< draft-ietf-httpbis-digest-headers-06.txt   draft-ietf-httpbis-digest-headers-07.txt >
HTTP R. Polli HTTP R. Polli
Internet-Draft Team Digitale, Italian Government Internet-Draft Team Digitale, Italian Government
Obsoletes: 3230 (if approved) L. Pardue Obsoletes: 3230 (if approved) L. Pardue
Intended status: Standards Track Cloudflare Intended status: Standards Track Cloudflare
Expires: 31 March 2022 27 September 2021 Expires: 20 May 2022 16 November 2021
Digest Fields Digest Fields
draft-ietf-httpbis-digest-headers-06 draft-ietf-httpbis-digest-headers-07
Abstract Abstract
This document defines HTTP fields that support integrity checksums. This document defines HTTP fields that support integrity checksums.
The Digest field can be used for the integrity of HTTP The Digest field can be used for the integrity of HTTP
representations. The Content-Digest field can be used for the representations. The Content-Digest field can be used for the
integrity of HTTP message content. Want-Digest and Want-Content- integrity of HTTP message content. Want-Digest and Want-Content-
Digest can be used to indicate a sender's desire to receive integrity Digest can be used to indicate a sender's desire to receive integrity
fields respectively. fields respectively.
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This Internet-Draft will expire on 31 March 2022. This Internet-Draft will expire on 20 May 2022.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Structure . . . . . . . . . . . . . . . . . . . 4 1.1. Document Structure . . . . . . . . . . . . . . . . . . . 4
1.2. Concept Overview . . . . . . . . . . . . . . . . . . . . 4 1.2. Concept Overview . . . . . . . . . . . . . . . . . . . . 4
1.3. Replacing RFC 3230 . . . . . . . . . . . . . . . . . . . 5 1.3. Replacing RFC 3230 . . . . . . . . . . . . . . . . . . . 5
1.4. Notational Conventions . . . . . . . . . . . . . . . . . 6 1.4. Notational Conventions . . . . . . . . . . . . . . . . . 6
2. Representation Digest . . . . . . . . . . . . . . . . . . . . 6 2. Representation Digest . . . . . . . . . . . . . . . . . . . . 6
3. The Digest Field . . . . . . . . . . . . . . . . . . . . . . 7 3. The Digest Field . . . . . . . . . . . . . . . . . . . . . . 7
4. The Content-Digest Field . . . . . . . . . . . . . . . . . . 8 4. The Content-Digest Field . . . . . . . . . . . . . . . . . . 8
5. Want-Digest and Want-Content-Digest Fields . . . . . . . . . 8 5. Want-Digest and Want-Content-Digest Fields . . . . . . . . . 9
6. Digest Algorithm Values . . . . . . . . . . . . . . . . . . . 9 6. Digest Algorithm Values . . . . . . . . . . . . . . . . . . . 9
7. Using Digest in State-Changing Requests . . . . . . . . . . . 13 7. Using Digest in State-Changing Requests . . . . . . . . . . . 12
7.1. Digest and Content-Location in Responses . . . . . . . . 13 7.1. Digest and Content-Location in Responses . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8.1. Digest Does Not Protect the Full HTTP Message . . . . . . 13 8.1. Digest Does Not Protect the Full HTTP Message . . . . . . 13
8.2. Digest for End-to-End Integrity . . . . . . . . . . . . . 14 8.2. Digest for End-to-End Integrity . . . . . . . . . . . . . 14
8.3. Usage in Signatures . . . . . . . . . . . . . . . . . . . 14 8.3. Usage in Signatures . . . . . . . . . . . . . . . . . . . 14
8.4. Usage in Trailer Fields . . . . . . . . . . . . . . . . . 15 8.4. Usage in Trailer Fields . . . . . . . . . . . . . . . . . 15
8.5. Usage with Encryption . . . . . . . . . . . . . . . . . . 15 8.5. Usage with Encryption . . . . . . . . . . . . . . . . . . 15
8.6. Algorithm Agility . . . . . . . . . . . . . . . . . . . . 15 8.6. Algorithm Agility . . . . . . . . . . . . . . . . . . . . 15
8.7. Duplicate digest-algorithm in field value . . . . . . . . 16 8.7. Duplicate digest-algorithm in field value . . . . . . . . 16
8.8. Resource exhaustion . . . . . . . . . . . . . . . . . . . 16 8.8. Resource exhaustion . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9.1. Establish the HTTP Digest Algorithm Values Registry . . . 16 9.1. Establish the HTTP Digest Algorithm Values Registry . . . 16
9.2. Obsolete "contentMD5" token in Digest Algorithm . . . . . 17 9.2. Obsolete "contentMD5" token in Digest Algorithm . . . . . 16
9.3. Changes Compared to RFC3230 . . . . . . . . . . . . . . . 17 9.3. Changes Compared to RFC3230 . . . . . . . . . . . . . . . 17
9.4. Changes Compared to RFC5843 . . . . . . . . . . . . . . . 17 9.4. Changes Compared to RFC5843 . . . . . . . . . . . . . . . 17
9.5. Want-Digest Field Registration . . . . . . . . . . . . . 17 9.5. Want-Digest Field Registration . . . . . . . . . . . . . 17
9.6. Digest Field Registration . . . . . . . . . . . . . . . . 18 9.6. Digest Field Registration . . . . . . . . . . . . . . . . 17
9.7. Want-Content-Digest Field Registration . . . . . . . . . 18 9.7. Want-Content-Digest Field Registration . . . . . . . . . 17
9.8. Content-Digest Field Registration . . . . . . . . . . . . 18 9.8. Content-Digest Field Registration . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18 10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 20 10.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Resource Representation and Representation-Data . . 22 Appendix A. Resource Representation and Representation-Data . . 21
Appendix B. Examples of Unsolicited Digest . . . . . . . . . . . 24 Appendix B. Examples of Unsolicited Digest . . . . . . . . . . . 23
B.1. Server Returns Full Representation Data . . . . . . . . . 24 B.1. Server Returns Full Representation Data . . . . . . . . . 23
B.2. Server Returns No Representation Data . . . . . . . . . . 24 B.2. Server Returns No Representation Data . . . . . . . . . . 24
B.3. Server Returns Partial Representation Data . . . . . . . 25 B.3. Server Returns Partial Representation Data . . . . . . . 24
B.4. Client and Server Provide Full Representation Data . . . 25 B.4. Client and Server Provide Full Representation Data . . . 25
B.5. Client Provides Full Representation Data, Server Provides B.5. Client Provides Full Representation Data, Server Provides
