Internet DRAFT - draft-polli-id-digest-algorithms
draft-polli-id-digest-algorithms
Network Working Group R. Polli
Internet-Draft Digital Transformation Department, Italian Government
Intended status: Experimental 2 December 2021
Expires: 5 June 2022
The "id-" prefix for Digest Algorithms
draft-polli-id-digest-algorithms-02
Abstract
This document defines the "id-" prefix for digest-algorithms used in
the Digest Fields. This prefix explicits that the computed checksum
value is independent from Content-Encoding.
Note to Readers
_RFC EDITOR: please remove this section before publication_
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/
(https://lists.w3.org/Archives/Public/ietf-http-wg/).
The source code and issues list for this draft can be found at
https://github.com/ioggstream/draft-polli-id-digest-algorithms
(https://github.com/ioggstream/draft-polli-id-digest-algorithms).
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 5 June 2022.
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The "id-" prefix for digest-algorithms . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
3.1. Disclosure of encrypted content . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Normative References . . . . . . . . . . . . . . . . . . . . 4
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 5
A.1. The id-sha-256 digest-algorithm . . . . . . . . . . . . . 5
FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Code Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Since draft-polli-id-digest-algorithms-01 . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The [DIGEST] defines a way to convey a checksum of a representation-
data as specified in [SEMANTICS].
As the representation data depends on the value of Content-Encoding,
it is useful to convey the checksum value of a representation without
any content coding applied.
This proposal introduces the id- prefix to specify that the provided
digest-algorithm value is computed on the representation-data without
any content coding applied.
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1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. These words may also appear in this
document in lower case as plain English words, absent their normative
meanings.
This document uses the Augmented BNF defined in [RFC5234] and updated
by [RFC7405].
The definitions "representation", "selected representation",
"representation data", "representation metadata", and "content" in
this document are to be interpreted as described in [SEMANTICS].
The definitions "digest-algorithm" and "representation-data-digest"
in this document are to be interpreted as described in [DIGEST].
2. The "id-" prefix for digest-algorithms
A new digest-algorithm to be registered within the HTTP Digest
Algorithm Values Registry (https://www.iana.org/assignments/http-dig-
alg/) MUST NOT start with the string id-.
The following two examples show two digest-algorithm names that
cannot be registered
id-sha-256
id-sha-512
For every digest-algorithm registered in the HTTP Digest Algorithm
Values (https://www.iana.org/assignments/http-dig-alg/) the associate
id- digest-algorithm has the following properties:
* the checksum is computed on the representation-data of the
resource when no content coding is applied;
* the checksum is computed according to the original digest-
algorithm "Description" field, and uses the same encoding of the
original digest-algorithm.
3. Security Considerations
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3.1. Disclosure of encrypted content
If the content coding provides encryption features, sending the
checksum of unencoded representation can disclose information about
the original content.
4. IANA Considerations
Please, add the following text to the "Note" section of the HTTP
Digest Algorithm Values (https://www.iana.org/assignments/http-dig-
alg/).
" For each registered Digest Algorithm, an associated id- algorithm
is defined.
The associated representation-data-digest is computed according to
Section 2 of this document. "
5. Normative References
[DIGEST] Polli, R. and L. Pardue, "Digest Fields", Work in
Progress, Internet-Draft, draft-ietf-httpbis-digest-
headers-07, 16 November 2021,
<https://www.ietf.org/archive/id/draft-ietf-httpbis-
digest-headers-07.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
RFC 7405, DOI 10.17487/RFC7405, December 2014,
<https://www.rfc-editor.org/info/rfc7405>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[SEMANTICS]
Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://www.ietf.org/archive/id/draft-ietf-httpbis-
semantics-19.txt>.
Appendix A. Examples
A.1. The id-sha-256 digest-algorithm
The following request conveys a brotli encoded json object
{"hello": "world"}
The Digest computed using the "sha-256" digest-algorithm present in
HTTP Digest Algorithm Values (https://www.iana.org/assignments/http-
dig-alg/) is content coding aware, while its associated "id-" digest-
algorithm is not.
POST /data HTTP/1.1
Content-Type: application/json
Content-Encoding: br
Digest: sha-256=4REjxQ4yrqUVicfSKYNO/cF9zNj5ANbzgDZt3/h3Qxo=,
id-sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
CwGAZiwiAeyJoZWxsbyI6ICJ3b3JsZCJ9Aw==
FAQ
_RFC Editor: Please remove this section before publication._
Q: Why to convey the checksum independent from the content
codings? This is useful to identify and validate a resource
downloaded from different sources using different content codings,
or to compare a resource with its stored or signed counterpart.
Q: How does it improve the life of checksum providers? If providers
use reverse proxies to eg. compress responses, this could
invalidate content coding aware checksums. Providing an id-
algorithm, allows the digest checksum to be validated.
Code Samples
_RFC Editor: Please remove this section before publication._
How can I generate an identity digest value?
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The following python3 code can be used to generate digests for json
objects using crc32c algorithm. 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, brotli, hashlib
identity = lambda x: x
def digest(item, content_coding=identity, algorithm=hashlib.sha256) -> bytes:
json_bytes = json.dumps(item).encode()
content_encoded = content_coding(json_bytes)
checksum = algorithm(content_encoded)
return base64.encodebytes(checksum.digest())
item = {"hello": "world"}
print("sha-256 digest value for a br-coded representation: ",
digest(item, content_coding=brotli.compress)
)
print("id-sha-256 digest value for a br-coded representation: ",
digest(item, content_coding=identity)
)
Acknowledgements
This specification was born from a thread created by James Manger and
the subsequent discussion here https://github.com/httpwg/http-
extensions/issues/885.
Change Log
_RFC Editor: Please remove this section before publication._
Since draft-polli-id-digest-algorithms-01
* Include id-sha-256 and id-sha-512.
Author's Address
Roberto Polli
Digital Transformation Department, Italian Government
Italy
Email: robipolli@gmail.com
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