Internet-Draft | The "id-" prefix for Digest Algorithms | December 2020 |
Polli | Expires 21 June 2021 | [Page] |
- Workgroup:
- Network Working Group
- Internet-Draft:
- draft-polli-id-digest-algorithms-01
- Published:
- Intended Status:
- Standards Track
- Expires:
The "id-" prefix for Digest Algorithms
Abstract
This document defines the "id-" prefix for digest-algorithms used in the Digest HTTP field. This prefix explicits that the value of the digest-algorithm 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/.¶
The source code and issues list for this draft can be found at https://github.com/ioggstream/draft-polli-Retry-Scope.¶
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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
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This Internet-Draft will expire on 21 June 2021.¶
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
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.¶
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 "payload body" 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 digest-algorithm to be registered within the HTTP Digest Algorithm Values MUST NOT start with the string "id-".¶
The following two examples show two digest-algorithm names that cannot be registered¶
id-crc32c id-adler32¶
For every digest-algorithm registered in the HTTP Digest Algorithm Values 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.¶
This definition is compatible, and thus extends, the definition of the "id-sha-256" and "id-sha-512" digest-algorithms contained in Section X of [DIGEST].¶
3. Security Considerations
3.1. Disclosure of encrypted content
Like the "id-sha-256" digest-algoritm defined in [DIGEST] if the content-coding provides encryption features, sending the checksum of unencoded representation can disclose information.¶
5. Examples
5.1. The id-crc32c digest-algorithm
The following request conveys a brotli encoded json object¶
{"hello": "world"}¶
The Digest
computed using the "crc32c" digest-algorithm present in
HTTP Digest Algorithm Values
is content-coding aware,
while its associated "id-" digest-algorithm is not "id-crc32c"¶
POST /data HTTP/1.1 Content-Type: application/json Content-Encoding: br Digest: id-crc32c=43794720, crc32c=DB329237 CwGAZG9nAw==¶
6. Normative References
- [DIGEST]
- Polli, R. and L. Pardue, "Digest Headers", Work in Progress, Internet-Draft, draft-ietf-httpbis-digest-headers-04, , <http://www.ietf.org/internet-drafts/draft-ietf-httpbis-digest-headers-04.txt>.
- [RFC2119]
- Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <https://www.rfc-editor.org/info/rfc5234>.
- [RFC7405]
- Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC 7405, DOI 10.17487/RFC7405, , <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, , <https://www.rfc-editor.org/info/rfc8174>.
- [SEMANTICS]
- Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, , <https://www.rfc-editor.org/info/rfc7231>.
Appendix A. 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.¶
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 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, crc32c identity = lambda x: x def digest(item, content_coding=identity, algorithm=crc32c.crc32c): json_bytes = json.dumps(item).encode() content_encoded = content_coding(json_bytes) checksum = algorithm(content_encoded) # encode result has uppercase hex return hex(checksum)[2:].upper() item = {"hello": "world"} print("crc32c digest value for a br-coded representation: ", digest(item, content_coding=brotli.compress) ) print("id-crc32c digest value for a br-coded representation: ", digest(item, content_coding=identity) )¶
Change Log
RFC EDITOR PLEASE DELETE THIS SECTION.¶