< draft-ietf-xmldsig-core-2-02.txt		draft-ietf-xmldsig-core-2-03.txt >
			A new Request for Comments is now available in online RFC libraries.
	INTERNET-DRAFT Donald Eastlake 3rd (Motorola)		RFC 3275
	OBSOLETES RFC 3075 Joseph Reagle (W3C)
	David Solo (Citigroup)
	Expires April 2002 October 2001
	XML-Signature Syntax and Processing
	<draft-ietf-xmldsig-core-2-02.txt>
	Status of This Document
	This document is a product of the joint IETF/W3C XMLDSIG working
	group. It is intended to become a Draft Standard. Distribution of
	this document is unlimited. Comments should be sent to the XMLDSIG WG
	mailing list <w3c-ietf-xmldsig@w3.org> and to the authors.
	This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC 2026. 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
	http://www.ietf.org/ietf/1id-abstracts.txt
	The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.
	Copyright Notice
	Copyright (c) 2000 The Internet Society & W3C (MIT, INRIA, Keio), All
	Rights Reserved. W3C liability, trademark, document use and software
	licensing rules apply.
	Abstract
	This document specifies XML 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.
	W3C Status of this document
	[NOTE: This section gives the status AS IT WILL BE if this document
	is approved as a Recommendation.]
	This document has been reviewed by W3C Members and other interested
	parties and has been endorsed by the Director as a W3C
	Recommendation. It is a stable document and may be used as reference
	material or cited as a normative reference from another document.
	W3C's role in making the Recommendation is to draw attention to the
	specification and to promote its widespread deployment. This enhances
	the functionality and interoperability of the Web.
	This specification was produced by the IETF/W3C XML Signature Working
	Group (W3C Activity Statement) which believes the specification is
	sufficient for the creation of independent interoperable
	implementations; the Interoperability Report shows at least 10
	implementations with at least two interoperable implementations over
	every feature.
	Patent disclosures relevant to this specification may be found on the
	Working Group's patent disclosure page, in conformance with W3C
	policy, and the IETF Page of Intellectual Property Rights Notices, in
	conformance with IETF policy.
	Please report errors in this document to w3c-ietf-xmldsig@w3.org
	(archive).
	Table of Contents
	Status of This Document....................................1
	Copyright Notice...........................................1
	Abstract...................................................2
	W3C Status of this document................................2
	Table of Contents..........................................3
	1. Introduction............................................5
	1.1 Editorial and Conformance Conventions..................5
	1.2 Design Philosophy......................................6
	1.3 Versions, Namespaces and Identifiers...................6
	1.4 Acknowledgements.......................................7
	2. Signature Overview and Examples.........................8
	2.1 Simple Example
	(Signature, SignedInfo, Methods, and References).......9
	2.1.1 More on Reference...................................10
	2.2 Extended Example (Object and SignatureProperty).......11
	2.3 Extended Example (Object and Manifest)................13
	3.0 Processing Rules......................................14
	3.1 Core Generation.......................................14
	3.1.1 Reference Generation................................14
	3.1.2 Signature Generation................................15
	3.2 Core Validation.......................................15
	3.2.1 Reference Validation................................15
	3.2.2 Signature Validation................................16
	4.0 Core Signature Syntax.................................16
	4.0.1 The ds:CryptoBinary Simple Type.....................17
	4.1 The Signature element.................................18
	4.2 The SignatureValue Element............................19
	4.3 The SignedInfo Element................................19
	4.3.1 The CanonicalizationMethod Element..................20
	4.3.2 The SignatureMethod Element.........................21
	4.3.3 The Reference Element...............................22
	4.3.3.1 The URI Attribute.................................23
	4.3.3.2 The Reference Processing Model....................24
	4.3.3.3 Same-Document URI-References......................26
	4.3.3.4 The Transforms Element............................27
	4.3.3.5 The DigestMethod Element..........................28
	4.3.3.6 The DigestValue Element...........................29
	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...........................34
	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...........................41
	5.1 The Manifest Element..................................42
	5.2 The SignatureProperties Element.......................42
	5.3 Processing Instructions in Signature Elements.........43
	5.4 Comments in Signature Elements........................44
	6.0 Algorithms............................................44
	6.1 Algorithm Identifiers and Implementation Requirements.44
	6.2 Message Digests.......................................45
	6.2.1 SHA-1...............................................45
	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..................................49
	6.6.1 Canonicalization....................................50
	6.6.2 Base64..............................................50
	6.6.3 XPath Filtering.....................................50
	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.............57
	8.0 Security Considerations...............................59
	8.1 Transforms............................................59
	8.1.1 Only What is Signed is Secure.......................59
	8.1.2 Only What is 'Seen' Should be Signed................60
	8.1.3 'See' What is Signed................................60
	8.2 Check the Security Model..............................61
	8.3 Algorithms, Key Lengths, Certificates, Etc............62
	9. Schema, DTD, Data Model, and Valid Examples............62
	10. Definitions...........................................63
	References................................................65
	Authors' Address..........................................70
	Expiration and File Name..................................70
	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).
	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#"
	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>
	...
	1.4 Acknowledgements
	The contributions of the following Working Group members to this
	specification are gratefully acknowledged:
	* Mark Bartel, JetForm Corporation (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)
	* Christian Geuer-Pollmann, University Siegen
	* Tom Gindin, IBM
	* Phillip Hallam-Baker, VeriSign Inc
	* Richard Himes, US Courts
	* Merlin Hughes, Baltimore
	* Gregor Karlinger, IAIK TU Graz
	* Brian LaMacchia, Microsoft (Author)
	* Peter Lipp, IAIK TU Graz
	* Joseph Reagle, W3C (Chair, Author/Editor)
	* Ed Simon (Author)
	* David Solo, Citigroup (Author/Editor)
	* Petteri Stenius, DONE Information, Ltd
	* Raghavan Srinivas, Sun
	* Kent Tamura, IBM
	* Winchel Todd Vincent III, GSU
	* Carl Wallace, Corsec Security, Inc.
	* Greg Whitehead, Signio Inc.
	As are the Last Call comments from the following:
	* Dan Connolly, W3C
	* Paul Biron, Kaiser Permanente, on behalf of the XML Schema WG.
	* Martin J. Duerst, W3C; and Masahiro Sekiguchi, Fujitsu; on
	behalf of the Internationalization WG/IG.
	* Jonathan Marsh, Microsoft, on behalf of the Extensible
	Stylesheet Language WG.
	2. Signature Overview and Examples
	This section provides an overview and examples of XML digital
	signature syntax. The specific processing is given in Pr ocessing
	Rules (section 3). The formal syntax is found in Core Signature
	Syntax (section 4) and Additional Signature Syntax (section 5).
	In this section, an informal representation and examples are used to
	describe the structure of the XML signature syntax. This
	representation and examples may omit attributes, details and
	potential features that are fully explained later.
	XML Signatures are applied to arbitrary digital content (data
	objects) via an indirection. Data objects are digested, the resulting
	value is placed in an element (with other information) and that
	element is then digested and cryptographically signed. XML digital
	signatures are represented by the Signature element which has the
	following structure (where "?" denotes zero or one occurrence; "+"
	denotes one or more occurrences; and "*" denotes zero or more
	occurrences):
	<Signature ID?>
	<SignedInfo>
	<CanonicalizationMethod/>
	<SignatureMethod/>
	(<Reference URI? >
	(<Transforms>)?
	<DigestMethod>
	<DigestValue>
	</Reference>)+
	</SignedInfo>
	<SignatureValue>
	(<KeyInfo>)?
	(<Object ID?>)*
	</Signature>
	Signatures are related to data objects via URIs [URI]. Within an XML
	document, signatures are related to local data objects via fragment
	identifiers. Such local data can be included within an enveloping
	signature or can enclose an enveloped signature. Detached signatures
	are over external network resources or local data objects that reside
	within the same XML document as sibling elements; in this case, the
	signature is enveloping (signature is parent) nor enveloped
	(signature is child). Since a Signature element (and its Id attribute
	value/name) may co-exist or be combined with other elements (and
	their IDs) within a single XML document, care should be taken in
	choosing names such that there are no subsequent collisions that
	violate the ID uniqueness validity constraint [XML].
	2.1 Simple Example (Signature, SignedInfo, Methods, and References)
	The following example is a detached signature of the content of the
	HTML4 in XML specification.
	[s01] <Signature Id="MyFirstSignature"
	xmlns="http://www.w3.org/2000/09/xmldsig#">
	[s02] <SignedInfo>
	[s03] <CanonicalizationMethod
	Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
	[s04] <SignatureMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/>
	[s05] <Reference URI="http://www.w3.org/TR/2000/REC-xhtml1-
	20000126/">
	[s06] <Transforms>
	[s07] <Transform Algorithm="http://www.w3.org/TR/2001/REC-
	xml-c14n-20010315"/>
	[s08] </Transforms>
	[s09] <DigestMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
	[s10] <DigestValue>j6lwx3rvEPO0vKtMup4NbeVu8nk=</DigestValue>
	[s11] </Reference>
	[s12] </SignedInfo>
	[s13] <SignatureValue>MC0CFFrVLtRlk=...</SignatureValue>
	[s14] <KeyInfo>
	[s15a] <KeyValue>
	[s15b] <DSAKeyValue>
	[s15c] <P>...</P><Q>...</Q><G>...</G><Y>...</Y>
	[s15d] </DSAKeyValue>
	[s15e] </KeyValue>
	[s16] </KeyInfo>
	[s17] </Signature>
	[s02-12] The required SignedInfo element is the information that is
	actually signed. Core validation of SignedInfo consists of two
	mandatory processes: validation of the signature over SignedInfo and
	validation of each Reference digest within SignedInfo. Note that the
	algorithms used in calculating the SignatureValue are also included
	in the signed information while the SignatureValue element is outside
	SignedInfo.
	[s03] The CanonicalizationMethod is the algorithm that is used to
	canonicalize the SignedInfo element before it is digested as part of
	the signature operation. Note that this example, and all examples in
	this specification, are not in canonical form.
	[s04] The SignatureMethod is the algorithm that is used to convert
	the canonicalized SignedInfo into the SignatureValue. It is a
	combination of a digest algorithm and a key dependent algorithm and
	possibly other algorithms such as padding, for example RSA-SHA1. The
	algorithm names are signed to resist attacks based on substituting a
	weaker algorithm. To promote application interoperability we specify
	a set of signature algorithms that MUST be implemented, though their
	use is at the discretion of the signature creator. We specify
	additional algorithms as RECOMMENDED or OPTIONAL for implementation;
	the design also permits arbitrary user specified algorithms.
	[s05-11] Each Reference element includes the digest method and
	resulting digest value calculated over the identified data object. It
	also may include transformations that produced the input to the
	digest operation. A data object is signed by computing its digest
	value and a signature over that value. The signature is later checked
	via reference and signature validation.
	[s14-16] KeyInfo indicates the key to be used to validate the
	signature. Possible forms for identification include certificates,
	key names, and key agreement algorithms and information -- we define
	only a few. KeyInfo is optional for two reasons. First, the signer
	may not wish to reveal key information to all document processing
	parties. Second, the information may be known within the
	application's context and need not be represented explicitly. Since
	KeyInfo is outside of SignedInfo, if the signer wishes to bind the
	keying information to the signature, a Reference can easily identify
	and include the KeyInfo as part of the signature.
	2.1.1 More on Reference
	[s05] <Reference URI="http://www.w3.org/TR/2000/REC-xhtml1-
	20000126/">
	[s06] <Transforms>
	[s07] <Transform Algorithm="http://www.w3.org/TR/2001/REC-
	xml-c14n-20010315"/>
	[s08] </Transforms>
	[s09] <DigestMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
	[s10] <DigestValue>j6lwx3rvEPO0vKtMup4NbeVu8nk=</DigestValue>
	[s11] </Reference>
	[s05] The optional URI attribute of Reference identifies the data
	object to be signed. This attribute may be omitted on at most one
	Reference in a Signature. (This limitation is imposed in order to
	ensure that references and objects may be matched unambiguously.)
	[s05-08] This identification, along with the transforms, is a
	description provided by the signer on how they obtained the signed
	data object in the form it was digested (i.e. the digested content).
	The verifier may obtain the digested content in another method so
	long as the digest verifies. In particular, the verifier may obtain
	the content from a different location such as a local store than that
	specified in the URI.
	[s06-08] Transforms is an optional ordered list of processing steps
	that were applied to the resource's content before it was digested.
	Transforms can include operations such as canonicalization,
	encoding/decoding (including compression/inflation), XSLT, XPath, XML
	schema validation, or XInclude. XPath transforms permit the signer to
	derive an XML document that omits portions of the source document.
	Consequently those excluded portions can change without affecting
	signature validity. For example, if the resource being signed
	encloses the signature itself, such a transform must be used to
	exclude the signature value from its own computation. If no
	Transforms element is present, the resource's content is digested
	directly. While the Working Group has specified mandatory (and
	optional) canonicalization and decoding algorithms, user specified
	transforms are permitted.
	[s09-10] DigestMethod is the algorithm applied to the data after
	Transforms is applied (if specified) to yield the DigestValue. The
	signing of the DigestValue is what binds a resources content to the
	signer's key.
	2.2 Extended Example (Object and SignatureProperty)
	This specification does not address mechanisms for making statements
	or assertions. Instead, this document defines what it means for
	something to be signed by an XML Signature (integrity, message
	authentication, and/or signer authentication). Applications that wish
	to represent other semantics must rely upon other technologies, such
	as [XML, RDF]. For instance, an application might use a foo:assuredby
	attribute within its own markup to reference a Signature element.
	Consequently, it's the application that must understand and know how
	to make trust decisions given the validity of the signature and the
	meaning of assuredby syntax. We also define a SignatureProperties
	element type for the inclusion of assertions about the signature
	itself (e.g., signature semantics, the time of signing or the serial
	number of hardware used in cryptographic processes). Such assertions
	may be signed by including a Reference for the SignatureProperties in
	SignedInfo. While the signing application should be very careful
	about what it signs (it should understand what is in the
	SignatureProperty) a receiving application has no obligation to
	understand that semantic (though its parent trust engine may wish
	to). Any content about the signature generation may be located within
	the SignatureProperty element. The mandatory Target attribute
	references the Signature element to which the property applies.
	Consider the preceding example with an additional reference to a
	local Object that includes a SignatureProperty element. (Such a
	signature would not only be detached [p02] but enveloping [p03].)
	[ ] <Signature Id="MySecondSignature" ...>
	[p01] <SignedInfo>
	[ ] ...
	[p02] <Reference URI="http://www.w3.org/TR/xml-stylesheet/">
	[ ] ...
	[p03] <Reference URI="#AMadeUpTimeStamp"
	[p04]
	Type="http://www.w3.org/2000/09/xmldsig#SignatureProperties">
	[p05] <DigestMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
	[p06] <DigestValue>k3453rvEPO0vKtMup4NbeVu8nk=</DigestValue>
	[p07] </Reference>
	[p08] </SignedInfo>
	[p09] ...
