Internet-Draft Digest Headers July 2021
Polli & Pardue Expires 20 January 2022 [Page]
Workgroup:
HTTP
Internet-Draft:
draft-ietf-httpbis-digest-headers
Obsoletes:
3230 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Authors:
R. Polli
Team Digitale, Italian Government
L. Pardue
Cloudflare

Digest Headers

Abstract

This document defines the HTTP Digest and Want-Digest fields, which allows client and server to negotiate an integrity checksum of the exchanged resource representation data.

This document obsoletes RFC 3230.

Note to Readers

RFC EDITOR: please remove this section before publication

Discussion of this draft takes place on the HTTP working group mailing list (ietf-http-wg@w3.org), which is archived at https://lists.w3.org/Archives/Public/ietf-http-wg/.

The source code and issues list for this draft can be found at https://github.com/httpwg/http-extensions.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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

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

This Internet-Draft will expire on 20 January 2022.

Table of Contents

1. Introduction

HTTP does not define a means to protect the integrity of representations. When HTTP messages are transferred between endpoints, the protocol might choose to make use of features of the lower layer in order to provide some integrity protection; for instance TCP checksums or TLS records [RFC2818].

This document defines the Digest HTTP integrity mechanism that acts on representation data. It operates independent of transport integrity, offering the potential to detect programming errors and corruption of data in flight or at rest. It can be used across multiple hops in order to provide end-to-end integrity guarantees, which can aid fault diagnosis when resources are transferred across hops and system boundaries. Finally, it can be used to validate integrity when reconstructing a resource fetched using different HTTP connections.

This document obsoletes [RFC3230].

1.1. Document Structure

This document describes Digest integrity for HTTP and is structured as follows:

  • Section 2 describes concepts related to representation digests,
  • Section 3 defines the Digest request and response header and trailer field,
  • Section 4 defines the Want-Digest request and response header and trailer field,
  • Section 5 and Appendix B.1 describe algorithms and their relation to Digest,
  • Section 6 details computing representation digests,
  • Appendix B.2 obsoletes Digest field parameters,
  • Section 7 describes the relationship between Digest and Subresource Integrity, and
  • Section 8 and Section 9 provide examples of using Digest and Want-Digest.

1.2. Concept Overview

This document defines the Digest request and response header and trailer field. At a high level the value contains a checksum, computed over selected representation data (Section 3.2; [SEMANTICS]), that the recipient can use to validate integrity. Digest supports algorithm agility. The Want-Digest field allows endpoints to express interest in Digest and preference of algorithms.

Basing Digest on the selected representation makes it straightforward to apply it to use-cases where the transferred data requires some sort of manipulation to be considered a representation, or conveys a partial representation of a resource, for example Range Requests (see Section 14.2 of [SEMANTICS]).

Historically, the Content-MD5 header field provided an HTTP integrity mechanism but HTTP/1.1 ([RFC7231], Appendix B) obsoleted it due to inconsistent handling of partial responses. [RFC3230] defined the concept of "instance" digests and a more flexible integrity scheme to help address issues with Content-MD5. It first introduced the Digest and Want-Digest fields. HTTP terminology has evolved since [RFC3230] was published. The concept of "instance" has been superseded by selected representation.

This document replaces [RFC3230]. The Digest and Want-Digest field definitions are updated to align with the terms and notational conventions in [SEMANTICS]. Changes are intended to be semantically compatible with existing implementations but note that negotiation of Content-MD5 is deprecated Appendix B.1, Digest field parameters are obsoleted Appendix B.2, "md5" and "sha" digest-algorithms are obsoleted, and the "adler32" algorithm is deprecated.

Calculating the value of Digest using selected representation means it is tied to the Content-Encoding and Content-Type header fields. Therefore, a given resource may have multiple different digest values. To allow both parties to exchange a Digest of a representation with no content codings (see Section 8.4.1 of [SEMANTICS]) two more digest-algorithms are added ("id-sha-256" and "id-sha-512").

Digest is used for representation integrity. It does not provide integrity for HTTP messages or fields. However, it can be combined with other mechanisms that protect representation metadata, such as digital signatures, in order to protect the phases of an HTTP exchange in whole or in part.

Digest does not define means for authentication, authorization or privacy.

1.3. Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

This document uses the Augmented BNF defined in [RFC5234] and updated by [RFC7405] along with the "#rule" extension defined in Section 5.6.1 of [SEMANTICS].

The definitions "representation", "selected representation", "representation data", "representation metadata", and "content" in this document are to be interpreted as described in [SEMANTICS].

Algorithm names respect the casing used in their definition document (eg. SHA-1, CRC32c) whereas digest-algorithm tokens are quoted (eg. "sha", "crc32c").

2. Representation Digest

The representation digest is an integrity mechanism for HTTP resources which uses a checksum that is calculated independently of the content (see Section 6.4 of [SEMANTICS]). It uses the representation data (see Section 8.1 of [SEMANTICS]), that can be fully or partially contained in the content, or not contained at all.

This takes into account the effect of the HTTP semantics on the messages; for example, the content can be affected by Range Requests or methods such as HEAD, while the way the content is transferred "on the wire" is dependent on other transformations (e.g. transfer codings for HTTP/1.1 - see Section 6.1 of [HTTP11]). To help illustrate how such things affect Digest, several examples are provided in Appendix A.

A representation digest consists of the value of a checksum computed on the entire selected representation data (see Section 8.1 of [SEMANTICS]) of a resource identified according to Section 6.4.2 of [SEMANTICS] together with an indication of the algorithm used:

   representation-data-digest = digest-algorithm "="
                                <encoded digest output>

When a message has no representation data it is still possible to assert that no representation data was sent computing the representation digest on an empty string (see Section 10.3).

