HTTP R. Polli
Internet-Draft Team Digitale, Italian Government
Intended status: Standards Track L. Pardue
Expires: March 11, 2021 Cloudflare
September 07, 2020
Digest Headers
draft-ietf-httpbis-digest-headers-03
Abstract
This document defines the HTTP Digest and Want-Digest fields, thus
allowing client and server to negotiate an integrity checksum of the
exchanged resource representation data.
This document obsoletes RFC 3230. It replaces the term "instance"
with "representation", which makes it consistent with the HTTP
Semantic and Context defined in draft-ietf-httpbis-semantics.
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/ [1].
The source code and issues list for this draft can be found at
https://github.com/httpwg/http-extensions [2].
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
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This Internet-Draft will expire on March 11, 2021.
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. A Brief History of HTTP Integrity Fields . . . . . . . . 4
1.2. This Proposal . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4. Notational Conventions . . . . . . . . . . . . . . . . . 5
2. Representation Digest . . . . . . . . . . . . . . . . . . . . 6
3. The Digest Field . . . . . . . . . . . . . . . . . . . . . . 6
4. The Want-Digest Field . . . . . . . . . . . . . . . . . . . . 7
5. Digest Algorithm Values . . . . . . . . . . . . . . . . . . . 8
6. Use of Digest when acting on resources . . . . . . . . . . . 10
6.1. Digest and PATCH . . . . . . . . . . . . . . . . . . . . 11
7. Deprecate Negotiation of Content-MD5 . . . . . . . . . . . . 11
8. Relationship to Subresource Integrity (SRI) . . . . . . . . . 11
8.1. Supporting Both SRI and Representation Digest . . . . . . 12
9. Examples of Unsolicited Digest . . . . . . . . . . . . . . . 13
9.1. Server Returns Full Representation Data . . . . . . . . . 13
9.2. Server Returns No Representation Data . . . . . . . . . . 13
9.3. Server Returns Partial Representation Data . . . . . . . 13
9.4. Client and Server Provide Full Representation Data . . . 14
9.5. Client Provides Full Representation Data, Server Provides
No Representation Data . . . . . . . . . . . . . . . . . 15
9.6. Client and Server Provide Full Representation Data,
Client Uses id-sha-256. . . . . . . . . . . . . . . . . . 15
9.7. POST Response does not Reference the Request URI . . . . 16
9.8. POST Response Describes the Request Status . . . . . . . 16
9.9. Digest with PATCH . . . . . . . . . . . . . . . . . . . . 17
9.10. Error responses . . . . . . . . . . . . . . . . . . . . . 18
9.11. Use with trailers and transfer coding . . . . . . . . . . 19
10. Examples of Want-Digest Solicited Digest . . . . . . . . . . 19
10.1. Server Selects Client's Least Preferred Algorithm . . . 20
10.2. Server Selects Algorithm Unsupported by Client . . . . . 20
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10.3. Server Does Not Support Client Algorithm and Returns an
Error . . . . . . . . . . . . . . . . . . . . . . . . . 20
11. Security Considerations . . . . . . . . . . . . . . . . . . . 21
11.1. Digest Does Not Protect the Full HTTP Message . . . . . 21
11.2. Broken Cryptographic Algorithms . . . . . . . . . . . . 21
11.3. Other Deprecated Algorithms . . . . . . . . . . . . . . 21
11.4. Digest for End-to-End Integrity . . . . . . . . . . . . 21
11.5. Digest and Content-Location in responses . . . . . . . . 22
11.6. Usage in signatures . . . . . . . . . . . . . . . . . . 22
11.7. Usage in trailers . . . . . . . . . . . . . . . . . . . 22
11.8. Usage with encryption . . . . . . . . . . . . . . . . . 23
11.9. Algorithm Agility . . . . . . . . . . . . . . . . . . . 23
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
12.1. Establish the HTTP Digest Algorithm Values . . . . . . . 23
12.2. The "status" Field in the HTTP Digest Algorithm Values . 23
12.3. Deprecate "MD5" Digest Algorithm . . . . . . . . . . . . 23
12.4. Update "UNIXsum" Digest Algorithm . . . . . . . . . . . 24
12.5. Update "UNIXcksum" Digest Algorithm . . . . . . . . . . 24
12.6. Update "CRC32c" Digest Algorithm . . . . . . . . . . . . 24
12.7. Obsolete "SHA" Digest Algorithm . . . . . . . . . . . . 24
12.8. Obsolete "ADLER32" Digest Algorithm . . . . . . . . . . 25
12.9. Obsolete "contentMD5" token in Digest Algorithm . . . . 25
