Internet DRAFT - draft-pardue-http-identity-digest
draft-pardue-http-identity-digest
HyperText Transfer Protocol L. Pardue
Internet-Draft Cloudflare
Intended status: Standards Track 8 March 2023
Expires: 9 September 2023
HTTP Identity Digest
draft-pardue-http-identity-digest-01
Abstract
The Repr-Digest and Content-Digest integrity fields are subject to
HTTP content coding considerations. There are some use cases that
benefit from the unambiguous exchange of integrity digests of
unencoded representation. The Identity-Digest and Want-Identity-
Digest fields complement existing integrity fields for this purpose.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://LPardue.github.io/draft-pardue-http-identity-digest/draft-
pardue-http-identity-digest.html. Status information for this
document may be found at https://datatracker.ietf.org/doc/draft-
pardue-http-identity-digest/.
Discussion of this document takes place on the HyperText Transfer
Protocol Working Group mailing list (mailto:http-wg@hplb.hp.com),
which is archived at https://www.ics.uci.edu/pub/ietf/http/hypermail.
Source for this draft and an issue tracker can be found at
https://github.com/LPardue/draft-pardue-http-identity-digest.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 9 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Complementary Integrity Fields . . . . . . . . . . . . . . . 4
4. The Identity-Digest Field . . . . . . . . . . . . . . . . . . 6
5. The Want-Identity-Digest Field . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Integrity fields defined in [DIGEST-FIELDS] are suitable for a
range of use cases. However, because the fields are subject to HTTP
content coding considerations, it is difficult to support use cases
that could benefit from the exchange of integrity digests of the
unencoded representation.
As a simple example, an application using HTTP might be presented
with request or response representation data that has been
transparently decoded. Attempting to verify the integrity of the
data against the Repr-Digest would first require re-encoding that
data using the same coding indicated by the Content-Encoding header
field (Section 8.4 of [HTTP]).
Receiver-side re-encoding for the purpose of Repr-Digest validation
is technically possible but it might not be practical for certain
kinds of environments. For instance, browsers tend to provide built-
in support for transparent decoding but little support for encoding;
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while this could be done via the use of additional libraries it would
create work in JavaScript that could contend with other activities.
Even on the server side, the re-encoding of received data might not
be acceptable; some coding algorithms are optimized towards efficient
decoding at the cost of complex encoding. This is all made more
complex if the the Content-Encoding field value indicates a series of
encodings.
A more complex example involves HTTP Range Requests (Section 14 of
[HTTP]), where a client fetches multiple partial representations from
different origins and "stitches" them back into a whole.
Unfortunately, if the origins apply different content coding, the
Repr-Digest field will vary by the server's selected encoding (i.e.
the Content-Encoding header field, Section 8.4 of [HTTP]). This
provides a challenge for a client - in order to verify the integrity
of the pieced-together whole it would need to remove the encoding of
each part, combine them, and then encode the result in order to
compare against one or more Repr-Digests.
The Accept-Encoding header field (Section 12.5.3 of [HTTP]) provides
the means to indicate preferences for content coding. It is possible
for an endpoint to indicate a preference for no encoding, for example
by sending the "identity" token. However, codings often provide data
compression that is advantageous. Disabling content coding in order
to simplify integrity checking is possibly an unacceptable trade off.
For a variety of reasons, decoding and re-encoding content in order
to benefit from HTTP integrity fields is not preferable. This
specification defines the Identity-Digest and Want-Identity-Digest
fields to support a simpler validation workflow in some scenarios
where content coding is applied. These fields complement the other
integrity fields defined in [DIGEST-FIELDS].
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the Augmented BNF defined in [RFC5234] and updated
by [RFC7405]. This includes the rules: LF (line feed)
This document uses the following terminology from Section 3 of
[STRUCTURED-FIELDS] to specify syntax and parsing: Boolean, Byte
Sequence, Dictionary, Integer, and List.
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The definitions "representation", "selected representation",
"representation data", "representation metadata", "user agent" and
"content" in this document are to be interpreted as described in
[HTTP].
Integrity fields: collective term for Content-Digest, Repr-Digest,
and Identity-Digest
Integrity preference fields: collective term for Want-Repr-Digest,
Want-Content-Digest, and Want-Identity-Digest
3. Complementary Integrity Fields
The following examples illustrate how Integrity fields can be used in
combination to address different and complementary needs,
particularly the cases described in Section 1. The unencoded data
used in the example is the string "An unexceptional string" following
by an LF character.
When a response message is not conveying partial or encoded
representation data, all Integrity fields contain the same value,
making validation trivial and identical.
GET /boringstring HTTP/1.1
Host: example.org
Figure 1: Simple GET request
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Length: 24
Content-Digest: \
sha-256=:5Bv3NIx05BPnh0jMph6v1RJ5Q7kl9LKMtQxmvc9+Z7Y=:
Repr-Digest: \
sha-256=:5Bv3NIx05BPnh0jMph6v1RJ5Q7kl9LKMtQxmvc9+Z7Y=:
Identity-Digest: \
sha-256=:5Bv3NIx05BPnh0jMph6v1RJ5Q7kl9LKMtQxmvc9+Z7Y=:
An unexceptional string
Figure 2: Response to GET request
When a response message conveys complete encoded content, the
Content-Digest and the Repr-Digest are the same, while the Identity-
Digest is different.
