draft-ietf-httpbis-digest-headers-00.txt   draft-ietf-httpbis-digest-headers-01.txt 
HTTP R. Polli HTTP R. Polli
Internet-Draft Team Digitale, Italian Government Internet-Draft Team Digitale, Italian Government
Intended status: Standards Track L. Pardue Intended status: Standards Track L. Pardue
Expires: January 5, 2020 Cloudflare Expires: May 6, 2020 Cloudflare
July 04, 2019 November 03, 2019
Resource Digests for HTTP Digest Headers
draft-ietf-httpbis-digest-headers-00 draft-ietf-httpbis-digest-headers-01
Abstract Abstract
This document defines the Digest and Want-Digest header fields for This document defines the Digest and Want-Digest header fields for
HTTP, thus allowing client and server to negotiate an integrity HTTP, thus allowing client and server to negotiate an integrity
checksum of the exchanged resource representation data. checksum of the exchanged resource representation data.
This document obsoletes RFC 3230. It replaces the term "instance" This document obsoletes RFC 3230. It replaces the term "instance"
with "representation", which makes it consistent with the HTTP with "representation", which makes it consistent with the HTTP
Semantic and Context defined in RFC 7231. Semantic and Context defined in RFC 7231.
skipping to change at page 1, line 48 skipping to change at page 1, line 48
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This Internet-Draft will expire on January 5, 2020. This Internet-Draft will expire on May 6, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Brief history of integrity headers . . . . . . . . . . . 4 1.1. A Brief History of Integrity Header Fields . . . . . . . 4
1.2. This proposal . . . . . . . . . . . . . . . . . . . . . . 4 1.2. This Proposal . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4. Notational Conventions . . . . . . . . . . . . . . . . . 5 1.4. Notational Conventions . . . . . . . . . . . . . . . . . 5
2. Resource representation and representation-data . . . . . . . 5 2. Resource Representation and Representation-Data . . . . . . . 6
3. Digest Algorithm values . . . . . . . . . . . . . . . . . . . 7 3. Digest Algorithm Values . . . . . . . . . . . . . . . . . . . 7
3.1. Representation digest . . . . . . . . . . . . . . . . . . 9 3.1. Representation Digest . . . . . . . . . . . . . . . . . . 9
3.1.1. digest-algorithm encoding examples . . . . . . . . . 9 3.1.1. digest-algorithm Encoding Examples . . . . . . . . . 10
4. Header Specifications . . . . . . . . . . . . . . . . . . . . 10 4. Header Field Specifications . . . . . . . . . . . . . . . . . 10
4.1. Want-Digest . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Want-Digest . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Digest . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. Digest . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Deprecate Negotiation of Content-MD5 . . . . . . . . . . . . 11 5. Use of Digest when acting on resources . . . . . . . . . . . 11
6. Broken cryptographic algorithms are NOT RECOMMENDED . . . . . 11 5.1. Digest and PATCH . . . . . . . . . . . . . . . . . . . . 12
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. Deprecate Negotiation of Content-MD5 . . . . . . . . . . . . 12
7.1. Unsolicited Digest response . . . . . . . . . . . . . . . 11 7. Broken Cryptographic Algorithms . . . . . . . . . . . . . . . 12
7.1.1. Representation data is fully contained in the payload 11 8. Relationship to Subresource Integrity (SRI) . . . . . . . . . 13
7.1.2. Representation data is not contained in the payload . 12 8.1. Supporting Both SRI and Representation Digest . . . . . . 14
7.1.3. Representation data is partially contained in the 9. Examples of Unsolicited Digest . . . . . . . . . . . . . . . 14
payload i.e. range request . . . . . . . . . . . . . 12 9.1. Server Returns Full Representation Data . . . . . . . . . 14
7.1.4. Digest in both Request and Response. Returned value 9.2. Server Returns No Representation Data . . . . . . . . . . 15
depends on representation metadata . . . . . . . . . 13 9.3. Server Returns Partial Representation Data . . . . . . . 15
7.2. Want-Digest solicited digest responses . . . . . . . . . 13 9.4. Client and Server Provide Full Representation Data . . . 15
7.2.1. Client request data is fully contained in the payload 13 9.5. Client Provides Full Representation Data, Server Provides
7.2.2. A client requests an unsupported Digest, the server No Representation Data . . . . . . . . . . . . . . . . . 16
MAY reply with an unsupported digest . . . . . . . . 14 9.6. Client and Server Provide Full Representation Data,
7.2.3. A client requests an unsupported Digest, the server Client Uses id-sha-256. . . . . . . . . . . . . . . . . . 17
MAY reply with a 400 . . . . . . . . . . . . . . . . 14 9.7. POST Response does not Reference the Request URI . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 9.8. POST Response Describes the Request Status . . . . . . . 18
8.1. Digest does not protect the full HTTP message . . . . . . 14 9.9. Digest with PATCH . . . . . . . . . . . . . . . . . . . . 19
8.2. Broken cryptographic algorithms . . . . . . . . . . . . . 15 10. Examples of Want-Digest Solicited Digest . . . . . . . . . . 19
8.3. Digest for end-to-end integrity . . . . . . . . . . . . . 15 10.1. Server Selects Client's Least Preferred Algorithm . . . 20
8.4. Usage in signatures . . . . . . . . . . . . . . . . . . . 15 10.2. Server Selects Algorithm Unsupported by Client . . . . . 20
8.5. Message Truncation . . . . . . . . . . . . . . . . . . . 16 10.3. Server Does Not Support Client Algorithm and Returns an
8.6. Algorithm Agility . . . . . . . . . . . . . . . . . . . . 16 Error . . . . . . . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 11. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9.1. Establish the HTTP Digest Algorithm Values . . . . . . . 16 11.1. Digest Does Not Protect the Full HTTP Message . . . . . 21
9.2. The "status" field in the HTTP Digest Algorithm Values . 16 11.2. Broken Cryptographic Algorithms . . . . . . . . . . . . 21
9.3. Obsolete "MD5" Digest Algorithm . . . . . . . . . . . . . 16 11.3. Other Deprecated Algorithms . . . . . . . . . . . . . . 21
9.4. Obsolete "SHA" Digest Algorithm . . . . . . . . . . . . . 16 11.4. Digest for End-to-End Integrity . . . . . . . . . . . . 21
9.5. The "ID-SHA-256" Digest Algorithm . . . . . . . . . . . . 17 11.5. Usage in Signatures . . . . . . . . . . . . . . . . . . 22
9.6. The "ID-SHA-512" Digest Algorithm . . . . . . . . . . . . 17 11.6. Message Truncation . . . . . . . . . . . . . . . . . . . 22
9.7. Changes compared to RFC5843 . . . . . . . . . . . . . . . 17 11.7. Algorithm Agility . . . . . . . . . . . . . . . . . . . 22