12.10. The "id-sha-256" Digest Algorithm . . . . . . . . . . . 25
12.11. The "id-sha-512" Digest Algorithm . . . . . . . . . . . 26
12.12. Changes compared to RFC5843 . . . . . . . . . . . . . . 26
12.13. Want-Digest Field Registration . . . . . . . . . . . . . 26
12.14. Digest Header Field Registration . . . . . . . . . . . . 26
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
13.1. Normative References . . . . . . . . . . . . . . . . . . 27
13.2. Informative References . . . . . . . . . . . . . . . . . 28
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Appendix A. Resource Representation and Representation-Data . . 30
Appendix B. FAQ . . . . . . . . . . . . . . . . . . . . . . . . 32
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 33
Code Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
E.1. Since draft-ietf-httpbis-digest-headers-00 . . . . . . . 34
E.2. Since draft-ietf-httpbis-digest-headers-01 . . . . . . . 35
E.3. Since draft-ietf-httpbis-digest-headers-02 . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
The core specification of HTTP does not define a means to protect the
integrity of resources. 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].
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However, there are cases where relying on this alone is insufficient.
An HTTP-level integrity mechanism that operates independent of
transfer can be used to detect programming errors and/or corruption
of data at rest, be used across multiple hops in order to provide
end-to-end integrity guarantees, aid fault diagnosis across hops and
system boundaries, and can be used to validate integrity when
reconstructing a resource fetched using different HTTP connections.
This document defines a mechanism that acts on HTTP representation-
data. It can be combined with other mechanisms that protect
representation-metadata, such as digital signatures, in order to
protect the desired parts of an HTTP exchange in whole or in part.
1.1. A Brief History of HTTP Integrity Fields
The Content-MD5 header field was originally introduced to provide
integrity, but HTTP/1.1 ([RFC7231], Appendix B) obsoleted it:
The Content-MD5 header field has been removed because it was
inconsistently implemented with respect to partial responses.
[RFC3230] provided a more flexible solution introducing the concept
of "instance", and the fields "Digest" and "Want-Digest".
1.2. This Proposal
The concept of "selected representation" defined in Section 7 of
[SEMANTICS] makes [RFC3230] definitions inconsistent with current
HTTP semantics. This document updates the "Digest" and "Want-Digest"
field definitions to align with [SEMANTICS] concepts.
Basing "Digest" on the selected representation makes it
straightforward to apply it to use-cases where the transferred data
does require some sort of manipulation to be considered a
representation, or conveys a partial representation of a resource eg.
Range Requests (see Section 9.3 of [SEMANTICS]).
Changes are semantically compatible with existing implementations and
better cover both the request and response cases.
The value of "Digest" is calculated on selected representation, which
is tied to the value contained in any "Content-Encoding" or "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 7.1.2 of [SEMANTICS]) two more
digest-algorithms are added ("id-sha-256" and "id-sha-512").
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1.3. Goals
The goals of this proposal are:
1. Digest coverage for either the resource's "representation data"
or "selected representation data" communicated via HTTP.
2. Support for multiple digest-algorithms.
3. Negotiation of the use of digests.
The goals do not include:
HTTP message integrity: The digest mechanism described here does not
cover the full HTTP message nor its semantic, as representation
metadata are not included in the checksum.
HTTP field integrity: The digest mechanisms described here cover
only representation and selected representation data, and do not
protect the integrity of associated representation metadata or
other message fields.
Authentication: The digest mechanisms described here are not meant
to support authentication of the source of a digest or of a
message or anything else. These mechanisms, therefore, are not a
sufficient defense against many kinds of malicious attacks.