The checksum is computed using one of the digest-algorithms listed in Section 5 and then encoded in the associated format.

3. The Digest Field

The Digest field contains a comma-separated list of one or more representation digest values as defined in Section 2. It can be used in both requests and responses.

   Digest = 1#representation-data-digest

For example:

Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
                   AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==

The relationship between Content-Location (see Section 8.7 of [SEMANTICS]) and Digest is demonstrated in Section 8.7. A comprehensive set of examples showing the impacts of representation metadata, payload transformations and HTTP methods on Digest is provided in Section 8 and Section 9.

A Digest field MAY contain multiple representation-data-digest values. For example, a server may provide representation-data-digest values using different algorithms, allowing it to support a population of clients with different evolving capabilities; this is particularly useful in support of transitioning away from weaker algorithms should the need arise (see Section 10.6).

Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
        id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

A recipient MAY ignore any or all of the representation-data-digests in a Digest field. This allows the recipient to choose which digest-algorithm(s) to use for validation instead of verifying every received representation-data-digest.

A sender MAY send a representation-data-digest using a digest-algorithm without knowing whether the recipient supports the digest-algorithm, or even knowing that the recipient will ignore it.

Digest can be sent in a trailer section. In this case, Digest MAY be merged in to the header section (See Section 6.5.1 of [SEMANTICS]).

When an incremental digest-algorithm is used, the sender and the receiver can dynamically compute the digest value while streaming the content.

4. The Want-Digest Field

The Want-Digest field indicates the sender's desire to receive a representation digest on messages associated with the request URI and representation metadata. It can be used in both requests and responses.

   Want-Digest = 1#want-digest-value
   want-digest-value = digest-algorithm [ ";" "q" "=" qvalue]
   qvalue = ( "0"  [ "."  0*1DIGIT ] ) /
            ( "1"  [ "."  0*1( "0" ) ] )

If a digest-algorithm is not accompanied by a "qvalue" (see Section 12.4.2 of[SEMANTICS]), it is treated as if its associated "qvalue" were 1.0.

The sender is willing to accept a digest-algorithm if and only if it is listed in a Want-Digest field of a message, and its "qvalue" is non-zero.

If multiple acceptable digest-algorithm values are given, the sender's preferred digest-algorithm is the one (or ones) with the highest "qvalue".

Two examples of its use are:

Want-Digest: sha-256
Want-Digest: sha-512;q=0.3, sha-256;q=1, unixsum;q=0

5. Digest Algorithm Values

Digest-algorithm values are used to indicate a specific digest computation.

   digest-algorithm = token

All digest-algorithm token values are case-insensitive but lower case is preferred; digest-algorithm token values MUST be compared in a case-insensitive fashion.

The Internet Assigned Numbers Authority (IANA) maintains a registry for digest-algorithm values. The registry is initialized with the tokens listed below.

Deprecated digest algorithms MUST NOT be used:

See the references above for further information.

sha-256
  • Description: The SHA-256 algorithm [RFC6234]. The output of this algorithm is encoded using the base64 encoding [RFC4648].
  • Reference: [RFC6234], [RFC4648], this document.
  • Status: standard
sha-512
  • Description: The SHA-512 algorithm [RFC6234]. The output of this algorithm is encoded using the base64 encoding [RFC4648].
  • Reference: [RFC6234], [RFC4648], this document.
  • Status: standard
md5
  • Description: The MD5 algorithm, as specified in [RFC1321]. The output of this algorithm is encoded using the base64 encoding [RFC4648]. This digest-algorithm is now vulnerable to collision attacks. See [NO-MD5] and [CMU-836068].
  • Reference: [RFC1321], [RFC4648], this document.
  • Status: deprecated
sha
unixsum
  • Description: The algorithm computed by the UNIX "sum" command, as defined by the Single UNIX Specification, Version 2 [UNIX]. The output of this algorithm is an ASCII decimal-digit string representing the 16-bit checksum, which is the first word of the output of the UNIX "sum" command.
  • Reference: [UNIX], this document.
  • Status: standard
unixcksum
  • Description: The algorithm computed by the UNIX "cksum" command, as defined by the Single UNIX Specification, Version 2 [UNIX]. The output of this algorithm is an ASCII digit string representing the 32-bit CRC, which is the first word of the output of the UNIX "cksum" command.
  • Reference: [UNIX], this document.
  • Status: standard

To allow sender and recipient to provide a checksum which is independent from Content-Encoding, the following additional digest-algorithms are defined:

id-sha-512
  • Description: The sha-512 digest of the representation-data of the resource when no content coding is applied
  • Reference: [RFC6234], [RFC4648], this document.
  • Status: standard
id-sha-256
  • Description: The sha-256 digest of the representation-data of the resource when no content coding is applied
  • Reference: [RFC6234], [RFC4648], this document.
  • Status: standard

If other digest-algorithm values are defined, the associated encoding MUST either be represented as a quoted string or MUST NOT include ";" or "," in the character sets used for the encoding.

6. Use of Digest when acting on resources

POST and PATCH requests can appear to convey partial representations but are semantically acting on resources. The enclosed representation, including its metadata, refers to that action.

In these requests the representation digest MUST be computed on the representation-data of that action. This is the only possible choice because representation digest requires complete representation metadata (see Section 2).

In responses,

The latter case might be done according to the HTTP semantics of the given method, for example using the Content-Location header field. In contrast, the Location header field does not affect Digest because it is not representation metadata.

