< draft-ietf-smime-compression-06.txt		draft-ietf-smime-compression-07.txt >
			A new Request for Comments is now available in online RFC libraries.
	Internet Draft Editor: Peter Gutmann		RFC 3274
	draft-ietf-smime-compression-06.txt University of Auckland
	August 30, 2001
	Expires February 2002
	Compressed Data Content Type for CMS
	Status of this memo
	This document is an Internet-Draft and is in full conformance with all
	provisions of Section 10 of RFC2026.
	Internet-Drafts are working documents of the Internet Engineering Task
	Force (IETF), its areas, and its working groups. Note that other
	groups may also distribute working documents as Internet-Drafts.
	Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference material
	or to cite them other than as "work in progress."
	The list of current Internet-Drafts can be accessed at		Title: Compressed Data Content Type for
	http://www.ietf.org/ietf/1id-abstracts.txt		Cryptographic Message Syntax (CMS)
			Author(s): P. Gutmann
			Status: Standards Track
			Date: June 2002
			Mailbox: pgut001@cs.auckland.ac.nz
			Pages: 6
			Characters: 11276
			Updates/Obsoletes/SeeAlso: None
	The list of Internet-Draft Shadow Directories can be accessed at		I-D Tag: draft-ietf-smime-compression-07.txt
	http://www.ietf.org/shadow.html.
	Abstract		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3274.txt
	The Cryptographic Message Syntax data format doesn't currently contain		This document defines a format for using compressed data as a
	any provisions for compressing data before processing it. Compressing		Cryptographic Message Syntax (CMS) content type. Compressing data
	data before transmission provides a number of advantages including the		before transmission provides a number of advantages, including the
	elimination of data redundancy which could help an attacker, speeding		elimination of data redundancy which could help an attacker, speeding
	up processing by reducing the amount of data to be processed by later		up processing by reducing the amount of data to be processed by later
	steps such as signing or encryption, and reducing overall message size.		steps (such as signing or encryption), and reducing overall message
	Although there have been proposals for adding compression at other		size. Although there have been proposals for adding compression at
	levels (for example at the MIME or SSL level) these don't address the		other levels (for example at the MIME or SSL level), these don't
	problem of compression of CMS content unless the compression is		address the problem of compression of CMS content unless the
	supplied by an external means (for example by intermixing MIME and		compression is supplied by an external means (for example by
	CMS). This document defines a format for using compressed data as a		intermixing MIME and CMS).
	CMS content type.
	1. Introduction
	This document describes a compressed data content type for CMS. This
	is implemented as a new ContentInfo type and is an extension to the
	types currently defined in CMS [RFC2630]. Future implementations of
	CMS should include this extension.
	The format of the messages are described in ASN.1 [ASN1].
	The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
	"RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
	interpreted as described in [RFC2119].
	1.1 Compressed Data Content Type
	The compressed-data content type consists of content of any type
	compressed using a specified algorithm. The following object
	identifier identifies the compressed-data content type:
	id-ct-compressedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
	us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) ct(1) 9 }
	The compressed-data content type shall have ASN.1 type CompressedData:
	CompressedData ::= SEQUENCE {
	version CMSVersion,
	compressionAlgorithm CompressionAlgorithmIdentifier,
	encapContentInfo EncapsulatedContentInfo
	}
	The fields of type CompressedData have the following meanings:
	version is the syntax version number. It MUST be 0. Details of the
	CMSVersion type are discussed in CMS [RFC2630], section 10.2.5.
	compressionAlgorithm is a compression algorithm identifier, as
	defined in section 2.
	encapContentInfo is the content which is compressed. Details of the
	EncapsulatedContentInfo type are discussed in CMS [RFC2630], section
	5.2.
	Implementations SHOULD use the SMIMECapabilities attribute to indicate
	their ability to process compressed content types. Details of
	SMIMECapabilities are discussed in MSG [RFC2633], section 2.5.2
	A compression SMIMECapability consists of the AlgorithmIdentifier for
	the supported compression algorithm, in the case of the algorithm
	specified in this document this is id-alg-zlibCompression as specified
	in section 2. Alternatively, the use of compression may be handled by
	prior arrangement (for example as part of an interoperability profile).
	The SMIMECapability SEQUENCE representing the ability to process
	content compressed with the algorithm identified by id-alg-
	zlibCompression MUST be DER-encoded as the following hexadecimal
	string:
	30 0D 06 0B 2A 86 48 86 F7 0D 01 09 10 03 08
	(but see also the implementation note in section 2.1).
	2. Compression Types
	CMS implementations SHOULD include ZLIB [RFC1950] [RFC1951], which is
	free of any intellectual property restrictions and has a freely-
	available, portable and efficient reference implementation. The
	following object identifier identifies ZLIB:
	id-alg-zlibCompress OBJECT IDENTIFIER ::= { iso(1) member-body(2)
	us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) alg(3) 8 }
	This algorithm has no parameters. The parameters field SHOULD be
	encoded as omitted, but MAY be encoded as NULL (see the implemenation
	note in section 2.1).
	2.1. Implementation notes
	ZLIB allows for a number of compression levels ranging from good but
	slow compression to less good but fast compression. The compression
	level is always compatible with the decompression algorithm, so there
	is no need to specify the compression level as an algorithm parameter.