Privacy: Digest mechanisms do not provide message privacy.
Authorization: The digest mechanisms described here are not meant to
support authorization or other kinds of access controls.
1.4. 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] and [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 of
[SEMANTICS].
The definitions "representation", "selected representation",
"representation data", "representation metadata", and "payload body"
in this document are to be interpreted as described in [SEMANTICS].
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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 payload body (see Section 7.3.3 of [SEMANTICS]). It uses the
representation data (see Section 7.1 of [SEMANTICS]), that can be
fully or partially contained in the payload body, or not contained at
all:
representation-data := Content-Encoding( Content-Type( bits ) )
This takes into account the effect of the HTTP semantics on the
messages; for example the payload body can be affected by Range
Requests or methods such as HEAD, while the way the payload body is
transferred "on the wire" is dependent on other transformations (eg.
transfer codings for HTTP/1.1 see 6.1 of [HTTP11]): Appendix A
contains several examples to help illustrate those effects.
A representation digest consists of the value of a checksum computed
on the entire selected "representation data" (see Section 7 of
[SEMANTICS]) of a resource identified according to Section 7.3.2 of
[SEMANTICS] together with an indication of the algorithm used (and
any parameters)
representation-data-digest = digest-algorithm "="
<encoded digest output>
The checksum is computed using one of the digest-algorithms listed in
Section 5 and then encoded in the associated format.
The example below shows the "sha-256" digest-algorithm which uses
base64 encoding.
sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
3. The Digest Field
The "Digest" field contains a list of one or more representation
digest values as defined in Section 2. It can be used in both
request and response.
Digest = "Digest" ":" OWS 1#representation-data-digest
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The relationship between "Content-Location" (see Section 7.2.5 of
[SEMANTICS]) and "Digest" is demonstrated in Section 9.7. A
comprehensive set of examples showing the impacts of representation
metadata, payload transformations and HTTP methods on Digest is
provided in Section 9 and Section 10.
A "Digest" field MAY contain multiple representation-data-digest
values. This could be useful for responses expected to reside in
caches shared by users with different browsers, for example.
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. When using incremental
digest-algorithms this allows the sender and the receiver to
dynamically compute the digest value while streaming the content.
Two examples of its use are
Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
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.
Want-Digest = "Want-Digest" ":" OWS 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", 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.
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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. For some digest-algorithms, one or more parameters can
be supplied.
digest-algorithm = token
The BNF for "parameter" is defined in Section 5.4.1.4 of [SEMANTICS].
All digest-algorithm values are case-insensitive but the lower case
is preferred.
The Internet Assigned Numbers Authority (IANA) acts as a registry for
digest-algorithm values. The registry contains the tokens listed
below.
Some digest-algorithms, although registered, rely on vulnerable
algorithms: the "md5" digest-algorithm MUST NOT be used due to
collision attacks [CMU-836068] and the "sha" digest-algorithm MUST
NOT be used due to collision attacks [IACR-2020-014].
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.
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* 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 MUST NOT be used as it's now
vulnerable to collision attacks [CMU-836068].
* Reference: [RFC1321], [RFC4648], this document.
* Status: deprecated
sha
* Description: The SHA-1 algorithm [RFC3174]. The output of this
algorithm is encoded using the base64 encoding [RFC4648]. This
digest-algorithm MUST NOT be used as it's now vulnerable to
collision attacks [IACR-2020-014].
* Reference: [RFC3174], [RFC6234], [RFC4648], this document.
* Status: deprecated
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.
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* 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,
o if the representation describes the status of the request,
"Digest" MUST be computed on the enclosed representation (see
Section 9.8 );
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o if there is a referenced resource "Digest" MUST be computed on the
selected representation of the referenced resource even if that is
different from the target resource. That might or might not
result in computing "Digest" on the enclosed representation.
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
[RFC5789]).
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 the POST one, but
with the resource's own semantic partly implied by the method and by
the patch document.
7. Deprecate Negotiation of Content-MD5
This RFC deprecates the negotiation of Content-MD5 as it has been
obsoleted by [RFC7231]. The "contentMD5" token defined in Section 5
of [RFC3230] MUST NOT be used as a digest-algorithm.