No Representation Data . . . . . . . . . . . . . . . . . 26 No Representation Data . . . . . . . . . . . . . . . . . 26
B.6. Client and Server Provide Full Representation Data, Client B.6. Client and Server Provide Full Representation Data . . . 26
Uses id-sha-256. . . . . . . . . . . . . . . . . . . . . 27
B.7. POST Response does not Reference the Request URI . . . . 27 B.7. POST Response does not Reference the Request URI . . . . 27
B.8. POST Response Describes the Request Status . . . . . . . 28 B.8. POST Response Describes the Request Status . . . . . . . 28
B.9. Digest with PATCH . . . . . . . . . . . . . . . . . . . . 29 B.9. Digest with PATCH . . . . . . . . . . . . . . . . . . . . 28
B.10. Error responses . . . . . . . . . . . . . . . . . . . . . 30 B.10. Error responses . . . . . . . . . . . . . . . . . . . . . 29
B.11. Use with Trailer Fields and Transfer Coding . . . . . . . 30 B.11. Use with Trailer Fields and Transfer Coding . . . . . . . 30
Appendix C. Examples of Want-Digest Solicited Digest . . . . . . 31 Appendix C. Examples of Want-Digest Solicited Digest . . . . . . 30
C.1. Server Selects Client's Least Preferred Algorithm . . . . 31 C.1. Server Selects Client's Least Preferred Algorithm . . . . 31
C.2. Server Selects Algorithm Unsupported by Client . . . . . 32 C.2. Server Selects Algorithm Unsupported by Client . . . . . 31
C.3. Server Does Not Support Client Algorithm and Returns an C.3. Server Does Not Support Client Algorithm and Returns an
Error . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Error . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Appendix D. Changes from RFC3230 . . . . . . . . . . . . . . . . 32 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 32
D.1. Deprecate Negotiation of Content-MD5 . . . . . . . . . . 33
D.2. Obsolete Digest Field Parameters . . . . . . . . . . . . 33
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 33
FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Code Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Code Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Since draft-ietf-httpbis-digest-headers-06 . . . . . . . . . . 35
Since draft-ietf-httpbis-digest-headers-05 . . . . . . . . . . 36 Since draft-ietf-httpbis-digest-headers-05 . . . . . . . . . . 36
Since draft-ietf-httpbis-digest-headers-04 . . . . . . . . . . 37 Since draft-ietf-httpbis-digest-headers-04 . . . . . . . . . . 36
Since draft-ietf-httpbis-digest-headers-03 . . . . . . . . . . 37 Since draft-ietf-httpbis-digest-headers-03 . . . . . . . . . . 36
Since draft-ietf-httpbis-digest-headers-02 . . . . . . . . . . 37 Since draft-ietf-httpbis-digest-headers-02 . . . . . . . . . . 36
Since draft-ietf-httpbis-digest-headers-01 . . . . . . . . . . 37 Since draft-ietf-httpbis-digest-headers-01 . . . . . . . . . . 37
Since draft-ietf-httpbis-digest-headers-00 . . . . . . . . . . 38 Since draft-ietf-httpbis-digest-headers-00 . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction 1. Introduction
HTTP does not define a means to protect the integrity of HTTP does not define a means to protect the integrity of
representations. When HTTP messages are transferred between representations. When HTTP messages are transferred between
endpoints, the protocol might choose to make use of features of the endpoints, the protocol might choose to make use of features of the
lower layer in order to provide some integrity protection; for lower layer in order to provide some integrity protection; for
instance, TCP checksums or TLS records [RFC2818]. instance, TCP checksums or TLS records [RFC2818].
This document defines two digest integrity mechanisms for HTTP. This document defines two digest integrity mechanisms for HTTP.
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* Section 3 defines the Digest request and response header and * Section 3 defines the Digest request and response header and
trailer field, trailer field,
* Section 4 defines the Content-Digest request and response header * Section 4 defines the Content-Digest request and response header
and trailer field, and trailer field,
* Section 5 defines the Want-Digest and Want-Content-Digest request * Section 5 defines the Want-Digest and Want-Content-Digest request
and response header and trailer field, and response header and trailer field,
* Section 6 and Appendix D.1 describe algorithms and their relation * Section 6 describes algorithms and their relation to Digest,
to Digest,
* Section 7 details computing representation digests, * Section 7 details computing representation digests,
* Appendix D.2 obsoletes Digest field parameters, and
* Appendix B and Appendix C provide examples of using Digest and * Appendix B and Appendix C provide examples of using Digest and
Want-Digest. Want-Digest.
1.2. Concept Overview 1.2. Concept Overview
This document defines the Digest request and response header and This document defines the Digest request and response header and
trailer field; see Section 3. At a high level, the value contains a trailer field; see Section 3. At a high level, the value contains a
checksum, computed over selected representation data (Section 3.2 of checksum, computed over selected representation data (Section 3.2 of
[SEMANTICS]), that the recipient can use to validate integrity. [SEMANTICS]), that the recipient can use to validate integrity.
Basing Digest on the selected representation makes it straightforward Basing Digest on the selected representation makes it straightforward
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required, this document introduces the Content-Digest request and required, this document introduces the Content-Digest request and
response header and trailer field; see Section 4. response header and trailer field; see Section 4.
Digest and Content-Digest support algorithm agility. The Want-Digest Digest and Content-Digest support algorithm agility. The Want-Digest
and Want-Content-Digest fields allows endpoints to express interest and Want-Content-Digest fields allows endpoints to express interest
in Digest and Content-Digest respectively, and preference of in Digest and Content-Digest respectively, and preference of
algorithms in either. algorithms in either.