6.1. Digest and PATCH

In PATCH requests, the representation digest MUST be computed on the patch document because the representation metadata refers to the patch document and not to the target resource (see Section 2 of [PATCH]).

In PATCH responses, the representation digest MUST be computed on the selected representation of the patched resource.

Digest usage with PATCH is thus very similar to POST, but with the resource's own semantic partly implied by the method and by the patch document.

6.2. Digest and Content-Location in Responses

When a state-changing method returns the Content-Location header field, the enclosed representation refers to the resource identified by its value and Digest is computed accordingly.

7. Relationship to Subresource Integrity (SRI)

Subresource Integrity [SRI] is an integrity mechanism that shares some similarities to the present document's mechanism. However, there are differences in motivating factors, threat model and specification of integrity digest generation, signalling and validation.

SRI allows a first-party authority to declare an integrity assertion on a resource served by a first or third party authority. This is done via the integrity attribute that can be added to script or link HTML elements. Therefore, the integrity assertion is always made out-of-band to the resource fetch. In contrast, the Digest field is supplied in-band alongside the selected representation, meaning that an authority can only declare an integrity assertion for itself. Methods to improve the security properties of representation digests are presented in Section 10. This contrast is interesting because on one hand self-assertion is less likely to be affected by coordination problems such as the first-party holding stale information about the third party, but on the other hand the self-assertion is only as trustworthy as the authority that provided it.

The SRI integrity attribute contains a cryptographic hash algorithm and digest value which is similar to representation-data-digest (see Section 2). The major differences are in serialization format.

SRI does not specify handling of partial representation data (e.g. Range requests). In contrast, this document specifies handling in terms that are fully compatible with core HTTP concepts (an example is provided in Section 8.3).

SRI specifies strong requirements on the selection of algorithm for generation and validation of digests. In contrast, the requirements in this document are weaker.

SRI defines no method for a client to declare an integrity assertion on resources it transfers to a server. In contrast, the Digest field can appear on requests.

7.1. Supporting Both SRI and Representation Digest

The SRI and Representation Digest mechanisms are different and complementary but one is not capable of replacing the other because they have different threat, security and implementation properties.

A user agent that supports both mechanisms is expected to apply the rules specified for each but since the two mechanisms are independent, the ordering is not important. However, a user agent supporting both could benefit from performing representation digest validation first because it does not always require a conversion into identity encoding.

A user agent supporting both mechanisms: - can legitimately ignore Digest when using SRI, because Section 3 specifies that "a recipient MAY ignore any or all of the representation-data-digests"; - enforce both Digest and SRI: in this case it can be useful to provide enough information to identify whether the mismatch happened at the Digest or the SRI level.

8. Examples of Unsolicited Digest

The following examples demonstrate interactions where a server responds with a Digest field even though the client did not solicit one using Want-Digest.

Some examples include JSON objects in the content. For presentation purposes, objects that fit completely within the line-length limits are presented on a single line using compact notation with no leading space. Objects that would exceed line-length limits are presented across multiple lines (one line per key-value pair) with 2 spaced of leading indentation.

Digest is media-type agnostic and does not provide canonicalization algorithms for specific formats. Examples of Digest are calculated inclusive of any space.

8.1. Server Returns Full Representation Data

Request:

GET /items/123 HTTP/1.1
Host: foo.example

Response:

HTTP/1.1 200 OK
Content-Type: application/json
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

{"hello": "world"}

8.2. Server Returns No Representation Data

In this example, a HEAD request is used to retrieve the checksum of a resource.

The response Digest field-value is calculated over the JSON object {"hello": "world"}, which is not shown because there is no payload data.

Request:

HEAD /items/123 HTTP/1.1
Host: foo.example

Response:

HTTP/1.1 200 OK
Content-Type: application/json
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

8.3. Server Returns Partial Representation Data

In this example, the client makes a range request and the server responds with partial content. The Digest field-value represents the entire JSON object {"hello": "world"}.

Request:

GET /items/123 HTTP/1.1
Host: foo.example
Range: bytes=1-7

Response:

HTTP/1.1 206 Partial Content
Content-Type: application/json
Content-Range: bytes 1-7/18
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

"hello"

8.4. Client and Server Provide Full Representation Data

The request contains a Digest field-value calculated on the enclosed representation. It also includes an Accept-Encoding: br header field that advertises the client supports brotli encoding.

The response includes a Content-Encoding: br that indicates the selected representation is brotli encoded. The Digest field-value is therefore different compared to the request.

For presentation purposes, the response body is displayed as a base64-encoded string because it contains non-printable characters.

Request:

PUT /items/123 HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

{"hello": "world"}

Response:

HTTP/1.1 200 Ok
Content-Type: application/json
Content-Location: /items/123
Content-Encoding: br
Content-Length: 22
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=

iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==

8.5. Client Provides Full Representation Data, Server Provides No Representation Data

The request Digest field-value is calculated on the enclosed payload.

The response Digest field-value depends on the representation metadata header fields, including Content-Encoding: br even when the response does not contain content.

Request:

PUT /items/123 HTTP/1.1
Host: foo.example
Content-Type: application/json
Content-Length: 18
Accept-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

{"hello": "world"}

Response:

HTTP/1.1 204 No Content
Content-Type: application/json
Content-Encoding: br
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=

8.6. Client and Server Provide Full Representation Data, Client Uses id-sha-256.

The response contains two digest values:

  • one with no content coding applied, which in this case accidentally matches the unencoded digest-value sent in the request;
  • one taking into account the Content-Encoding.

