10
o Editorial or minor changes
H.4. Since draft-ietf-httpbis-digest-headers-09
o Editorial or minor changes
H.5. Since draft-ietf-httpbis-digest-headers-08
o Add note about migrating from RFC 3230. #1968, #1971
o Clarify what Want-* means in responses. #2097
o Editorial changes to structure and to align to HTTP style guide.
H.6. Since draft-ietf-httpbis-digest-headers-07
o Introduced Repr-Digest and Want-Repr-Digest, and deprecated Digest
and Want-Digest. Use of Structured Fields. #1993, #1919
o IANA refactoring. #1983
o No normative text in security considerations. #1972
H.7. Since draft-ietf-httpbis-digest-headers-06
o Remove id-sha-256 and id-sha-512 from the list of supported
algorithms #855
H.8. Since draft-ietf-httpbis-digest-headers-05
o Reboot digest-algorithm values registry #1567
o Add Content-Digest #1542
o Remove SRI section #1478
H.9. Since draft-ietf-httpbis-digest-headers-04
o Improve SRI section #1354
o About duplicate digest-algorithms #1221
o Improve security considerations #852
o md5 and sha deprecation references #1392
o Obsolete 3230 #1395
o Editorial #1362
H.10. Since draft-ietf-httpbis-digest-headers-03
o Reference semantics-12
o Detail encryption quirks
o Details on Algorithm agility #1250
o Obsolete parameters #850
H.11. Since draft-ietf-httpbis-digest-headers-02
o Deprecate SHA-1 #1154
o Avoid id-* with encrypted content
o Digest is independent of MESSAGING and HTTP/1.1 is not normative
#1215
o Identity is not a valid field value for content-encoding #1223
o Mention trailers #1157
o Reference httpbis-semantics #1156
o Add contentMD5 as an obsoleted digest-algorithm #1249
o Use lowercase digest-algorithms names in the doc and in the
digest-algorithm IANA table.
H.12. Since draft-ietf-httpbis-digest-headers-01
o Digest of error responses is computed on the error representation-
data #1004
o Effect of HTTP semantics on payload and message body moved to
appendix #1122
o Editorial refactoring, moving headers sections up. #1109-#1112,
#1116, #1117, #1122-#1124
H.13. Since draft-ietf-httpbis-digest-headers-00
o Align title with document name
o Add id-sha-* algorithm examples #880
o Reference [RFC6234] and [RFC3174] instead of FIPS-1
o Deprecate MD5
o Obsolete ADLER-32 but don't forbid it #828
o Update CRC32C value in IANA table #828
o Use when acting on resources (POST, PATCH) #853
o Added Relationship with SRI, draft Use Cases #868, #971
o Warn about the implications of "Content-Location"
Authors' Addresses Authors' Addresses
Roberto Polli Roberto Polli
Team Digitale, Italian Government Team Digitale, Italian Government
Italy Italy
Email: robipolli@gmail.com Email: robipolli@gmail.com
Lucas Pardue Lucas Pardue
Cloudflare Cloudflare
Email: lucaspardue.24.7@gmail.com Email: lucas@lucaspardue.com
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