Digest field calculations are tied to the Content-Encoding and Digest field calculations are tied to the Content-Encoding and
Content-Type header fields. Therefore, a given resource may have Content-Type header fields. Therefore, a given resource may have
multiple different checksum values when transferred with HTTP. To multiple different checksum values when transferred with HTTP.
allow both parties to exchange a simple checksum 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 fields do not provide integrity for HTTP messages or fields. Digest fields do not provide integrity for HTTP messages or fields.
However, they can be combined with other mechanisms that protect However, they can be combined with other mechanisms that protect
metadata, such as digital signatures, in order to protect the phases metadata, such as digital signatures, in order to protect the phases
of an HTTP exchange in whole or in part. of an HTTP exchange in whole or in part.
This specification does not define means for authentication, This specification does not define means for authentication,
authorization or privacy. authorization or privacy.
1.3. Replacing RFC 3230 1.3. Replacing RFC 3230
Historically, the Content-MD5 header field provided an HTTP integrity Historically, the Content-MD5 header field provided an HTTP integrity
mechanism but HTTP/1.1 ([RFC7231], Appendix B) obsoleted it due to mechanism but HTTP/1.1 ([RFC7231], Appendix B) obsoleted it due to
inconsistent handling of partial responses. [RFC3230] defined the inconsistent handling of partial responses. [RFC3230] defined the
concept of "instance" digests and a more flexible integrity scheme to concept of "instance" digests and a more flexible integrity scheme to
help address issues with Content-MD5. It first introduced the Digest help address issues with Content-MD5. It first introduced the Digest
and Want-Digest fields. HTTP terminology has evolved since [RFC3230] and Want-Digest fields. HTTP terminology has evolved since [RFC3230]
was published. The concept of "instance" has been superseded by was published. The concept of "instance" has been superseded by
selected representation. selected representation.
This document replaces [RFC3230]. The Digest and Want-Digest field This document replaces [RFC3230]. The changes described in the
definitions are updated to align with the terms and notational following paragraphs are intended to be semantically compatible with
conventions in [SEMANTICS]. Changes are intended to be semantically existing implementations where possible.
compatible with existing implementations but note that negotiation of
Content-MD5 is deprecated Appendix D.1 and has been replaced by The Digest and Want-Digest field definitions are updated to align
Content-Digest negotiation via Want-Content-Digest. Digest field with the terms and notational conventions in [SEMANTICS].
parameters are obsoleted Appendix D.2 and the algorithm table has
been updated to reflect the current state of the art. Negotiation of Content-MD5 is deprecated and has been replaced by
Content-Digest negotiation via Want-Content-Digest.
Sections 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.
The algorithm table has been updated to reflect the current state of
the art, (see Section 6).
1.4. Notational Conventions 1.4. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This document uses the Augmented BNF defined in [RFC5234] and updated This document uses the Augmented BNF defined in [RFC5234] and updated
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3. The Digest Field 3. The Digest Field
The Digest field contains a comma-separated list of one or more The Digest field contains a comma-separated list of one or more
representation digest values as defined in Section 2. It can be used representation digest values as defined in Section 2. It can be used
in both requests and responses. in both requests and responses.
Digest = 1#representation-data-digest Digest = 1#representation-data-digest
For example: For example:
Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm Digest: sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew== AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
A Digest field MAY contain multiple representation-data-digest A Digest field MAY contain multiple representation-data-digest
values. For example, a server may provide representation-data-digest values. For example, a server may provide representation-data-digest
values using different algorithms, allowing it to support a values using different algorithms, allowing it to support a
population of clients with different evolving capabilities; this is population of clients with different evolving capabilities; this is
particularly useful in support of transitioning away from weaker particularly useful in support of transitioning away from weaker
algorithms should the need arise (see Section 8.6). algorithms should the need arise (see Section 8.6).
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=, Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
A recipient MAY ignore any or all of the representation-data-digests A recipient MAY ignore any or all of the representation-data-digests
in a Digest field. This allows the recipient to choose which digest- in a Digest field. This allows the recipient to choose which digest-
algorithm(s) to use for validation instead of verifying every algorithm(s) to use for validation instead of verifying every
received representation-data-digest. received representation-data-digest.
A sender MAY send a representation-data-digest using a digest- A sender MAY send a representation-data-digest using a digest-
algorithm without knowing whether the recipient supports the digest- algorithm without knowing whether the recipient supports the digest-
algorithm, or even knowing that the recipient will ignore it. algorithm, or even knowing that the recipient will ignore it.
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applying a digest-algorithm to the actual message content (see applying a digest-algorithm to the actual message content (see
Section 6.4 of [SEMANTICS]). It can be used in both requests and Section 6.4 of [SEMANTICS]). It can be used in both requests and
responses. responses.
Content-Digest = 1#content-digest Content-Digest = 1#content-digest
content-digest = digest-algorithm "=" content-digest = digest-algorithm "="
<encoded digest output> <encoded digest output>
For example: For example:
Content-Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm Content-Digest: sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew== AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
A Content-Digest field MAY contain multiple content-digest values, A Content-Digest field MAY contain multiple content-digest values,
similarly to Digest (see Section 3) similarly to Digest (see Section 3)
Content-Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=, Content-Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
A recipient MAY ignore any or all of the content-digests in a A recipient MAY ignore any or all of the content-digests in a
Content-Digest field. This allows the recipient to choose which Content-Digest field. This allows the recipient to choose which
digest-algorithm(s) to use for validation instead of verifying every digest-algorithm(s) to use for validation instead of verifying every
received content-digest. received content-digest.
A sender MAY send a content-digest using a digest-algorithm without A sender MAY send a content-digest using a digest-algorithm without
knowing whether the recipient supports the digest-algorithm, or even knowing whether the recipient supports the digest-algorithm, or even
knowing that the recipient will ignore it. knowing that the recipient will ignore it.