As the response body contains non-printable characters, it is displayed as a base64-encoded string.

Request:

PUT /items/123 HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

{"hello": "world"}

Response:

HTTP/1.1 200 OK
Content-Type: application/json
Content-Encoding: br
Content-Location: /items/123
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
        id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==

8.7. POST Response does not Reference the Request URI

The request Digest field-value is computed on the enclosed representation (see Section 6).

The representation enclosed in the response refers to the resource identified by Content-Location (see [SEMANTICS], Section 6.4.2). Digest is thus computed on the enclosed representation.

Request:

POST /books HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept: application/json
Accept-Encoding: identity
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=

{"title": "New Title"}

Response:

HTTP/1.1 201 Created
Content-Type: application/json
Content-Location: /books/123
Location: /books/123
Digest: id-sha-256=yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE=

{
  "id": "123",
  "title": "New Title"
}

Note that a 204 No Content response without content but with the same Digest field-value would have been legitimate too.

8.8. POST Response Describes the Request Status

The request Digest field-value is computed on the enclosed representation (see Section 6).

The representation enclosed in the response describes the status of the request, so Digest is computed on that enclosed representation.

Response Digest has no explicit relation with the resource referenced by Location.

Request:

POST /books HTTP/1.1
Host: foo.example
Content-Type: application/json
Accept: application/json
Accept-Encoding: identity
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=
Location: /books/123

{"title": "New Title"}

Response:

HTTP/1.1 201 Created
Content-Type: application/json
Digest: id-sha-256=2LBp5RKZGpsSNf8BPXlXrX4Td4Tf5R5bZ9z7kdi5VvY=
Location: /books/123

{
  "status": "created",
  "id": "123",
  "ts": 1569327729,
  "instance": "/books/123"
}

8.9. Digest with PATCH

This case is analogous to a POST request where the target resource reflects the effective request URI.

The PATCH request uses the application/merge-patch+json media type defined in [RFC7396].

Digest is calculated on the enclosed payload, which corresponds to the patch document.

The response Digest field-value is computed on the complete representation of the patched resource.

Request:

PATCH /books/123 HTTP/1.1
Host: foo.example
Content-Type: application/merge-patch+json
Accept: application/json
Accept-Encoding: identity
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=

{"title": "New Title"}

Response:

HTTP/1.1 200 OK
Content-Type: application/json
Digest: id-sha-256=yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE=

{
  "id": "123",
  "title": "New Title"
}

Note that a 204 No Content response without content but with the same Digest field-value would have been legitimate too.

8.10. Error responses

In error responses, the representation-data does not necessarily refer to the target resource. Instead, it refers to the representation of the error.

In the following example a client attempts to patch the resource located at /books/123. However, the resource does not exist and the server generates a 404 response with a body that describes the error in accordance with [RFC7807].

The response Digest field-value is computed on this enclosed representation.

Request:

PATCH /books/123 HTTP/1.1
Host: foo.example
Content-Type: application/merge-patch+json
Accept: application/json
Accept-Encoding: identity
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=

{"title": "New Title"}

Response:

HTTP/1.1 404 Not Found
Content-Type: application/problem+json
Digest: sha-256=KPqhVXAT25LLitV1w0O167unHmVQusu+fpxm65zAsvk=

{
  "title": "Not Found",
  "detail": "Cannot PATCH a non-existent resource",
  "status": 404
}

8.11. Use with Trailer Fields and Transfer Coding

An origin server sends Digest as trailer field, so it can calculate digest-value while streaming content and thus mitigate resource consumption. The Digest field-value is the same as in Section 8.1 because Digest is designed to be independent from the use of one or more transfer codings (see Section 2).

Request:

GET /items/123 HTTP/1.1
Host: foo.example

Response:

HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked
Trailer: Digest

8\r\n
{"hello"\r\n
8
: "world\r\n
2\r\n
"}\r\n
0\r\n
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

9. Examples of Want-Digest Solicited Digest

The following examples demonstrate interactions where a client solicits a Digest using Want-Digest.

Some examples include JSON objects in the content. For presentation purposes, objects that fit completely within the line-length limits are presented on a single line using compact notation with no leading space. Objects that would exceed line-length limits are presented across multiple lines (one line per key-value pair) with 2 spaced of leading indentation.

Digest is media-type agnostic and does not provide canonicalization algorithms for specific formats. Examples of Digest are calculated inclusive of any space.

9.1. Server Selects Client's Least Preferred Algorithm

The client requests a digest, preferring "sha". The server is free to reply with "sha-256" anyway.

Request:

GET /items/123 HTTP/1.1
Host: foo.example
Want-Digest: sha-256;q=0.3, sha;q=1

Response:

HTTP/1.1 200 OK
Content-Type: application/json
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

{"hello": "world"}

9.2. Server Selects Algorithm Unsupported by Client

The client requests a "sha" digest only. The server is currently free to reply with a Digest containing an unsupported algorithm.

Request:

GET /items/123 HTTP/1.1
Host: foo.example
Want-Digest: sha;q=1

Response:

HTTP/1.1 200 OK
Content-Type: application/json
Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
                   +AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==

{"hello": "world"}

9.3. Server Does Not Support Client Algorithm and Returns an Error

The client requests a "sha" Digest, the server advises "sha-256" and "sha-512".

