RFC3075 - XML-Signature Syntax and Processing

Network Working Group D. Eastlake

Request for Comments: 3075 Motorola

Category: Standards Track J. Reagle

W3C/MIT

D. Solo

Citigroup

March 2001

XML-Signature Syntax and Processing

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Rights Reserved.

Abstract

This document specifies XML (Extensible Markup Language) digital

signature processing rules and syntax. XML Signatures provide

integrity, message authentication, and/or signer authentication

services for data of any type, whether located within the XML that

includes the signature or elsewhere.

Table of Contents

1. IntrodUCtion ................................................ 3

1. Editorial Conventions .................................. 3

2. Design Philosophy ...................................... 4

3. Versions, Namespaces and Identifiers ................... 4

4. Acknowledgements ....................................... 5

2. Signature Overview and Examples ............................. 6

1. Simple Example (Signature, SignedInfo, Methods, and

References) ............................................ 7

1. More on Reference ................................. 9

2. Extended Example (Object and SignatureProperty) ........ 10

3. Extended Example (Object and Manifest) ................. 11

3. Processing Rules ............................................ 13

1. Core Generation .... ................................... 13

1. Reference Generation .............................. 13

2. Signature Generation .............................. 13

2. Core Validation ........................................ 13

1. Reference Validation .............................. 14

2. Signature Validation .............................. 14

4. Core Signature Syntax ....................................... 14

1. The Signature element .................................. 15

2. The SignatureValue Element ............................. 16

3. The SignedInfo Element ................................. 16

1. The CanonicalizationMethod Element ................ 17

2. The SignatureMethod Element ....................... 18

3. The Reference Element ............................. 19

1. The URI Attribute ............................ 19

2. The Reference Processing Model ............... 21

3. Same-Document URI-References ................. 23

4. The Transforms Element ....................... 24

5. The DigestMethod Element ..................... 25

6. The DigestValue Element ...................... 26

4. The KeyInfo Element .................................... 26

1. The KeyName Element ............................... 27

2. The KeyValue Element .............................. 28

3. The RetrievalMethod Element ....................... 28

4. The X509Data Element .............................. 29

5. The PGPData Element ............................... 31

6. The SPKIData Element .............................. 32

7. The MgmtData Element .............................. 32

5. The Object Element ..................................... 33

5. Additional Signature Syntax ................................. 34

1. The Manifest Element ................................... 34

2. The SignatureProperties Element ........................ 35

3. Processing Instructions ................................ 36

4. Comments in dsig Elements .............................. 36

6. Algorithms .................................................. 36

1. Algorithm Identifiers and Implementation Requirements .. 36

2. Message Digests ........................................ 38

1. SHA-1 ............................................. 38

3. Message Authentication Codes ........................... 38

1. HMAC .............................................. 38

4. Signature Algorithms ................................... 39

1. DSA ............................................... 39

2. PKCS1 ............................................. 40

5. Canonicalization Algorithms ............................ 42

1. Minimal Canonicalization .......................... 43

2. Canonical XML ..................................... 43

6. Transform Algorithms ................................... 44

1. Canonicalization .................................. 44

2. Base64 ............................................ 44

3. XPath Filtering ................................... 45

4. Enveloped Signature Transform ..................... 48

5. XSLT Transform .................................... 48

7. XML Canonicalization and Syntax Constraint Considerations ... 49

1. XML 1.0, Syntax Constraints, and Canonicalization ..... 50

2. DOM/SAX Processing and Canonicalization ................ 51

8. Security Considerations ..................................... 52

1. Transforms ............................................. 52

1. Only What is Signed is Secure ..................... 52

2. Only What is "Seen" Should be Signed .............. 53

3. "See" What is Signed .............................. 53

2. Check the Security Model ............................... 54

3. Algorithms, Key Lengths, Etc. .......................... 54

9. Schema, DTD, Data Model,and Valid Examples .................. 55

10. Definitions ................................................. 56

11. References .................................................. 58

12. Authors' Addresses .......................................... 63

13. Full Copyright Statement .................................... 64

1.0 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 uses both XML Schemas [XML-schema] and DTDs [XML].

(Readers unfamiliar with DTD syntax may wish to refer to Ron

Bourret's "Declaring Elements and Attributes in an XML DTD"

[Bourret].) The schema definition is presently 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 keywords 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 XML-namespace 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/PR-xslt-19991008

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#"> ]>

...

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

* Peter Lipp, IAIK TU Graz

* Joseph Reagle, W3C (Chair, Author/Editor)

* Ed Simon, Entrust Technologies Inc. (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.