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algorithm values. Registrations MUST include the following fields: algorithm values. Registrations MUST include the following fields:
* Digest algorithm: the token value. The registry can be used to * Digest algorithm: the token value. The registry can be used to
reserve token values reserve token values
* Status: the status of the algorithm. Use "standard" for * Status: the status of the algorithm. Use "standard" for
standardized algorithms without known problems; "experimental" or standardized algorithms without known problems; "experimental" or
some other appropriate value some other appropriate value
- e.g. according to the type and status of the primary document - e.g. according to the type and status of the primary document
in which the algorithm is defined; "deprecated" when the in which the algorithm is defined; "insecure" when the
algorithm is insecure or otherwise undesirable; "reserved" when algorithm is insecure; "reserved" when Digest algorithm
Digest algorithm references a reserved token value references a reserved token value
* Description: the description of the digest-algorithm and its * Description: the description of the digest-algorithm and its
encoding encoding
* Reference: a set of pointers to the primary documents defining the * Reference: a set of pointers to the primary documents defining the
digest-algorithm digest-algorithm
The associated encoding for new digest-algorithms MUST either be The associated encoding for new digest-algorithms MUST either be
represented as a quoted string or MUST NOT include ";" or "," in the represented as a quoted string or MUST NOT include ";" or "," in the
character sets used for the encoding. character sets used for the encoding.
Deprecated digest algorithms MUST NOT be used. Insecure digest algorithms MAY be used to preserve integrity against
accidental change, but MUST NOT be used in a potentially adversarial
setting; for example, when signing the digest of content for
authenticity.
The registry is initialized with the tokens listed below. The registry is initialized with the tokens listed below.
sha-512 sha-512
* Digest Algorithm: sha-512 * Digest Algorithm: sha-512
* Description: The SHA-512 algorithm [RFC6234]. The output of * Description: The SHA-512 algorithm [RFC6234]. The output of
this algorithm is encoded using the base64 encoding [RFC4648]. this algorithm is encoded using the base64 encoding [RFC4648].
* Reference: [RFC6234], [RFC4648], this document. * Reference: [RFC6234], [RFC4648], this document.
skipping to change at page 10, line 40 skipping to change at page 11, line 4
* Description: The SHA-512 algorithm [RFC6234]. The output of * Description: The SHA-512 algorithm [RFC6234]. The output of
this algorithm is encoded using the base64 encoding [RFC4648]. this algorithm is encoded using the base64 encoding [RFC4648].
* Reference: [RFC6234], [RFC4648], this document. * Reference: [RFC6234], [RFC4648], this document.
* Status: standard * Status: standard
sha-256 sha-256
* Digest Algorithm: sha-256 * Digest Algorithm: sha-256
* Description: The SHA-256 algorithm [RFC6234]. The output of * Description: The SHA-256 algorithm [RFC6234]. The output of
this algorithm is encoded using the base64 encoding [RFC4648]. this algorithm is encoded using the base64 encoding [RFC4648].
* Reference: [RFC6234], [RFC4648], this document. * Reference: [RFC6234], [RFC4648], this document.
* Status: standard * Status: standard
md5 md5
* Digest Algorithm: md5 * Digest Algorithm: md5
* Description: The MD5 algorithm, as specified in [RFC1321]. The * Description: The MD5 algorithm, as specified in [RFC1321]. The
output of this algorithm is encoded using the base64 encoding output of this algorithm is encoded using the base64 encoding
[RFC4648]. This digest-algorithm is now vulnerable to [RFC4648]. This digest-algorithm is now vulnerable to
collision attacks. See [NO-MD5] and [CMU-836068]. collision attacks. See [NO-MD5] and [CMU-836068].
* Reference: [RFC1321], [RFC4648], this document. * Reference: [RFC1321], [RFC4648], this document.
* Status: deprecated * Status: insecure
sha sha
* Digest Algorithm: sha * Digest Algorithm: sha
* Description: The SHA-1 algorithm [RFC3174]. The output of this * Description: The SHA-1 algorithm [RFC3174]. The output of this
algorithm is encoded using the base64 encoding [RFC4648]. This algorithm is encoded using the base64 encoding [RFC4648]. This
digest-algorithm is now vulnerable to collision attacks. See digest-algorithm is now vulnerable to collision attacks. See
[NO-SHA1] and [IACR-2020-014]. [NO-SHA1] and [IACR-2020-014].
* Reference: [RFC3174], [RFC6234], [RFC4648], this document. * Reference: [RFC3174], [RFC6234], [RFC4648], this document.
* Status: deprecated * Status: insecure
unixsum unixsum
* Digest Algorithm: unixsum * Digest Algorithm: unixsum
* Description: The algorithm computed by the UNIX "sum" command, * Description: The algorithm computed by the UNIX "sum" command,
as defined by the Single UNIX Specification, Version 2 [UNIX]. as defined by the Single UNIX Specification, Version 2 [UNIX].
The output of this algorithm is an ASCII decimal-digit string The output of this algorithm is an ASCII decimal-digit string
representing the 16-bit checksum, which is the first word of representing the 16-bit checksum, which is the first word of
the output of the UNIX "sum" command. the output of the UNIX "sum" command.
* Reference: [UNIX], this document. * Reference: [UNIX], this document.
* Status: deprecated * Status: insecure
unixcksum unixcksum
* Digest Algorithm: unixcksum * Digest Algorithm: unixcksum
* Description: The algorithm computed by the UNIX "cksum" * Description: The algorithm computed by the UNIX "cksum"
command, as defined by the Single UNIX Specification, Version 2 command, as defined by the Single UNIX Specification, Version 2
[UNIX]. The output of this algorithm is an ASCII digit string [UNIX]. The output of this algorithm is an ASCII digit string
representing the 32-bit CRC, which is the first word of the representing the 32-bit CRC, which is the first word of the
output of the UNIX "cksum" command. output of the UNIX "cksum" command.
* Reference: [UNIX], this document. * Reference: [UNIX], this document.
* Status: deprecated * Status: insecure
adler32 adler32
* Digest Algorithm: adler32 * Digest Algorithm: adler32
* Description: The ADLER32 algorithm is a checksum specified in * Description: The ADLER32 algorithm is a checksum specified in
[RFC1950] "ZLIB Compressed Data Format". The 32-bit output is [RFC1950] "ZLIB Compressed Data Format". The 32-bit output is
encoded in hexadecimal (using between 1 and 8 ASCII characters 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, from 0-9, A-F, and a-f; leading 0's are allowed). For example,
adler32=03da0195 and adler32=3DA0195 are both valid checksums adler32=03da0195 and adler32=3DA0195 are both valid checksums
for the 4-byte message "Wiki". This algorithm is obsoleted and for the 4-byte message "Wiki". This algorithm is obsoleted and
SHOULD NOT be used. SHOULD NOT be used.