Request:

GET /items/123 HTTP/1.1
Host: foo.example
Want-Digest: sha;q=1

Response:

HTTP/1.1 400 Bad Request
Want-Digest: sha-256, sha-512

10. Security Considerations

10.1. Digest Does Not Protect the Full HTTP Message

This document specifies a data integrity mechanism that protects HTTP representation data, but not HTTP header and trailer fields, from certain kinds of accidental corruption.

Digest is not intended to be a general protection against malicious tampering with HTTP messages. This can be achieved by combining it with other approaches such as transport-layer security or digital signatures.

10.2. Digest for End-to-End Integrity

Digest can help detect representation data modification due to implementation errors, undesired "transforming proxies" (see Section 7.7 of [SEMANTICS]) or other actions as the data passes across multiple hops or system boundaries. Even a simple mechanism for end-to-end representation data integrity is valuable because user-agent can validate that resource retrieval succeeded before handing off to a HTML parser, video player etc. for parsing.

Identity digest-algorithms (e.g. "id-sha-256" and "id-sha-512") are particularly useful for end-to-end integrity because they allow piecing together a resource from different sources with different HTTP messaging characteristics. For example, different servers that apply different content codings.

Note that using Digest alone does not provide end-to-end integrity of HTTP messages over multiple hops, since metadata could be manipulated at any stage. Methods to protect metadata are discussed in Section 10.3.

10.3. Usage in Signatures

Digital signatures are widely used together with checksums to provide the certain identification of the origin of a message [NIST800-32]. Such signatures can protect one or more HTTP fields and there are additional considerations when Digest is included in this set.

Since the Digest field is a hash of a resource representation, it explicitly depends on the representation metadata (eg. the values of Content-Type, Content-Encoding etc). A signature that protects Digest but not other representation metadata can expose the communication to tampering. For example, an actor could manipulate the Content-Type field-value and cause a digest validation failure at the recipient, preventing the application from accessing the representation. Such an attack consumes the resources of both endpoints. See also Section 6.2.

Digest SHOULD always be used over a connection that provides integrity at the transport layer that protects HTTP fields.

A Digest field using NOT RECOMMENDED digest-algorithms SHOULD NOT be used in signatures.

Using signatures to protect the Digest of an empty representation allows receiving endpoints to detect if an eventual payload has been stripped or added.

Any mangling of Digest, including de-duplication of representation-data-digest values or combining different field values (see Section 5.2 of [SEMANTICS]) might affect signature validation.

10.4. Usage in Trailer Fields

Before sending Digest in a trailer section, the sender should consider that intermediaries are explicitly allowed to drop any trailer (see Section 6.5.2 of [SEMANTICS]).

When Digest is used in trailer fields, the receiver gets the digest value after the content and may thus be tempted to process the data before validating the digest value. It is preferable that data is only be processed after validating the Digest.

Not every digest-algorithm is suitable for use in the trailer section, some may require to pre-process the whole payload before sending a message (eg. see [I-D.thomson-http-mice]).

10.5. Usage with Encryption

Digest may expose details of encrypted payload when the checksum is computed on the unencrypted data. For example, the use of the "id-sha-256" digest-algorithm in conjunction with the encrypted content-coding [RFC8188].

The representation-data-digest of an encrypted payload can change between different messages depending on the encryption algorithm used; in those cases its value could not be used to provide a proof of integrity "at rest" unless the whole (e.g. encoded) content is persisted.

10.6. Algorithm Agility

The security properties of digest-algorithms are not fixed. Algorithm Agility (see [RFC7696]) is achieved by providing implementations with flexibility choose digest-algorithms from the IANA Digest Algorithm Values registry in Section 11.1.

To help endpoints understand weaker algorithms from stronger ones, this document adds to the IANA Digest Algorithm Values registry a new "Status" field containing the most-recent appraisal of the digest-algorithm; the allowed values are specified in Section 11.2.

An endpoint might have a preference for algorithms, such as preferring "standard" algorithms over "deprecated" ones. Transition from weak algorithms is supported by negotiation of digest-algorithm using Want-Digest (see Section 4) or by sending multiple representation-data-digest values from which the receiver chooses. Endpoints are advised that sending multiple values consumes resources, which may be wasted if the receiver ignores them (see Section 3).

10.7. Duplicate digest-algorithm in field value

An endpoint might receive multiple representation-data-digest values (see Section 3) that use the same digest-algorithm with different or identical digest-values. For example:

Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=,
        sha-256=47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=

A receiver is permitted to ignore any representation-data-digest value, so validation of duplicates is left as an implementation decision. Endpoints might select all, some or none of the values for checksum comparison and, based on the intersection of those results, conditionally pass or fail digest validation.

10.8. Resource exhaustion

Digest validation consumes computational resources. In order to avoid resource exhaustion, implementations can restrict validation of the algorithm types, number of validations, or the size of content.

11. IANA Considerations

11.1. Establish the HTTP Digest Algorithm Values Registry

This memo sets this specification to be the establishing document for the HTTP Digest Algorithm Values registry.

11.2. The "status" Field in the HTTP Digest Algorithm Values Registry

This memo adds the field "Status" to the HTTP Digest Algorithm Values registry. The allowed values for the "Status" fields are described below.

Status
  • "standard" for standardized algorithms without known problems;
  • "experimental", "obsoleted" or some other appropriate value - e.g. according to the type and status of the primary document in which the algorithm is defined;
  • "deprecated" when the algorithm is insecure or otherwise undesirable.