8. 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 11. This contrast is interesting
because on one hand self-assertion is less likely to be affected by
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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.
The SRI digest value is calculated over the identity encoding of the
resource, not the selected representation (as specified for
"representation-data-digest" in this document). Section 3.4.5 of
[SRI] describes the benefit of the identity approach - the SRI
"integrity" attribute can contain multiple algorithm-value pairs
where each applies to a different identity encoded payload. This
allows for protection of distinct resources sharing a URL. However,
this is a contrast to the design of representation digests, where
multiple "Digest" field-values all protect the same representation.
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 9.3).
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.
8.1. 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.
There is a chance that a user agent supporting both mechanisms may
find one validates successfully while the other fails. This document
specifies no requirements or guidance for user agents that experience
such cases.
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9. 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".
9.1. Server Returns Full Representation Data
Request:
GET /items/123
Response:
HTTP/1.1 200 OK
Content-Type: application/json
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"}
9.2. Server Returns No Representation Data
Requests without a payload body can still send a "Digest" field
applying the digest-algorithm to an empty representation.
As there is no content coding applied, the "sha-256" and the "id-sha-
256" digest-values in the response are the same.
Request:
HEAD /items/123 HTTP/1.1
Digest: sha-256=47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=
Response:
HTTP/1.1 200 OK
Content-Type: application/json
Digest: id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
9.3. Server Returns Partial Representation Data
Request:
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GET /items/123
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"
9.4. Client and Server Provide Full Representation Data
The request contains a "Digest" field 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.
The response body is displayed as a base64-encoded string because it
contains non-printable characters.
Request:
PUT /items/123
Content-Type: application/json
Accept-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"}
Response:
Content-Type: application/json
Content-Encoding: br
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==
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9.5. Client Provides Full Representation Data, Server Provides No
Representation Data
Request "Digest" value is calculated on the enclosed payload.
Response "Digest" value depends on the representation metadata header
fields, including "Content-Encoding: br" even when the response does
not contain a payload body.
Request:
PUT /items/123
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=
9.6. Client and Server Provide Full Representation Data, Client Uses
id-sha-256.
The response contains two digest values:
o one with no content coding applied, which in this case
accidentally matches the unencoded digest-value sent in the
request;
o 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
Content-Type: application/json
Accept-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"}
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Response:
HTTP/1.1 200 OK
Content-Type: application/json
Content-Encoding: br
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==
9.7. POST Response does not Reference the Request URI
Request "Digest" 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 7.3.2).
"Digest" is thus computed on the enclosed representation.
Request:
POST /books HTTP/1.1
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
Digest: id-sha-256=BZlF2v0IzjuxN01RQ97EUXriaNNLhtI8Chx8Eq+XYSc=
Content-Location: /books/123
{"id": "123", "title": "New Title"}
Note that a "204 No Content" response without a payload body but with
the same "Digest" field-value would have been legitimate too.
9.8. POST Response Describes the Request Status
Request "Digest" value is computed on the enclosed representation
(see Section 6).
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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
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=0o/WKwSfnmIoSlop2LV/ISaBDth05IeW27zzNMUh5l8=
Location: /books/123
{
"status": "created",
"id": "123",
"ts": 1569327729,
"instance": "/books/123"
}
9.9. 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" is computed on the complete representation of
the patched resource.
Request:
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PATCH /books/123 HTTP/1.1
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=BZlF2v0IzjuxN01RQ97EUXriaNNLhtI8Chx8Eq+XYSc=
{"id": "123", "title": "New Title"}
Note that a "204 No Content" response without a payload body but with
the same "Digest" field-value would have been legitimate too.
9.10. 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 digest of the response is computed on this enclosed
representation.
Request:
PATCH /books/123 HTTP/1.1
Content-Type: application/merge-patch+json
Accept: application/json
Accept-Encoding: identity
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=
{"title": "New Title"}
Response:
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HTTP/1.1 404 Not Found
Content-Type: application/problem+json
Digest: sha-256=UJSojgEzqUe4UoHzmNl5d2xkmrW3BOdmvsvWu1uFeu0=
{
"title": "Not Found",
"detail": "Cannot PATCH a non-existent resource",
"status": 404
}
9.11. Use with trailers and transfer coding
An origin server sends "Digest" in the HTTP trailer, so it can
calculate digest-value while streaming content and thus mitigate
resource consumption. The field value is the same as in Section 9.1
because "Digest" is designed to be independent from the use of one or
more transfer codings (see Section 2).