* Reference: [RFC1950], this document. * Reference: [RFC1950], this document.
* Status: deprecated * Status: insecure
crc32c crc32c
* Digest Algorithm: crc32c * Digest Algorithm: crc32c
* Description: The CRC32c algorithm is a 32-bit cyclic redundancy * Description: The CRC32c algorithm is a 32-bit cyclic redundancy
check. It achieves a better hamming distance (for better check. It achieves a better hamming distance (for better
error-detection performance) than many other 32-bit CRC error-detection performance) than many other 32-bit CRC
functions. Other places it is used include iSCSI and SCTP. functions. Other places it is used include iSCSI and SCTP.
The 32-bit output is encoded in hexadecimal (using between 1 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 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 allowed). For example, crc32c=0a72a4df and crc32c=A72A4DF are
both valid checksums for the 3-byte message "dog". both valid checksums for the 3-byte message "dog".
* Reference: [RFC4960] appendix B, this document. * Reference: [RFC4960] appendix B, this document.
* Status: deprecated. * Status: insecure
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
7. Using Digest in State-Changing Requests 7. Using Digest in State-Changing Requests
When the representation enclosed in a state-changing request does not When the representation enclosed in a state-changing request does not
describe the target resource, the representation digest MUST be describe the target resource, the representation digest MUST be
computed on the representation-data. This is the only possible computed on the representation-data. This is the only possible
choice because representation digest requires complete representation choice because representation digest requires complete representation
metadata (see Section 2). metadata (see Section 2).
In responses, In responses,
skipping to change at page 14, line 20 skipping to change at page 14, line 15
8.2. Digest for End-to-End Integrity 8.2. Digest for End-to-End Integrity
Digest fields can help detect representation data or content Digest fields can help detect representation data or content
modification due to implementation errors, undesired "transforming modification due to implementation errors, undesired "transforming
proxies" (see Section 7.7 of [SEMANTICS]) or other actions as the proxies" (see Section 7.7 of [SEMANTICS]) or other actions as the
data passes across multiple hops or system boundaries. Even a simple data passes across multiple hops or system boundaries. Even a simple
mechanism for end-to-end representation data integrity is valuable mechanism for end-to-end representation data integrity is valuable
because user-agent can validate that resource retrieval succeeded because user-agent can validate that resource retrieval succeeded
before handing off to a HTML parser, video player etc. for parsing. 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 fields alone does not provide end-to-end Note that using digest fields alone does not provide end-to-end
integrity of HTTP messages over multiple hops, since metadata could integrity of HTTP messages over multiple hops, since metadata could
be manipulated at any stage. Methods to protect metadata are be manipulated at any stage. Methods to protect metadata are
discussed in Section 8.3. discussed in Section 8.3.
8.3. Usage in Signatures 8.3. Usage in Signatures
Digital signatures are widely used together with checksums to provide Digital signatures are widely used together with checksums to provide
the certain identification of the origin of a message [NIST800-32]. the certain identification of the origin of a message [NIST800-32].
Such signatures can protect one or more HTTP fields and there are Such signatures can protect one or more HTTP fields and there are
skipping to change at page 15, line 31 skipping to change at page 15, line 23
the trailer section prevents digest validation, possibly leading to the trailer section prevents digest validation, possibly leading to
processing of invalid data. processing of invalid data.
Not every digest-algorithm is suitable for use in the trailer Not every digest-algorithm is suitable for use in the trailer
section, some may require to pre-process the whole payload before section, some may require to pre-process the whole payload before
sending a message (e.g. see [I-D.thomson-http-mice]). sending a message (e.g. see [I-D.thomson-http-mice]).
8.5. Usage with Encryption 8.5. Usage with Encryption
Digest fields may expose details of encrypted payload when the Digest fields may expose details of encrypted payload when the
checksum is computed on the unencrypted data. For example, the use checksum is computed on the unencrypted data.
of the "id-sha-256" digest-algorithm in conjunction with the
encrypted content-coding [RFC8188].
The checksum of an encrypted payload can change between different The checksum of an encrypted payload can change between different
messages depending on the encryption algorithm used; in those cases messages depending on the encryption algorithm used; in those cases
its value could not be used to provide a proof of integrity "at rest" its value could not be used to provide a proof of integrity "at rest"
unless the whole (e.g. encoded) content is persisted. unless the whole (e.g. encoded) content is persisted.
8.6. Algorithm Agility 8.6. Algorithm Agility
The security properties of digest-algorithms are not fixed. The security properties of digest-algorithms are not fixed.
Algorithm Agility (see [RFC7696]) is achieved by providing Algorithm Agility (see [RFC7696]) is achieved by providing
implementations with flexibility choose digest-algorithms from the implementations with flexibility choose digest-algorithms from the
IANA Digest Algorithm Values registry in Section 9.1. IANA Digest Algorithm Values registry in Section 9.1.
To help endpoints distinguish weaker algorithms from stronger ones, To help endpoints distinguish weaker algorithms from stronger ones,
this document adds to the IANA Digest Algorithm Values registry a new this document adds to the IANA Digest Algorithm Values registry a new
"Status" field containing the most recent appraisal of the digest- "Status" field containing the most recent appraisal of the digest-
algorithm. algorithm.
An endpoint might have a preference for algorithms, such as An endpoint might have a preference for algorithms, such as
preferring "standard" algorithms over "deprecated" ones. Transition preferring "standard" algorithms over "insecure" ones. Transition
from weak algorithms is supported by negotiation of digest-algorithm from weak algorithms is supported by negotiation of digest-algorithm
using Want-Digest or Want-Content-Digest (see Section 5) or by using Want-Digest or Want-Content-Digest (see Section 5) or by
sending multiple representation-data-digest values from which the sending multiple representation-data-digest values from which the
receiver chooses. Endpoints are advised that sending multiple values receiver chooses. Endpoints are advised that sending multiple values
consumes resources, which may be wasted if the receiver ignores them consumes resources, which may be wasted if the receiver ignores them
(see Section 3). (see Section 3).