	[p10] <Object>
	[p11] <SignatureProperties>
	[p12] <SignatureProperty Id="AMadeUpTimeStamp"
	Target="#MySecondSignature">
	[p13] <timestamp xmlns="http://www.ietf.org/rfcXXXX.txt">
	[p14] <date>19990908</date>
	[p15] <time>14:34:34:34</time>
	[p16] </timestamp>
	[p17] </SignatureProperty>
	[p18] </SignatureProperties>
	[p19] </Object>
	[p20]</Signature>
	[p04] The optional Type attribute of Reference provides information
	about the resource identified by the URI. In particular, it can
	indicate that it is an Object, SignatureProperty, or Manifest
	element. This can be used by applications to initiate special
	processing of some Reference elements. References to an XML data
	element within an Object element SHOULD identify the actual element
	pointed to. Where the element content is not XML (perhaps it is
	binary or encoded data) the reference should identify the Object and
	the Reference Type, if given, SHOULD indicate Object. Note that Type
	is advisory and no action based on it or checking of its correctness
	is required by core behavior.
	[p10] Object is an optional element for including data objects within
	the signature element or elsewhere. The Object can be optionally
	typed and/or encoded.
	[p11-18] Signature properties, such as time of signing, can be
	optionally signed by identifying them from within a Reference. (These
	properties are traditionally called signature "attributes" although
	that term has no relationship to the XML term "attribute".)
	2.3 Extended Example (Object and Manifest)
	The Manifest element is provided to meet additional requirements not
	directly addressed by the mandatory parts of this specification. Two
	requirements and the way the Manifest satisfies them follow.
	First, applications frequently need to efficiently sign multiple data
	objects even where the signature operation itself is an expensive
	public key signature. This requirement can be met by including
	multiple Reference elements within SignedInfo since the inclusion of
	each digest secures the data digested. However, some applications may
	not want the core validation behavior associated with this approach
	because it requires every Reference within SignedInfo to undergo
	reference validation -- the DigestValue elements are checked. These
	applications may wish to reserve reference validation decision logic
	to themselves. For example, an application might receive a signature
	valid SignedInfo element that includes three Reference elements. If a
	single Reference fails (the identified data object when digested does
	not yield the specified DigestValue) the signature would fail core
	validation. However, the application may wish to treat the signature
	over the two valid Reference elements as valid or take different
	actions depending on which fails. To accomplish this, SignedInfo
	would reference a Manifest element that contains one or more
	Reference elements (with the same structure as those in SignedInfo).
	Then, reference validation of the Manifest is under application
	control.
	Second, consider an application where many signatures (using
	different keys) are applied to a large number of documents. An
	inefficient solution is to have a separate signature (per key)
	repeatedly applied to a large SignedInfo element (with many
	References); this is wasteful and redundant. A more efficient
	solution is to include many references in a single Manifest that is
	then referenced from multiple Signature elements.
	The example below includes a Reference that signs a Manifest found
	within the Object element.
	[ ] ...
	[m01] <Reference URI="#MyFirstManifest"
	[m02] Type="http://www.w3.org/2000/09/xmldsig#Manifest">
	[m03] <DigestMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
	[m04] <DigestValue>345x3rvEPO0vKtMup4NbeVu8nk=</DigestValue>
	[m05] </Reference>
	[ ] ...
	[m06] <Object>
	[m07] <Manifest Id="MyFirstManifest">
	[m08] <Reference>
	[m09] ...
	[m10] </Reference>
	[m11] <Reference>
	[m12] ...
	[m13] </Reference>
	[m14] </Manifest>
	[m15] </Object>
	3.0 Processing Rules
	The sections below describe the operations to be performed as part of
	signature generation and validation.
	3.1 Core Generation
	The REQUIRED steps include the generation of Reference elements and
	the SignatureValue over SignedInfo.
	3.1.1 Reference Generation
	For each data object being signed:
	1. Apply the Transforms, as determined by the application, to the
	data object.
	2. Calculate the digest value over the resulting data object.
	3. Create a Reference element, including the (optional)
	identification of the data object, any (optional) transform
	elements, the digest algorithm and the DigestValue. (Note, it
	is the canonical form of these references that are signed in
	3.1.2 and validated in 3.2.1 .)
	3.1.2 Signature Generation
	1. Create SignedInfo element with SignatureMethod,
	CanonicalizationMethod and Reference(s).
	2. Canonicalize and then calculate the SignatureValue over
	SignedInfo based on algorithms specified in SignedInfo.
	3. Construct the Signature element that includes SignedInfo,
	Object(s) (if desired, encoding may be different than that
	used for signing), KeyInfo (if required), and SignatureValue.
	Note, if the Signature includes same-document references, [XML] or
	[XML-schema] validation of the document might introduce changes that
	break the signature. Consequently, applications should be careful to
	consistently process the document or refrain from using external
	contributions (e.g., defaults and entities).
	3.2 Core Validation
	The REQUIRED steps of core validation include (1) reference
	validation, the verification of the digest contained in each
	Reference in SignedInfo, and (2) the cryptographic signature
	validation of the signature calculated over SignedInfo.
	Note, there may be valid signatures that some signature applications
	are unable to validate. Reasons for this include failure to implement
	optional parts of this specification, inability or unwillingness to
	execute specified algorithms, or inability or unwillingness to
	dereference specified URIs (some URI schemes may cause undesirable
	side effects), etc.
	Comparison of values in reference and signature validation are over
	the numeric (e.g., integer) or decoded octet sequence of the value.
	Different implementations may produce different encoded digest and
	signature values when processing the same resources because of
	variances in their encoding, such as accidental white space. But if
	one uses numeric or octet comparison (choose one) on both the stated
	and computed values these problems are eliminated.
	3.2.1 Reference Validation
	1. Canonicalize the SignedInfo element based on the
	CanonicalizationMethod in SignedInfo.
	2. For each Reference in SignedInfo:
	2.1 Obtain the data object to be digested. (For example, the
	signature application may dereference the URI and execute
	Transforms provided by the signer in the Reference
	element, or it may obtain the content through other means
	such as a local cache.)
	2.2 Digest the resulting data object using the DigestMethod
	specified in its Reference specification.
	2.3 Compare the generated digest value against DigestValue in
	the SignedInfo Reference; if there is any mismatch,
	validation fails.
	Note, SignedInfo is canonicalized in step 1. The application must
	ensure that the CanonicalizationMethod has no dangerous side affects,
	such as rewriting URIs, (see CanonicalizationMethod (section 4.3))
	and that it Sees What is Signed, which is the canonical form.
	3.2.2 Signature Validation
	1. Obtain the keying information from KeyInfo or from an external
	source.
	2. Obtain the canonical form of the SignatureMethod using the
	CanonicalizationMethod and use the result (and previously
	obtained KeyInfo) to confirm the SignatureValue over the
	SignedInfo element.
	Note, KeyInfo (or some transformed version thereof) may be signed via
	a Reference element. Transformation and validation of this reference
	(3.2.1) is orthogonal to Signature Validation which uses the KeyInfo
	as parsed.
	Additionally, the SignatureMethod URI may have been altered by the
	canonicalization of SignedInfo (e.g., absolutization of relative
	URIs) and it is the canonical form that MUST be used. However, the
	required canonicalization [XML-C14N] of this specification does not
	change URIs.
	4.0 Core Signature Syntax
	The general structure of an XML signature is described in Signature
	Overview (section 2). This section provides detailed syntax of the
	core signature features. Features described in this section are
	mandatory to implement unless otherwise indicated. The syntax is
	defined via DTDs and [XML-Schema] with the following XML preamble,
	declaration, and internal entity.
	Schema Definition:
	<?xml version="1.0" encoding="utf-8"?>
	<!DOCTYPE schema
	PUBLIC "-//W3C//DTD XMLSchema 200102//EN"
	"http://www.w3.org/2001/XMLSchema.dtd"
	[
	<!ATTLIST schema
	xmlns:ds CDATA #FIXED "http://www.w3.org/2000/09/xmldsig#">
	<!ENTITY dsig 'http://www.w3.org/2000/09/xmldsig#'>
	<!ENTITY % p ''>
	<!ENTITY % s ''>
	]>
	<schema xmlns="http://www.w3.org/2001/XMLSchema"
	xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
	targetNamespace="http://www.w3.org/2000/09/xmldsig#"
	version="0.1" elementFormDefault="qualified">
	DTD:
	<!--
	The following entity declarations enable external/flexible content
	in the Signature content model.
	#PCDATA emulates schema:string; when combined with element types
	it emulates schema mixed="true".
	%foo.ANY permits the user to include their own element types from
	other namespaces, for example:
	<!ENTITY % KeyValue.ANY '| ecds:ECDSAKeyValue'>
	...
	<!ELEMENT ecds:ECDSAKeyValue (#PCDATA) >
	-->
	<!ENTITY % Object.ANY ''>
	<!ENTITY % Method.ANY ''>
	<!ENTITY % Transform.ANY ''>
	<!ENTITY % SignatureProperty.ANY ''>
	<!ENTITY % KeyInfo.ANY ''>
	<!ENTITY % KeyValue.ANY ''>
	<!ENTITY % PGPData.ANY ''>
	<!ENTITY % X509Data.ANY ''>
	<!ENTITY % SPKIData.ANY ''>
	4.0.1 The ds:CryptoBinary Simple Type
	This specification defines the ds:CryptoBinary simple type for
	representing arbitrary-length integers (e.g. "bignums") in XML as
	octet strings. The integer value is first converted to a "big endian"
	bitstring. The bitstring is then padded with leading zero bits so
	that the total number of bits == 0 mod 8 (so that there are an
	integral number of octets). If the bitstring contains entire leading
	octets that are zero, these are removed (so the high-order octet is
	always non-zero). This octet string is then base64 [MIME] encoded.
	(The conversion from integer to octet string is equivalent to IEEE
	1363's I2OSP [1363] with minimal length).
	This type is used by "bignum" values such as RSAKeyValue and
	DSAKeyValue. If a value can be of type base64Binary or
	ds:CryptoBinary they are defined as base64Binary. For example, if the
	signature algorithm is RSA or DSA then SignatureValue represents a
	bignum and could be ds:CryptoBinary. However, if HMAC-SHA1 is the
	signature algorithm then SignatureValue could have leading zero
	octets that must be preserved. Thus SignatureValue is generically
	defined as of type base64Binary.
	Schema Definition:
	<simpleType name="CryptoBinary">
	<restriction base="base64Binary">
	</restriction>
	</simpleType>
	4.1 The Signature element
	The Signature element is the root element of an XML Signature.
	Implementation MUST generate laxly schema valid [XML-schema]
	Signature elements as specified by the following schema:
	Schema Definition:
	<element name="Signature" type="ds:SignatureType"/>
	<complexType name="SignatureType">
	<sequence>
	<element ref="ds:SignedInfo"/>
	<element ref="ds:SignatureValue"/>
	<element ref="ds:KeyInfo" minOccurs="0"/>
	<element ref="ds:Object" minOccurs="0" maxOccurs="unbounded"/>
	</sequence>
	<attribute name="Id" type="ID" use="optional"/>
	</complexType>
	DTD:
	<!ELEMENT Signature (SignedInfo, SignatureValue, KeyInfo?,
	Object*) >
	<!ATTLIST Signature
	xmlns CDATA #FIXED 'http://www.w3.org/2000/09/xmldsig#'
	Id ID #IMPLIED >
	4.2 The SignatureValue Element
	The SignatureValue element contains the actual value of the digital
	signature; it is always encoded using base64 [MIME]. While we
	identify two SignatureMethod algorithms, one mandatory and one
	optional to implement, user specified algorithms may be used as well.
	Schema Definition:
	<element name="SignatureValue" type="ds:SignatureValueType"/>
	<complexType name="SignatureValueType">
	<simpleContent>
	<extension base="base64Binary">
	<attribute name="Id" type="ID" use="optional"/>
	</extension>
	</simpleContent>
	</complexType>
	DTD:
	<!ELEMENT SignatureValue (#PCDATA) >
	<!ATTLIST SignatureValue
	Id ID #IMPLIED>
	4.3 The SignedInfo Element
	The structure of SignedInfo includes the canonicalization algorithm,
	a signature algorithm, and one or more references. The SignedInfo
	element may contain an optional ID attribute that will allow it to be
	referenced by other signatures and objects.
	SignedInfo does not include explicit signature or digest properties
	(such as calculation time, cryptographic device serial number, etc.).
	If an application needs to associate properties with the signature or
	digest, it may include such information in a SignatureProperties
	element within an Object element.
	Schema Definition:
	<element name="SignedInfo" type="ds:SignedInfoType"/>
	<complexType name="SignedInfoType">
	<sequence>
	<element ref="ds:CanonicalizationMethod"/>
	<element ref="ds:SignatureMethod"/>
	<element ref="ds:Reference" maxOccurs="unbounded"/>
	</sequence>
	<attribute name="Id" type="ID" use="optional"/>
	</complexType>
	DTD:
	<!ELEMENT SignedInfo (CanonicalizationMethod,
	SignatureMethod, Reference+) >
	<!ATTLIST SignedInfo
	Id ID #IMPLIED
	4.3.1 The CanonicalizationMethod Element
	CanonicalizationMethod is a required element that specifies the
	canonicalization algorithm applied to the SignedInfo element prior to
	performing signature calculations. This element uses the general
	structure for algorithms described in Algorithm Identifiers and
	Implementation Requirements (section 6.1). Implementations MUST
	support the REQUIRED canonicalization algorithms.
	Alternatives to the REQUIRED canonicalization algorithms (section
	6.5), such as Canonical XML with Comments (section 6.5.1) or a
	minimal canonicalization (such as CRLF and charset normalization),
	may be explicitly specified but are NOT REQUIRED. Consequently, their
	use may not interoperate with other applications that do not support
	the specified algorithm (see XML Canonicalization and Syntax
	Constraint Considerations, section 7). Security issues may also arise
	in the treatment of entity processing and comments if non-XML aware
	canonicalization algorithms are not properly constrained (see section
	8.2: Only What is "Seen" Should be Signed).
	The way in which the SignedInfo element is presented to the
	canonicalization method is dependent on that method. The following
	applies to algorithms which process XML as nodes or characters:
	* XML based canonicalization implementations MUST be provided
	with a [XPath] node-set originally formed from the document
	containing the SignedInfo and currently indicating the
	SignedInfo, its descendants, and the attribute and namespace
	nodes of SignedInfo and its descendant elements.
	* Text based canonicalization algorithms (such as CRLF and
	charset normalization) should be provided with the UTF-8 octets
	that represent the well-formed SignedInfo element, from the
	first character to the last character of the XML
	representation, inclusive. This includes the entire text of the
	start and end tags of the SignedInfo element as well as all
	descendant markup and character data (i.e., the text) between
	those tags. Use of text based canonicalization of SignedInfo is
	NOT RECOMMENDED.
	We recommend applications that implement a text-based instead of
	XML-based canonicalization -- such as resource constrained apps --
	generate canonicalized XML as their output serialization so as to
	mitigate interoperability and security concerns. For instance, such
	an implementation SHOULD (at least) generate standalone XML instances
	[XML].
	NOTE: The signature application must exercise great care in accepting
	and executing an arbitrary CanonicalizationMethod. For example, the
	canonicalization method could rewrite the URIs of the References
	being validated. Or, the method could massively transform SignedInfo
	so that validation would always succeed (i.e., converting it to a
	trivial signature with a known key over trivial data). Since
	CanonicalizationMethod is inside SignedInfo, in the resulting
	canonical form it could erase itself from SignedInfo or modify the
	SignedInfo element so that it appears that a different
	canonicalization function was used! Thus a Signature which appears to
	authenticate the desired data with the desired key, DigestMethod, and
	SignatureMethod, can be meaningless if a capricious
	CanonicalizationMethod is used.