2.0 Signature Overview and Examples

This section provides an overview and examples of XML digital

signature syntax. The specific processing is given in Processing

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):

(CanonicalizationMethod)

(SignatureMethod)

(<Reference (URI=)? >

(Transforms)?

(DigestMethod)

(DigestValue)

</Reference>)+

</SignedInfo>

(SignatureValue)

(KeyInfo)?

(Object)*

</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

resides within the same XML document as sibling elements; in this

case, the signature is neither 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/2000/CR-xml-c14n-20001026"/>

[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/2000/

CR-xml-c14n-20001026"/>

[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.

[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

and the signature design permits arbitrary user algorithm

specification.

[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/2000/

CR-xml-c14n-20001026"/>

[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 and XPath.

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 we specify 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 (message authentication,

integrity, 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/rfc3075.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 follows.

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.

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.

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.

3.2.1 Reference Validation

For each Reference in SignedInfo:

1. Canonicalize the SignedInfo element based on the

CanonicalizationMethod in SignedInfo.

2. Obtain the data object to be digested. (The signature application

may rely upon the identification (URI) and Transforms provided by

the signer in the Reference element, or it may obtain the content

through other means such as a local cache.)

3. Digest the resulting data object using the DigestMethod specified

in its Reference specification.

4. 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 to ensure the application

Sees What is Signed, which is the canonical form. For instance, if

the CanonicalizationMethod rewrote the URIs (e.g., absolutizing

relative URIs) the signature processing must be cognizant of this.

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 validate 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, internal entity, and simpleType:

Schema Definition:

<!DOCTYPE schema

PUBLIC "-//W3C//DTD XMLSCHEMA 200010//EN"

"http://www.w3.org/2000/10/XMLSchema.dtd"

[

<!ATTLIST schema

xmlns:ds CDATA #FIXED "http://www.w3.org/2000/09/xmldsig#">

<!ENTITY dsig 'http://www.w3.org/2000/09/xmldsig#'>

<schema xmlns="http://www.w3.org/2000/10/XMLSchema"

xmlns:ds="&dsig;"

targetNamespace="&dsig;"

version="0.1"

elementFormDefault="qualified">

</restriction>

</simpleType>

DTD:

<!-- These entity declarations permit the flexible parts of Signature

content model to be easily expanded -->

<!ENTITY % Object.ANY '(#PCDATASignatureSignatureProperties

Manifest)*'>

<!ENTITY % Method.ANY '(#PCDATAHMACOutputLength)*'>

<!ENTITY % Transform.ANY '(#PCDATAXPathXSLT)'>

<!ENTITY % SignatureProperty.ANY '(#PCDATA)*'>

<!ENTITY % Key.ANY '(#PCDATAKeyNameKeyValueRetrievalMethod

X509DataPGPDataMgmtDataDSAKeyValueRSAKeyValue)*'>

4.1 The Signature element

The Signature element is the root element of an XML Signature.

Signature elements MUST be laxly schema valid [XML-schema] with

respect to the following schema definition:

Schema Definition:

</sequence>

</complexType>

</element>

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

specify a mandatory and optional to implement SignatureMethod

algorithms, user specified algorithms are permitted. Schema

Definition:

DTD:

<!ELEMENT SignatureValue (#PCDATA) >

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:

</sequence>

</complexType>

</element>

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 Canonical XML [XML-C14N] method.

Alternatives to the REQUIRED Canonical XML algorithm (section 6.5.2),

such as Canonical XML with Comments (section 6.5.2) and Minimal

Canonicalization (the CRLF and charset normalization specified in

section 6.5.1), may be explicitly specified but are NOT REQUIRED.

Consequently, their use may not interoperate with other applications

that do no 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

minimal or other 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 the two types of algorithms specified by this document:

* Canonical XML [XML-C14N] (with or without comments)

implementation MUST be provided with an 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 (such that the namespace context and

similar ancestor information of the SignedInfo is preserved).

* Minimal canonicalization implementations MUST be provided with

the 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.

We RECOMMEND that resource constrained applications that do not

implement the Canonical XML [XML-C14N] algorithm and instead choose

minimal canonicalization (or some other form) be implemented to

generate Canonical XML as their output serialization so as to easily

mitigate some of these interoperability and security concerns.

(While a result might not be the canonical form of the original, it

can still be in canonical form.) For instance, such an

implementation SHOULD (at least) generate standalone XML instances

[XML].