9.8. Want-Digest Header Field Registration . . . . . . . . . . 17 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
9.9. Digest Header Field Registration . . . . . . . . . . . . 18 12.1. Establish the HTTP Digest Algorithm Values . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 12.2. The "status" Field in the HTTP Digest Algorithm Values . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . 18 12.3. Deprecate "MD5" Digest Algorithm . . . . . . . . . . . . 23
10.2. Informative References . . . . . . . . . . . . . . . . . 20 12.4. Update "CRC32C" Digest Algorithm . . . . . . . . . . . . 23
10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 20 12.5. Obsolete "SHA" Digest Algorithm . . . . . . . . . . . . 23
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 21 12.6. Obsolete "ADLER32" Digest Algorithm . . . . . . . . . . 24
Appendix B. FAQ . . . . . . . . . . . . . . . . . . . . . . . . 21 12.7. The "ID-SHA-256" Digest Algorithm . . . . . . . . . . . 24
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 22 12.8. The "ID-SHA-512" Digest Algorithm . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 12.9. Changes compared to RFC5843 . . . . . . . . . . . . . . 24
12.10. Want-Digest Header Field Registration . . . . . . . . . 25
12.11. Digest Header Field Registration . . . . . . . . . . . . 25
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
13.1. Normative References . . . . . . . . . . . . . . . . . . 25
13.2. Informative References . . . . . . . . . . . . . . . . . 28
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Appendix A. FAQ . . . . . . . . . . . . . . . . . . . . . . . . 28
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 29
Code Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
D.1. Since draft-ietf-httpbis-digest-headers-00 . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction 1. Introduction
Integrity protection for HTTP content is multi layered and is usually The core specification of HTTP does not define a means to protect the
achieved across the protocol stack: TCP checksums and TLS [RFC2818] integrity of resources. When HTTP messages are transferred between
record to name but some. endpoints, the protocol might choose to make use of features of the
lower layer in order to provide some integrity protection; for
The HTTP protocol does not provide means to protect the various instance TCP checksums or TLS records [RFC2818].
message parts. Besides, it might be desirable to add additional
guarantees to the ones provided by the transport layer (eg. HTTPS).
This may be in order to:
o detect programming errors and corruption of stored data;
o address the need for the representation-data to remain unmodified
throughout multiple hops;
o implement signature mechanisms that cover the desired parts of an However, there are cases where relying on this alone is insufficient.
HTTP exchange; 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.
o provide additional protection against failures or attack (see This document defines a mechanism that acts on HTTP representation-
[SRI]). 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. Brief history of integrity headers 1.1. A Brief History of Integrity Header Fields
The Content-MD5 header field was originally introduced to provide The Content-MD5 header field was originally introduced to provide
integrity, but HTTP/1.1 [RFC7231] in appendix-B obsoleted it: integrity, but HTTP/1.1 ([RFC7231], Appendix B) obsoleted it:
The Content-MD5 header field has been removed because it was The Content-MD5 header field has been removed because it was
inconsistently implemented with respect to partial responses. inconsistently implemented with respect to partial responses.
[RFC3230] provided a more flexible solution introducing the concept [RFC3230] provided a more flexible solution introducing the concept
of "instance", and the headers "Digest" and "Want-Digest". of "instance", and the header fields "Digest" and "Want-Digest".
1.2. This proposal 1.2. This Proposal
The concept of "selected representation" defined in [RFC7231] made The concept of "selected representation" defined in [RFC7231] made
[RFC3230] definitions inconsistent with the current standard. A [RFC3230] definitions inconsistent with the current standard. A
refresh was then required. refresh was then required.
This document updates the "Digest" and "Want-Digest" header field This document updates the "Digest" and "Want-Digest" header field
definitions to align with [RFC7231] concepts. definitions to align with [RFC7231] concepts.
This approach can be easily adapted to use-cases where the This approach can be easily adapted to use-cases where the
transferred data does require some sort of manipulation to be transferred data does require some sort of manipulation to be
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2. Support for multiple digest algorithms. 2. Support for multiple digest algorithms.
3. Negotiation of the use of digests. 3. Negotiation of the use of digests.
The goals do not include: The goals do not include:
HTTP Message integrity: The digest mechanism described here does not HTTP Message integrity: The digest mechanism described here does not
cover the full HTTP message nor its semantic, as representation cover the full HTTP message nor its semantic, as representation
metadata are not included in the checksum. metadata are not included in the checksum.
Header integrity: The digest mechanisms described here cover only Header field integrity: The digest mechanisms described here cover
representation and selected representation data, and do not only representation and selected representation data, and do not
protect the integrity of associated representation metadata protect the integrity of associated representation metadata or
headers or other message headers. other message header fields.
Authentication: The digest mechanisms described here are not meant Authentication: The digest mechanisms described here are not meant
to support authentication of the source of a digest or of a to support authentication of the source of a digest or of a
message or anything else. These mechanisms, therefore, are not a message or anything else. These mechanisms, therefore, are not a
sufficient defense against many kinds of malicious attacks. sufficient defense against many kinds of malicious attacks.
Privacy: Digest mechanisms do not provide message privacy. Privacy: Digest mechanisms do not provide message privacy.
Authorization: The digest mechanisms described here are not meant to Authorization: The digest mechanisms described here are not meant to
support authorization or other kinds of access controls. support authorization or other kinds of access controls.