	Schema Definition:
	<element name="CanonicalizationMethod"
	type="ds:CanonicalizationMethodType"/>
	<complexType name="CanonicalizationMethodType" mixed="true">
	<sequence>
	<any namespace="##any" minOccurs="0" maxOccurs="unbounded"/>
	<!-- (0,unbounded) elements from (1,1) namespace -->
	</sequence>
	<attribute name="Algorithm" type="anyURI" use="required"/>
	</complexType>
	DTD:
	<!ELEMENT CanonicalizationMethod (#PCDATA %Method.ANY;)* >
	<!ATTLIST CanonicalizationMethod
	Algorithm CDATA #REQUIRED >
	4.3.2 The SignatureMethod Element
	SignatureMethod is a required element that specifies the algorithm
	used for signature generation and validation. This algorithm
	identifies all cryptographic functions involved in the signature
	operation (e.g. hashing, public key algorithms, MACs, padding, etc.).
	This element uses the general structure here for algorithms described
	in section 6.1: Algorithm Identifiers and Implementation
	Requirements. While there is a single identifier, that identifier may
	specify a format containing multiple distinct signature values.
	Schema Definition:
	<element name="SignatureMethod" type="ds:SignatureMethodType"/>
	<complexType name="SignatureMethodType" mixed="true">
	<sequence>
	<element name="HMACOutputLength" minOccurs="0"
	type="ds:HMACOutputLengthType"/>
	<any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
	<!-- (0,unbounded) elements from (1,1) external namespace -->
	</sequence>
	<attribute name="Algorithm" type="anyURI" use="required"/>
	</complexType>
	DTD:
	<!ELEMENT SignatureMethod
	(#PCDATA|HMACOutputLength %Method.ANY;)* >
	<!ATTLIST SignatureMethod
	Algorithm CDATA #REQUIRED >
	4.3.3 The Reference Element
	Reference is an element that may occur one or more times. It
	specifies a digest algorithm and digest value, and optionally an
	identifier of the object being signed, the type of the object, and/or
	a list of transforms to be applied prior to digesting. The
	identification (URI) and transforms describe how the digested content
	(i.e., the input to the digest method) was created. The Type
	attribute facilitates the processing of referenced data. For
	example, while this specification makes no requirements over external
	data, an application may wish to signal that the referent is a
	Manifest. An optional ID attribute permits a Reference to be
	referenced from elsewhere.
	Schema Definition:
	<element name="Reference" type="ds:ReferenceType"/>
	<complexType name="ReferenceType">
	<sequence>
	<element ref="ds:Transforms" minOccurs="0"/>
	<element ref="ds:DigestMethod"/>
	<element ref="ds:DigestValue"/>
	</sequence>
	<attribute name="Id" type="ID" use="optional"/>
	<attribute name="URI" type="anyURI" use="optional"/>
	<attribute name="Type" type="anyURI" use="optional"/>
	</complexType>
	DTD:
	<!ELEMENT Reference (Transforms?, DigestMethod, DigestValue) >
	<!ATTLIST Reference
	Id ID #IMPLIED
	URI CDATA #IMPLIED
	Type CDATA #IMPLIED>
	4.3.3.1 The URI Attribute
	The URI attribute identifies a data object using a URI-Reference, as
	specified by RFC2396 [URI]. The set of allowed characters for URI
	attributes is the same as for XML, namely [Unicode]. However, some
	Unicode characters are disallowed from URI references including all
	non-ASCII characters and the excluded characters listed in RFC2396
	[URI, section 2.4]. However, the number sign (#), percent sign (%),
	and square bracket characters re-allowed in RFC 2732 [URI-Literal]
	are permitted. Disallowed characters must be escaped as follows:
	1. Each disallowed character is converted to [UTF-8] as one or
	more octets.
	2. Any octets corresponding to a disallowed character are escaped
	with the URI escaping mechanism (that is, converted to %HH,
	where HH is the hexadecimal notation of the octet value).
	3. The original character is replaced by the resulting character
	sequence.
	XML signature applications MUST be able to parse URI syntax. We
	RECOMMEND they be able to dereference URIs in the HTTP scheme.
	Dereferencing a URI in the HTTP scheme MUST comply with the Status
	Code Definitions of [HTTP] (e.g., 302, 305 and 307 redirects are
	followed to obtain the entity-body of a 200 status code response).
	Applications should also be cognizant of the fact that protocol
	parameter and state information, (such as HTTP cookies, HTML device
	profiles or content negotiation), may affect the content yielded by
	dereferencing a URI.
	If a resource is identified by more than one URI, the most specific
	should be used (e.g. http://www.w3.org/2000/06/interop-
	pressrelease.html.en instead of http://www.w3.org/2000/06/interop-
	pressrelease). (See the Reference Validation (section 3.2.1) for a
	further information on reference processing.)
	If the URI attribute is omitted altogether, the receiving application
	is expected to know the identity of the object. For example, a
	lightweight data protocol might omit this attribute given the
	identity of the object is part of the application context. This
	attribute may be omitted from at most one Reference in any particular
	SignedInfo, or Manifest.
	The optional Type attribute contains information about the type of
	object being signed. This is represented as a URI. For example:
	Type="http://www.w3.org/2000/09/xmldsig#Object"
	Type="http://www.w3.org/2000/09/xmldsig#Manifest"
	The Type attribute applies to the item being pointed at, not its
	contents. For example, a reference that identifies an Object element
	containing a SignatureProperties element is still of type #Object.
	The type attribute is advisory. No validation of the type information
	is required by this specification.
	4.3.3.2 The Reference Processing Model
	Note: XPath is RECOMMENDED. Signature applications need not conform
	to [XPath] specification in order to conform to this specification.
	However, the XPath data model, definitions (e.g., node-sets) and
	syntax is used within this document in order to describe
	functionality for those that want to process XML-as-XML (instead of
	octets) as part of signature generation. For those that want to use
	these features, a conformant [XPath] implementation is one way to
	implement these features, but it is not required. Such applications
	could use a sufficiently functional replacement to a node-set and
	implement only those XPath expression behaviors REQUIRED by this
	specification. However, for simplicity we generally will use XPath
	terminology without including this qualification on every point.
	Requirements over "XPath node-sets" can include a node-set functional
	equivalent. Requirements over XPath processing can include
	application behaviors that are equivalent to the corresponding XPath
	behavior.
	The data-type of the result of URI dereferencing or subsequent
	Transforms is either an octet stream or an XPath node-set.
	The Transforms specified in this document are defined with respect to
	the input they require. The following is the default signature
	application behavior:
	* If the data object is an octet stream and the next transform
	requires a node-set, the signature application MUST attempt to
	parse the octets yielding the required node-set via [XML]
	well-formed processing.
	* If the data object is a node-set and the next transform
	requires octets, the signature application MUST attempt to
	convert the node-set to an octet stream using Canonical XML
	[XML-C14N].
	Users may specify alternative transforms that override these defaults
	in transitions between transforms that expect different inputs. The
	final octet stream contains the data octets being secured. The digest
	algorithm specified by DigestMethod is then applied to these data
	octets, resulting in the DigestValue.
	Unless the URI-Reference is a 'same-document' reference as defined in
	[URI, Section 4.2], the result of dereferencing the URI-Reference
	MUST be an octet stream. In particular, an XML document identified by
	URI is not parsed by the signature application unless the URI is a
	same-document reference or unless a transform that requires XML
	parsing is applied. (See Transforms (section 4.3.3.1).)
	When a fragment is preceded by an absolute or relative URI in the
	URI-Reference, the meaning of the fragment is defined by the
	resource's MIME type. Even for XML documents, URI dereferencing
	(including the fragment processing) might be done for the signature
	application by a proxy. Therefore, reference validation might fail
	if fragment processing is not performed in a standard way (as defined
	in the following section for same-document references). Consequently,
	we RECOMMEND that the URI attribute not include fragment identifiers
	and that such processing be specified as an additional XPath
	Transform.
	When a fragment is not preceded by a URI in the URI-Reference, XML
	signature applications MUST support the null URI and barename
	XPointer. We RECOMMEND support for the same-document XPointers
	'#xpointer(/)' and canonicalization that preserves comments.
	(Otherwise URI="#foo" will automatically remove comments before the
	canonicalization can even be invoked.) All other support for
	XPointers is OPTIONAL, especially all support for barename and other
	XPointers in external resources since the application may not have
	control over how the fragment is generated (leading to
	interoperability problems and validation failures).
	The following examples demonstrate what the URI attribute identifies
	and how it is dereferenced:
	URI="http://example.com/bar.xml"
	Identifies the octets that represent the external resource file
	extension.
	URI="http://example.com/bar.xml#chapter1"
	Identifies the element with ID attribute value 'chapter1' of the
	external XML resource 'http://example.com/bar.xml', provided as
	an octet stream. Again, for the sake of interoperability, the
	element identified as 'chapter1' should be obtained using an
	XPath transform rather than a URI fragment (barename XPointer
	resolution in external resources is not REQUIRED in this
	specification).
	URI=""
	Identifies the node-set (minus any comment nodes) of the XML
	resource containing the signature
	URI="#chapter1"
	Identifies a node-set containing the element with ID attribute
	value (and its applications) modify this node-set to include the
	element plus all descendents including namespaces and attributes
	-- but not comments.
	4.3.3.3 Same-Document URI-References
	Dereferencing a same-document reference MUST result in an XPath
	node-set suitable for use by Canonical XML [XML-C14N]. Specifically,
	dereferencing a null URI (URI="") MUST result in an XPath node-set
	that includes every non-comment node of the XML document containing
	the URI attribute. In a fragment URI, the characters after the number
	sign ('#') character conform to the XPointer syntax [Xptr]. When
	processing an XPointer, the application MUST behave as if the root
	node of the XML document containing the URI attribute were used to
	initialize the XPointer evaluation context. The application MUST
	behave as if the result of XPointer processing were a node-set
	derived from the resultant location-set as follows:
	1. discard point nodes
	2. replace each range node with all XPath nodes having full or
	partial content within the range
	3. replace the root node with its children (if it is in the
	node-set)
	4. replace any element node E with E plus all descendants of E
	(text, comment, PI, element) and all namespace and attribute
	nodes of E and its descendant elements.
	5. if the URI is not a full XPointer, then delete all comment
	nodes
	The second to last replacement is necessary because XPointer
	typically indicates a subtree of an XML document's parse tree using
	just the element node at the root of the subtree, whereas Canonical
	XML treats a node-set as a set of nodes in which absence of
	descendant nodes results in absence of their representative text from
	the canonical form.
	The last step is performed for null URIs, barename XPointers and
	child sequence XPointers. It's necessary because when [XML-C14N] is
	passed a node-set, it processes the node-set as is: with or without
	comments. Only when it's called with an octet stream does it invoke
	its own XPath expressions (default or without comments). Therefore to
	retain the default behavior of stripping comments when passed a
	node-set, they are removed in the last step if the URI is not a full
	XPointer. To retain comments while selecting an element by an
	identifier ID, use the following full XPointer:
	URI='#xpointer(id('ID'))'. To retain comments while selecting the
	entire document, use the following full XPointer: URI='#xpointer(/)'.
	This XPointer contains a simple XPath expression that includes the
	root node, which the second to last step above replaces with all
	nodes of the parse tree (all descendants, plus all attributes, plus
	all namespaces nodes).
	4.3.3.4 The Transforms Element
	The optional Transforms element contains an ordered list of Transform
	elements; these describe how the signer obtained the data object that
	was digested. The output of each Transform serves as input to the
	next Transform. The input to the first Transform is the result of
	dereferencing the URI attribute of the Reference element. The output
	from the last Transform is the input for the DigestMethod algorithm.
	When transforms are applied the signer is not signing the native
	(original) document but the resulting (transformed) document. (See
	Only What is Signed is Secure (section 8.1).)
	Each Transform consists of an Algorithm attribute and content
	parameters, if any, appropriate for the given algorithm. The
	Algorithm attribute value specifies the name of the algorithm to be
	performed, and the Transform content provides additional data to
	govern the algorithm's processing of the transform input. (See
	Algorithm Identifiers and Implementation Requirements (section 6).)
	As described in The Reference Processing Model (section 4.3.3.2),
	some transforms take an XPath node-set as input, while others require
	an octet stream. If the actual input matches the input needs of the
	transform, then the transform operates on the unaltered input. If the
	transform input requirement differs from the format of the actual
	input, then the input must be converted.
	Some Transforms may require explicit MIME type, charset (IANA
	registered "character set"), or other such information concerning the
	data they are receiving from an earlier Transform or the source data,
	although no Transform algorithm specified in this document needs such
	explicit information. Such data characteristics are provided as
	parameters to the Transform algorithm and should be described in the
	specification for the algorithm.
	Examples of transforms include but are not limited to base64 decoding
	[MIME], canonicalization [XML-C14N], XPath filtering [XPath], and
	XSLT [XSLT]. The generic definition of the Transform element also
	allows application-specific transform algorithms. For example, the
	transform could be a decompression routine given by a Java class
	appearing as a base64 encoded parameter to a Java Transform
	algorithm. However, applications should refrain from using
	application-specific transforms if they wish their signatures to be
	verifiable outside of their application domain. Transform Algorithms
	(section 6.6) defines the list of standard transformations.
	Schema Definition:
	<element name="Transforms" type="ds:TransformsType"/>
	<complexType name="TransformsType">
	<sequence>
	<element ref="ds:Transform" maxOccurs="unbounded"/>
	</sequence>
	</complexType>
	<element name="Transform" type="ds:TransformType"/>
	<complexType name="TransformType" mixed="true">
	<choice minOccurs="0" maxOccurs="unbounded">
	<any namespace="##other" processContents="lax"/>
	<!-- (1,1) elements from (0,unbounded) namespaces -->
	<element name="XPath" type="string"/>
	</choice>
	<attribute name="Algorithm" type="anyURI" use="required"/>
	</complexType>
	DTD:
	<!ELEMENT Transforms (Transform+)>
	<!ELEMENT Transform (#PCDATA|XPath %Transform.ANY;)* >
	<!ATTLIST Transform
	Algorithm CDATA #REQUIRED >
	<!ELEMENT XPath (#PCDATA) >
	4.3.3.5 The DigestMethod Element
	DigestMethod is a required element that identifies the digest
	algorithm to be applied to the signed object. This element uses the
	general structure here for algorithms specified in Algorithm
	Identifiers and Implementation Requirements (section 6.1).
	If the result of the URI dereference and application of Transforms is
	an XPath node-set (or sufficiently functional replacement implemented
	by the application) then it must be converted as described in the
	Reference Processing Model (section 4.3.3.2). If the result of URI
	dereference and application of transforms is an octet stream, then no
	conversion occurs (comments might be present if the Canonical XML
	with Comments was specified in the Transforms). The digest algorithm
	is applied to the data octets of the resulting octet stream.
	Schema Definition:
	<element name="DigestMethod" type="ds:DigestMethodType"/>
	<complexType name="DigestMethodType" mixed="true">
	<sequence>
	<any namespace="##other" processContents="lax"
	minOccurs="0" maxOccurs="unbounded"/>
	</sequence>
	<attribute name="Algorithm" type="anyURI" use="required"/>
	</complexType>
	DTD:
	<!ELEMENT DigestMethod (#PCDATA %Method.ANY;)* >
	<!ATTLIST DigestMethod
	Algorithm CDATA #REQUIRED >
	4.3.3.6 The DigestValue Element
	DigestValue is an element that contains the encoded value of the
	digest. The digest is always encoded using base64 [MIME].