Schema Definition:

</sequence>

</complexType>

</element>

DTD:

<!ELEMENT CanonicalizationMethod %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:

</sequence>

</complexType>

</element>

DTD:

<!ELEMENT SignatureMethod %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:

</sequence>

</complexType>

</element>

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 RFC2732 [URI-Literal]

are permitted. Disallowed characters must be escaped as follows:

1. Each disallowed character is converted to [UTF-8] as one or more

bytes.

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 byte 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 a 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 nodesets" 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 a an octet stream and the next

transformrequires a node-set, the signature application MUST

attempt to parse the octets.

* If the data object is a node-set and the next transformrequires

octets, the signature application MUST attempt to convert the

node-set to an octet stream using the REQUIRED canonicalization

algorithm [XML-C14N].

Users may specify alternative transforms that over-ride 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 transformthat 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 '#xpointer(id("ID"))' if the application also

intends to support Minimal Canonicalization or Canonical XML with

Comments. (Otherwise URI="#foo" will automatically remove comments

before the Canonical XML with Comments 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

'http//example.com/bar.xml', that is probably XML document

given its 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 transformrather than a URI fragment

(barename XPointer resolution in external resources is not

REQUIRED in this specification).

URI=""

Identifies the nodeset (minus any comment nodes) of the XML

resource containing the signature

URI="#chapter1"

Identifies a nodeset containing the element with ID attribute

value 'chapter1' of the XML resource containing the signature.

XML Signature (and its applications) modify this nodeset 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. 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. 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 Transform 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:

</sequence>

</complexType>

</element>

<any namespace="##other" processContents="lax" minOccurs="0"

maxOccurs="unbounded"/>

</choice>

</complexType>

</element>

DTD:

<!ELEMENT Transforms (Transform+)>

<!ELEMENT Transform %Transform.ANY; >

<!ATTLIST Transform

Algorithm CDATA #REQUIRED >

<!ELEMENT XPath (#PCDATA) >

<!ELEMENT XSLT (#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 Minimal

Canonicalization or 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:

<any namespace="##any" processContents="lax" minOccurs="0"

maxOccurs="unbounded"/>

</sequence>

</complexType>

</element>

DTD:

<!ELEMENT DigestMethod %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:

DTD:

<!ELEMENT DigestValue (#PCDATA) >

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

place their own key identification and exchange semantics within this

element type through the XML-namespace facility [XML-ns].

If KeyInfo is omitted, the recipient is expected to be able to

identify the key based on application context information. 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 following list summarizes the KeyInfo types defined by this

specification; these can be used within the RetrievalMethod Type

attribute to describe the remote KeyInfo structure as represented as

an octect stream.

* 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 structures, we

specify one additional type to indicate a binary X.509 Certificate

* http://www.w3.org/2000/09/xmldsig#rawX509Certificate

Schema Definition:

<any processContents="lax" namespace="##other" minOccurs="0"

maxOccurs="unbounded"/>

</choice>

</complexType>

</element>

DTD:

<!ELEMENT KeyInfo %Key.ANY; >

<!ATTLIST KeyInfo

Id ID #IMPLIED >

4.4.1 The KeyName Element

The KeyName element contains a string value 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:

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).

Schema Definition:

<any namespace="##other" processContents="lax" minOccurs="0"

maxOccurs="unbounded"/>

</choice>

</complexType>

</element>

DTD:

<!ELEMENT KeyValue %Key.ANY; >

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. Note, if the

result of dereferencing and transforming the specified URI is a node

set, then it may need to be to be canonicalized. All of the KeyInfo

types defined by this specification (section 4.4) represent octets,

consequently the Signature application is expected to attempt to

canonicalize the nodeset via the The Reference Processing Model

(section 4.3.3.2)

Type is an optional identifier for the type of data to be retrieved.

Schema Definition

</sequence>

</complexType>

</element>

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

revocation lists). Five types of X509Data are defined

1. The X509IssuerSerial element, which contains an X.509 issuer

distinguished name/serial number pair that SHOULD be compliant

with RFC2253 [LDAP-DN],

2. The X509SubjectName element, which contains an X.509 subject

distinguished name that SHOULD be compliant with RFC2253 [LDAP-

DN],

3. The X509SKI element, which contains an X.509 subject key

identifier value.

4. The X509Certificate element, which contains a base64-encoded

[X509v3] certificate, and

5. The X509CRL element, which contains a base64-encoded certificate

revocation list (CRL) [X509v3].