Request:
GET /items/123
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=
10. Examples of Want-Digest Solicited Digest
The following examples demonstrate interactions where a client
solicits a "Digest" using "Want-Digest".
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10.1. 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
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"}
10.2. 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
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"}
10.3. Server Does Not Support Client Algorithm and Returns an Error
The client requests a sha Digest, the server advises for sha-256 and
sha-512
Request:
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GET /items/123
Want-Digest: sha;q=1
Response:
HTTP/1.1 400 Bad Request
Want-Digest: sha-256, sha-512
11. Security Considerations
11.1. Digest Does Not Protect the Full HTTP Message
This document specifies a data integrity mechanism that protects HTTP
"representation data", but not HTTP "representation metadata" fields,
from certain kinds of accidental corruption.
"Digest" is not intended as 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.
11.2. Broken Cryptographic Algorithms
Cryptographic algorithms are intended to provide a proof of integrity
suited towards cryptographic constructions such as signatures.
However, these rely on collision-resistance for their security proofs
[CMU-836068]. The "MD5" and "SHA-1" digest algorithms are vulnerable
to collisions attacks, so they MUST NOT be used with "Digest".
11.3. Other Deprecated Algorithms
The ADLER32 algorithm defined in [RFC1950] has been deprecated by
[RFC3309] because under certain conditions it provides weak detection
of errors and is now NOT RECOMMENDED for use with "Digest".
11.4. Digest for End-to-End Integrity
"Digest" alone does not provide end-to-end integrity of HTTP messages
over multiple hops, as it just covers the "representation data" and
not the "representation metadata".
Besides, it allows to protect "representation data" from buggy
manipulation, buggy compression, etc.
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Moreover identity digest algorithms (eg. "id-sha-256" and "id-sha-
512") allow piecing together a resource from different sources (e.g.
different servers that perhaps apply different content codings)
enabling the user-agent to detect that the application-layer tasks
completed properly, before handing off to say the HTML parser, video
player etc.
Even a simple mechanism for end-to-end validation is thus valuable.
11.5. 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.
11.6. 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 11.5.
"Digest" SHOULD always be used over a connection which 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.
11.7. Usage in trailers
When used in trailers, the receiver gets the digest value after the
payload body and may thus be tempted to process the data before
validating the digest value. Instead, data should only be processed
after validating the Digest.
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If received in trailers, "Digest" MUST NOT be discarded; instead it
MAY be merged in the header section (See Section 5.6.2 of
[SEMANTICS]).
Not every digest-algorithm is suitable for trailers, as they may
require to pre-process the whole payload before sending a message
(eg. see [I-D.thomson-http-mice]).
11.8. Usage with encryption
"Digest" may expose information details of encrypted payload when the
checksum is computed on the unencrypted data. An example of that is
the use of the "id-sha-256" digest algorithm in conjuction with the
encrypted content-coding [RFC8188].
11.9. Algorithm Agility
...
12. IANA Considerations
12.1. Establish the HTTP Digest Algorithm Values
This memo sets this spec to be the establishing document for the HTTP
Digest Algorithm Values [3]
12.2. The "status" Field in the HTTP Digest Algorithm Values
This memo adds the field "Status" to the HTTP Digest Algorithm Values
[4] registry. The allowed values for the "Status" fields are
described below.
Status Specify "standard", "experimental", "historic", "obsoleted",
or "deprecated" according to the type and status of the primary
document in which the algorithm is defined.
12.3. Deprecate "MD5" Digest Algorithm
This memo updates the "MD5" digest-algorithm in the HTTP Digest
Algorithm Values [5] registry:
o Digest Algorithm: md5
o Description: As specified in Section 5.
o Status: As specified in Section 5.