	Schema Definition:
	<element name="DigestValue" type="ds:DigestValueType"/>
	<simpleType name="DigestValueType">
	<restriction base="base64Binary"/>
	</simpleType>
	DTD:
	<!ELEMENT DigestValue (#PCDATA) >
	<!-- base64 encoded digest value -->
	4.4 The KeyInfo Element
	KeyInfo is an optional element that enables the recipient(s) to
	obtain the key needed to validate the signature. KeyInfo may contain
	keys, names, certificates and other public key management
	information, such as in-band key distribution or key agreement data.
	This specification defines a few simple types but applications may
	extend those types or all together replace them with their own key
	identification and exchange semantics using the XML namespace
	facility. [XML-ns] However, questions of trust of such key
	information (e.g., its authenticity or strength) are out of scope of
	this specification and left to the application.
	If KeyInfo is omitted, the recipient is expected to be able to
	identify the key based on application context. Multiple declarations
	within KeyInfo refer to the same key. While applications may define
	and use any mechanism they choose through inclusion of elements from
	a different namespace, compliant versions MUST implement KeyValue
	(section 4.4.2) and SHOULD implement RetrievalMethod (section 4.4.3).
	The schema/DTD specifications of many of KeyInfo's children (e.g.,
	PGPData, SPKIData, X509Data) permit their content to be
	extended/complemented with elements from another namespace. This may
	be done only if it is safe to ignore these extension elements while
	claiming support for the types defined in this specification.
	Otherwise, external elements, including alternative structures to
	those defined by this specification, MUST be a child of KeyInfo. For
	example, should a complete XML-PGP standard be defined, its root
	element MUST be a child of KeyInfo. (Of course, new structures from
	external namespaces can incorporate elements from the &dsig;
	namespace via features of the type definition language. For instance,
	they can create a DTD that mixes their own and dsig qualified
	elements, or a schema that permits, includes, imports, or derives new
	types based on &dsig; elements.)
	The following list summarizes the KeyInfo types that are allocated an
	identifier in the &dsig; namespace; these can be used within the
	RetrievalMethod Type attribute to describe a remote KeyInfo
	structure.
	* http://www.w3.org/2000/09/xmldsig#DSAKeyValue
	* http://www.w3.org/2000/09/xmldsig#RSAKeyValue
	* http://www.w3.org/2000/09/xmldsig#X509Data
	* http://www.w3.org/2000/09/xmldsig#PGPData
	* http://www.w3.org/2000/09/xmldsig#SPKIData
	* http://www.w3.org/2000/09/xmldsig#MgmtData
	In addition to the types above for which we define an XML structure,
	we specify one additional type to indicate a binary (ASN.1 DER) X.509
	Certificate.
	* http://www.w3.org/2000/09/xmldsig#rawX509Certificate
	Schema Definition:
	<element name="KeyInfo" type="ds:KeyInfoType"/>
	<complexType name="KeyInfoType" mixed="true">
	<choice maxOccurs="unbounded">
	<element ref="ds:KeyName"/>
	<element ref="ds:KeyValue"/>
	<element ref="ds:RetrievalMethod"/>
	<element ref="ds:X509Data"/>
	<element ref="ds:PGPData"/>
	<element ref="ds:SPKIData"/>
	<element ref="ds:MgmtData"/>
	<any processContents="lax" namespace="##other"/>
	<!-- (1,1) elements from (0,unbounded) namespaces -->
	</choice>
	<attribute name="Id" type="ID" use="optional"/>
	</complexType>
	DTD:
	<!ELEMENT KeyInfo (#PCDATA|KeyName|KeyValue|RetrievalMethod|
	X509Data|PGPData|SPKIData|MgmtData %KeyInfo.ANY;)* >
	<!ATTLIST KeyInfo
	Id ID #IMPLIED >
	4.4.1 The KeyName Element
	The KeyName element contains a string value (in which white space is
	significant) which may be used by the signer to communicate a key
	identifier to the recipient. Typically, KeyName contains an
	identifier related to the key pair used to sign the message, but it
	may contain other protocol-related information that indirectly
	identifies a key pair. (Common uses of KeyName include simple string
	names for keys, a key index, a distinguished name (DN), an email
	address, etc.)
	Schema Definition:
	<element name="KeyName" type="string"/>
	DTD:
	<!ELEMENT KeyName (#PCDATA) >
	4.4.2 The KeyValue Element
	The KeyValue element contains a single public key that may be useful
	in validating the signature. Structured formats for defining DSA
	(REQUIRED) and RSA (RECOMMENDED) public keys are defined in Signature
	Algorithms (section 6.4). The KeyValue element may include externally
	defined public keys values represented as PCDATA or element types
	from an external namespace.
	Schema Definition:
	<element name="KeyValue" type="ds:KeyValueType"/>
	<complexType name="KeyValueType" mixed="true">
	<choice>
	<element ref="ds:DSAKeyValue"/>
	<element ref="ds:RSAKeyValue"/>
	<any namespace="##other" processContents="lax"/>
	</choice>
	</complexType>
	DTD:
	<!ELEMENT KeyValue (#PCDATA|DSAKeyValue|RSAKeyValue
	%KeyValue.ANY;)* >
	4.4.2.1 The DSAKeyValue Element
	Identifier
	Type="http//www.w3.org/2000/09/xmldsig#DSAKeyValue" (this can be
	used within a RetrievalMethod or Reference element to identify
	the referent's type)
	DSA keys and the DSA signature algorithm are specified in [DSS]. DSA
	public key values can have the following fields:
	P
	a prime modulus meeting the [DSS] requirements
	Q
	an integer in the range 2**159 < Q < 2**160 which is a prime
	divisor of P-1
	G
	an integer with certain properties with respect to P and Q
	Y
	G**X mod P (where X is part of the private key and not made
	public)
	J
	(P - 1) / Q
	seed
	a DSA prime generation seed
	pgenCounter
	a DSA prime generation counter
	Parameter J is avilable for inclusion solely for efficiency as it is
	calculatable from P and Q. Parameters seed and pgenCounter are used
	in the DSA prime number generation algorithm specified in [DSS]. As
	such, they are optional but must either both be present or both be
	absent. This prime generation algorithm is designed to provide
	assurance that a weak prime is not being used and it yields a P and Q
	value. Parameters P, Q, and G can be public and common to a group of
	users. They might be known from application context. As such, they
	are optional but P and Q must either both appear or both be absent.
	If all of P, Q, seed, and pgenCounter are present, implementations
	are not required to check if they are consistent and are free to use
	either P and Q or seed and pgenCounter. All parameters are encoded as
	base64 [MIME] values.
	Arbitrary-length integers (e.g. "bignums" such as RSA moduli) are
	represented in XML as octet strings as defined by the ds:CryptoBinary
	type.
	Schema Definition:
	<element name="DSAKeyValue" type="ds:DSAKeyValueType"/>
	<complexType name="DSAKeyValueType">
	<sequence>
	<sequence minOccurs="0">
	<element name="P" type="ds:CryptoBinary"/>
	<element name="Q" type="ds:CryptoBinary"/>
	</sequence>
	<element name="G" type="ds:CryptoBinary" minOccurs="0"/>
	<element name="Y" type="ds:CryptoBinary"/>
	<element name="J" type="ds:CryptoBinary" minOccurs="0"/>
	<sequence minOccurs="0">
	<element name="Seed" type="ds:CryptoBinary"/>
	<element name="PgenCounter" type="ds:CryptoBinary"/>
	</sequence>
	</sequence>
	</complexType>
	DTD Definition:
	<!ELEMENT DSAKeyValue ((P, Q)?, G?, Y, J?, (Seed, PgenCounter)?) >
	<!ELEMENT P (#PCDATA) >
	<!ELEMENT Q (#PCDATA) >
	<!ELEMENT G (#PCDATA) >
	<!ELEMENT Y (#PCDATA) >
	<!ELEMENT J (#PCDATA) >
	<!ELEMENT Seed (#PCDATA) >
	<!ELEMENT PgenCounter (#PCDATA) >
	4.4.2.2 The RSAKeyValue Element
	Identifier
	Type="http//www.w3.org/2000/09/xmldsig#RSAKeyValue" (this can be
	used within a RetrievalMethod or Reference element to identify
	the referent's type)
	RSA key values have two fields: Modulus and Exponent.
	<RSAKeyValue>
	<Modulus>
	xA7SEU+e0yQH5rm9kbCDN9o3aPIo7HbP7tX6WOocLZAtNfyxSZDU16ksL6W
	jubafOqNEpcwR3RdFsT7bCqnXPBe5ELh5u4VEy19MzxkXRgrMvavzyBpVRg
	BUwUlV5foK5hhmbktQhyNdy/6LpQRhDUDsTvK+g9Ucj47es9AQJ3U=
	</Modulus>
	<Exponent>AQAB</Exponent>
	</RSAKeyValue>
	Arbitrary-length integers (e.g. "bignums" such as RSA moduli) are
	represented in XML as octet strings as defined by the ds:CryptoBinary
	type.
	Schema Definition:
	<element name="RSAKeyValue" type="ds:RSAKeyValueType"/>
	<complexType name="RSAKeyValueType">
	<sequence>
	<element name="Modulus" type="ds:CryptoBinary"/>
	<element name="Exponent" type="ds:CryptoBinary"/>
	</sequence>
	</complexType>
	DTD Definition:
	<!ELEMENT RSAKeyValue (Modulus, Exponent) >
	<!ELEMENT Modulus (#PCDATA) >
	<!ELEMENT Exponent (#PCDATA) >
	4.4.3 The RetrievalMethod Element
	A RetrievalMethod element within KeyInfo is used to convey a
	reference to KeyInfo information that is stored at another location.
	For example, several signatures in a document might use a key
	verified by an X.509v3 certificate chain appearing once in the
	document or remotely outside the document; each signature's KeyInfo
	can reference this chain using a single RetrievalMethod element
	instead of including the entire chain with a sequence of
	X509Certificate elements.
	RetrievalMethod uses the same syntax and dereferencing behavior as
	Reference's URI (section 4.3.3.1) and The Reference Processing Model
	(section 4.3.3.2) except that there is no DigestMethod or DigestValue
	child elements and presence of the URI is mandatory.
	Type is an optional identifier for the type of data to be retrieved.
	The result of dereferencing a RetrievalMethod Reference for all
	KeyInfo types defined by this specification (section 4.4) with a
	corresponding XML structure is an XML element or document with that
	element as the root. The rawX509Certificate KeyInfo (for which there
	is no XML structure) returns a binary X509 certificate.
	Schema Definition
	<element name="RetrievalMethod" type="ds:RetrievalMethodType"/>
	<complexType name="RetrievalMethodType">
	<sequence>
	<element ref="ds:Transforms" minOccurs="0"/>
	</sequence>
	<attribute name="URI" type="anyURI"/>
	<attribute name="Type" type="anyURI" use="optional"/>
	</complexType>
	DTD
	<!ELEMENT RetrievalMethod (Transforms?) >
	<!ATTLIST RetrievalMethod
	URI CDATA #REQUIRED
	Type CDATA #IMPLIED >
	4.4.4 The X509Data Element
	Identifier
	Type="http://www.w3.org/2000/09/xmldsig#X509Data " (this can be
	used within a RetrievalMethod or Reference element to identify
	the referent's type)
	An X509Data element within KeyInfo contains one or more identifiers
	of keys or X509 certificates (or certificates' identifiers or a
	revocation list). The content of X509Data is:
	1. At least one element, from the following set of element types;
	any of these may appear together or more than once iff (if and
	only if) each instance describes or is related to the same
	certificate:
	2.
	o The X509IssuerSerial element, which contains an X.509
	issuer distinguished name/serial number pair that SHOULD
	be compliant with RFC2253 [LDAP-DN],
	o The X509SubjectName element, which contains an X.509
	subject distinguished name that SHOULD be compliant with
	RFC2253 [LDAP-DN],
	o The X509SKI element, which contains the base64 encoded
	plain (i.e. non-DER-encoded) value of a X509 V.3
	SubjectKeyIdentifier extension.
	o The X509Certificate element, which contains a base64-
	encoded [X509v3] certificate, and
	o Elements from an external namespace which
	accompanies/complements any of the elements above.
	o The X509CRL element, which contains a base64-encoded
	certificate revocation list (CRL) [X509v3].
	Any X509IssuerSerial, X509SKI, and X509SubjectName elements that
	appear MUST refer to the certificate or certificates containing the
	validation key. All such elements that refer to a particular
	individual certificate MUST be grouped inside a single X509Data
	element and if the certificate to which they refer appears, it MUST
	also be in that X509Data element.
	Any X509IssuerSerial, X509SKI, and X509SubjectName elements that
	relate to the same key but different certificates MUST be grouped
	within a single KeyInfo but MAY occur in multiple X509Data elements.
	All certificates appearing in an X509Data element MUST relate to the
	validation key by either containing it or being part of a
	certification chain that terminates in a certificate containing the
	validation key.
	No ordering is implied by the above constraints. The comments in the
	following instance demonstrate these constraints:
	<KeyInfo>
	<X509Data> <!-- two pointers to certificate-A -->
	<X509IssuerSerial>
	<X509IssuerName>CN=TAMURA Kent, OU=TRL, O=IBM,
	L=Yamato-shi, ST=Kanagawa, C=JP</X509IssuerName>
	<X509SerialNumber>12345678</X509SerialNumber>
	</X509IssuerSerial>
	<X509SKI>31d97bd7</X509SKI>
	</X509Data>
	<X509Data><!-- single pointer to certificate-B -->
	<X509SubjectName>Subject of Certificate B</X509SubjectName>
	</X509Data>
	<X509Data> <!-- certificate chain -->
	<!--Signer cert, issuer CN=arbolCA,OU=FVT,O=IBM,C=US, serial 4-->
	<X509Certificate>MIICXTCCA..</X509Certificate>
	<!-- Intermediate cert subject CN=arbolCA,OU=FVT,O=IBM,C=US
	issuer CN=tootiseCA,OU=FVT,O=Bridgepoint,C=US -->
	<X509Certificate>MIICPzCCA...</X509Certificate>
	<!-- Root cert subject CN=tootiseCA,OU=FVT,O=Bridgepoint,C=US -->
	<X509Certificate>MIICSTCCA...</X509Certificate>
	</X509Data>
	</KeyInfo>
	Note, there is no direct provision for a PKCS#7 encoded "bag" of
	certificates or CRLs. However, a set of certificates and CRLs can
	occur within an X509Data element and multiple X509Data elements can
	occur in a KeyInfo. Whenever multiple certificates occur in an
	X509Data element, at least one such certificate must contain the
	public key which verifies the signature.
	Also, strings in DNames (X509IssuerSerial,X509SubjectName, and
	KeyNameif approriate) should be encoded as follows:
	* Consider the string as consisting of Unicode characters.
	* Escape occurrences of the following special characters by
	prefixing it with the "\" character: a "#" character occurring
	at the beginning of the string or one of the characters ",",
	"+", """, "\", "<", ">" or ";"
	* Escape all occurrences of ASCII control characters (Unicode
	range \x00 - \x 1f) by replacing them with "\" followed by a
	two digit hex number showing its Unicode number.
	* Escape any trailing white space by replacing "\ " with "\20".
	* Since a XML document logically consists of characters, not
	octets, the resulting Unicode string is finally encoded
	according to the character encoding used for producing the
	physical representation of the XML document.