Multiple declarations about a single certificate (e.g., a

X509SubjectName and X509IssuerSerial element) MUST be grouped inside

a single X509Data element; multiple declarations about the same key

but different certificates (related to that single key) MUST be

grouped within a single KeyInfo element but MAY occur in multiple

X509Data elements. For example, the following block contains two

pointers to certificate-A (issuer/serial number and SKI) and a single

reference to certificate-B (SubjectName) and also shows use of

certificate elements

<X509IssuerName>CN=TAMURA Kent, OU=TRL, O=IBM,

L=Yamato-shi, ST=Kanagawa, C=JP</X509IssuerName>

</X509IssuerSerial>

</X509Data>

<X509SubjectName>Subject of Certificate B</X509SubjectName>

</X509Data>

<X509Certificate>MIICXTCCA..</X509Certificate>

<!-- Intermediate cert subject CN=arbolCA,OU=FVTO=IBM,C=US

issuer,CN=tootiseCA,OU=FVT,O=Bridgepoint,C=US -->

<X509Certificate>MIICPzCCA...</X509Certificate>

<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 or a CRL 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.

Schema Definition

</choice>

</sequence>

</choice>

</complexType>

</element>

</sequence>

</complexType>

</element>

DTD

<!ELEMENT X509Data ((X509IssuerSerial X509SKI X509SubjectName

X509Certificate)+ X509CRL)>

<!ELEMENT X509IssuerSerial (X509IssuerName, X509SerialNumber) >

<!ELEMENT X509IssuerName (#PCDATA) >

<!ELEMENT X509SubjectName (#PCDATA) >

<!ELEMENT X509SerialNumber (#PCDATA) >

<!ELEMENT X509SKI (#PCDATA) >

<!ELEMENT X509Certificate (#PCDATA) >

<!ELEMENT X509CRL (#PCDATA) >

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 string 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]. Other sub-types of the PGPData element may be defined

by the OpenPGP working group.

Schema Definition:

<any namespace="##other" processContents="lax" minOccurs="0"

maxOccurs="unbounded"/>

</sequence>

</choice>

</complexType>

</element>

DTD:

<!ELEMENT PGPData (PGPKeyID, PGPKeyPacket) >

<!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.

The content of this element type is expected to be a Canonical S-

expression.

Schema Definition:

DTD:

<!ELEMENT SPKIData (#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.

Schema Definition:

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 MimeType attribute is an optional attribute which describes the

data within the Object. This is a string with values defined by

[MIME]. For example, if the Object contains XML, the MimeType could

be text/xml. This attribute is purely advisory; no validation of the

MimeType information is required by this specification.

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.

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).

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:

</sequence>

</complexType>

</element>

DTD:

<!ELEMENT Object %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:

</sequence>

</complexType>

</element>

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:

</sequence>

</complexType>

</element>

<any namespace="##other" processContents="lax" minOccurs="0"

maxOccurs="unbounded"/>

</choice>

</complexType>

</element>

DTD:

<!ELEMENT SignatureProperties (SignatureProperty+) >

<!ATTLIST SignatureProperties

Id ID #IMPLIED >

<!ELEMENT SignatureProperty %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 specified 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.

(Note that the normative identifier is the complete URI in the table

though they are sometimes abbreviated in XML syntax (e.g.,

"&dsig;base64").)

Algorithm Type

Algorithm - Requirements - Algorithm URI

Digest

SHA1 - REQUIRED - &dsig;sha1

Encoding

base64 - REQUIRED - &dsig;base64

MAC

HMAC-SHA1 - REQUIRED - &dsig;hmac-sha1

Signature

DSAwithSHA1(DSS) - REQUIRED - &dsig;dsa-sha1

RSAwithSHA1 - RECOMMENDED - &dsig;rsa-sha1

Canonicalization

minimal - RECOMMENDED - &dsig;minimal

Canonical XML with Comments - RECOMMENDED -

http://www.w3.org/TR/2000/CR-xml-c14n-20001026#WithComments

Canonical XML (omits comments) - REQUIRED -

http://www.w3.org/TR/2000/CR-xml-c14n-20001026

Transform

XSLT - OPTIONAL - http://www.w3.org/TR/1999/REC-xslt-19991116

XPath - RECOMMENDED -

http://www.w3.org/TR/1999/REC-xpath-19991116

Enveloped Signature* - REQUIRED - &dsig;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 cryptography 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:

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>

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:

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:

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.