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GET /boringstring HTTP/1.1
Host: example.org
Accept-Encoding: gzip
Figure 3: GET request with content negotiation
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Encoding: gzip
Content-Digest: \
sha-256=:XyjvEuFb1P5rqc2le3vQm7M96DwZhvmOwqHLu2xVpY4=:
Repr-Digest: \
sha-256=:XyjvEuFb1P5rqc2le3vQm7M96DwZhvmOwqHLu2xVpY4=:
Identity-Digest: \
sha-256=:5Bv3NIx05BPnh0jMph6v1RJ5Q7kl9LKMtQxmvc9+Z7Y=:
1f 8b 08 00 79 1f 08 64 00 ff
73 cc 53 28 cd 4b ad 48 4e 2d
28 c9 cc cf 4b cc 51 28 2e 29
ca cc 4b e7 02 00 7e af 07 44
18 00 00 00
Figure 4: Response with gzip encoding
Finally, when a response message contains partial and encoded
content, all Integrity fields vary. The Content-Digest can be used
to validate the integrity of the received part. Repr-Digest or
Identity-Digest can be used later after reconstruction, the choice of
which to use is left to the application, which would consider a range
of factors outside the scope of discussion.
GET /boringstring HTTP/1.1
Host: example.org
Accept-Encoding: gzip
Range: bytes=0-10
Figure 5: Range request with content negotiation
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NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Encoding: gzip
Content-Digest: \
sha-256=:SotB7Pa5A7iHSBdh9mg1Ev/ktAzrxU4Z8ldcCIUyfI4=:
Repr-Digest: \
sha-256=:XyjvEuFb1P5rqc2le3vQm7M96DwZhvmOwqHLu2xVpY4=:
Identity-Digest: \
sha-256=:5Bv3NIx05BPnh0jMph6v1RJ5Q7kl9LKMtQxmvc9+Z7Y=:
1f 8b 08 00 79 1f 08 64 00 ff
Figure 6: Partial response with gzip encoding
4. The Identity-Digest Field
The Identity-Digest HTTP field can be used in requests and responses
to communicate digests that are calculated using a hashing algorithm
applied to the representation with no content coding (a.k.a. an
identity encoding). Apart from the content coding concerns, it
behaves similarly to Repr-Digest.
Identity-Digest is a Dictionary (see Section 3.2 of
[STRUCTURED-FIELDS]) where each:
* key conveys the hashing algorithm used to compute the digest;
* value is a Byte Sequence (Section 3.3.5 of [STRUCTURED-FIELDS]),
that conveys an encoded version of the byte output produced by the
digest calculation.
For example:
NOTE: '\' line wrapping per RFC 8792
Identity-Digest: \
sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\
yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:
The Dictionary type can be used, for example, to attach multiple
digests calculated using different hashing algorithms.
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NOTE: '\' line wrapping per RFC 8792
Identity-Digest: \
sha-256=:d435Qo+nKZ+gLcUHn7GQtQ72hiBVAgqoLsZnZPiTGPk=:,\
sha-512=:YMAam51Jz/jOATT6/zvHrLVgOYTGFy1d6GJiOHTohq4yP+pgk4vf2aCs\
yRZOtw8MjkM7iw7yZ/WkppmM44T3qg==:
A recipient MAY ignore any or all digests. This allows the recipient
to choose which hashing algorithm(s) to use for validation instead of
verifying every digest.
A sender MAY send a digest without knowing whether the recipient
supports a given hashing algorithm, or even knowing that the
recipient will ignore it.
Identity-Digest can be sent in a trailer section. In this case,
Identity-Digest MAY be merged into the header section; see
Section 6.5.1 of [HTTP].
5. The Want-Identity-Digest Field
Want-Identity-Digest indicates that the sender would like to receive
a representation digest on messages associated with the request URI
and representation metadata where no content coding is applied, using
the Identity-Digest field.
If Want-Identity-Digest is used in a response, it indicates that the
server would like the client to provide the Identity-Digest field on
future requests.
Want-Identity-Digest is only a hint. The receiver of the field can
ignore it and send an Integrity field using any algorithm or omit
fields entirely. It is not a protocol error if preferences are
ignored. Applications that use Integrity fields and Integrity
preferences can define expectations or constraints that operate in
addition to this specification.
Want-Identity-Digest is of type Dictionary where each:
* key conveys the hashing algorithm;
* value is an Integer (Section 3.3.1 of [STRUCTURED-FIELDS]) that
conveys an ascending, relative, weighted preference. It must be
in the range 0 to 10 inclusive. 1 is the least preferred, 10 is
the most preferred, and a value of 0 means "not acceptable".
Examples:
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Want-Identity-Digest: sha-256=1
Want-Identity-Digest: sha-512=3, sha-256=10, unixsum=0
6. Security Considerations
The considerations in [DIGEST-FIELDS] apply. There are no known
additional considerations.
7. IANA Considerations
This document has no IANA actions (yet)
8. Normative References
[DIGEST-FIELDS]
Polli, R. and L. Pardue, "Digest Fields", Work in
Progress, Internet-Draft, draft-ietf-httpbis-digest-
headers-11, 6 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
digest-headers-11>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
RFC 7405, DOI 10.17487/RFC7405, December 2014,
<https://www.rfc-editor.org/rfc/rfc7405>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[STRUCTURED-FIELDS]
Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
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Acknowledgments
Early drafts of [DIGEST-FIELDS] included a mechanism to support the
exchange of digests where no content coding is applied, which was
removed before publication. While the design here is different, it
is motivated by discussion of the previous design in the HTTP WG.
The motivating use cases still mostly apply identically.
Author's Address
Lucas Pardue
Cloudflare
Email: lucaspardue.24.7@gmail.com
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