	Schema Definition
	<element name="X509Data" type="ds:X509DataType"/>
	<complexType name="X509DataType">
	<sequence maxOccurs="unbounded">
	<choice>
	<element name="X509IssuerSerial"
	type="ds:X509IssuerSerialType"/>
	<element name="X509SKI" type="base64Binary"/>
	<element name="X509SubjectName" type="string"/>
	<element name="X509Certificate" type="base64Binary"/>
	<element name="X509CRL" type="base64Binary"/>
	<any namespace="##other" processContents="lax"/>
	</choice>
	</sequence>
	</complexType>
	<complexType name="X509IssuerSerialType">
	<sequence>
	<element name="X509IssuerName" type="string"/>
	<element name="X509SerialNumber" type="integer"/>
	</sequence>
	</complexType>
	DTD
	<!ELEMENT X509Data ((X509IssuerSerial | X509SKI | X509SubjectName
	| X509Certificate | X509CRL)+ %X509.ANY;)>
	<!ELEMENT X509IssuerSerial (X509IssuerName, X509SerialNumber) >
	<!ELEMENT X509IssuerName (#PCDATA) >
	<!ELEMENT X509SubjectName (#PCDATA) >
	<!ELEMENT X509SerialNumber (#PCDATA) >
	<!ELEMENT X509SKI (#PCDATA) >
	<!ELEMENT X509Certificate (#PCDATA) >
	<!ELEMENT X509CRL (#PCDATA) >
	<!-- Note, this DTD and schema permit X509Data to be empty;
	this is precluded by the text in KeyInfo Element (section
	4.4) which states that at least one element from the dsig
	namespace should be present in the PGP, SPKI, and X509
	structures. This is easily expressed for the other key
	types, but not for X509Data because of its rich structure.
	-->
	4.4.5 The PGPData Element
	Identifier
	Type="http://www.w3.org/2000/09/xmldsig#PGPData " (this can be
	used within a RetrievalMethod or Reference element to identify
	the referent's type)
	The PGPData element within KeyInfo is used to convey information
	related to PGP public key pairs and signatures on such keys. The
	PGPKeyID's value is a base64Binary sequence containing a standard PGP
	public key identifier as defined in [PGP, section 11.2]. The
	PGPKeyPacket contains a base64-encoded Key Material Packet as defined
	in [PGP, section 5.5]. These children element types can be
	complemented/extended by siblings from an external namespace within
	PGPData, or PGPData can be replaced all together with an alternative
	PGP XML structure as a child of KeyInfo. PGPData must contain one
	PGPKeyID and/or one PGPKeyPacket and 0 or more elements from an
	external namespace.
	Schema Definition:
	<element name="PGPData" type="ds:PGPDataType"/>
	<complexType name="PGPDataType">
	<choice>
	<sequence>
	<element name="PGPKeyID" type="base64Binary"/>
	<element name="PGPKeyPacket" type="base64Binary"
	minOccurs="0"/>
	<any namespace="##other" processContents="lax" minOccurs="0"
	maxOccurs="unbounded"/>
	</sequence>
	<sequence>
	<element name="PGPKeyPacket" type="base64Binary"/>
	<any namespace="##other" processContents="lax" minOccurs="0"
	maxOccurs="unbounded"/>
	</sequence>
	</choice>
	</complexType>
	DTD:
	<!ELEMENT PGPData ((PGPKeyID, PGPKeyPacket?) | (PGPKeyPacket)
	%PGPData.ANY;) >
	<!ELEMENT PGPKeyPacket (#PCDATA) >
	<!ELEMENT PGPKeyID (#PCDATA) >
	4.4.6 The SPKIData Element
	Identifier
	Type="http://www.w3.org/2000/09/xmldsig#SPKIData " (this can be
	used within a RetrievalMethod or Reference element to identify
	the referent's type)
	The SPKIData element within KeyInfo is used to convey information
	related to SPKI public key pairs, certificates and other SPKI data.
	SPKISexp is the base64 encoding of a SPKI canonical S-expression.
	SPKIData must have at least one SPKISexp; SPKISexp can be
	complemented/extended by siblings from an external namespace within
	SPKIData, or SPKIData can be entirely replaced with an alternative
	SPKI XML structure as a child of KeyInfo.
	Schema Definition:
	<element name="SPKIData" type="ds:SPKIDataType"/>
	<complexType name="SPKIDataType">
	<sequence maxOccurs="unbounded">
	<element name="SPKISexp" type="base64Binary"/>
	<any namespace="##other" processContents="lax" minOccurs="0"/>
	</sequence>
	</complexType>
	DTD:
	<!ELEMENT SPKIData (SPKISexp %SPKIData.ANY;) >
	<!ELEMENT SPKISexp (#PCDATA) >
	4.4.7 The MgmtData Element
	Identifier
	Type="http://www.w3.org/2000/09/xmldsig#MgmtData " (this can be
	used within a RetrievalMethod or Reference element to identify
	the referent's type)
	The MgmtData element within KeyInfo is a string value used to convey
	in-band key distribution or agreement data. For example, DH key
	exchange, RSA key encryption, etc. Use of this element is NOT
	RECOMMENDED. It provides a syntactic hook where in-band key
	distribution or agreement data can be placed. However, superior
	interoperable child elements of KeyInfo for the transmission of
	encrypted keys and for key agreement are being specified by the W3C
	XML Encryption Working Group and they should be used instead of
	MgmtData.
	Schema Definition:
	<element name="MgmtData" type="string"/>
	DTD:
	<!ELEMENT MgmtData (#PCDATA)>
	4.5 The Object Element
	Identifier
	Type="http://www.w3.org/2000/09/xmldsig#Object" (this can be used
	within a Reference element to identify the referent's type)
	Object is an optional element that may occur one or more times. When
	present, this element may contain any data. The Object element may
	include optional MIME type, ID, and encoding attributes.
	The Object's Encoding attributed may be used to provide a URI that
	identifies the method by which the object is encoded (e.g., a binary
	file).
	The MimeType attribute is an optional attribute which describes the
	data within the Object (independent of its encoding). This is a
	string with values defined by [MIME]. For example, if the Object
	contains base64 encoded PNG, the Encoding may be specified as
	'base64' and the MimeType as MimeType information is required by this
	specification. Applications which require normative type and encoding
	information for signature validation should specify Transforms with
	well defined resulting types and/or encodings.
	The Object's Id is commonly referenced from a Reference in
	SignedInfo, or Manifest. This element is typically used for
	enveloping signatures where the object being signed is to be included
	in the signature element. The digest is calculated over the entire
	Object element including start and end tags.
	Note, if the application wishes to exclude the <Object> tags from the
	digest calculation the Reference must identify the actual data object
	(easy for XML documents) or a transform must be used to remove the
	Object tags (likely where the data object is non-XML). Exclusion of
	the object tags may be desired for cases where one wants the
	signature to remain valid if the data object is moved from inside a
	signature to outside the signature (or vice versa), or where the
	content of the Object is an encoding of an original binary document
	and it is desired to extract and decode so as to sign the original
	bitwise representation.
	Schema Definition:
	<element name="Object" type="ds:ObjectType"/>
	<complexType name="ObjectType" mixed="true">
	<sequence minOccurs="0" maxOccurs="unbounded">
	<any namespace="##any" processContents="lax"/>
	</sequence>
	<attribute name="Id" type="ID" use="optional"/>
	<attribute name="MimeType" type="string" use="optional"/>
	<attribute name="Encoding" type="anyURI" use="optional"/>
	</complexType>
	DTD:
	<!ELEMENT Object (#PCDATA|Signature|SignatureProperties|Manifest
	%Object.ANY;)* >
	<!ATTLIST Object
	Id ID #IMPLIED
	MimeType CDATA #IMPLIED
	Encoding CDATA #IMPLIED >
	5.0 Additional Signature Syntax
	This section describes the optional to implement Manifest and
	SignatureProperties elements and describes the handling of XML
	processing instructions and comments. With respect to the elements
	Manifest and SignatureProperties this section specifies syntax and
	little behavior -- it is left to the application. These elements can
	appear anywhere the parent's content model permits; the Signature
	content model only permits them within Object.
	5.1 The Manifest Element
	Identifier
	Type="http://www.w3.org/2000/09/xmldsig#Manifest" (this can be
	used within a Reference element to identify the referent's type)
	The Manifest element provides a list of References. The difference
	from the list in SignedInfo is that it is application defined which,
	if any, of the digests are actually checked against the objects
	referenced and what to do if the object is inaccessible or the digest
	compare fails. If a Manifest is pointed to from SignedInfo, the
	digest over the Manifest itself will be checked by the core signature
	validation behavior. The digests within such a Manifest are checked
	at the application's discretion. If a Manifest is referenced from
	another Manifest, even the overall digest of this two level deep
	Manifest might not be checked.
	Schema Definition:
	<element name="Manifest" type="ds:ManifestType"/>
	<complexType name="ManifestType">
	<sequence>
	<element ref="ds:Reference" maxOccurs="unbounded"/>
	</sequence>
	<attribute name="Id" type="ID" use="optional"/>
	</complexType>
	DTD:
	<!ELEMENT Manifest (Reference+) >
	<!ATTLIST Manifest
	Id ID #IMPLIED >
	5.2 The SignatureProperties Element
	Identifier
	Type="http://www.w3.org/2000/09/xmldsig#SignatureProperties"
	(this can be used within a Reference element to identify the
	referent's type)
	Additional information items concerning the generation of the
	signature(s) can be placed in a SignatureProperty element (i.e.,
	date/time stamp or the serial number of cryptographic hardware used
	in signature generation).
	Schema Definition:
	<element name="SignatureProperties"
	type="ds:SignaturePropertiesType"/>
	<complexType name="SignaturePropertiesType">
	<sequence>
	<element ref="ds:SignatureProperty" maxOccurs="unbounded"/>
	</sequence>
	<attribute name="Id" type="ID" use="optional"/>
	</complexType>
	<element name="SignatureProperty"
	type="ds:SignaturePropertyType"/>
	<complexType name="SignaturePropertyType" mixed="true">
	<choice maxOccurs="unbounded">
	<any namespace="##other" processContents="lax"/>
	<!-- (1,1) elements from (1,unbounded) namespaces -->
	</choice>
	<attribute name="Target" type="anyURI" use="required"/>
	<attribute name="Id" type="ID" use="optional"/>
	</complexType>
	DTD:
	<!ELEMENT SignatureProperties (SignatureProperty+) >
	<!ATTLIST SignatureProperties
	Id ID #IMPLIED >
	<!ELEMENT SignatureProperty (#PCDATA %SignatureProperty.ANY;)* >
	<!ATTLIST SignatureProperty
	Target CDATA #REQUIRED
	Id ID #IMPLIED >
	5.3 Processing Instructions in Signature Elements
	No XML processing instructions (PIs) are used by this specification.
	Note that PIs placed inside SignedInfo by an application will be
	signed unless the CanonicalizationMethod algorithm discards them.
	(This is true for any signed XML content.) All of the
	CanonicalizationMethods identified within this specification retain
	PIs. When a PI is part of content that is signed (e.g., within
	SignedInfo or referenced XML documents) any change to the PI will
	obviously result in a signature failure.
	5.4 Comments in Signature Elements
	XML comments are not used by this specification.
	Note that unless CanonicalizationMethod removes comments within
	SignedInfo or any other referenced XML (which [XML-C14N] does), they
	will be signed. Consequently, if they are retained, a change to the
	comment will cause a signature failure. Similarly, the XML signature
	over any XML data will be sensitive to comment changes unless a
	comment-ignoring canonicalization/transform method, such as the
	Canonical XML [XML-C14N], is specified.
	6.0 Algorithms
	This section identifies algorithms used with the XML digital
	signature specification. Entries contain the identifier to be used in
	Signature elements, a reference to the formal specification, and
	definitions, where applicable, for the representation of keys and the
	results of cryptographic operations.
	6.1 Algorithm Identifiers and Implementation Requirements
	Algorithms are identified by URIs that appear as an attribute to the
	element that identifies the algorithms' role (DigestMethod,
	Transform, SignatureMethod, or CanonicalizationMethod). All
	algorithms used herein take parameters but in many cases the
	parameters are implicit. For example, a SignatureMethod is implicitly
	given two parameters: the keying info and the output of
	CanonicalizationMethod. Explicit additional parameters to an
	algorithm appear as content elements within the algorithm role
	element. Such parameter elements have a descriptive element name,
	which is frequently algorithm specific, and MUST be in the XML
	Signature namespace or an algorithm specific namespace.
	This specification defines a set of algorithms, their URIs, and
	requirements for implementation. Requirements are specified over
	implementation, not over requirements for signature use. Furthermore,
	the mechanism is extensible; alternative algorithms may be used by
	signature applications.
	Digest
	1. Required SHA1
	http://www.w3.org/2000/09/xmldsig#sha1
	Encoding
	1. Required base64
	http://www.w3.org/2000/09/xmldsig#base64
	MAC
	1. Required HMAC-SHA1
	http://www.w3.org/2000/09/xmldsig#hmac-sha1
	Signature
	1. Required DSAwithSHA1 (DSS)
	http://www.w3.org/2000/09/xmldsig#dsa-sha1
	2. Recommended RSAwithSHA1
	http://www.w3.org/2000/09/xmldsig#rsa-sha1
	Canonicalization
	1. Required Canonical XML (omits comments)
	http://www.w3.org/TR/2001/REC-xml-c14n-20010315
	2. Recommended Canonical XML with Comments
	http://www.w3.org/TR/2001/REC-xml-c14n-20010315#WithComments
	Transform
	1. Optional XSLT
	http://www.w3.org/TR/1999/REC-xslt-19991116
	2. Recommended XPath
	http://www.w3.org/TR/1999/REC-xpath-19991116
	3. Required Enveloped Signature*
	http://www.w3.org/2000/09/xmldsig#enveloped-signature
	* The Enveloped Signature transform removes the Signature element
	from the calculation of the signature when the signature is within
	the content that it is being signed. This MAY be implemented via the
	RECOMMENDED XPath specification specified in 6.6.4: Enveloped
	Signature Transform; it MUST have the same effect as that specified
	by the XPath Transform.
	6.2 Message Digests
	Only one digest algorithm is defined herein. However, it is expected
	that one or more additional strong digest algorithms will be
	developed in connection with the US Advanced Encryption Standard
	effort. Use of MD5 [MD5] is NOT RECOMMENDED because recent advances
	in cryptanalysis have cast doubt on its strength.
	6.2.1 SHA-1
	Identifier:
	http://www.w3.org/2000/09/xmldsig#sha1
	The SHA-1 algorithm [SHA-1] takes no explicit parameters. An example
	of an SHA-1 DigestAlg element is:
	<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
	A SHA-1 digest is a 160-bit string. The content of the DigestValue
	element shall be the base64 encoding of this bit string viewed as a
	20-octet octet stream. For example, the DigestValue element for the
	message digest:
	A9993E36 4706816A BA3E2571 7850C26C 9CD0D89D
	from Appendix A of the SHA-1 standard would be:
	<DigestValue>qZk+NkcGgWq6PiVxeFDCbJzQ2J0=</DigestValue>
	6.3 Message Authentication Codes
	MAC algorithms take two implicit parameters, their keying material
	determined from KeyInfo and the octet stream output by
	CanonicalizationMethod. MACs and signature algorithms are
	syntactically identical but a MAC implies a shared secret key.