8.7. Duplicate digest-algorithm in field value 8.7. Duplicate digest-algorithm in field value
An endpoint might receive multiple representation-data-digest values An endpoint might receive multiple representation-data-digest values
skipping to change at page 17, line 26 skipping to change at page 17, line 15
* Reference: Section 9.2 of this document, Section 5 of [RFC3230]. * Reference: Section 9.2 of this document, Section 5 of [RFC3230].
* Status: obsoleted * Status: obsoleted
9.3. Changes Compared to RFC3230 9.3. Changes Compared to RFC3230
The contentMD5 digest-algorithm token defined in Section 5 of The contentMD5 digest-algorithm token defined in Section 5 of
[RFC3230] has been added to the HTTP Digest Algorithm Values Registry [RFC3230] has been added to the HTTP Digest Algorithm Values Registry
with the "obsoleted" status. with the "obsoleted" status.
All digest-algorithms defined in [RFC3230] are now "deprecated". All digest-algorithms defined in [RFC3230] are now "insecure".
9.4. Changes Compared to RFC5843 9.4. Changes Compared to RFC5843
The digest-algorithm tokens for "MD5", "SHA", "SHA-256", "SHA-512" The digest-algorithm tokens for "MD5", "SHA", "SHA-256", "SHA-512"
have been updated to lowercase. have been updated to lowercase.
The status of "MD5" and "SHA" has been updated to "deprecated", and The status of "MD5" and "SHA" has been updated to "insecure", and
their description has been modified accordingly. their description has been modified accordingly.
The "id-sha-256" and "id-sha-512" algorithms have been added to the
registry.
9.5. Want-Digest Field Registration 9.5. Want-Digest Field Registration
This section registers the Want-Digest field in the "Hypertext This section registers the Want-Digest field in the "Hypertext
Transfer Protocol (HTTP) Field Name Registry" [SEMANTICS]. Transfer Protocol (HTTP) Field Name Registry" [SEMANTICS].
Field name: Want-Digest Field name: Want-Digest
Status: permanent Status: permanent
Specification document(s): Section 5 of this document Specification document(s): Section 5 of this document
skipping to change at page 21, line 48 skipping to change at page 21, line 27
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms", Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/rfc/rfc7696>. <https://www.rfc-editor.org/rfc/rfc7696>.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP [RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016, APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<https://www.rfc-editor.org/rfc/rfc7807>. <https://www.rfc-editor.org/rfc/rfc7807>.
[RFC8188] Thomson, M., "Encrypted Content-Encoding for HTTP",
RFC 8188, DOI 10.17487/RFC8188, June 2017,
<https://www.rfc-editor.org/rfc/rfc8188>.
Appendix A. Resource Representation and Representation-Data Appendix A. Resource Representation and Representation-Data
The following examples show how representation metadata, payload The following examples show how representation metadata, payload
transformations and method impacts on the message and content. When transformations and method impacts on the message and content. When
the content contains non-printable characters (e.g. when it is the content contains non-printable characters (e.g. when it is
compressed) it is shown as a Base64-encoded string. compressed) it is shown as a Base64-encoded string.
PUT /entries/1234 HTTP/1.1 PUT /entries/1234 HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
skipping to change at page 27, line 5 skipping to change at page 26, line 30
{"hello": "world"} {"hello": "world"}
HTTP/1.1 204 No Content HTTP/1.1 204 No Content
Content-Type: application/json Content-Type: application/json
Content-Encoding: br Content-Encoding: br
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo= Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
Figure 18: Empty response with Digest Figure 18: Empty response with Digest
B.6. Client and Server Provide Full Representation Data, Client Uses B.6. Client and Server Provide Full Representation Data
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. The response contains two digest values using different algorithms.
As the response body contains non-printable characters, it is As the response body contains non-printable characters, it is
displayed as a base64-encoded string. displayed as a base64-encoded string.
PUT /items/123 HTTP/1.1 PUT /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
Accept-Encoding: br Accept-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"} {"hello": "world"}
Figure 19: PUT Request with Digest Figure 19: PUT Request with Digest
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Encoding: br Content-Encoding: br
Content-Location: /items/123 Content-Location: /items/123
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=, Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= sha-512=pxo7aYzcGI88pnDnoSmAnaOEVys0MABhgvHY9+VI+ElE6
0jBCwnMPyA/s3NF3ZO5oIWA7lf8ukk+\n5KJzm3p5og==
iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw== iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==
Figure 20: Response with Digest of Encoded Content Figure 20: Response with Digest of Encoded Content
B.7. POST Response does not Reference the Request URI B.7. POST Response does not Reference the Request URI
The request Digest field-value is computed on the enclosed The request Digest field-value is computed on the enclosed
representation (see Section 7). representation (see Section 7).
skipping to change at page 28, line 20 skipping to change at page 27, line 41
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ= Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=
{"title": "New Title"} {"title": "New Title"}
Figure 21: POST Request with Digest Figure 21: POST Request with Digest
HTTP/1.1 201 Created HTTP/1.1 201 Created
Content-Type: application/json Content-Type: application/json
Content-Location: /books/123 Content-Location: /books/123
Location: /books/123 Location: /books/123
Digest: id-sha-256=yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE= Digest: sha-256=yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE=
{ {
"id": "123", "id": "123",
"title": "New Title" "title": "New Title"
} }
Figure 22: Response with Digest of Resource Figure 22: Response with Digest of Resource
Note that a 204 No Content response without content but with the same Note that a 204 No Content response without content but with the same
Digest field-value would have been legitimate too. In that case, Digest field-value would have been legitimate too. In that case,
skipping to change at page 29, line 4 skipping to change at page 28, line 24
by Location. by Location.
