rfc3275.txt

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Network Working Group                                    D. Eastlake 3rd
Request for Comments: 3275                                      Motorola
Obsoletes: 3075                                                J. Reagle
Category: Standards Track                                            W3C
                                                                 D. Solo
                                                               Citigroup
                                                              March 2002


    (Extensible Markup Language) XML-Signature Syntax and Processing

Status of this Memo

   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.

   Copyright Notice

   Copyright (c) 2002 The Internet Society & W3C (MIT, INRIA, Keio), All
   Rights Reserved.

Abstract

   This document specifies XML (Extensible Markup Language) digital
   signature processing rules and syntax.  XML Signatures provide
   integrity, message authentication, and/or signer authentication
   services for data of any type, whether located within the XML that
   includes the signature or elsewhere.

Table of Contents

   1. Introduction...................................................  3
   1.1 Editorial and Conformance Conventions.........................  4
   1.2 Design Philosophy.............................................  4
   1.3 Versions, Namespaces and Identifiers..........................  4
   1.4 Acknowledgements..............................................  6
   1.5 W3C Status....................................................  6
   2. Signature Overview and Examples................................  7
   2.1 Simple Example (Signature, SignedInfo, Methods, and References) 8
   2.1.1 More on Reference...........................................  9
   2.2 Extended Example (Object and SignatureProperty)............... 10
   2.3 Extended Example (Object and Manifest)........................ 12
   3.0 Processing Rules.............................................. 13
   3.1 Core Generation............................................... 13
   3.1.1 Reference Generation........................................ 13



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   3.1.2 Signature Generation........................................ 13
   3.2 Core Validation............................................... 14
   3.2.1 Reference Validation........................................ 14
   3.2.2 Signature Validation........................................ 15
   4.0 Core Signature Syntax......................................... 15
   4.0.1 The ds:CryptoBinary Simple Type............................. 17
   4.1 The Signature element......................................... 17
   4.2 The SignatureValue Element.................................... 18
   4.3 The SignedInfo Element........................................ 18
   4.3.1 The CanonicalizationMethod Element.......................... 19
   4.3.2 The SignatureMethod Element................................. 21
   4.3.3 The Reference Element....................................... 21
   4.3.3.1 The URI Attribute......................................... 22
   4.3.3.2 The Reference Processing Model............................ 23
   4.3.3.3 Same-Document URI-References.............................. 25
   4.3.3.4 The Transforms Element.................................... 26
   4.3.3.5 The DigestMethod Element.................................. 28
   4.3.3.6 The DigestValue Element................................... 28
   4.4 The KeyInfo Element........................................... 29
   4.4.1 The KeyName Element......................................... 31
   4.4.2 The KeyValue Element........................................ 31
   4.4.2.1 The DSAKeyValue Element................................... 32
   4.4.2.2 The RSAKeyValue Element................................... 33
   4.4.3 The RetrievalMethod Element................................. 34
   4.4.4 The X509Data Element........................................ 35
   4.4.5 The PGPData Element......................................... 38
   4.4.6 The SPKIData Element........................................ 39
   4.4.7 The MgmtData Element........................................ 40
   4.5 The Object Element............................................ 40
   5.0 Additional Signature Syntax................................... 42
   5.1 The Manifest Element.......................................... 42
   5.2 The SignatureProperties Element............................... 43
   5.3 Processing Instructions in Signature Elements................. 44
   5.4 Comments in Signature Elements................................ 44
   6.0 Algorithms.................................................... 44
   6.1 Algorithm Identifiers and Implementation Requirements......... 44
   6.2 Message Digests............................................... 46
   6.2.1 SHA-1....................................................... 46
   6.3 Message Authentication Codes.................................. 46
   6.3.1 HMAC........................................................ 46
   6.4 Signature Algorithms.......................................... 47
   6.4.1 DSA......................................................... 47
   6.4.2 PKCS1 (RSA-SHA1)............................................ 48
   6.5 Canonicalization Algorithms................................... 49
   6.5.1 Canonical XML............................................... 49
   6.6 Transform Algorithms.......................................... 50
   6.6.1 Canonicalization............................................ 50
   6.6.2 Base64...................................................... 50



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   6.6.3 XPath Filtering............................................. 51
   6.6.4 Enveloped Signature Transform............................... 54
   6.6.5 XSLT Transform.............................................. 54
   7. XML Canonicalization and Syntax Constraint Considerations...... 55
   7.1 XML 1.0, Syntax Constraints, and Canonicalization............. 56
   7.2 DOM/SAX Processing and Canonicalization....................... 57
   7.3 Namespace Context and Portable Signatures..................... 58
   8.0 Security Considerations....................................... 59
   8.1 Transforms.................................................... 59
   8.1.1 Only What is Signed is Secure............................... 60
   8.1.2 Only What is 'Seen' Should be Signed........................ 60
   8.1.3 'See' What is Signed........................................ 61
   8.2 Check the Security Model...................................... 62
   8.3 Algorithms, Key Lengths, Certificates, Etc.................... 62
   9. Schema, DTD, Data Model, and Valid Examples.................... 63
   10. Definitions................................................... 63
   Appendix: Changes from RFC 3075................................... 67
   References........................................................ 67
   Authors' Addresses................................................ 72
   Full Copyright Statement.......................................... 73

1. Introduction

   This document specifies XML syntax and processing rules for creating
   and representing digital signatures.  XML Signatures can be applied
   to any digital content (data object), including XML.  An XML
   Signature may be applied to the content of one or more resources.
   Enveloped or enveloping signatures are over data within the same XML
   document as the signature; detached signatures are over data external
   to the signature element.  More specifically, this specification
   defines an XML signature element type and an XML signature
   application; conformance requirements for each are specified by way
   of schema definitions and prose respectively.  This specification
   also includes other useful types that identify methods for
   referencing collections of resources, algorithms, and keying and
   management information.