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12.4. Update "UNIXsum" Digest Algorithm
This memo updates the "UNIXsum" digest algorithm in the HTTP Digest
Algorithm Values [6] registry:
o Digest Algorithm: As specified in Section 5.
o Description: As specified in Section 5.
o Status: As specified in Section 5.
12.5. Update "UNIXcksum" Digest Algorithm
This memo updates the "UNIXcksum" digest algorithm in the HTTP Digest
Algorithm Values [7] registry:
o Digest Algorithm: As specified in Section 5.
o Description: As specified in Section 5.
o Status: As specified in Section 5.
12.6. Update "CRC32c" Digest Algorithm
This memo updates the "CRC32c" digest-algorithm in the HTTP Digest
Algorithm Values [8] registry:
o Digest Algorithm: crc32c
o 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".
o Reference: [RFC4960] appendix B, this document.
o Status: standard.
12.7. Obsolete "SHA" Digest Algorithm
This memo updates the "SHA" digest-algorithm in the HTTP Digest
Algorithm Values [9] registry:
o Digest Algorithm: sha
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o Description: As specified in Section 5.
o Status: As specified in Section 5.
12.8. Obsolete "ADLER32" Digest Algorithm
This memo updates the "ADLER32" digest-algorithm in the HTTP Digest
Algorithm Values [10] registry:
o Digest Algorithm: adler32
o 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.
o Status: obsoleted
12.9. Obsolete "contentMD5" token in Digest Algorithm
This memo adds the "contentMD5" token in the HTTP Digest Algorithm
Values [11] registry:
o Digest Algorithm: contentMD5
o 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.
o Reference: Section 12.9 of this document, Section 5 of [RFC3230].
o Status: obsoleted
12.10. The "id-sha-256" Digest Algorithm
This memo registers the "id-sha-256" digest algorithm in the HTTP
Digest Algorithm Values [12] registry:
o Digest Algorithm: id-sha-256
o Description: As specified in Section 5.
o Status: As specified in Section 5.
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12.11. The "id-sha-512" Digest Algorithm
This memo registers the "id-sha-512" digest algorithm in the HTTP
Digest Algorithm Values [13] registry:
o Digest Algorithm: id-sha-512
o Description: As specified in Section 5.
o Status: As specified in Section 5.
12.12. 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.
12.13. 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
12.14. Digest Header Field Registration
This section registers the "Digest" field in the "Hypertext Transfer
Protocol (HTTP) Field Name Registry" [SEMANTICS].
Field name: "Digest"
Status: permanent
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Specification document(s): Section 3 of this document
13. References
13.1. Normative References
[CMU-836068]
Carnagie Mellon University, Software Engineering
Institute, "MD5 Vulnerable to collision attacks", December
2008, <https://www.kb.cert.org/vuls/id/836068/>.
[IACR-2020-014]
Leurent, G. and T. Peyrin, "SHA-1 is a Shambles", January
2020, <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", February
2001, <https://nvlpubs.nist.gov/nistpubs/Legacy/SP/
nistspecialpublication800-32.pdf>.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992,
<https://www.rfc-editor.org/info/rfc1321>.
[RFC1950] Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format
Specification version 3.3", RFC 1950,
DOI 10.17487/RFC1950, May 1996,
<https://www.rfc-editor.org/info/rfc1950>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
<https://www.rfc-editor.org/info/rfc3174>.
[RFC3230] Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
RFC 3230, DOI 10.17487/RFC3230, January 2002,
<https://www.rfc-editor.org/info/rfc3230>.
[RFC3309] Stone, J., Stewart, R., and D. Otis, "Stream Control
Transmission Protocol (SCTP) Checksum Change", RFC 3309,
DOI 10.17487/RFC3309, September 2002,
<https://www.rfc-editor.org/info/rfc3309>.
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[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5843] Bryan, A., "Additional Hash Algorithms for HTTP Instance
Digests", RFC 5843, DOI 10.17487/RFC5843, April 2010,
<https://www.rfc-editor.org/info/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, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
RFC 7405, DOI 10.17487/RFC7405, December 2014,
<https://www.rfc-editor.org/info/rfc7405>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[SEMANTICS]
Fielding, R., Nottingham, M., and J. Reschke, "HTTP
Semantics", draft-ietf-httpbis-semantics-11 (work in
progress), August 2020.