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"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 BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 ([RFC2119] and [RFC8174]) when, and only when, they appear in all 14 ([RFC2119] and [RFC8174]) when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This document uses the Augmented BNF defined in [RFC5234] and updated This document uses the Augmented BNF defined in [RFC5234] and updated
by [RFC7405] along with the "#rule" extension defined in Section 7 of by [RFC7405] along with the "#rule" extension defined in Section 7 of
[RFC7230]. [RFC7230].
The definitions "representation", "selected representation", The definitions "representation", "selected representation",
"representation data", "representation metadata" and "payload body" "representation data", "representation metadata", and "payload body"
in this document are to be interpreted as described in [RFC7230] and in this document are to be interpreted as described in [RFC7230] and
[RFC7231]. [RFC7231].
2. Resource representation and representation-data The definition "validator" in this document is to be interpreted as
described in Section 7.2 of [RFC7231].
2. Resource Representation and Representation-Data
To avoid inconsistencies, an integrity mechanism for HTTP messages To avoid inconsistencies, an integrity mechanism for HTTP messages
should decouple the checksum calculation: should decouple the checksum calculation from:
o from the payload body - which may be altered by mechanism like o the payload body - which may be altered by mechanism like Range
Range Requests [RFC7233] or the method (eg. HEAD); Requests [RFC7233] or the method (eg. HEAD);
o and from the message body - which depends on "Transfer-Encoding" o and the message body - which depends on "Transfer-Encoding" and
and whatever tranformations the intermediaries may apply. whatever transformations the intermediaries may apply.
The following examples show how representation metadata, payload The following examples show how representation metadata, payload
tranformations and method impacts on the message and payload body. transformations and method impacts on the message and payload body.
Here is a gzip-compressed json object Here is a gzip-compressed json object
Request: Request:
PUT /entries/1234 HTTP/1.1 PUT /entries/1234 HTTP/1.1
Content-Type: application/json Content-Type: application/json
Content-Encoding: gzip Content-Encoding: gzip
H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA= H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=
Now the same payload body conveys a malformed json object. Now the same payload body conveys a malformed json object.
Request: Request:
PUT /entries/1234 HTTP/1.1 PUT /entries/1234 HTTP/1.1
Content-Type: application/json Content-Type: application/json
H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA= H4sIAItWyFwC/6tWSlSyUlAypANQqgUAREcqfG0AAAA=
A Range-Request alters the payload body, conveying a partial A Range-Request alters the payload body, conveying a partial
representation. representation.
Request: Request:
GET /entries/1234 HTTP/1.1 GET /entries/1234 HTTP/1.1
Range: bytes=1-7 Range: bytes=1-7
Response: Response:
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Content-Encoding: gzip Content-Encoding: gzip
Content-Type: application/json Content-Type: application/json
Content-Range: bytes=1-7 Content-Range: bytes 1-7/18
iwgAla3RXA== iwgAla3RXA==
Now the method too alters the payload body. Now the method too alters the payload body.
Request: Request:
HEAD /entries/1234 HTTP/1.1 HEAD /entries/1234 HTTP/1.1
Accept: application/json Accept: application/json
Accept-Encoding: gzip Accept-Encoding: gzip
Response: Response:
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Encoding: gzip Content-Encoding: gzip
3. Digest Algorithm values 3. Digest Algorithm Values
Digest algorithm values are used to indicate a specific digest Digest algorithm values are used to indicate a specific digest
computation. For some algorithms, one or more parameters may be computation. For some algorithms, one or more parameters may be
supplied. supplied.
digest-algorithm = token digest-algorithm = token
The BNF for "parameter" is as is used in [RFC7230]. All digest- The BNF for "parameter" is as is used in [RFC7230]. All digest-
algorithm values are case-insensitive. algorithm values are case-insensitive.
The Internet Assigned Numbers Authority (IANA) acts as a registry for The Internet Assigned Numbers Authority (IANA) acts as a registry for
digest-algorithm values. The registry contains the following tokens. digest-algorithm values. The registry contains the following tokens.
SHA-256: SHA-256:
* Description: The SHA-256 algorithm [FIPS180-3]. 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: [FIPS180-3], [RFC4648], this document. * Reference: [RFC6234], [RFC4648], this document.
* Status: standard * Status: standard
SHA-512: SHA-512:
* Description: The SHA-512 algorithm [FIPS180-3]. 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: [FIPS180-3], [RFC4648], this document. * Reference: [RFC6234], [RFC4648], this document.
* Status: standard * Status: standard
MD5: 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]. The MD5 algorithm is NOT RECOMMENDED as it's now [RFC4648]. The MD5 algorithm MUST NOT be used as it's now
vulnerable to collision attacks [CMU-836068]. vulnerable to collision attacks [CMU-836068].
* Reference: [RFC1321], [RFC4648], this document. * Reference: [RFC1321], [RFC4648], this document.
* Status: obsoleted * Status: deprecated
SHA: SHA:
* Description: The SHA-1 algorithm [FIPS180-1]. The output of * Description: The SHA-1 algorithm [RFC3174]. The output of this
this algorithm is encoded using the base64 encoding [RFC4648]. algorithm is encoded using the base64 encoding [RFC4648]. The
The SHA algorithm is NOT RECOMMENDED as it's now vulnerable to SHA algorithm is NOT RECOMMENDED as it's now vulnerable to
collision attacks [IACR-2019-459]. collision attacks [IACR-2019-459].
* Reference: [FIPS180-3], [RFC4648], this document. * Reference: [RFC3174], [RFC6234], [RFC4648], this document.
* Status: obsoleted * Status: obsoleted
UNIXsum: 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.
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To allow sender and recipient to provide a checksum which is To allow sender and recipient to provide a checksum which is
independent from "Content-Encoding", the following additional independent from "Content-Encoding", the following additional
algorithms are defined: algorithms are defined:
ID-SHA-512: ID-SHA-512:
* Description: The sha-512 digest of the representation-data of * Description: The sha-512 digest of the representation-data of
the resource when no content coding is applied (eg. "Content- the resource when no content coding is applied (eg. "Content-
Encoding: identity") Encoding: identity")
* Reference: [FIPS180-3], [RFC4648], this document. * Reference: [RFC6234], [RFC4648], this document.