   The XML Signature is a method of associating a key with referenced
   data (octets); it does not normatively specify how keys are
   associated with persons or institutions, nor the meaning of the data
   being referenced and signed.  Consequently, while this specification
   is an important component of secure XML applications, it itself is
   not sufficient to address all application security/trust concerns,
   particularly with respect to using signed XML (or other data formats)
   as a basis of human-to-human communication and agreement.  Such an
   application must specify additional key, algorithm, processing and
   rendering requirements.  For further information, please see Security
   Considerations (section 8).



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1.1 Editorial and Conformance Conventions

   For readability, brevity, and historic reasons this document uses the
   term "signature" to generally refer to digital authentication values
   of all types.  Obviously, the term is also strictly used to refer to
   authentication values that are based on public keys and that provide
   signer authentication.  When specifically discussing authentication
   values based on symmetric secret key codes we use the terms
   authenticators or authentication codes.  (See Check the Security
   Model, section 8.3.)

   This specification provides an XML Schema [XML-schema] and DTD [XML].
   The schema definition is normative.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   specification are to be interpreted as described in RFC2119
   [KEYWORDS]:

      "they MUST only be used where it is actually required for
      interoperation or to limit behavior which has potential for
      causing harm (e.g., limiting retransmissions)"

   Consequently, we use these capitalized key words to unambiguously
   specify requirements over protocol and application features and
   behavior that affect the interoperability and security of
   implementations.  These key words are not used (capitalized) to
   describe XML grammar; schema definitions unambiguously describe such
   requirements and we wish to reserve the prominence of these terms for
   the natural language descriptions of protocols and features.  For
   instance, an XML attribute might be described as being "optional."
   Compliance with the Namespaces in XML specification [XML-ns] is
   described as "REQUIRED."

1.2 Design Philosophy

   The design philosophy and requirements of this specification are
   addressed in the XML-Signature Requirements document [XML-Signature-
   RD].

1.3 Versions, Namespaces and Identifiers

   No provision is made for an explicit version number in this syntax.
   If a future version is needed, it will use a different namespace.
   The XML namespace [XML-ns] URI that MUST be used by implementations
   of this (dated) specification is:

      xmlns="http://www.w3.org/2000/09/xmldsig#"



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   This namespace is also used as the prefix for algorithm identifiers
   used by this specification.  While applications MUST support XML and
   XML namespaces, the use of internal entities [XML] or our "dsig" XML
   namespace prefix and defaulting/scoping conventions are OPTIONAL; we
   use these facilities to provide compact and readable examples.

   This specification uses Uniform Resource Identifiers [URI] to
   identify resources, algorithms, and semantics.  The URI in the
   namespace declaration above is also used as a prefix for URIs under
   the control of this specification.  For resources not under the
   control of this specification, we use the designated Uniform Resource
   Names [URN] or Uniform Resource Locators [URL] defined by its
   normative external specification.  If an external specification has
   not allocated itself a Uniform Resource Identifier we allocate an
   identifier under our own namespace.  For instance:

   SignatureProperties is identified and defined by this specification's
   namespace:
      http://www.w3.org/2000/09/xmldsig#SignatureProperties

   XSLT is identified and defined by an external URI
      http://www.w3.org/TR/1999/REC-xslt-19991116

   SHA1 is identified via this specification's namespace and defined via
   a normative reference
      http://www.w3.org/2000/09/xmldsig#sha1
      FIPS PUB 180-1. Secure Hash Standard. U.S. Department of
      Commerce/National Institute of Standards and Technology.

   Finally, in order to provide for terse namespace declarations we
   sometimes use XML internal entities [XML] within URIs.  For instance:

      <?xml version='1.0'?>
      <!DOCTYPE Signature SYSTEM
        "xmldsig-core-schema.dtd" [ <!ENTITY dsig
        "http://www.w3.org/2000/09/xmldsig#"> ]>
      <Signature xmlns="&dsig;" Id="MyFirstSignature">
        <SignedInfo>
        ...












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1.4 Acknowledgements

   The contributions of the following Working Group members to this
   specification are gratefully acknowledged:

      * Mark Bartel, Accelio (Author)
      * John Boyer, PureEdge (Author)
      * Mariano P. Consens, University of Waterloo
      * John Cowan, Reuters Health
      * Donald Eastlake 3rd, Motorola  (Chair, Author/Editor)
      * Barb Fox, Microsoft (Author)