POST /books HTTP/1.1 POST /books HTTP/1.1
Host: foo.example Host: foo.example
Content-Type: application/json Content-Type: application/json
Accept: application/json Accept: application/json
Accept-Encoding: identity Accept-Encoding: identity
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ= Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=
{"title": "New Title"} {"title": "New Title"}
Figure 23: POST Request with Digest Figure 23: POST Request with Digest
HTTP/1.1 201 Created HTTP/1.1 201 Created
Content-Type: application/json Content-Type: application/json
Digest: id-sha-256=2LBp5RKZGpsSNf8BPXlXrX4Td4Tf5R5bZ9z7kdi5VvY= Digest: sha-256=2LBp5RKZGpsSNf8BPXlXrX4Td4Tf5R5bZ9z7kdi5VvY=
Location: /books/123 Location: /books/123
{ {
"status": "created", "status": "created",
"id": "123", "id": "123",
"ts": 1569327729, "ts": 1569327729,
"instance": "/books/123" "instance": "/books/123"
} }
Figure 24: Response with Digest of Representation Figure 24: Response with Digest of Representation
skipping to change at page 30, line 7 skipping to change at page 29, line 21
Accept: application/json Accept: application/json
Accept-Encoding: identity Accept-Encoding: identity
Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ= Digest: sha-256=bWopGGNiZtbVgHsG+I4knzfEJpmmmQHf7RHDXA3o1hQ=
{"title": "New Title"} {"title": "New Title"}
Figure 25: PATCH Request with Digest Figure 25: PATCH Request with Digest
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Digest: id-sha-256=yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE= Digest: sha-256=yxOAqEeoj+reqygSIsLpT0LhumrNkIds5uLKtmdLyYE=
{ {
"id": "123", "id": "123",
"title": "New Title" "title": "New Title"
} }
Figure 26: Response with Digest of Representation Figure 26: Response with Digest of Representation
Note that a 204 No Content response without content but with the same Note that a 204 No Content response without content but with the same
Digest field-value would have been legitimate too. Digest field-value would have been legitimate too.
skipping to change at page 32, line 15 skipping to change at page 31, line 37
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"} {"hello": "world"}
Figure 31: Response with Different Algorithm Figure 31: Response with Different Algorithm
C.2. Server Selects Algorithm Unsupported by Client C.2. Server Selects Algorithm Unsupported by Client
The client requests a "sha" digest only. The server is currently The client requests a only "sha" digest because that is the only
free to reply with a Digest containing an unsupported algorithm. algorithm it supports. The server is not obliged to produce a
response containing a "sha" digest, it instead uses a different
algorithm.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Want-Digest: sha;q=1 Want-Digest: sha;q=1
Figure 32: GET Request with Want-Digest Figure 32: GET Request with Want-Digest
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm Digest: sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm
+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew== +AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
{"hello": "world"} {"hello": "world"}
Figure 33: Response with Unsupported Algorithm Figure 33: Response with Unsupported Algorithm
C.3. Server Does Not Support Client Algorithm and Returns an Error C.3. Server Does Not Support Client Algorithm and Returns an Error
The client requests a "sha" Digest, the server advises "sha-256" and Appendix C.2 is an example where a server ignores the client's
"sha-512". preferred digest algorithm. Alternatively a server can also reject
the request and return an error.
In this example, the client requests a "sha" Digest, and the server
returns an error with problem details [RFC7807] contained in the
content. The problem details contain a list of the digest algorithms
that the server supports. This is purely an example, this
specification does not define any format or requirements for such
content.
GET /items/123 HTTP/1.1 GET /items/123 HTTP/1.1
Host: foo.example Host: foo.example
Want-Digest: sha;q=1 Want-Digest: sha;q=1
Figure 34: GET Request with Want-Digest Figure 34: GET Request with Want-Digest
HTTP/1.1 400 Bad Request HTTP/1.1 400 Bad Request
Want-Digest: sha-256, sha-512 Content-Type: application/problem+json
Figure 35: Response with Want-Digest
Appendix D. Changes from RFC3230
D.1. Deprecate Negotiation of Content-MD5
This RFC deprecates the negotiation of Content-MD5 as it has been
obsoleted by [RFC7231].
See Section 4 for a new checksum negotiation mechanism for HTTP
message content.
D.2. Obsolete Digest Field Parameters
Sections 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 "title": "Bad Request",
parameters are used as an input to validate the checksum, an attacker "detail": "Supported digest-algorithms: sha-256, sha-512",
could alter them to steer the validation behavior. "status": 400
}
A digest-algorithm can still be parameterized by defining its own way Figure 35: Response advertising the supported algorithms
to encode parameters into the representation-data-digest, in such a
way as to mitigate security risks related to its computation.
Acknowledgements Acknowledgements
The vast majority of this document is inherited from [RFC3230], so The vast majority of this document is inherited from [RFC3230], so
thanks to J. Mogul and A. Van Hoff for their great work. The thanks to J. Mogul and A. Van Hoff for their great work. The
original idea of refreshing this document arose from an interesting original idea of refreshing this document arose from an interesting
discussion with M. Nottingham, J. Yasskin and M. Thomson when discussion with M. Nottingham, J. Yasskin and M. Thomson when
reviewing the MICE content coding. reviewing the MICE content coding.
Thanks to Julian Reschke for his valuable contributions to this Thanks to Julian Reschke for his valuable contributions to this
skipping to change at page 34, line 32 skipping to change at page 33, line 48
encoding. encoding.
5. Why remove references to Digest Authentication? 5. Why remove references to Digest Authentication?
This specification seems to me completely unrelated to Digest This specification seems to me completely unrelated to Digest
Authentication but for the word "Digest". Authentication but for the word "Digest".
6. What changes in Want-Digest? 6. What changes in Want-Digest?
The contentMD5 token defined in Section 5 of [RFC3230] is The contentMD5 token defined in Section 5 of [RFC3230] is
deprecated by Appendix D.1. deprecated by this document.
To clarify that Digest and Want-Digest can be used in both To clarify that Digest and Want-Digest can be used in both
requests and responses - [RFC3230] carefully uses sender and requests and responses - [RFC3230] carefully uses sender and
receiver in their definition - we added examples on using Want- receiver in their definition - we added examples on using Want-
Digest in responses to advertise the supported digest-algorithms Digest in responses to advertise the supported digest-algorithms
and the inability to accept requests with unsupported digest- and the inability to accept requests with unsupported digest-
algorithms. algorithms.