* Status: standard * Status: standard
ID-SHA-256: ID-SHA-256:
* Description: The sha-256 digest of the representation-data of * Description: The sha-256 digest of the representation-data of
the resource when no content coding is applied (eg. "Content- the resource when no content coding is applied (eg. "Content-
Encoding: identity") Encoding: identity")
* Reference: [FIPS180-3], [RFC4648], this document. * Reference: [RFC6234], [RFC4648], this document.
* Status: standard * Status: standard
If other digest-algorithm values are defined, the associated encoding If other digest-algorithm values are defined, the associated encoding
MUST either be represented as a quoted string, or MUST NOT include MUST either be represented as a quoted string, or MUST NOT include
";" or "," in the character sets used for the encoding. ";" or "," in the character sets used for the encoding.
3.1. Representation digest 3.1. Representation Digest
A representation digest is the value of the output of a digest A representation digest is the value of the output of a digest
algorithm, together with an indication of the algorithm used (and any algorithm, together with an indication of the algorithm used (and any
parameters). parameters).
representation-data-digest = digest-algorithm "=" representation-data-digest = digest-algorithm "="
<encoded digest output> <encoded digest output>
As explained in Section 2 the digest is computed on the entire As explained in Section 2 the digest is computed on the entire
selected "representation data" of the resource defined in [RFC7231]: selected "representation data" of the resource defined in [RFC7231]:
representation-data := Content-Encoding( Content-Type( bits ) ) representation-data := Content-Encoding( Content-Type( bits ) )
The encoded digest output uses the encoding format defined for the The encoded digest output uses the encoding format defined for the
specific digest-algorithm. specific digest-algorithm.
3.1.1. digest-algorithm encoding examples 3.1.1. digest-algorithm Encoding Examples
The "sha-256" digest-algorithm uses base64 encoding. Note that The "sha-256" digest-algorithm uses base64 encoding. Note that
digest-algoritm values are case insensitive. digest-algorithm values are case insensitive.
sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
The "UNIXsum" digest-algorithm uses ASCII string of decimal digits. The "UNIXsum" digest-algorithm uses ASCII string of decimal digits.
UNIXsum=30637 UNIXsum=30637
4. Header Specifications 4. Header Field Specifications
The following headers are defined The following headers are defined
4.1. Want-Digest 4.1. Want-Digest
The Want-Digest message header field indicates the sender's desire to The Want-Digest message header field indicates the sender's desire to
receive a representation digest on messages associated with the receive a representation digest on messages associated with the
Request- URI and representation metadata. request URI and representation metadata.
Want-Digest = "Want-Digest" ":" OWS 1#want-digest-value Want-Digest = "Want-Digest" ":" OWS 1#want-digest-value
want-digest-value = digest-algorithm [ ";" "q" "=" qvalue] want-digest-value = digest-algorithm [ ";" "q" "=" qvalue]
qvalue = ( "0" [ "." 0*1DIGIT ] ) / ( "1" [ "." 0*1( "0" ) ] ) qvalue = ( "0" [ "." 0*1DIGIT ] ) / ( "1" [ "." 0*1( "0" ) ] )
If a digest-algorithm is not accompanied by a qvalue, it is treated If a digest-algorithm is not accompanied by a qvalue, it is treated
as if its associated qvalue were 1.0. as if its associated qvalue were 1.0.
The sender is willing to accept a digest-algorithm if and only if it The sender is willing to accept a digest-algorithm if and only if it
is listed in a Want-Digest header field of a message, and its qvalue is listed in a Want-Digest header field of a message, and its qvalue
is non-zero. is non-zero.
If multiple acceptable digest-algorithm values are given, the If multiple acceptable digest-algorithm values are given, the
sender's preferred digest-algorithm is the one (or ones) with the sender's preferred digest-algorithm is the one (or ones) with the
highest qvalue. highest qvalue.
Examples: Two examples of its use are
Want-Digest: sha-256 Want-Digest: sha-256
Want-Digest: SHA-512;q=0.3, sha-256;q=1, md5;q=0 Want-Digest: SHA-512;q=0.3, sha-256;q=1, md5;q=0
4.2. Digest 4.2. Digest
The Digest header field provides a digest of the representation data The Digest header field provides a digest of the representation data.
Digest = "Digest" ":" OWS 1#representation-data-digest Digest = "Digest" ":" OWS 1#representation-data-digest
"Representation data" might be: "Representation data" might be:
o fully contained in the message body, o fully contained in the message body,
o partially-contained in the message body, o partially-contained in the message body,
o or not at all contained in the message body. o or not at all contained in the message body.
The resource is specified by the effective Request-URI and any cache- The resource is specified by the effective request URI and any
validator contained in the message. "validator" contained in the message.
For example, in a response to a HEAD request, the digest is For example, in a response to a HEAD request, the digest is
calculated using the representation data that would have been calculated using the representation data that would have been
enclosed in the payload body if the same request had been a GET. enclosed in the payload body if the same request had been a GET.
Digest can be used in requests too. Returned value depends on the Digest can be used in requests too.
representation metadata headers.
The "Digest" value depends on the representation metadata.
A Digest header field MAY contain multiple representation-data-digest A Digest header field MAY contain multiple representation-data-digest
values. This could be useful for responses expected to reside in values. This could be useful for responses expected to reside in
caches shared by users with different browsers, for example. caches shared by users with different browsers, for example.
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 header field. This allows the recipient to chose which in a Digest header field. This allows the recipient to chose which
digest-algorithm(s) to use for validation instead of verifying every digest-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.
... Two examples of its use are
5. Deprecate Negotiation of Content-MD5 Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=, id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
This RFC deprecates the negotiation of Content-MD5 as this header has 5. Use of Digest when acting on resources
been obsoleted by [RFC7231]
6. Broken cryptographic algorithms are NOT RECOMMENDED POST and PATCH requests may appear to convey partial representations
but are semantically acting on resources. The enclosed
representation, including its metadata refers to that action.