	6.3.1 HMAC
	Identifier:
	http://www.w3.org/2000/09/xmldsig#hmac-sha1
	The HMAC algorithm (RFC2104 [HMAC]) takes the truncation length in
	bits as a parameter; if the parameter is not specified then all the
	bits of the hash are output. An example of an HMAC SignatureMethod
	element:
	<SignatureMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1">
	<HMACOutputLength>128</HMACOutputLength>
	</SignatureMethod>
	The output of the HMAC algorithm is ultimately the output (possibly
	truncated) of the chosen digest algorithm. This value shall be base64
	encoded in the same straightforward fashion as the output of the
	digest algorithms. Example: the SignatureValue element for the HMAC-
	SHA1 digest
	9294727A 3638BB1C 13F48EF8 158BFC9D
	from the test vectors in [HMAC] would be
	<SignatureValue>kpRyejY4uxwT9I74FYv8nQ==</SignatureValue>
	Schema Definition:
	<simpleType name="HMACOutputLengthType">
	<restriction base="integer"/>
	</simpleType>
	DTD:
	<!ELEMENT HMACOutputLength (#PCDATA)>
	6.4 Signature Algorithms
	Signature algorithms take two implicit parameters, their keying
	material determined from KeyInfo and the octet stream output by
	CanonicalizationMethod. Signature and MAC algorithms are
	syntactically identical but a signature implies public key
	cryptography.
	6.4.1 DSA
	Identifier:
	http://www.w3.org/2000/09/xmldsig#dsa-sha1
	The DSA algorithm [DSS] takes no explicit parameters. An example of a
	DSA SignatureMethod element is:
	<SignatureMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/>
	The output of the DSA algorithm consists of a pair of integers
	usually referred by the pair (r, s). The signature value consists of
	the base64 encoding of the concatenation of two octet-streams that
	respectively result from the octet-encoding of the values r and s in
	that order. Integer to octet-stream conversion must be done according
	to the I2OSP operation defined in the RFC 2437 [PKCS1] specification
	with a l parameter equal to 20. For example, the SignatureValue
	element for a DSA signature (r, s) with values specified in
	hexadecimal:
	r = 8BAC1AB6 6410435C B7181F95 B16AB97C 92B341C0
	s = 41E2345F 1F56DF24 58F426D1 55B4BA2D B6DCD8C8
	from the example in Appendix 5 of the DSS standard would be
	<SignatureValue>
	i6watmQQQ1y3GB+VsWq5fJKzQcBB4jRfH1bfJFj0JtFVtLotttzYyA==
	</SignatureValue>
	6.4.2 PKCS1 (RSA-SHA1)
	Identifier:
	http://www.w3.org/2000/09/xmldsig#rsa-sha1
	The expression "RSA algorithm" as used in this draft refers to the
	RSASSA-PKCS1-v1_5 algorithm described in RFC 2437 [PKCS1]. The RSA
	algorithm takes no explicit parameters. An example of an RSA
	SignatureMethod element is:
	<SignatureMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
	The SignatureValue content for an RSA signature is the base64 [MIME]
	encoding of the octet string computed as per RFC 2437 [PKCS1, section
	8.1.1: Signature generation for the RSASSA-PKCS1-v1_5 signature
	scheme]. As specified in the EMSA-PKCS1-V1_5-ENCODE function RFC 2437
	[PKCS1, section 9.2.1], the value input to the signature function
	MUST contain a pre-pended algorithm object identifier for the hash
	function, but the availability of an ASN.1 parser and recognition of
	OIDs is not required of a signature verifier. The PKCS#1 v1.5
	representation appears as:
	CRYPT (PAD (ASN.1 (OID, DIGEST (data))))
	Note that the padded ASN.1 will be of the following form:
	01 | FF* | 00 | prefix | hash
	where "|" is concatenation, "01", "FF", and "00" are fixed octets of
	the corresponding hexadecimal value, "hash" is the SHA1 digest of the
	data, and "prefix" is the ASN.1 BER SHA1 algorithm designator prefix
	required in PKCS1 [RFC 2437], that is,
	hex 30 21 30 09 06 05 2B 0E 03 02 1A 05 00 04 14
	This prefix is included to make it easier to use standard
	cryptographic libraries. The FF octet MUST be repeated the maximum
	number of times such that the value of the quantity being CRYPTed is
	one octet shorter than the RSA modulus.
	The resulting base64 [MIME] string is the value of the child text
	node of the SignatureValue element, e.g.
	<SignatureValue>
	IWijxQjUrcXBYoCei4QxjWo9Kg8D3p9tlWoT4t0/gyTE96639
	In0FZFY2/rvP+/bMJ01EArmKZsR5VW3rwoPxw=
	6.5 Canonicalization Algorithms
	If canonicalization is performed over octets, the canonicalization
	algorithms take two implicit parameters: the content and its charset.
	The charset is derived according to the rules of the transport
	protocols and media types (e.g, RFC2376 [XML-MT] defines the media
	types for XML). This information is necessary to correctly sign and
	verify documents and often requires careful server side
	configuration.
	Various canonicalization algorithms require conversion to [UTF-8].The
	two algorithms below understand at least [UTF-8] and [UTF-16] as
	input encodings. We RECOMMEND that externally specified algorithms do
	the same. Knowledge of other encodings is OPTIONAL.
	Various canonicalization algorithms transcode from a non-Unicode
	encoding to Unicode. The two algorithms below perform text
	normalization during transcoding [NFC, NFC-Corrigendum]. We RECOMMEND
	that externally specified canonicalization algorithms do the same.
	(Note, there can be ambiguities in converting existing charsets to
	Unicode, for an example see the XML Japanese Profile [XML-Japanese]
	Note.)
	6.5.1 Canonical XML
	Identifier for REQUIRED Canonical XML (omits comments):
	http://www.w3.org/TR/2001/REC-xml-c14n-20010315
	Identifier for Canonical XML with Comments:
	http://www.w3.org/TR/2001/REC-xml-c14n-20010315#WithComments
	An example of an XML canonicalization element is:
	<CanonicalizationMethod
	Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
	The normative specification of Canonical XML is [XML-C14N]. The
	algorithm is capable of taking as input either an octet stream or an
	XPath node-set (or sufficiently functional alternative). The
	algorithm produces an octet stream as output. Canonical XML is easily
	parameterized (via an additional URI) to omit or retain comments.
	6.6 Transform Algorithms
	A Transform algorithm has a single implicit parameter: an octet
	stream from the Reference or the output of an earlier Transform.
	Application developers are strongly encouraged to support all
	transforms listed in this section as RECOMMENDED unless the
	application environment has resource constraints that would make such
	support impractical. Compliance with this recommendation will
	maximize application interoperability and libraries should be
	available to enable support of these transforms in applications
	without extensive development.
	6.6.1 Canonicalization
	Any canonicalization algorithm that can be used for
	CanonicalizationMethod (such as those in Canonicalization Algorithms
	(section 6.5)) can be used as a Transform.
	6.6.2 Base64
	Identifiers:
	http://www.w3.org/2000/09/xmldsig#base64
	The normative specification for base64 decoding transforms is [MIME].
	The base64 Transform element has no content. The input is decoded by
	the algorithms. This transform is useful if an application needs to
	sign the raw data associated with the encoded content of an element.
	This transform requires an octet stream for input. If an XPath node-
	set (or sufficiently functional alternative) is given as input, then
	it is converted to an octet stream by performing operations logically
	equivalent to 1) applying an XPath transform with expression
	self::text(), then 2) taking the string-value of the node-set. Thus,
	if an XML element is identified by a barename XPointer in the
	Reference URI, and its content consists solely of base64 encoded
	character data, then this transform automatically strips away the
	start and end tags of the identified element and any of its
	descendant elements as well as any descendant comments and processing
	instructions. The output of this transform is an octet stream.
	6.6.3 XPath Filtering
	Identifier:
	http://www.w3.org/TR/1999/REC-xpath-19991116
	The normative specification for XPath expression evaluation is
	[XPath]. The XPath expression to be evaluated appears as the
	character content of a transform parameter child element named XPath.
	The input required by this transform is an XPath node-set. Note that
	if the actual input is an XPath node-set resulting from a null URI or
	barename XPointer dereference, then comment nodes will have been
	omitted. If the actual input is an octet stream, then the application
	MUST convert the octet stream to an XPath node-set suitable for use
	by Canonical XML with Comments. (A subsequent application of the
	REQUIRED Canonical XML algorithm would strip away these comments.) In
	other words, the input node-set should be equivalent to the one that
	would be created by the following process:
	1. Initialize an XPath evaluation context by setting the initial
	node equal to the input XML document's root node, and set the
	context position and size to 1.
	2. Evaluate the XPath expression (//. | //@* | //namespace::*)
	The evaluation of this expression includes all of the document's
	nodes (including comments) in the node-set representing the octet
	stream.
	The transform output is also an XPath node-set. The XPath expression
	appearing in the XPath parameter is evaluated once for each node in
	the input node-set. The result is converted to a boolean. If the
	boolean is true, then the node is included in the output node-set. If
	the boolean is false, then the node is omitted from the output node-
	set.
	Note: Even if the input node-set has had comments removed, the
	comment nodes still exist in the underlying parse tree and can
	separate text nodes. For example, the markup <e>Hello, <!-- comment
	-->world!</e> contains two text nodes. Therefore, the expression
	self::text()[string()="Hello, world!"] would fail. Should this
	problem arise in the application, it can be solved by either
	canonicalizing the document before the XPath transform to physically
	remove the comments or by matching the node based on the parent
	element's string value (e.g. by using the expression
	self::text()[string(parent::e)="Hello, world!"]).
	The primary purpose of this transform is to ensure that only
	specifically defined changes to the input XML document are permitted
	after the signature is affixed. This is done by omitting precisely
	those nodes that are allowed to change once the signature is affixed,
	and including all other input nodes in the output. It is the
	responsibility of the XPath expression author to include all nodes
	whose change could affect the interpretation of the transform output
	in the application context.
	An important scenario would be a document requiring two enveloped
	signatures. Each signature must omit itself from its own digest
	calculations, but it is also necessary to exclude the second
	signature element from the digest calculations of the first signature
	so that adding the second signature does not break the first
	signature.
	The XPath transform establishes the following evaluation context for
	each node of the input node-set:
	* A context node equal to a node of the input node-set.
	* A context position, initialized to 1.
	* A context size, initialized to 1.
	* A library of functions equal to the function set defined in
	[XPath] plus a function named here.
	* A set of variable bindings. No means for initializing these is
	defined. Thus, the set of variable bindings used when
	evaluating the XPath expression is empty, and use of a variable
	reference in the XPath expression results in an error.
	* The set of namespace declarations in scope for the XPath
	expression.
	As a result of the context node setting, the XPath expressions
	appearing in this transform will be quite similar to those used in
	used in [XSLT], except that the size and position are always 1 to
	reflect the fact that the transform is automatically visiting every
	node (in XSLT, one recursively calls the command apply-templates to
	visit the nodes of the input tree).
	The function here() is defined as follows:
	Function: node-set here()
	The here function returns a node-set containing the attribute or
	processing instruction node or the parent element of the text node
	that directly bears the XPath expression. This expression results in
	an error if the containing XPath expression does not appear in the
	same XML document against which the XPath expression is being
	evaluated.
	As an example, consider creating an enveloped signature (a Signature
	element that is a descendant of an element being signed). Although
	the signed content should not be changed after signing, the elements
	within the Signature element are changing (e.g. the digest value must
	be put inside the DigestValue and the SignatureValue must be
	subsequently calculated). One way to prevent these changes from
	invalidating the digest value in DigestValue is to add an XPath
	Transform that omits all Signature elements and their descendants.
	For example,
	<Document>
	...
	<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
	<SignedInfo>
	...
	<Reference URI="">
	<Transforms>
	<Transform Algorithm="http://www.w3.org/TR/1999/REC-
	xpath-19991116">
	<XPath xmlns:dsig="&dsig;">
	not(ancestor-or-self::dsig:Signature)
	</XPath>
	</Transform>
	</Transforms>
	<DigestMethod
	Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
	<DigestValue></DigestValue>
	</Reference>
	</SignedInfo>
	<SignatureValue></SignatureValue>
	</Signature>
	...
	</Document>
	Due to the null Reference URI in this example, the XPath transform
	input node-set contains all nodes in the entire parse tree starting
	at the root node (except the comment nodes). For each node in this
	node-set, the node is included in the output node-set except if the
	node or one of its ancestors has a tag of Signature that is in the
	namespace given by the replacement text for the entity &dsig;.
	A more elegant solution uses the here function to omit only the
	Signature containing the XPath Transform, thus allowing enveloped
	signatures to sign other signatures. In the example above, use the
	XPath element:
	<XPath xmlns:dsig="&dsig;">
	count(ancestor-or-self::dsig:Signature |
	here()/ancestor::dsig:Signature[1]) >
	count(ancestor-or-self::dsig:Signature)</XPath>
	Since the XPath equality operator converts node sets to string values
	before comparison, we must instead use the XPath union operator (|).
	For each node of the document, the predicate expression is true if
	and only if the node-set containing the node and its Signature
	element ancestors does not include the enveloped Signature element
	containing the XPath expression (the union does not produce a larger
	set if the enveloped Signature element is in the node-set given by
	ancestor-or-self::Signature).
	6.6.4 Enveloped Signature Transform
	Identifier:
	http://www.w3.org/2000/09/xmldsig#enveloped-signature
	An enveloped signature transform T removes the whole Signature
	element containing T from the digest calculation of the Reference
	element containing T. The entire string of characters used by an XML
	processor to match the Signature with the XML production element is
	removed. The output of the transform is equivalent to the output that
	would result from replacing T with an XPath transform containing the
	following XPath parameter element:
	<XPath xmlns:dsig="&dsig;">
	count(ancestor-or-self::dsig:Signature |
	here()/ancestor::dsig:Signature[1]) >
	count(ancestor-or-self::dsig:Signature)</XPath>
	The input and output requirements of this transform are identical to
	those of the XPath transform , but may only be applied to a node-set
	from its parent XML document. Note that it is not necessary to use an
	XPath expression evaluator to create this transform. However, this
	transform MUST produce output in exactly the same manner as the XPath
	transform parameterized by the XPath expression above.
	6.6.5 XSLT Transform
	Identifier:
	http://www.w3.org/TR/1999/REC-xslt-19991116
	The normative specification for XSL Transformations is [XSLT].
	Specification of a namespace-qualified stylesheet element, which MUST
	be the sole child of the Transform element, indicates that the
	specified style sheet should be used. Whether this instantiates in-
	line processing of local XSLT declarations within the resource is
	determined by the XSLT processing model; the ordered application of
	multiple stylesheet may require multiple Transforms. No special
	provision is made for the identification of a remote stylesheet at a
	given URI because it can be communicated via an xsl:include or
	xsl:import within the stylesheet child of the Transform.
	This transform requires an octet stream as input. If the actual input
	is an XPath node-set, then the signature application should attempt
	to convert it to octets (apply Canonical XML]) as described in the
	Reference Processing Model (section 4.3.3.2).
	The output of this transform is an octet stream. The processing rules
	for the XSL style sheet or transform element are stated in the XSLT
	specification [XSLT]. We RECOMMEND that XSLT transform authors use an
	output method of xml for XML and HTML. As XSLT implementations do not
	produce consistent serializations of their output, we further
	RECOMMEND inserting a transform after the XSLT transform to
	canonicalize the output. These steps will help to ensure
	interoperability of the resulting signatures among applications that
	support the XSLT transform. Note that if the output is actually HTML,
	then the result of these steps is logically equivalent [XHTML].