7. Does this specification change supported algorithms? 7. Does this specification change supported algorithms?
Yes. This RFC updates [RFC5843] which is still delegated for all Yes. This RFC updates [RFC5843] which is still delegated for all
algorithms updates, and adds two more algorithms: "id-sha-256" algorithms updates. To simplify a future transition to
and "id-sha-512" which allows to send a checksum of a resource Structured Fields [I-D.ietf-httpbis-header-structure] we suggest
representation with no content codings applied. To simplify a to use lowercase for digest-algorithms.
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? 8. What about mid-stream trailer fields?
While mid-stream trailer fields (https://github.com/httpwg/http- While mid-stream trailer fields (https://github.com/httpwg/http-
core/issues/313#issuecomment-584389706) are interesting, since core/issues/313#issuecomment-584389706) are interesting, since
this specification is a rewrite of [RFC3230] we do not think we this specification is a rewrite of [RFC3230] we do not think we
should face that. As a first thought, nothing in this document should face that. As a first thought, nothing in this document
precludes future work that would find a use for mid-stream precludes future work that would find a use for mid-stream
trailers, for example an incremental digest-algorithm. A trailers, for example an incremental digest-algorithm. A
document defining such a digest-algorithm is best positioned to document defining such a digest-algorithm is best positioned to
describe how it is used. describe how it is used.
Code Samples Code Samples
skipping to change at page 36, line 5 skipping to change at page 35, line 5
How can I generate and validate the Digest values shown in the How can I generate and validate the Digest values shown in the
examples throughout this document? examples throughout this document?
The following python3 code can be used to generate digests for JSON The following python3 code can be used to generate digests for JSON
objects using SHA algorithms for a range of encodings. Note that objects using SHA algorithms for a range of encodings. Note that
these are formatted as base64. This function could be adapted to these are formatted as base64. This function could be adapted to
other algorithms and should take into account their specific other algorithms and should take into account their specific
formatting rules. formatting rules.
import base64, json, hashlib, brotli, logging import base64, json, hashlib, brotli, logging
log = logging.getLogger() log = logging.getLogger()
def encode_item(item, encoding=lambda x: x): def encode_item(item, encoding=lambda x: x):
indent = 2 if isinstance(item, dict) and len(item) > 1 else None indent = 2 if isinstance(item, dict) and len(item) > 1 else None
json_bytes = json.dumps(item, indent=indent).encode() json_bytes = json.dumps(item, indent=indent).encode()
return encoding(json_bytes) return encoding(json_bytes)
def digest_bytes(bytes_, algorithm=hashlib.sha256): def digest_bytes(bytes_, algorithm=hashlib.sha256):
checksum_bytes = algorithm(bytes_).digest() checksum_bytes = algorithm(bytes_).digest()
log.warning("Log bytes: \n[%r]", bytes_) log.warning("Log bytes: \n[%r]", bytes_)
return base64.encodebytes(checksum_bytes).strip() return base64.encodebytes(checksum_bytes).strip()
def digest(item, encoding=lambda x: x, algorithm=hashlib.sha256): def digest(item, encoding=lambda x: x, algorithm=hashlib.sha256):
content_encoded = encode_item(item, encoding) content_encoded = encode_item(item, encoding)
return digest_bytes(content_encoded, algorithm) return digest_bytes(content_encoded, algorithm)
item = {"hello": "world"} item = {"hello": "world"}
print("Encoding | digest-algorithm | digest-value") print("Encoding | digest-algorithm | digest-value")
print("Identity | sha256 |", digest(item)) print("Identity | sha256 |", digest(item))
# Encoding | digest-algorithm | digest-value # Encoding | digest-algorithm | digest-value
# Identity | sha256 | X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= # Identity | sha256 | X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
print("Encoding | digest-algorithm | digest-value") print("Encoding | digest-algorithm | digest-value")
print("Brotli | sha256 |", digest(item, encoding=brotli.compress)) print("Brotli | sha256 |", digest(item, encoding=brotli.compress))
# Encoding | digest-algorithm | digest-value # Encoding | digest-algorithm | digest-value
# Brotli | sha256 | 4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo= # Brotli | sha256 | 4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
print("Encoding | digest-algorithm | digest-value") print("Encoding | digest-algorithm | digest-value")
print("Identity | sha512 |", digest(item, algorithm=hashlib.sha512)) print("Identity | sha512 |", digest(item, algorithm=hashlib.sha512))
# Encoding | digest-algorithm | digest-value print("Identity | sha512 |", digest(item, algorithm=hashlib.sha512, encoding=brotli.compress))
# Identity | sha512 | b'WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm' # Encoding | digest-algorithm | digest-value
# '+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==' # Identity | sha512 | b'WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm'
# '+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew=='
# Brotli | sha512 | b'pxo7aYzcGI88pnDnoSmAnaOEVys0MABhgvHY9+VI+ElE6'
# '0jBCwnMPyA/s3NF3ZO5oIWA7lf8ukk+\n5KJzm3p5og=='
Changes Changes
_RFC Editor: Please remove this section before publication._ _RFC Editor: Please remove this section before publication._
Since draft-ietf-httpbis-digest-headers-06
* Remove id-sha-256 and id-sha-512 from the list of supported
algorithms #855
Since draft-ietf-httpbis-digest-headers-05 Since draft-ietf-httpbis-digest-headers-05
* Reboot digest-algorithm values registry #1567 * Reboot digest-algorithm values registry #1567
* Add Content-Digest #1542 * Add Content-Digest #1542
* Remove SRI section #1478 * Remove SRI section #1478
Since draft-ietf-httpbis-digest-headers-04 Since draft-ietf-httpbis-digest-headers-04
* Improve SRI section #1354 * Improve SRI section #1354
* About duplicate digest-algorithms #1221 * About duplicate digest-algorithms #1221
* Improve security considerations #852 * Improve security considerations #852
 End of changes. 69 change blocks. 
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