11.3. Deprecate "MD5" Digest Algorithm

This memo updates the "MD5" digest-algorithm in the HTTP Digest Algorithm Values registry:

11.4. Update "UNIXsum" Digest Algorithm

This memo updates the "UNIXsum" digest-algorithm in the HTTP Digest Algorithm Values registry:

11.5. Update "UNIXcksum" Digest Algorithm

This memo updates the "UNIXcksum" digest-algorithm in the HTTP Digest Algorithm Values registry:

11.6. Update "CRC32c" Digest Algorithm

This memo updates the "CRC32c" digest-algorithm in the HTTP Digest Algorithm Values registry:

  • Digest Algorithm: crc32c
  • Description: The CRC32c algorithm is a 32-bit cyclic redundancy check. It achieves a better hamming distance (for better error-detection performance) than many other 32-bit CRC functions. Other places it is used include iSCSI and SCTP. The 32-bit output is encoded in hexadecimal (using between 1 and 8 ASCII characters from 0-9, A-F, and a-f; leading 0's are allowed). For example, crc32c=0a72a4df and crc32c=A72A4DF are both valid checksums for the 3-byte message "dog".
  • Reference: [RFC4960] appendix B, this document.
  • Status: standard.

11.7. Deprecate "SHA" Digest Algorithm

This memo updates the "SHA" digest-algorithm in the HTTP Digest Algorithm Values registry:

11.8. Obsolete "ADLER32" Digest Algorithm

This memo updates the "ADLER32" digest-algorithm in the HTTP Digest Algorithm Values registry:

  • Digest Algorithm: adler32
  • Description: The ADLER32 algorithm is a checksum specified in [RFC1950] "ZLIB Compressed Data Format". The 32-bit output is encoded in hexadecimal (using between 1 and 8 ASCII characters from 0-9, A-F, and a-f; leading 0's are allowed). For example, adler32=03da0195 and adler32=3DA0195 are both valid checksums for the 4-byte message "Wiki". This algorithm is obsoleted and SHOULD NOT be used.
  • Status: obsoleted

11.9. Obsolete "contentMD5" token in Digest Algorithm

This memo adds the "contentMD5" token in the HTTP Digest Algorithm Values registry:

  • Digest Algorithm: contentMD5
  • Description: Section 5 of [RFC3230] defined the "contentMD5" token to be used only in Want-Digest. This token is obsoleted and MUST NOT be used.
  • Reference: Section 11.9 of this document, Section 5 of [RFC3230].
  • Status: obsoleted

11.10. The "id-sha-256" Digest Algorithm

This memo registers the "id-sha-256" digest-algorithm in the HTTP Digest Algorithm Values registry:

11.11. The "id-sha-512" Digest Algorithm

This memo registers the "id-sha-512" digest-algorithm in the HTTP Digest Algorithm Values registry:

11.12. Changes Compared to RFC3230

&#65532; The contentMD5 digest-algorithm token defined in Section 5 of [RFC3230] is removed from the HTTP Digest Algorithm Values Registry.

11.13. Changes Compared to RFC5843

The digest-algorithm values for "MD5", "SHA", "SHA-256", "SHA-512", "UNIXcksum", "UNIXsum", "ADLER32" and "CRC32c" have been updated to lowercase.

The status of "MD5" has been updated to "deprecated", and its description states that this algorithm MUST NOT be used.

The status of "SHA" has been updated to "deprecated", and its description states that this algorithm MUST NOT be used.

The status for "CRC2c", "UNIXsum" and "UNIXcksum" has been updated to "standard".

The "id-sha-256" and "id-sha-512" algorithms have been added to the registry.

11.14. Want-Digest Field Registration

This section registers the Want-Digest field in the "Hypertext Transfer Protocol (HTTP) Field Name Registry" [SEMANTICS].

Field name: Want-Digest

Status: permanent

Specification document(s): Section 4 of this document

11.15. Digest Field Registration

This section registers the Digest field in the "Hypertext Transfer Protocol (HTTP) Field Name Registry" [SEMANTICS].

Field name: Digest

Status: permanent

Specification document(s): Section 3 of this document

12. References

12.1. Normative References

[CMU-836068]
Carnagie Mellon University, Software Engineering Institute, "MD5 Vulnerable to collision attacks", , <https://www.kb.cert.org/vuls/id/836068/>.
[IACR-2020-014]
Leurent, G. and T. Peyrin, "SHA-1 is a Shambles", , <https://eprint.iacr.org/2020/014.pdf>.
[NIST800-32]
National Institute of Standards and Technology, U.S. Department of Commerce, "Introduction to Public Key Technology and the Federal PKI Infrastructure", , <https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-32.pdf>.
[RFC1321]
Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, DOI 10.17487/RFC1321, , <https://datatracker.ietf.org/doc/html/rfc1321>.
[RFC1950]
Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format Specification version 3.3", RFC 1950, DOI 10.17487/RFC1950, , <https://datatracker.ietf.org/doc/html/rfc1950>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://datatracker.ietf.org/doc/html/rfc2119>.
[RFC3174]
Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC 3174, DOI 10.17487/RFC3174, , <https://datatracker.ietf.org/doc/html/rfc3174>.
[RFC3230]
Mogul, J. and A. Van Hoff, "Instance Digests in HTTP", RFC 3230, DOI 10.17487/RFC3230, , <https://datatracker.ietf.org/doc/html/rfc3230>.
[RFC4648]
Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, , <https://datatracker.ietf.org/doc/html/rfc4648>.
[RFC4960]
Stewart, R., Ed., "Stream Control Transmission Protocol", RFC 4960, DOI 10.17487/RFC4960, , <https://datatracker.ietf.org/doc/html/rfc4960>.
[RFC5234]
Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, , <https://datatracker.ietf.org/doc/html/rfc5234>.
[RFC5843]
Bryan, A., "Additional Hash Algorithms for HTTP Instance Digests", RFC 5843, DOI 10.17487/RFC5843, , <https://datatracker.ietf.org/doc/html/rfc5843>.
[RFC6234]
Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI 10.17487/RFC6234, , <https://datatracker.ietf.org/doc/html/rfc6234>.
[RFC7405]
Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC 7405, DOI 10.17487/RFC7405, , <https://datatracker.ietf.org/doc/html/rfc7405>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://datatracker.ietf.org/doc/html/rfc8174>.
[SEMANTICS]
Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP Semantics", Work in Progress, Internet-Draft, draft-ietf-httpbis-semantics-16, , <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-semantics-16>.
[UNIX]
The Open Group, "The Single UNIX Specification, Version 2 - 6 Vol Set for UNIX 98", .

