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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Draft Editor: Peter Gutmann 2 draft-ietf-smime-compression-03.txt University of Auckland 3 November 21, 2000 4 Expires May 2001 6 Compressed Data Content Type for S/MIME 8 Status of this memo 10 This document is an Internet-Draft and is in full conformance with all 11 provisions of Section 10 of RFC2026. 13 Internet-Drafts are working documents of the Internet Engineering Task 14 Force (IETF), its areas, and its working groups. Note that other 15 groups may also distribute working documents as Internet-Drafts. 17 Internet-Drafts are draft documents valid for a maximum of six months 18 and may be updated, replaced, or obsoleted by other documents at any 19 time. It is inappropriate to use Internet- Drafts as reference 20 material or to cite them other than as "work in progress." 22 The list of current Internet-Drafts can be accessed at 23 http://www.ietf.org/ietf/1id-abstracts.txt 25 The list of Internet-Draft Shadow Directories can be accessed at 26 http://www.ietf.org/shadow.html. 28 Abstract 30 The Cryptographic Message Syntax data format doesn't currently contain 31 any provisions for compressing data before processing it. Compressing 32 data before transmission provides a number of advantages including the 33 elimination of data redundancy which could help an attacker, speeding 34 up processing by reducing the amount of data to be processed by later 35 steps such as signing or encryption, and reducing overall message 36 size. Although there have been proposals for adding compression at 37 other levels (for example at the MIME or SSL level) these don't 38 address the problem of compression of CMS content unless the 39 compression is supplied by an external means (for example by 40 intermixing MIME and CMS). This document defines a format for using 41 compressed data as a CMS content type. 43 1. Introduction 45 This document describes a compressed data content type for S/MIME. 46 This is implemented as a new ContentInfo type and is an extension to 47 the types currently defined in CMS [RFC2630]. Future implementations 48 of CMS SHOULD include this extension. 50 The format of the messages are described in ASN.1 [ASN1]. 52 The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", 53 "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be 54 interpreted as described in [RFC2119]. 56 1.1 Compressed Data Content Type 58 The compressed-data content type consists of content of any type 59 compressed using a specified algorithm. The following object 60 identifier identifies the compressed-data content type: 62 id-ct-compressedData OBJECT IDENTIFIER ::= { iso(1) member-body(2) 63 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) ct(1) 9 } 65 The compressed-data content type shall have ASN.1 type 66 CompressedData: 68 CompressedData ::= SEQUENCE { 69 version CMSVersion, 70 compressionAlgorithm CompressionAlgorithmIdentifier, 71 encapContentInfo EncapsulatedContentInfo 72 } 74 The fields of type CompressedData have the following meanings: 76 version is the syntax version number. It MUST be 0. Details of 77 the CMSVersion type are discussed in CMS [RFC2630], section 78 10.2.5. 80 compressionAlgorithm is a compression algorithm identifier, as 81 defined in section 2. 83 encapContentInfo is the content which is compressed. Details of 84 the EncapsulatedContentInfo type are discussed in CMS [RFC2630], 85 section 5.2. 87 Implementations SHOULD use the SMIMECapabilities attribute to indicate 88 their ability to process compressed content types. A compression 89 SMIMECapability consists of the AlgorithmIdentifier for the supported 90 compression algorithm, in the case of the algorithm specified in this 91 document this is id-alg-zlibCompression with parameters NULL. 92 Alternatively, the use of compression may be handled by prior 93 arrangement (for example as part of an interoperability profile). 95 2. Compression Types 97 CMS implementations SHOULD include ZLIB [RFC1950] [RFC1951], which is 98 free of any intellectual property restrictions and has a freely- 99 available, portable and efficient reference implementation. The 100 following object identifier identifies ZLIB: 102 id-alg-zlibCompress OBJECT IDENTIFIER ::= { iso(1) member-body(2) 103 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) alg(3) 8 } 105 The parameters for this algorithm are NULL. 107 3. Security Considerations 109 This RFC is not concerned with security, except for the fact that 110 compressing data before encryption can enhance the security provided 111 by other processing steps by reducing the quantity of known plaintext 112 available to an attacker. 114 Author Address 116 Peter Gutmann 117 University of Auckland 118 Private Bag 92019 119 Auckland, New Zealand 120 pgut001@cs.auckland.ac.nz 122 References 124 ASN1 CCITT Recommendation X.208: Specification of Abstract Syntax 125 Notation One (ASN.1), 1988. 127 RFC2119 Key Words for Use in RFC's to Indicate Requirement Levels, 128 S.Bradner, March 1997. 130 RFC1950 ZLIB Compressed Data Format Specification version 3.3, 131 P.Deutsch and J-L Gailly, May 1996. 133 RFC1951 DEFLATE Compressed Data Format Specification version 1.3, 134 P.Deutsch, May 1996. 136 RFC2630 Cryptographic Message Syntax, R.Housley, June 1999. 138 Appendix A: ASN.1 Module 140 CompressedDataContent 141 { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 142 smime(16) modules(0) compress(11) } 144 DEFINITIONS IMPLICIT TAGS ::= 145 BEGIN 147 IMPORTS 148 CMSVersion, EncapsulatedContentInfo FROM CryptographicMessageSyntax 149 { iso(1) member-body(2) us(840) rsadsi(113549) 150 pkcs(1) pkcs-9(9) smime(16) modules(0) cms(1) }, 151 AlgorithmIdentifier FROM AuthenticationFramework 152 { joint-iso-itu-t ds(5) module(1) authenticationFramework(7) 3 }; 154 CompressedData ::= SEQUENCE { 155 version CMSVersion, -- Always set to 0 156 compressionAlgorithm CompressionAlgorithmIdentifier, 157 encapContentInfo EncapsulatedContentInfo 158 } 160 CompressionAlgorithmIdentifer ::= AlgorithmIdentifier 162 END 164 Full Copyright Statement 166 Copyright (C) The Internet Society 2000. 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