	7. XML Canonicalization and Syntax Constraint Considerations
	Digital signatures only work if the verification calculations are
	performed on exactly the same bits as the signing calculations. If
	the surface representation of the signed data can change between
	signing and verification, then some way to standardize the changeable
	aspect must be used before signing and verification. For example,
	even for simple ASCII text there are at least three widely used line
	ending sequences. If it is possible for signed text to be modified
	from one line ending convention to another between the time of
	signing and signature verification, then the line endings need to be
	canonicalized to a standard form before signing and verification or
	the signatures will break.
	XML is subject to surface representation changes and to processing
	which discards some surface information. For this reason, XML digital
	signatures have a provision for indicating canonicalization methods
	in the signature so that a verifier can use the same canonicalization
	as the signer.
	Throughout this specification we distinguish between the
	canonicalization of a Signature element and other signed XML data
	objects. It is possible for an isolated XML document to be treated as
	if it were binary data so that no changes can occur. In that case,
	the digest of the document will not change and it need not be
	canonicalized if it is signed and verified as such. However, XML
	that is read and processed using standard XML parsing and processing
	techniques is frequently changed such that some of its surface
	representation information is lost or modified. In particular, this
	will occur in many cases for the Signature and enclosed SignedInfo
	elements since they, and possibly an encompassing XML document, will
	be processed as XML.
	Similarly, these considerations apply to Manifest, Object, and
	SignatureProperties elements if those elements have been digested,
	their DigestValue is to be checked, and they are being processed as
	XML.
	The kinds of changes in XML that may need to be canonicalized can be
	divided into four categories. There are those related to the basic
	[XML], as described in 7.1 below. There are those related to [DOM],
	[SAX], or similar processing as described in 7.2 below. Third, there
	is the possibility of coded character set conversion, such as between
	UTF-8 and UTF-16, both of which all [XML] compliant processors are
	required to support, which is described in the paragraph immediately
	below. And, fourth, there are changes that related to namespace
	declaration and XML namespace attribute context as described in 7.3
	below.
	Any canonicalization algorithm should yield output in a specific
	fixed coded character set. All canonicalization algorithms identified
	in this document use UTF-8 (without a byte order mark (BOM)) and do
	not provide character normalization. We RECOMMEND that signature
	applications create XML content (Signature elements and their
	descendents/content) in Normalization Form C [NFC, NFC-Corrigendum]
	and check that any XML being consumed is in that form as well; (if
	not, signatures may consequently fail to validate). Additionally,
	none of these algorithms provide data type normalization.
	Applications that normalize data types in varying formats (e.g.,
	(true, false) or (1,0)) may not be able to validate each other's
	signatures.
	7.1 XML 1.0, Syntax Constraints, and Canonicalization
	XML 1.0 [XML] defines an interface where a conformant application
	reading XML is given certain information from that XML and not other
	information. In particular,
	1. line endings are normalized to the single character #xA by
	dropping #xD characters if they are immediately followed by a
	#xA and replacing them with #xA in all other cases,
	2. missing attributes declared to have default values are
	provided to the application as if present with the default
	value,
	3. character references are replaced with the corresponding
	character,
	4. entity references are replaced with the corresponding declared
	entity,
	5. attribute values are normalized by
	5.1 replacing character and entity references as above,
	5.2 replacing occurrences of #x9, #xA, and #xD with #x20
	(space) except that the sequence #xD#xA is replaced by a
	single space, and
	5.3 if the attribute is not declared to be CDATA, stripping
	all leading and trailing spaces and replacing all interior
	runs of spaces with a single space.
	Note that items (2), (4), and (5.3) depend on the presence of a
	schema, DTD or similar declarations. The Signature element type is
	laxly schema valid [XML-schema], consequently external XML or even
	XML within the same document as the signature may be (only) well-
	formed or from another namespace (where permitted by the signature
	schema); the noted items may not be present. Thus, a signature with
	such content will only be verifiable by other signature applications
	if the following syntax constraints are observed when generating any
	signed material including the SignedInfo element:
	1. attributes having default values be explicitly present,
	2. all entity references (except "amp", "lt", "gt", "apos",
	"quot", and other character entities not representable in the
	encoding chosen) be expanded,
	3. attribute value white space be normalized
	7.2 DOM/SAX Processing and Canonicalization
	In addition to the canonicalization and syntax constraints discussed
	above, many XML applications use the Document Object Model [DOM] or
	the Simple API for XML [SAX]. DOM maps XML into a tree structure of
	nodes and typically assumes it will be used on an entire document
	with subsequent processing being done on this tree. SAX converts XML
	into a series of events such as a start tag, content, etc. In either
	case, many surface characteristics such as the ordering of attributes
	and insignificant white space within start/end tags is lost. In
	addition, namespace declarations are mapped over the nodes to which
	they apply, losing the namespace prefixes in the source text and, in
	most cases, losing where namespace declarations appeared in the
	original instance.
	If an XML Signature is to be produced or verified on a system using
	the DOM or SAX processing, a canonical method is needed to serialize
	the relevant part of a DOM tree or sequence of SAX events. XML
	canonicalization specifications, such as [XML-C14N], are based only
	on information which is preserved by DOM and SAX. For an XML
	Signature to be verifiable by an implementation using DOM or SAX, not
	only must the XML 1.0 syntax constraints given in the previous
	section be followed but an appropriate XML canonicalization MUST be
	specified so that the verifier can re-serialize DOM/SAX mediated
	input into the same octet stream that was signed.
	7.3 Namespace Context and Portable Signatures
	In [XPath] and consequently the Canonical XML data model an element
	has namespace nodes that correspond to those declarations within the
	element and its ancestors:
	"Note: An element E has namespace nodes that represent its
	namespace declarations as well as any namespace declarations made
	by its ancestors that have not been overridden in E's
	declarations, the default namespace if it is non-empty, and the
	declaration of the prefix xml." [XML-C14N]
	When serializing a Signature element or signed XML data that's the
	child of other elements using these data models, that Signature
	element and its children, may contain namespace declarations from its
	ancestor context. In addition, the Canonical XML and Canonical XML
	with Comments algorithms import all xml namespace attributes (such as
	xml:lang) from the nearest ancestor in which they are declared to the
	apex node of canonicalized XML unless they are already declared at
	that node. This may frustrate the intent of the signer to create a
	signature in one context which remains valid in another. For example,
	given a signature which is a child of B and a grandchild of A:
	<A xmlns:n1="&foo;">
	<B xmlns:n2="&bar;">
	<Signature xmlns="&dsig;"> ...
	<Reference URI="#signme"/> ...
	</Signature>
	<C ID="signme" xmlns="&baz;"/>
	</B>
	</A>
	when either the element B or the signed element C is moved into a
	[SOAP] envelope for transport:
	<SOAP:Envelope
	xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/">
	...
	<SOAP:Body>
	<B xmlns:n2="&bar;">
	<Signature xmlns="&dsig;">
	...
	</Signature>
	<C ID="signme" xmlns="&baz;"/>
	</B>
	</SOAP:Body>
	</SOAP:Envelope>
	The canonical form of the signature in this context will contain new
	namespace declarations from the SOAP:Envelope context, invalidating
	the signature. Also, the canonical form will lack namespace
	declarations it may have originally had from element A's context,
	also invalidating the signature. To avoid these problems, the
	application may:
	1. Rely upon the enveloping application to properly divorce its
	body (the signature payload) from the context (the envelope)
	before the signature is validated. Or,
	2. Use a canonicalization method that "repels/excludes" instead
	of "attracts" ancestor context. [XML-C14N] purposefully
	attracts such context.
	8.0 Security Considerations
	The XML Signature specification provides a very flexible digital
	signature mechanism. Implementors must give consideration to their
	application threat models and to the following factors.
	8.1 Transforms
	A requirement of this specification is to permit signatures to "apply
	to a part or totality of a XML document." (See [XML-Signature-RD,
	section 3.1.3].) The Transforms mechanism meets this requirement by
	permitting one to sign data derived from processing the content of
	the identified resource. For instance, applications that wish to
	sign a form, but permit users to enter limited field data without
	invalidating a previous signature on the form might use [XPath] to
	exclude those portions the user needs to change. Transforms may be
	arbitrarily specified and may include encoding transforms,
	canonicalization instructions or even XSLT transformations. Three
	cautions are raised with respect to this feature in the following
	sections.
	Note, core validation behavior does not confirm that the signed data
	was obtained by applying each step of the indicated transforms.
	(Though it does check that the digest of the resulting content
	matches that specified in the signature.) For example, some
	applications may be satisfied with verifying an XML signature over a
	cached copy of already transformed data. Other applications might
	require that content be freshly dereferenced and transformed.
	8.1.1 Only What is Signed is Secure
	First, obviously, signatures over a transformed document do not
	secure any information discarded by transforms: only what is signed
	is secure.
	Note that the use of Canonical XML [XML-C14N] ensures that all
	internal entities and XML namespaces are expanded within the content
	being signed. All entities are replaced with their definitions and
	the canonical form explicitly represents the namespace that an
	element would otherwise inherit. Applications that do not
	canonicalize XML content (especially the SignedInfo element) SHOULD
	NOT use internal entities and SHOULD represent the namespace
	explicitly within the content being signed since they can not rely
	upon canonicalization to do this for them. Also, users concerned with
	the integrity of the element type definitions associated with the XML
	instance being signed may wish to sign those definitions as well
	(i.e., the schema, DTD, or natural language description associated
	with the namespace/identifier).
	Second, an envelope containing signed information is not secured by
	the signature. For instance, when an encrypted envelope contains a
	signature, the signature does not protect the authenticity or
	integrity of unsigned envelope headers nor its ciphertext form, it
	only secures the plaintext actually signed.
	8.1.2 Only What is 'Seen' Should be Signed
	Additionally, the signature secures any information introduced by the
	transform: only what is "seen" (that which is represented to the user
	via visual, auditory or other media) should be signed. If signing is
	intended to convey the judgment or consent of a user (an automated
	mechanism or person), then it is normally necessary to secure as
	exactly as practical the information that was presented to that user.
	Note that this can be accomplished by literally signing what was
	presented, such as the screen images shown a user. However, this may
	result in data which is difficult for subsequent software to
	manipulate. Instead, one can sign the data along with whatever
	filters, style sheets, client profile or other information that
	affects its presentation.
	8.1.3 'See' What is Signed
	Just as a user should only sign what he or she "sees," persons and
	automated mechanism that trust the validity of a transformed document
	on the basis of a valid signature should operate over the data that
	was transformed (including canonicalization) and signed, not the
	original pre-transformed data. This recommendation applies to
	transforms specified within the signature as well as those included
	as part of the document itself. For instance, if an XML document
	includes an embedded style sheet [XSLT] it is the transformed
	document that should be represented to the user and signed. To meet
	this recommendation where a document references an external style
	sheet, the content of that external resource should also be signed as
	via a signature Reference otherwise the content of that external
	content might change which alters the resulting document without
	invalidating the signature.
	Some applications might operate over the original or intermediary
	data but should be extremely careful about potential weaknesses
	introduced between the original and transformed data. This is a trust
	decision about the character and meaning of the transforms that an
	application needs to make with caution. Consider a canonicalization
	algorithm that normalizes character case (lower to upper) or
	character composition ('e and accent' to consequently inconsequential
	to signature validity but material to a DOM processor. For instance,
	by changing the case of a character one might influence the result of
	an XPath selection. A serious risk is introduced if that change is
	normalized for signature validation but the processor operates over
	the original data and returns a different result than intended.
	As a result:
	* All documents operated upon and generated by signature
	applications MUST be in [NFC, NFC-Corrigendum] (otherwise
	intermediate processors might unintentionally break the
	signature)
	* Encoding normalizations SHOULD NOT be done as part of a
	signature transform, or (to state it another way) if
	normalization does occur, the application SHOULD always "see"
	(operate over) the normalized form.
	8.2 Check the Security Model
	This specification uses public key signatures and keyed hash
	authentication codes. These have substantially different security
	models. Furthermore, it permits user specified algorithms which may
	have other models.
	With public key signatures, any number of parties can hold the public
	key and verify signatures while only the parties with the private key
	can create signatures. The number of holders of the private key
	should be minimized and preferably be one. Confidence by verifiers in
	the public key they are using and its binding to the entity or
	capabilities represented by the corresponding private key is an
	important issue, usually addressed by certificate or online authority
	systems.
	Keyed hash authentication codes, based on secret keys, are typically
	much more efficient in terms of the computational effort required but
	have the characteristic that all verifiers need to have possession of
	the same key as the signer. Thus any verifier can forge signatures.
	This specification permits user provided signature algorithms and
	keying information designators. Such user provided algorithms may
	have different security models. For example, methods involving
	biometrics usually depend on a physical characteristic of the
	authorized user that can not be changed the way public or secret keys
	can be and may have other security model differences.
	8.3 Algorithms, Key Lengths, Certificates, Etc.
	The strength of a particular signature depends on all links in the
	security chain. This includes the signature and digest algorithms
	used, the strength of the key generation [RANDOM] and the size of the
	key, the security of key and certificate authentication and
	distribution mechanisms, certificate chain validation policy,
	protection of cryptographic processing from hostile observation and
	tampering, etc.
	Care must be exercised by applications in executing the various
	algorithms that may be specified in an XML signature and in the
	processing of any "executable content" that might be provided to such
	algorithms as parameters, such as XSLT transforms. The algorithms
	specified in this document will usually be implemented via a trusted
	library but even there perverse parameters might cause unacceptable
	processing or memory demand. Even more care may be warranted with
	application defined algorithms.
	The security of an overall system will also depend on the security
	and integrity of its operating procedures, its personnel, and on the
	administrative enforcement of those procedures. All the factors
	listed in this section are important to the overall security of a
	system; however, most are beyond the scope of this specification.
	9. Schema, DTD, Data Model, and Valid Examples
	XML Signature Schema Instance
	http://www.w3.org/Signature/Drafts/xmldsig-core/xmldsig-core-
	schema.xsd
	Valid XML schema instance based on the 20001024 Schema/DTD [XML-
	Schema].
	XML Signature DTD
	http://www.w3.org/Signature/Drafts/xmldsig-core/xmldsig-core-
	schema.dtd
	RDF Data Model
	http://www.w3.org/Signature/Drafts/xmldsig-core/xmldsig-datamodel-
	20000112.gif
	XML Signature Object Example
	http://www.w3.org/Signature/Drafts/xmldsig-core/signature-example.xml
	A cryptographical fabricated XML example that includes foreign
	content and validates under the schema, it also uses schemaLocation
	to aid automated schema fetching and validation.
	RSA XML Signature Example
	http://www.w3.org/Signature/Drafts/xmldsig-core/signature-example-
	rsa.xml
	An XML Signature example with generated cryptographic values by
	Merlin Hughes and validated by Gregor Karlinger.
	DSA XML Signature Example
	http://www.w3.org/Signature/Drafts/xmldsig-core/signature-example-
	dsa.xml
	Similar to above but uses DSA.