12.2. Informative References

[HTTP11]
Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP/1.1", Work in Progress, Internet-Draft, draft-ietf-httpbis-messaging-16, , <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-messaging-16>.
[I-D.ietf-httpbis-header-structure]
Nottingham, M. and P. Kamp, "Structured Field Values for HTTP", Work in Progress, Internet-Draft, draft-ietf-httpbis-header-structure-19, , <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-header-structure-19>.
[I-D.thomson-http-mice]
Thomson, M. and J. Yasskin, "Merkle Integrity Content Encoding", Work in Progress, Internet-Draft, draft-thomson-http-mice-03, , <https://datatracker.ietf.org/doc/html/draft-thomson-http-mice-03>.
[NO-MD5]
Turner, S. and L. Chen, "Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms", RFC 6151, DOI 10.17487/RFC6151, , <https://datatracker.ietf.org/doc/html/rfc6151>.
[NO-SHA1]
Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security Considerations for the SHA-0 and SHA-1 Message-Digest Algorithms", RFC 6194, DOI 10.17487/RFC6194, , <https://datatracker.ietf.org/doc/html/rfc6194>.
[PATCH]
Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC 5789, DOI 10.17487/RFC5789, , <https://datatracker.ietf.org/doc/html/rfc5789>.
[RFC2818]
Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, , <https://datatracker.ietf.org/doc/html/rfc2818>.
[RFC7231]
Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, , <https://datatracker.ietf.org/doc/html/rfc7231>.
[RFC7396]
Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396, DOI 10.17487/RFC7396, , <https://datatracker.ietf.org/doc/html/rfc7396>.
[RFC7696]
Housley, R., "Guidelines for Cryptographic Algorithm Agility and Selecting Mandatory-to-Implement Algorithms", BCP 201, RFC 7696, DOI 10.17487/RFC7696, , <https://datatracker.ietf.org/doc/html/rfc7696>.
[RFC7807]
Nottingham, M. and E. Wilde, "Problem Details for HTTP APIs", RFC 7807, DOI 10.17487/RFC7807, , <https://datatracker.ietf.org/doc/html/rfc7807>.
[RFC8188]
Thomson, M., "Encrypted Content-Encoding for HTTP", RFC 8188, DOI 10.17487/RFC8188, , <https://datatracker.ietf.org/doc/html/rfc8188>.
[SRI]
Akhawe, D., Braun, F., Marier, F., and J. Weinberger, "Subresource Integrity", W3C Recommendation REC-SRI-20160623, , <https://www.w3.org/TR/2016/REC-SRI-20160623/>.

Appendix A. Resource Representation and Representation-Data

The following examples show how representation metadata, payload transformations and method impacts on the message and content. When the content contains non-printable characters (eg. when it is compressed) it is shown as base64-encoded string.

A request with a JSON object without any content coding.

Request:

PUT /entries/1234 HTTP/1.1
Host: foo.example
Content-Type: application/json

{"hello": "world"}

Here is a gzip-compressed JSON object using a content coding.

Request:

PUT /entries/1234 HTTP/1.1
Host: foo.example
Content-Type: application/json
Content-Encoding: gzip

H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=

Now the same content conveys a malformed JSON object.

Request:

PUT /entries/1234 HTTP/1.1
Host: foo.example
Content-Type: application/json

H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=

A Range-Request alters the content, conveying a partial representation.

Request:

GET /entries/1234 HTTP/1.1
Host: foo.example
Range: bytes=1-7

Response:

HTTP/1.1 206 Partial Content
Content-Encoding: gzip
Content-Type: application/json
Content-Range: bytes 1-7/18

iwgAla3RXA==

Now the method too alters the content.

Request:

HEAD /entries/1234 HTTP/1.1
Host: foo.example
Accept: application/json
Accept-Encoding: gzip

Response:

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

Finally the semantics of an HTTP response might decouple the effective request URI from the enclosed representation. In the example response below, the Content-Location header field indicates that the enclosed representation refers to the resource available at /authors/123.

Request:

POST /authors/ HTTP/1.1
Host: foo.example
Accept: application/json
Content-Type: application/json

{"author": "Camilleri"}

Response:

HTTP/1.1 201 Created
Content-Type: application/json
Content-Location: /authors/123
Location: /authors/123

{"id": "123", "author": "Camilleri"}

Appendix B. Changes from RFC3230

B.1. Deprecate Negotiation of Content-MD5

This RFC deprecates the negotiation of Content-MD5 as it has been obsoleted by [RFC7231].

B.2. Obsolete Digest Field Parameters

Section 4.1.1 and 4.2 of [RFC3230] defined field parameters. This document obsoletes the usage of parameters with Digest because this feature has not been widely deployed and complicates field-value processing.