The MD5 algorithm is NOT RECOMMENDED as it's now vulnerable to 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 3.1).
In responses,
o if the representation describes the status of the request,
"Digest" MUST be computed on the enclosed representation (see
Section 9.8 );
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 may or may not result in
computing "Digest" on the enclosed representation.
The latter case might be done accordingly to the HTTP semantics of
the given method, for example using the "Content-Location" header
field.
Differently from "Content-Location", which is representation
metadata, the "Location" header field does not affect "Digest".
5.1. Digest and PATCH
In PATCH requests the representation digest MUST be computed on the
patch document.
This is 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.
6. Deprecate Negotiation of Content-MD5
This RFC deprecates the negotiation of Content-MD5 as it has been
obsoleted by [RFC7231]
7. Broken Cryptographic Algorithms
The MD5 algorithm MUST NOT be used as it has been found vulnerable to
collision attacks [CMU-836068]. collision attacks [CMU-836068].
The SHA algorithm is NOT RECOMMENDED as it's now vulnerable to The SHA algorithm is NOT RECOMMENDED as it has been found vulnerable
collision attacks [IACR-2019-459]. to collision attacks [IACR-2019-459].
7. Examples 8. Relationship to Subresource Integrity (SRI)
7.1. Unsolicited Digest response 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 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"
header 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 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 3.1). 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"
header field can appear on requests.
8.1. Supporting Both SRI and Representation Digest
The SRI and Representation Digest mechanism are different and
complementary but one is not capable of replacing the other because
they have 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 the it does not require a conversion to 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.
9. Examples of Unsolicited Digest
The following examples demonstrate interactions where a server
responds with a "Digest" header field even though the client did not
solicit one using "Want-Digest".
9.1. Server Returns Full Representation Data
7.1.1. Representation data is fully contained in the payload
Request: Request:
GET /items/123 GET /items/123
Response: Response:
HTTP/1.1 200 Ok HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Encoding: identity Content-Encoding: identity
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"} {"hello": "world"}
7.1.2. Representation data is not contained in the payload 9.2. Server Returns No Representation Data
As there is no content coding applied, the "sha-256" and the "id-sha-
256" digest-values are the same.
Request: Request:
HEAD /items/123 HEAD /items/123
Response: Response:
HTTP/1.1 200 Ok HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Encoding: identity Content-Encoding: identity
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
7.1.3. Representation data is partially contained in the payload i.e. 9.3. Server Returns Partial Representation Data
range request
Request: Request:
GET /items/123 GET /items/123
Range: bytes=1-7 Range: bytes=1-7
Response: Response:
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Content-Type: application/json Content-Type: application/json
Content-Encoding: identity Content-Encoding: identity
Content-Range: bytes 1-7/18 Content-Range: bytes 1-7/18
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
"hello" "hello"
7.1.4. Digest in both Request and Response. Returned value depends on 9.4. Client and Server Provide Full Representation Data
representation metadata
Digest can be used in requests too. Returned value depends on the The request contains a "Digest" header calculated on the enclosed
representation metadata headers. 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.
Request: Request:
PUT /items/123 PUT /items/123
Content-Type: application/json Content-Type: application/json
Content-Encoding: identity Content-Encoding: identity
Accept-Encoding: br Accept-Encoding: br
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo= Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"} {"hello": "world"}
Response: Response:
Content-Type: application/json Content-Type: application/json
Content-Encoding: br Content-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw== iwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==
7.2. Want-Digest solicited digest responses 9.5. Client Provides Full Representation Data, Server Provides No
Representation Data
7.2.1. Client request data is fully contained in the payload 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-Encoding: identity
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".
Request:
PUT /items/123 HTTP/1.1
Content-Type: application/json
Content-Encoding: identity
Accept-Encoding: br
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"}
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 5).
The representation enclosed in the response refers to the resource
identified by "Content-Location" (see [RFC7231] Section 3.1.4.2 and
Section 3.1.4.1 point 4).
"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 5).
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:
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.
10. Examples of Want-Digest Solicited Digest
The following examples demonstrate interactions where a client
solicits a "Digest" using "Want-Digest".
10.1. Server Selects Client's Least Preferred Algorithm
The client requests a digest, preferring sha. The server is free to The client requests a digest, preferring sha. The server is free to
reply with sha-256 anyway. reply with sha-256 anyway.
Request: Request:
GET /items/123 GET /items/123 HTTP/1.1
Want-Digest: sha-256;q=0.3, sha;q=1 Want-Digest: sha-256;q=0.3, sha;q=1
Response: Response:
HTTP/1.1 200 Ok HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Encoding: identity Content-Encoding: identity
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
{"hello": "world"} {"hello": "world"}
7.2.2. A client requests an unsupported Digest, the server MAY reply 10.2. Server Selects Algorithm Unsupported by Client
with an unsupported digest
The client requests a sha digest only. The server is currently free The client requests a sha digest only. The server is currently free
to reply with a Digest containing an unsupported algorithm to reply with a Digest containing an unsupported algorithm.
Request: Request:
GET /items/123 GET /items/123
Want-Digest: sha;q=1 Want-Digest: sha;q=1
Response: Response:
HTTP/1.1 200 Ok HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
Content-Encoding: identity Content-Encoding: identity
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE= Digest: id-sha-512=WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==
{"hello": "world"} {"hello": "world"}
7.2.3. A client requests an unsupported Digest, the server MAY reply 10.3. Server Does Not Support Client Algorithm and Returns an Error
with a 400
The client requests a sha Digest, the server advises for sha-256 and The client requests a sha Digest, the server advises for sha-256 and
sha-512 sha-512
Request: Request:
GET /items/123 GET /items/123
Want-Digest: sha;q=1 Want-Digest: sha;q=1
Response: Response:
HTTP/1.1 400 Bad Request HTTP/1.1 400 Bad Request
Want-Digest: sha-256, sha-512 Want-Digest: sha-256, sha-512
...