	10. Definitions
	Authentication Code (Protected Checksum)
	A value generated from the application of a shared key to a
	message via a cryptographic algorithm such that it has the
	properties of message authentication (and integrity) but not
	signer authentication. Equivalent to protected checksum, "A
	checksum that is computed for a data object by means that protect
	against active attacks that would attempt to change the checksum
	to make it match changes made to the data object." [SEC]
	Authentication, Message
	The property, given an authentication code/protected checksum,
	that tampering with both the data and checksum, so as to
	introduce changes while seemingly preserving integrity, are still
	detected. "A signature should identify what is signed, making it
	impracticable to falsify or alter either the signed matter or the
	signature without detection." [Digital Signature Guidelines,
	ABA].
	Authentication, Signer
	The property that the identity of the signer is as claimed. "A
	signature should indicate who signed a document, message or
	record, and should be difficult for another person to produce
	without authorization." [Digital Signature Guidelines, ABA] Note,
	signer authentication is an application decision (e.g., does the
	signing key actually correspond to a specific identity) that is
	supported by, but out of scope, of this specification.
	Checksum
	"A value that (a) is computed by a function that is dependent on
	the contents of a data object and (b) is stored or transmitted
	together with the object, for the purpose of detecting changes in
	the data." [SEC]
	Core
	The syntax and processing defined by this specification,
	including core validation. We use this term to distinguish other
	markup, processing, and applications semantics from our own.
	Data Object (Content/Document)
	The actual binary/octet data being operated on (transformed,
	digested, or signed) by an application -- frequently an HTTP
	entity [HTTP]. Note that the proper noun Object designates a
	specific XML element. Occasionally we refer to a data object as
	a document or as a resource's content. The term element content
	is used to describe the data between XML start and end tags
	[XML]. The term XML document is used to describe data objects
	which conform to the XML specification [XML].
	Integrity
	"The property that data has not been changed, destroyed, or lost
	in an unauthorized or accidental manner." [SEC] A simple checksum
	can provide integrity from incidental changes in the data;
	message authentication is similar but also protects against an
	active attack to alter the data whereby a change in the checksum
	is introduced so as to match the change in the data.
	Object
	An XML Signature element wherein arbitrary (non-core) data may be
	placed. An Object element is merely one type of digital data (or
	document) that can be signed via a Reference.
	Resource
	"A resource can be anything that has identity. Familiar examples
	include an electronic document, an image, a service (e.g.,
	'today's weather report for Los Angeles'), and a collection of
	other resources.... The resource is the conceptual mapping to an
	entity or set of entities, not necessarily the entity which
	corresponds to that mapping at any particular instance in time.
	Thus, a resource can remain constant even when its content---the
	entities to which it currently corresponds---changes over time,
	provided that the conceptual mapping is not changed in the
	process." [URI] In order to avoid a collision of the term entity
	within the URI and XML specifications, we use the term data
	object, content or document to refer to the actual bits/octets
	being operated upon.
	Signature
	Formally speaking, a value generated from the application of a
	private key to a message via a cryptographic algorithm such that
	it has the properties of integrity, message authentication and/or
	signer authentication. (However, we sometimes use the term
	signature generically such that it encompasses Authentication
	Code values as well, but we are careful to make the distinction
	when the property of signer authentication is relevant to the
	exposition.) A signature may be (non-exclusively) described as
	detached, enveloping, or enveloped.
	Signature, Application		Title: (Extensible Markup Language) XML-Signature Syntax
	An application that implements the MANDATORY (REQUIRED/MUST)		and Processing
	portions of this specification; these conformance requirements		Author(s): D. Eastlake 3rd, J. Reagle, D. Solo
	are over application behavior, the structure of the Signature		Status: Standards Track
	element type and its children (including SignatureValue) and the		Date: March 2002
	specified algorithms.		Mailbox: Donald.Eastlake@motorola.com, reagle@w3.org,
	Signature, Detached		dsolo@alum.mit.edu
	The signature is over content external to the Signature element,		Pages: 73
	and can be identified via a URI or transform. Consequently, the		Characters: 164198
	signature is "detached" from the content it signs. This		Obsoletes: 3075
	definition typically applies to separate data objects, but it
	also includes the instance where the Signature and data object
	reside within the same XML document but are sibling elements.
	Signature, Enveloping
	The signature is over content found within an Object element of
	the signature itself. The Object (or its content) is identified
	via a Reference (via a URI fragment identifier or transform).
	Signature, Enveloped
	The signature is over the XML content that contains the signature
	as an element. The content provides the root XML document
	element. Obviously, enveloped signatures must take care not to
	include their own value in the calculation of the SignatureValue.
	Transform
	The processing of a data from its source to its derived form.
	Typical transforms include XML Canonicalization, XPath, and XSLT.
	Validation, Core
	The core processing requirements of this specification requiring
	signature validation and SignedInfo reference validation.
	Validation, Reference
	The hash value of the identified and transformed content,
	specified by Reference, matches its specified DigestValue.
	Validation, Signature
	The SignatureValue matches the result of processing SignedInfo
	with CanonicalizationMethod and SignatureMethod as specified in
	Core Validation (section 3.2).
	Validation, Trust/Application
	The application determines that the semantics associated with a
	signature are valid. For example, an application may validate the
	time stamps or the integrity of the signer key -- though this
	behavior is external to this core specification.
	References		I-D Tag: draft-ietf-xmldsig-core-2-03.txt
	ABA		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3275.txt
	Digital Signature Guidelines.
	http://www.abanet.org/scitech/ec/isc/dsgfree.html
	DOM
	Document Object Model (DOM) Level 1 Specification. W3C
	Recommendation. V. Apparao, S. Byrne, M. Champion, S. Isaacs, I.
	Jacobs, A. Le Hors, G. Nicol, J. Robie, R. Sutor, C. Wilson, L.
	Wood. October 1998. http://www.w3.org/TR/1998/REC-DOM-Level-1-
	19981001/
	DSS
	FIPS PUB 186-2 . Digital Signature Standard (DSS). U.S.
	Department of Commerce/National Institute of Standards and
	Technology. http://csrc.nist.gov/publications/fips/fips186-
	2/fips186-2.pdf
	HMAC
	RFC 2104 . HMAC: Keyed-Hashing for Message Authentication. H.
	Krawczyk, M. Bellare, R. Canetti. February 1997.
	http://www.ietf.org/rfc/rfc2104.txt
	HTTP
	RFC 2616 . Hypertext Transfer Protocol -- HTTP/1.1. J. Gettys, J.
	Mogul, H. Frystyk, L. Masinter, P. Leach, T. Berners-Lee. June
	1999. http://www.ietf.org/rfc/rfc2616.txt
	KEYWORDS
	RFC 2119 Key words for use in RFCs to Indicate Requirement
	Levels. S. Bradner. March 1997.
	http://www.ietf.org/rfc/rfc2119.txt
	LDAP-DN
	RFC 2253 . Lightweight Directory Access Protocol (v3): UTF-8
	String Representation of Distinguished Names. M. Wahl, S. Kille,
	T. Howes. December 1997. http://www.ietf.org/rfc/rfc2253.txt
	MD5
	RFC 1321 . The MD5 Message-Digest Algorithm. R. Rivest. April
	1992. http://www.ietf.org/rfc/rfc1321.txt
	MIME
	RFC 2045 . Multipurpose Internet Mail Extensions (MIME) Part One:
	Format of Internet Message Bodies. N. Freed & N. Borenstein.
	November 1996. http://www.ietf.org/rfc/rfc2045.txt
	NFC
	TR15, Unicode Normalization Forms. M. Davis, M. D’rst. Revision
	18: November 1999.
	http://www.unicode.org/unicode/reports/tr15/tr15-18.html.
	NFC-Corrigendum Normalization Corrigendum. The Unicode Consortium.
	http://www.unicode.org/unicode/uni2errata/Normalization_Corrigendum.html.
	PGP
	RFC 2440 OpenPGP Message Format. J. Callas, L. Donnerhacke, H.
	Finney, R. Thayer. November 1998.
	http://www.ietf.org/rfc/rfc2440.txt
	RANDOM
	RFC 1750 Randomness Recommendations for Security. D. Eastlake, S.
	Crocker, J. Schiller. December 1994.
	http://www.ietf.org/rfc/rfc1750.txt
	RDF
	Resource Description Framework (RDF) Schema Specification 1.0.
	W3C Candidate Recommendation. D. Brickley, R.V. Guha. March 2000.
	http://www.w3.org/TR/2000/CR-rdf-schema-20000327/ Resource
	Description Framework (RDF) Model and Syntax Specification. W3C
	Recommendation. O. Lassila, R. Swick. February 1999.
	http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/
	1363
	IEEE 1363: Standard Specifications for Public Key Cryptography.
	August 2000.
	PKCS1
	RFC 2437 . PKCS #1: RSA Cryptography Specifications Version 2.0.
	B. Kaliski, J. Staddon. October 1998.
	http://www.ietf.org/rfc/rfc2437.txt
	SAX
	SAX: The Simple API for XML. D. Megginson, et al. May 1998.
	http://www.megginson.com/SAX/index.html
	SEC
	RFC 2828 . Internet Security Glossary. R. Shirey. May 2000.
	http://www.faqs.org/rfcs/rfc2828.html
	SHA-1
	FIPS PUB 180-1. Secure Hash Standard. U.S. Department of
	Commerce/National Institute of Standards and Technology.
	http://csrc.nist.gov/publications/fips/fips180-1/fip180-1.txt
	SOAP
	Simple Object Access Protocol (SOAP) Version 1.1. W3C Note. D.
	Box, D. Ehnebuske, G. Kakivaya, A. Layman, N. Mendelsohn, H.
	Frystyk Nielsen, S. Thatte, D. Winer. May 2001.
	http://www.w3.org/TR/2000/NOTE-SOAP-20000508/
	Unicode
	The Unicode Consortium. The Unicode Standard.
	http://www.unicode.org/unicode/standard/standard.html
	UTF-16
	RFC 2781 . UTF-16, an encoding of ISO 10646. P. Hoffman , F.
	Yergeau. February 2000. http://www.ietf.org/rfc/rfc2781.txt
	UTF-8
	RFC 2279 . UTF-8, a transformation format of ISO 10646. F.
	Yergeau. January 1998. http://www.ietf.org/rfc/rfc2279.txt
	URI
	RFC 2396 . Uniform Resource Identifiers (URI): Generic Syntax. T.
	Berners-Lee, R. Fielding, L. Masinter. August 1998.
	http://www.ietf.org/rfc/rfc2396.txt
	URI-Literal
	RFC 2732 . Format for Literal IPv6 Addresses in URL's. R. Hinden,
	B. Carpenter, L. Masinter. December 1999.
	http://www.ietf.org/rfc/rfc2732.txt
	URL
	RFC 1738. Uniform Resource Locators (URL). T. Berners-Lee, L.
	Masinter, and M. McCahill. December 1994.
	http://www.ietf.org/rfc/rfc1738.txt
	URN
	RFC 2141 . URN Syntax. R. Moats. May 1997.
	http://www.ietf.org/rfc/rfc2141.txt RFC 2611 . URN Namespace
	Definition Mechanisms. L. Daigle, D. van Gulik, R. Iannella, P.
	Falstrom. June 1999. http://www.ietf.org/rfc/rfc2611.txt		This document specifies XML (Extensible Markup Language) digital
	X509v3		signature processing rules and syntax. XML Signatures provide
	ITU-T Recommendation X.509 version 3 (1997). "Information		integrity, message authentication, and/or signer authentication
	Technology - Open Systems Interconnection - The Directory		services for data of any type, whether located within the XML that
	Authentication Framework" ISO/IEC 9594-8:1997.		includes the signature or elsewhere.
	XHTML 1.0
	XHTML(tm) 1.0: The Extensible Hypertext Markup Language. W3C
	Recommendation. S. Pemberton, D. Raggett, et al. January 2000.
	http://www.w3.org/TR/2000/REC-xhtml1-20000126/
	XLink
	XML Linking Language. W3C Recommendation. S. DeRose, E. Maler, D.
	Orchard. June 2001. http://www.w3.org/TR/2000/REC-xlink-
	20010627/
	XML
	Extensible Markup Language (XML) 1.0 (Second Edition). W3C
	Recommendation. T. Bray, E. Maler, J. Paoli, C. M. Sperberg-
	McQueen. October 2000. http://www.w3.org/TR/2000/REC-xml-
	20001006
	XML-C14N
	Canonical XML. W3C Recommendation. J. Boyer. March 2001.
	http://www.w3.org/TR/2001/REC-xml-c14n-20010315
	http://www.ietf.org/rfc/rfc3076.txt
	XML-Japanese
	XML Japanese Profile. W3C Note. M. Murata April 2000
	http://www.w3.org/TR/2000/NOTE-japanese-xml-20000414/
	XML-MT
	RFC 2376 . XML Media Types. E. Whitehead, M. Murata. July 1998.
	http://www.ietf.org/rfc/rfc2376.txt
	XML-ns
	Namespaces in XML. W3C Recommendation. T. Bray, D. Hollander, A.
	Layman. January 1999. http://www.w3.org/TR/1999/REC-xml-names-
	19990114
	XML-schema
	XML Schema Part 1: Structures. W3C Recommendation. D. Beech, M.
	Maloney, N. Mendelsohn, H. Thompson. May 2001.
	http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/ XML Schema
	Part 2: Datatypes W3C Recommendation. P. Biron, A. Malhotra. May
	2001. http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/
	XML-Signature-RD
	RFC 2807. XML Signature Requirements. W3C Working Draft. J.
	Reagle, April 2000. http://www.w3.org/TR/1999/WD-xmldsig-
	requirements-19991014 http://www.ietf.org/rfc/rfc2807.txt
	XPath
	XML Path Language (XPath) Version 1.0. W3C Recommendation. J.
	Clark, S. DeRose. October 1999. http://www.w3.org/TR/1999/REC-
	xpath-19991116
	XPointer
	XML Pointer Language (XPointer). W3C Working Draft. S. DeRose, R.
	Daniel, E. Maler. January 2001. http://www.w3.org/TR/2001/WD-
	xptr-20010108
	XSL		This document is a product of the XML Digital Signatures Working Group
	Extensible Stylesheet Language (XSL). W3C Proposed		of the IETF.
	Recommendation. S. Adler, A. Berglund, J. Caruso, S. Deach, P.
	Grosso, E. Gutentag, A. Milowski, S. Parnell, J. Richman, S.
	Zilles. August 2001. http://www.w3.org/TR/2001/PR-xsl-20010828/
	XSLT
	XSL Transforms (XSLT) Version 1.0. W3C Recommendation. J. Clark.
	November 1999. http://www.w3.org/TR/1999/REC-xslt-19991116.html
	Authors' Address		This is now a Draft Standard Protocol.
	Donald E. Eastlake 3rd		This document specifies an Internet standards track protocol for
	Motorola, 20 Forbes Boulevard		the Internet community, and requests discussion and suggestions
	Mansfield, MA 02048 USA		for improvements. Please refer to the current edition of the
	Phone: 1-508-261-5434		"Internet Official Protocol Standards" (STD 1) for the
	Email: Donald.Eastlake@motorola.com		standardization state and status of this protocol. Distribution
			of this memo is unlimited.
	Joseph M. Reagle Jr., W3C		This announcement is sent to the IETF list and the RFC-DIST list.
	Massachusetts Institute of Technology		Requests to be added to or deleted from the IETF distribution list
	Laboratory for Computer Science		should be sent to IETF-REQUEST@IETF.ORG. Requests to be
	NE43-350, 545 Technology Square		added to or deleted from the RFC-DIST distribution list should
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