[RFC3230] intended field parameters to provide a common way to attach additional information to a representation-data-digest. However, if parameters are used as an input to validate the checksum, an attacker could alter them to steer the validation behavior.

A digest-algorithm can still be parameterized by defining its own way to encode parameters into the representation-data-digest, in such a way as to mitigate security risks related to its computation.

Acknowledgements

The vast majority of this document is inherited from [RFC3230], so thanks to J. Mogul and A. Van Hoff for their great work. The original idea of refreshing this document arose from an interesting discussion with M. Nottingham, J. Yasskin and M. Thomson when reviewing the MICE content coding.

FAQ

RFC Editor: Please remove this section before publication.

  1. Why remove all references to content-md5?

    Those were unnecessary to understanding and using this specification.

  2. Why remove references to instance manipulation?

    Those were unnecessary for correctly using and applying the specification. An example with Range Request is more than enough. This document uses the term "partial representation" which should group all those cases.

  3. How to use Digest with PATCH method?

    See Section 6.

  4. Why remove references to delta-encoding?

    Unnecessary for a correct implementation of this specification. The revised specification can be nicely adapted to "delta encoding", but all the references here to delta encoding don't add anything to this RFC. Another job would be to refresh delta encoding.

  5. Why remove references to Digest Authentication?

    This specification seems to me completely unrelated to Digest Authentication but for the word "Digest".

  6. What changes in Want-Digest?

    The contentMD5 token defined in Section 5 of [RFC3230] is deprecated by Appendix B.1.

    To clarify that Digest and Want-Digest can be used in both requests and responses - [RFC3230] carefully uses sender and receiver in their definition - we added examples on using Want-Digest in responses to advertise the supported digest-algorithms and the inability to accept requests with unsupported digest-algorithms.

  7. Does this specification change supported algorithms?

    Yes. This RFC updates [RFC5843] which is still delegated for all algorithms updates, and adds two more algorithms: "id-sha-256" and "id-sha-512" which allows to send a checksum of a resource representation with no content codings applied. To simplify a future transition to Structured Fields [I-D.ietf-httpbis-header-structure] we suggest to use lowercase for digest-algorithms.

  8. What about mid-stream trailer fields?

    While mid-stream trailer fields are interesting, since this specification is a rewrite of [RFC3230] we do not think we should face that. As a first thought, nothing in this document precludes future work that would find a use for mid-stream trailers, for example an incremental digest-algorithm. A document defining such a digest-algorithm is best positioned to describe how it is used.

Code Samples

RFC Editor: Please remove this section before publication.

How can I generate and validate the Digest values 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 encode_item(item, encoding=lambda x: x):
    indent = 2 if isinstance(item, dict) and len(item) > 1 else None
    json_bytes = json.dumps(item, indent=indent).encode()
    return encoding(json_bytes)


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(item, encoding=lambda x: x, algorithm=hashlib.sha256):
    content_encoded = encode_item(item, encoding)
    return digest_bytes(content_encoded, algorithm)


item = {"hello": "world"}

print("Encoding | digest-algorithm | digest-value")
print("Identity | sha256 |", digest(item))
# Encoding | digest-algorithm | digest-value
# Identity | sha256 | X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

print("Encoding | digest-algorithm | digest-value")
print("Brotli | sha256 |", digest(item, encoding=brotli.compress))
# Encoding | digest-algorithm | digest-value
# Brotli | sha256 | 4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=

print("Encoding | digest-algorithm | digest-value")
print("Identity | sha512 |", digest(item, algorithm=hashlib.sha512))
# Encoding | digest-algorithm | digest-value
# Identity | sha512 | b'WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm'
#                      '+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew=='

Changes

RFC Editor: Please remove this section before publication.

Since draft-ietf-httpbis-digest-headers-04

  • Improve SRI section #1354
  • About duplicate digest-algorithms #1221
  • Improve security considerations #852
  • md5 and sha deprecation references #1392
  • Obsolete 3230 #1395
  • Editorial #1362

Since draft-ietf-httpbis-digest-headers-03

  • Reference semantics-12
  • Detail encryption quirks
  • Details on Algorithm agility #1250
  • Obsolete parameters #850

Since draft-ietf-httpbis-digest-headers-02

  • Deprecate SHA-1 #1154
  • Avoid id-* with encrypted content
  • Digest is independent from MESSAGING and HTTP/1.1 is not normative #1215
  • Identity is not a valid field value for content-encoding #1223
  • Mention trailers #1157
  • Reference httpbis-semantics #1156
  • Add contentMD5 as an obsoleted digest-algorithm #1249
  • Use lowercase digest-algorithms names in the doc and in the digest-algorithm IANA table.

Since draft-ietf-httpbis-digest-headers-01

  • Digest of error responses is computed on the error representation-data #1004
  • Effect of HTTP semantics on payload and message body moved to appendix #1122
  • Editorial refactoring, moving headers sections up. #1109-#1112, #1116, #1117, #1122-#1124

Since draft-ietf-httpbis-digest-headers-00

  • Align title with document name
  • Add id-sha-* algorithm examples #880
  • Reference [RFC6234] and [RFC3174] instead of FIPS-1
  • Deprecate MD5
  • Obsolete ADLER-32 but don't forbid it #828
  • Update CRC32C value in IANA table #828
  • Use when acting on resources (POST, PATCH) #853
  • Added Relationship with SRI, draft Use Cases #868, #971
  • Warn about the implications of Content-Location

Authors' Addresses

Roberto Polli
Team Digitale, Italian Government
Italy
Lucas Pardue
Cloudflare