[UNIX] The Open Group, "The Single UNIX Specification, Version 2
- 6 Vol Set for UNIX 98", February 1997.
13.2. Informative References
[HTTP11] Fielding, R., Nottingham, M., and J. Reschke, "HTTP/1.1
Messaging", draft-ietf-httpbis-messaging-11 (work in
progress), August 2020.
[]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", draft-ietf-httpbis-header-structure-19 (work in
progress), June 2020.
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[I-D.thomson-http-mice]
Thomson, M. and J. Yasskin, "Merkle Integrity Content
Encoding", draft-thomson-http-mice-03 (work in progress),
August 2018.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, DOI 10.17487/RFC5789, March 2010,
<https://www.rfc-editor.org/info/rfc5789>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014,
<https://www.rfc-editor.org/info/rfc7396>.
[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",
RFC 8188, DOI 10.17487/RFC8188, June 2017,
<https://www.rfc-editor.org/info/rfc8188>.
[SRI] Akhawe, D., Braun, F., Marier, F., and J. Weinberger,
"Subresource Integrity", W3C Recommendation REC-SRI-
20160623, June 2016,
<https://www.w3.org/TR/2016/REC-SRI-20160623/>.
13.3. URIs
[1] https://lists.w3.org/Archives/Public/ietf-http-wg/
[2] https://github.com/httpwg/http-extensions
[3] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[4] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[5] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[6] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
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[7] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[8] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[9] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[10] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[11] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[12] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[13] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[14] https://github.com/httpwg/http-core/
issues/313#issuecomment-584389706
Appendix A. Resource Representation and Representation-Data
The following examples show how representation metadata, payload
transformations and method impacts on the message and payload body.
When the payload body 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
Content-Type: application/json
{"hello": "world"}
Here is a gzip-compressed json object using a content coding.
Request:
PUT /entries/1234 HTTP/1.1
Content-Type: application/json
Content-Encoding: gzip
H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=
Now the same payload body conveys a malformed json object.
Request:
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PUT /entries/1234 HTTP/1.1
Content-Type: application/json
H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=
A Range-Request alters the payload body, conveying a partial
representation.
Request:
GET /entries/1234 HTTP/1.1
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 payload body.
Request:
HEAD /entries/1234 HTTP/1.1
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:
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POST /authors/ HTTP/1.1
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. FAQ
1. Why remove all references to content-md5?
Those were unnecessary to understanding and using this spec.
2. Why remove references to instance manipulation?
Those were unnecessary for correctly using and applying the spec.
An example with Range Request is more than enough. This doc 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 spec. The
revised spec 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 RFC 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 Section 7.
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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 spec changes supported algorithms?
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 trailers?
While mid-stream trailers [14] 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.
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.
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.
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import base64, json, hashlib, brotli
def digest(item, encoding=lambda x: x, algorithm=hashlib.sha256):
json_bytes = json.dumps(item).encode()
content_encoded = encoding(json_bytes)
checksum_bytes = algorithm(content_encoded).digest()
return base64.encodebytes(checksum_bytes).strip()
item = {"hello": "world"}
print("Encoding | digest-algorithm | digest-value")
print("Identity | sha256 |", digest(item))
# Encoding | digest-algorithm | digest-value
# Identity | sha256 | 4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
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/7XgHaAy8pmojAkGWoRx2UFChF41A2s
vX+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==\n'
Changes
_RFC Editor: Please remove this section before publication._
E.1. 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
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o Added Relationship with SRI, draft Use Cases #868, #971
o Warn about the implications of "Content-Location"
E.2. 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
E.3. Since draft-ietf-httpbis-digest-headers-02
o Deprecate SHA-1 #1154
o Avoid id-* with encrypted content
o Digest is independent from 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.
Authors' Addresses
Roberto Polli
Team Digitale, Italian Government
Email: robipolli@gmail.com
Lucas Pardue
Cloudflare
Email: lucaspardue.24.7@gmail.com
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