8. Security Considerations 11. Security Considerations
8.1. Digest does not protect the full HTTP message 11.1. Digest Does Not Protect the Full HTTP Message
This document specifies a data integrity mechanism that protects HTTP This document specifies a data integrity mechanism that protects HTTP
"representation data", but not HTTP "representation metadata" "representation data", but not HTTP "representation metadata" header
headers, from certain kinds of accidental corruption. fields, from certain kinds of accidental corruption.
While it is not intended as general protection against malicious "Digest" is not intended as general protection against malicious
tampering with HTTP messages, this goal can be achieved using tampering with HTTP messages, this can be achieved by combining it
"Digest" together with a transport-layer security mechanism and with other approaches such as transport-layer security or digital
digital signatures. signatures.
8.2. Broken cryptographic algorithms 11.2. Broken Cryptographic Algorithms
Cryptogrphic alorithms are intended to provide a proof of integrity Cryptographic algorithms are intended to provide a proof of integrity
suited towards cryptographic constructions such as signatures. suited towards cryptographic constructions such as signatures.
However, these rely on collision-resistance for their security proofs However, these rely on collision-resistance for their security proofs
[CMU-836068]. The MD5 and SHA-1 algorithms are vulnerable to [CMU-836068]. The MD5 and SHA-1 algorithms are vulnerable to
collisions attacks and they are NOT RECOMMENDED. collisions attacks, so MD5 MUST NOT be used and SHA-1 is NOT
RECOMMENDED for use with "Digest".
8.3. Digest for end-to-end integrity 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 "Digest" alone does not provide end-to-end integrity of HTTP messages
over multiple hops, as it just covers the "representation data" and over multiple hops, as it just covers the "representation data" and
not the "representation metadata". not the "representation metadata".
Besides, it allows to protect "representation data" from buggy Besides, it allows to protect "representation data" from buggy
manipulation, buggy compression, etc. manipulation, buggy compression, etc.
Moreover identity digest algorithms (eg. ID-SHA-256 and ID-SHA-512) Moreover identity digest algorithms (eg. ID-SHA-256 and ID-SHA-512)
allow piecing together a resource from different sources (e.g. allow piecing together a resource from different sources (e.g.
different servers that perhaps apply different content codings) different servers that perhaps apply different content codings)
enabling the user-agent to detect that the application-layer tasks enabling the user-agent to detect that the application-layer tasks
completed properly, before handing off to say the HTML parser, video completed properly, before handing off to say the HTML parser, video
player etc. player etc.
Even a simple mechanism for end-to-end validation is thus valuable. Even a simple mechanism for end-to-end validation is thus valuable.
8.4. Usage in signatures 11.5. 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 header fields and there are
additional considerations when "Digest" is included in this set.
It's important to note that, being the "Digest" header an hash of a Since the "Digest" header field is a hash of a resource
resource representation, signing only the "Digest" header, without representation, it explicitly depends on the "representation
all the "representation metatada" (eg. the values of "Content-Type" metadata" (eg. the values of "Content-Type", "Content-Encoding" etc).
and "Content-Encoding") may expose the communication to tampering. A signature that protects "Digest" but not other "representation
metadata" may 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.
"Digest" SHOULD always be used over a connection which provides "Digest" SHOULD always be used over a connection which provides
integrity at transport layer that protects HTTP headers. integrity at transport layer that protects HTTP header fields.
A "Digest" header using NOT RECOMMENDED digest-algorithms SHOULD NOT A "Digest" header field using NOT RECOMMENDED digest-algorithms
be used in signatures. SHOULD NOT be used in signatures.
8.5. Message Truncation 11.6. Message Truncation
... ...
8.6. Algorithm Agility 11.7. Algorithm Agility
... ...
9. IANA Considerations 12. IANA Considerations
9.1. Establish the HTTP Digest Algorithm Values 12.1. Establish the HTTP Digest Algorithm Values
This memo sets this spec to be the establishing document for the HTTP This memo sets this spec to be the establishing document for the HTTP
Digest Algorithm Values [4] Digest Algorithm Values [4]
9.2. The "status" field in the HTTP Digest Algorithm Values 12.2. The "status" Field in the HTTP Digest Algorithm Values
This memo adds the field "Status" to the HTTP Digest Algorithm Values This memo adds the field "Status" to the HTTP Digest Algorithm Values
[5] registry. The allowed values for the "Status" fields are [5] registry. The allowed values for the "Status" fields are
described below. described below.
Status Specify "standard", "experimental", "historic", "obsoleted", Status Specify "standard", "experimental", "historic", "obsoleted",
or "deprecated" according to the type and status of the primary or "deprecated" according to the type and status of the primary
document in which the algorithm is defined. document in which the algorithm is defined.
9.3. Obsolete "MD5" Digest Algorithm 12.3. Deprecate "MD5" Digest Algorithm
This memo updates the "MD5" digest algorithm in the HTTP Digest This memo updates the "MD5" digest algorithm in the HTTP Digest
Algorithm Values [6] registry: Algorithm Values [6] registry:
o Digest Algorithm: MD5 o Digest Algorithm: MD5
o Description: As specified in Section 3. o Description: As specified in Section 3.
o Status: As specified in Section 3. o Status: As specified in Section 3.
9.4. Obsolete "SHA" Digest Algorithm 12.4. Update "CRC32C" Digest Algorithm
This memo updates the "SHA" digest algorithm in the HTTP Digest This memo updates the "CRC32c" digest algorithm in the HTTP Digest
Algorithm Values [7] registry: Algorithm Values [7] registry:
o Digest Algorithm: SHA 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.
12.5. Obsolete "SHA" Digest Algorithm
This memo updates the "SHA" digest algorithm in the HTTP Digest
Algorithm Values [8] registry:
o Digest Algorithm: SHA
o Description: As specified in Section 3. o Description: As specified in Section 3.
o Status: As specified in Section 3. o Status: As specified in Section 3.