	There are two possible encodings for the ZLIB null parameters field
	which arise from the fact that when the 1988 syntax for
	AlgorithmIdentifier was translated into the 1997 syntax, the OPTIONAL
	associated with the AlgorithmIdentifier parameters got lost. Later it
	was recovered via a defect report, but by then everyone thought that
	algorithm parameters were mandatory. Because of this some
	implementations will encode null parameters as an ASN.1 NULL element
	and some will omit them entirely (see for example section 12 of CMS
	[RFC2630]). Although the correct encoding is to omit the parameters
	field, implementations may encounter encodings which use an ASN.1 NULL
	element for the parameters.
	3. Security Considerations
	This RFC is not concerned with security, except for the fact that
	compressing data before encryption can enhance the security provided by
	other processing steps by reducing the quantity of known plaintext
	available to an attacker.
	4. IANA Considerations
	The CompressedData content type and compression algorithms are
	identified by object identifiers (OIDs). OIDs were assigned from an
	arc contributed to the S/MIME Working Group by the RSA Security.
	Should additional compression algorithms be introduced, the advocates
	for such algorithms are expected to assign the necessary OIDs from
	their own arcs. No action by the IANA is necessary for this document
	or any anticipated updates.
	Author Address
	Peter Gutmann
	University of Auckland
	Private Bag 92019
	Auckland, New Zealand
	pgut001@cs.auckland.ac.nz
	References
	ASN1 CCITT Recommendation X.208: Specification of Abstract Syntax
	Notation One (ASN.1), 1988.
	RFC2119 Key Words for Use in RFC's to Indicate Requirement Levels,
	S.Bradner, March 1997.
	RFC1950 ZLIB Compressed Data Format Specification version 3.3,
	P.Deutsch and J-L Gailly, May 1996.
	RFC1951 DEFLATE Compressed Data Format Specification version 1.3,
	P.Deutsch, May 1996.
	RFC2630 Cryptographic Message Syntax, R.Housley, June 1999.
	RFC2633 S/MIME Version 3 Message Specification, B.Ramsdell, June
	1999.
	Appendix A: ASN.1 Module
	CompressedDataContent
	{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
	smime(16) modules(0) compress(11) }
	DEFINITIONS IMPLICIT TAGS ::=
	BEGIN
	IMPORTS
	CMSVersion, EncapsulatedContentInfo FROM CryptographicMessageSyntax
	{ iso(1) member-body(2) us(840) rsadsi(113549)
	pkcs(1) pkcs-9(9) smime(16) modules(0) cms(1) }
	AlgorithmIdentifier FROM AuthenticationFramework
	{ joint-iso-itu-t ds(5) module(1) authenticationFramework(7) 3 };
	CompressedData ::= SEQUENCE {
	version CMSVersion, -- Always set to 0
	compressionAlgorithm CompressionAlgorithmIdentifier,
	encapContentInfo EncapsulatedContentInfo
	}
	CompressionAlgorithmIdentifier ::= AlgorithmIdentifier
	id-alg-zlibCompress OBJECT IDENTIFIER ::= { iso(1) member-body(2)
	us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) alg(3) 8 }
			This document is a product of the S/MIME Mail Security Working Group
			of the IETF.
	id-ct-compressedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)		This is now a Proposed Standard Protocol.
	us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) ct(1) 9 }
	END		This document specifies an Internet standards track protocol for
			the Internet community, and requests discussion and suggestions
			for improvements. Please refer to the current edition of the
			"Internet Official Protocol Standards" (STD 1) for the
			standardization state and status of this protocol. Distribution
			of this memo is unlimited.
	Full Copyright Statement		This announcement is sent to the IETF list and the RFC-DIST list.
			Requests to be added to or deleted from the IETF distribution list
			should be sent to IETF-REQUEST@IETF.ORG. Requests to be
			added to or deleted from the RFC-DIST distribution list should
			be sent to RFC-DIST-REQUEST@RFC-EDITOR.ORG.
	Copyright (C) The Internet Society 2001. All Rights Reserved.		Details on obtaining RFCs via FTP or EMAIL may be obtained by sending
			an EMAIL message to rfc-info@RFC-EDITOR.ORG with the message body
			help: ways_to_get_rfcs. For example:
	This document and translations of it may be copied and furnished to		To: rfc-info@RFC-EDITOR.ORG
	others, and derivative works that comment on or otherwise explain it or		Subject: getting rfcs
	assist in its implementation may be prepared, copied, published and
	distributed, in whole or in part, without restriction of any kind,
	provided that the above copyright notice and this paragraph are
	included on all such copies and derivative works. However, this
	document itself may not be modified in any way, such as by removing the
	copyright notice or references to the Internet Society or other
	Internet organizations, except as needed for the purpose of developing
	Internet standards in which case the procedures for copyrights defined
	in the Internet Standards process must be followed, or as required to
	translate it into languages other than English.
	The limited permissions granted above are perpetual and will not be		help: ways_to_get_rfcs
	revoked by the Internet Society or its successors or assigns.
	This document and the information contained herein is provided on an		Requests for special distribution should be addressed to either the
	"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING		author of the RFC in question, or to RFC-Manager@RFC-EDITOR.ORG. Unless
	TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT		specifically noted otherwise on the RFC itself, all RFCs are for
	NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL		unlimited distribution.echo
	NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR		Submissions for Requests for Comments should be sent to
	FITNESS FOR A PARTICULAR PURPOSE.		RFC-EDITOR@RFC-EDITOR.ORG. Please consult RFC 2223, Instructions to RFC
			Authors, for further information.
End of changes. 15 change blocks.
	220 lines changed or deleted		42 lines changed or added
This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/