9.5. The "ID-SHA-256" Digest Algorithm 12.6. Obsolete "ADLER32" Digest Algorithm
This memo updates the "ADLER32" digest algorithm in the HTTP Digest
Algorithm Values [9] 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
12.7. The "ID-SHA-256" Digest Algorithm
This memo registers the "ID-SHA-256" digest algorithm in the HTTP This memo registers the "ID-SHA-256" digest algorithm in the HTTP
Digest Algorithm Values [8] registry: Digest Algorithm Values [10] registry:
o Digest Algorithm: ID-SHA-256 o Digest Algorithm: ID-SHA-256
o Description: As specified in Section 3. o Description: As specified in Section 3.
o Status: As specified in Section 3. o Status: As specified in Section 3.
9.6. The "ID-SHA-512" Digest Algorithm 12.8. The "ID-SHA-512" Digest Algorithm
This memo registers the "ID-SHA-512" digest algorithm in the HTTP This memo registers the "ID-SHA-512" digest algorithm in the HTTP
Digest Algorithm Values [9] registry: Digest Algorithm Values [11] registry:
o Digest Algorithm: ID-SHA-512 o Digest Algorithm: ID-SHA-512
o Description: As specified in Section 3. o Description: As specified in Section 3.
o Status: As specified in Section 3. o Status: As specified in Section 3.
9.7. Changes compared to RFC5843 12.9. Changes compared to RFC5843
The status has been updated to "obsoleted" for both "SHA" and "MD5", The status of "MD5" has been updated to "deprecated", and its
and their descriptions states that those algorithms are NOT description states that this algorithm MUST NOT be used.
RECOMMENDED.
The status for all other algorithms have been updated to "standard". The status of "SHA" has been updated to "obsoleted", and its
description states that this algorithm is NOT RECOMMENDED.
The status for "CRC32C" has been updated to "standard".
The "ID-SHA-256" and "ID-SHA-512" algorithms have been added to the The "ID-SHA-256" and "ID-SHA-512" algorithms have been added to the
registry. registry.
9.8. Want-Digest Header Field Registration 12.10. Want-Digest Header Field Registration
This section registers the "Want-Digest" header field in the This section registers the "Want-Digest" header field in the
"Permanent Message Header Field Names" registry ([RFC3864]). "Permanent Message Header Field Names" registry ([RFC3864]).
Header field name: "Want-Digest" Header field name: "Want-Digest"
Applicable protocol: http Applicable protocol: http
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): Section 4.1 of this document Specification document(s): Section 4.1 of this document
9.9. Digest Header Field Registration 12.11. Digest Header Field Registration
This section registers the "Digest" header field in the "Permanent This section registers the "Digest" header field in the "Permanent
Message Header Field Names" registry ([RFC3864]). Message Header Field Names" registry ([RFC3864]).
Header field name: "Digest" Header field name: "Digest"
Applicable protocol: http Applicable protocol: http
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): Section 4.2 of this document Specification document(s): Section 4.2 of this document
10. References 13. References
10.1. Normative References 13.1. Normative References
[CMU-836068] [CMU-836068]
Carnagie Mellon University, Software Engineering Carnagie Mellon University, Software Engineering
Institute, ., "MD5 Vulnerable to collision attacks", Institute, "MD5 Vulnerable to collision attacks", December
December 2008, <https://www.kb.cert.org/vuls/id/836068/>. 2008, <https://www.kb.cert.org/vuls/id/836068/>.
[FIPS180-1]
Department of Commerce, National., "NIST FIPS 180-1,
Secure Hash Standard", April 1995,
<http://csrc.nist.gov/fips/fip180-1.txt>.
[FIPS180-3]
Department of Commerce, National., "NIST FIPS 180-3,
Secure Hash Standard", October 2008,
<https://csrc.nist.gov/csrc/media/publications/fips/180/3/
archive/2008-10-31/documents/fips180-3_final.pdf>.
[IACR-2019-459] [IACR-2019-459]
Inria, France; Nanyang Technological University, Leurent, G. and T. Peyrin, "From Collisions to Chosen-
Singapore; Temasek Laboratories, Singapore, ., "From Prefix Collisions Application to Full SHA-1", May 2019,
Collisions to Chosen-Prefix Collisions Application to Full <https://eprint.iacr.org/2019/459.pdf>.
SHA-1", May 2019, <https://eprint.iacr.org/2019/459.pdf>.
[NIST800-32] [NIST800-32]
Department of Commerce, National., "Introduction to Public National Institute of Standards and Technology, U.S.
Key Technology and the Federal PKI Infrastructure", Department of Commerce, "Introduction to Public Key
February 2001, Technology and the Federal PKI Infrastructure", February
<https://nvlpubs.nist.gov/nistpubs/Legacy/SP/ 2001, <https://nvlpubs.nist.gov/nistpubs/Legacy/SP/
nistspecialpublication800-32.pdf>. nistspecialpublication800-32.pdf>.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992, DOI 10.17487/RFC1321, April 1992,
<https://www.rfc-editor.org/info/rfc1321>. <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 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <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", [RFC3230] Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
RFC 3230, DOI 10.17487/RFC3230, January 2002, RFC 3230, DOI 10.17487/RFC3230, January 2002,
<https://www.rfc-editor.org/info/rfc3230>. <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>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004, DOI 10.17487/RFC3864, September 2004,
<https://www.rfc-editor.org/info/rfc3864>. <https://www.rfc-editor.org/info/rfc3864>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>. <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 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
[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>.
[RFC5843] Bryan, A., "Additional Hash Algorithms for HTTP Instance [RFC5843] Bryan, A., "Additional Hash Algorithms for HTTP Instance
Digests", RFC 5843, DOI 10.17487/RFC5843, April 2010, Digests", RFC 5843, DOI 10.17487/RFC5843, April 2010,
<https://www.rfc-editor.org/info/rfc5843>. <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>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>. <https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
skipping to change at page 20, line 18 skipping to change at page 27, line 46
<https://www.rfc-editor.org/info/rfc7233>. <https://www.rfc-editor.org/info/rfc7233>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
RFC 7405, DOI 10.17487/RFC7405, December 2014, RFC 7405, DOI 10.17487/RFC7405, December 2014,
<https://www.rfc-editor.org/info/rfc7405>. <https://www.rfc-editor.org/info/rfc7405>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[UNIX] The Open Group, ., "The Single UNIX Specification, Version [UNIX] The Open Group, "The Single UNIX Specification, Version 2
2 - 6 Vol Set for UNIX 98", February 1997. - 6 Vol Set for UNIX 98", February 1997.
10.2. Informative References 13.2. Informative References
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000, DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>. <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>.
[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396, [RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014, DOI 10.17487/RFC7396, October 2014,
<https://www.rfc-editor.org/info/rfc7396>. <https://www.rfc-editor.org/info/rfc7396>.
[SRI] Akhawe, D., Braun, F., Marier, F., and J. Weinberger, [SRI] Akhawe, D., Braun, F., Marier, F., and J. Weinberger,
"Subresource Integrity", June 2016. "Subresource Integrity", W3C Recommendation REC-SRI-
20160623, June 2016,
<https://www.w3.org/TR/2016/REC-SRI-20160623/>.
10.3. URIs 13.3. URIs
[1] https://lists.w3.org/Archives/Public/ietf-http-wg/ [1] https://lists.w3.org/Archives/Public/ietf-http-wg/
[2] https://github.com/httpwg/http-extensions [2] https://github.com/httpwg/http-extensions
[3] https://tools.ietf.org/html/rfc7231#section-3.1.2.1 [3] https://tools.ietf.org/html/rfc7231#section-3.1.2.1
[4] 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 [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 [6] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
[7] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml [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 [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 [9] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
Appendix A. Change Log [10] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
RFC EDITOR PLEASE DELETE THIS SECTION. [11] https://www.iana.org/assignments/http-dig-alg/http-dig-alg.xhtml
Appendix B. FAQ Appendix A. FAQ
1. Why remove all references to content-md5? 1. Why remove all references to content-md5?
Those were unnecessary to understanding and using this spec. Those were unnecessary to understanding and using this spec.
2. Why remove references to instance manipulation? 2. Why remove references to instance manipulation?
Those were unnecessary for correctly using and applying the spec. Those were unnecessary for correctly using and applying the spec.
An example with Range Request is more than enough. This doc uses An example with Range Request is more than enough. This doc uses
the term "partial representation" which should group all those the term "partial representation" which should group all those
cases. cases.
3. How to use "Digest" with "PATCH" method? 3. How to use "Digest" with "PATCH" method?
The PATCH verb brings some complexities (eg. about representation See Section 5.
metadata headers, patch document format, ...),
* PATCH entity-headers apply to the patch document and MUST NOT
be applied to the target resource, see [RFC5789], Section 2.
* servers shouldn't assume PATCH semantics for generic media
types like "application/json" but should instead use a proper
content-type, eg [RFC7396]
* a "200 OK" response to a PATCH request would contain the
digest of the patched item, and the etag of the new object.
This behavior - tighly coupled to the application logic -
gives the client low probability of guessing the actual
outcome of this operation (eg. concurrent changes, ...)
4. Why remove references to delta-encoding? 4. Why remove references to delta-encoding?
Unnecessary for a correct implementation of this spec. The Unnecessary for a correct implementation of this spec. The
revised spec can be nicely adapted to "delta encoding", but all revised spec can be nicely adapted to "delta encoding", but all
the references here to delta encoding don't add anything to this the references here to delta encoding don't add anything to this
RFC. Another job would be to refresh delta encoding. RFC. Another job would be to refresh delta encoding.
5. Why remove references to Digest Authentication? 5. Why remove references to Digest Authentication?
skipping to change at page 22, line 4 skipping to change at page 29, line 29
revised spec can be nicely adapted to "delta encoding", but all revised spec can be nicely adapted to "delta encoding", but all
the references here to delta encoding don't add anything to this the references here to delta encoding don't add anything to this
RFC. Another job would be to refresh delta encoding. RFC. Another job would be to refresh delta encoding.
5. Why remove references to Digest Authentication? 5. Why remove references to Digest Authentication?
This RFC seems to me completely unrelated to Digest This RFC 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"?
We allow to use the "Want-Digest" in responses to advertise the We allow to use the "Want-Digest" in responses to advertise the
supported digest-algorithms and the inability to accept requests supported digest-algorithms and the inability to accept requests
with unsupported digest-algorithms. with unsupported digest-algorithms.
7. Does this spec changes supported algorithms? 7. Does this spec changes supported algorithms?
This RFC updates [RFC5843] which is still delegated for all This RFC updates [RFC5843] which is still delegated for all
algorithms updates, and adds two more algorithms: ID-SHA-256 and algorithms updates, and adds two more algorithms: ID-SHA-256 and
ID-SHA-512 which allows to send a checksum of a resource ID-SHA-512 which allows to send a checksum of a resource
representation with no content codings applied. representation with no content codings applied.
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.
Code Samples
_RFC Editor: Please remove this section before publication._
How can I generate and validate the Digest values shown in the
examples throughout this document?
The following python3 code can be used to generate digests for json
objects using SHA algorithms for a range of encodings. Note that
these are formatted as base64. This function could be adapted to
other algorithms and should take into account their specific
formatting rules.
import base64, json, hashlib, brotli
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("Identity encoding, sha256", digest(item))
# Out: Identity encoding, sha256 4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
print("Brotli encoding, sha256", digest(item, encoding=brotli.compress))
# Out: Brotli encoding, sha256 4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=
print("Identity encoding, sha512", digest(item, algorithm=hashlib.sha512))
# Out: Identity encoding, sha512 b'WZDPaVn/7XgHaAy8pmojAkGWoRx2UFChF41A2svX+TaPm+AbwAgBWnrIiYllu7BNNyealdVLvRwE\nmTHWXvJwew==\n'
Changes
_RFC Editor: Please remove this section before publication._
D.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
o Added Relationship with SRI, draft Use Cases #868, #971
Authors' Addresses Authors' Addresses
Roberto Polli Roberto Polli
Team Digitale, Italian Government Team Digitale, Italian Government
Email: robipolli@gmail.com Email: robipolli@gmail.com
Lucas Pardue Lucas Pardue
Cloudflare Cloudflare
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