Integer to octet-stream conversion must be done according to the

I2OSP operation defined in the RFC2437 [PKCS1] specification with a

k 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

i6watmQQQ1y3GB+VsWq5fJKzQcBB4jRfH1bfJFj0JtFVtLotttzYyA==</SignatureValue>

DSA key values have the following set of fields: P, Q, G and Y are

mandatory when appearing as a key value, J, seed and pgenCounter are

optional but should be present. (The seed and pgenCounter fields

must appear together or be absent). All parameters are encoded as

base64 [MIME] values.

Schema:

</sequence>

</sequence>

</complexType>

</element>

DTD:

<!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) >

6.4.2 PKCS1

Identifier:

http://www.w3.org/2000/09/xmldsig#rsa-sha1

Arbitrary-length integers (e.g., "bignums" such as RSA modulii) are

represented 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 even number of bytes). If the bitstring

contains entire leading bytes that are zero, these are removed (so

the high-order byte 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).

The expression "RSA algorithm" as used in this document refers to the

RSASSA-PKCS1-v1_5 algorithm described in RFC2437 [PKCS1]. The RSA

algorithm takes no explicit parameters. An example of an RSA

SignatureMethod element is: <SignatureMethod Algorithm="&dsig;rsa-

sha1"/>

The SignatureValue content for an RSA signature is the base64 [MIME]

encoding of the octet string computed as per RFC2437 [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 concatentation, "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 [RFC2437], 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>IWijxQjUrcXBYoCei4QxjWo9Kg8D3p9tlWoT4

t0/gyTE96639In0FZFY2/rvP+/bMJ01EArmKZsR5VW3rwoPxw=

</SignatureValue>

RSA key values have two fields Modulus and Exponent

<Modulus>xA7SEU+e0yQH5rm9kbCDN9o3aPIo7HbP7tX6WOocLZAtNfyxSZDU16ksL6W

jubafOqNEpcwR3RdFsT7bCqnXPBe5ELh5u4VEy19MzxkXRgrMvavzyBpVRgBUwUlV

5foK5hhmbktQhyNdy/6LpQRhDUDsTvK+g9Ucj47es9AQJ3U=

</Modulus>

</RSAKeyValue>

Schema:

</sequence>

</complexType>

</element>

DTD:

<!ELEMENT RSAKeyValue (Modulus, Exponent) >

<!ELEMENT Modulus (#PCDATA) >

<!ELEMENT Exponent (#PCDATA) >

6.5 Canonicalization Algorithms

If canonicalization is performed over octets, the canonicalization

algorithms take two implicit parameter: 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]. 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 Minimal Canonicalization

Identifier:

http://www.w3.org/2000/09/xmldsig#minimal

An example of a minimal canonicalization element is:

The minimal canonicalization algorithm:

* converts the character encoding to UTF-8 (without any byte

order mark (BOM)). If an encoding is given in the XML

declaration, it must be removed. Implementations MUST

understand at least [UTF-8] and [UTF-16] as input encodings.

Non-Unicode to Unicode transcoding MUST perform text

normalization [NFC].

* normalizes line endings as provided by [XML]. (See XML and

Canonicalization and Syntactical Considerations (section 7).)

This algorithm requires as input the octet stream of the resource to

be processed; the algorithm outputs an octet stream. When used to

canonicalize SignedInfo the algorithm MUST be provided with the

octets that represent the well-formed SignedInfo element (and its

children and content) as described in The CanonicalizationMethod

Element (section 4.3.1).

If the signature application has a node set, then the signature

application must convert it into octets as described in The Reference

Processing Model (section 4.3.3.2). However, Minimal

Canonicalization is NOT RECOMMENDED for processing XPath node-sets,

the results of same-document URI references, and the output of other

types of XML based transforms. It is only RECOMMENDED for simple

character normalization of well formed XML that has no namespace or

external entity complications.

6.5.2 Canonical XML

Identifier for REQUIRED Canonical XML (omits comments):

http://www.w3.org/TR/2000/CR-xml-c14n-20001026

Identifier for Canonical XML with Comments:

http://www.w3.org/TR/2000/CR-xml-c14n-20001026#WithComments

An example of an XML canonicalization element is:

<CanonicalizationMethod Algorithm="http://www.w3.org/TR/2000/CR-xml-

c14n-20001026"/>

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 parameters: 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 base 64 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.

Note: The function definition for here() is intended to be consistent

with its definition in XPointer. However, some minor differences are

presently being discussed between the Working Groups.

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,

...

<Transform

Algorithm="http://www.w3.org/TR/1999/REC-xpath-19991116">

not(ancestor-or-self::dsig:Signature)

</XPath>

</Transform>

</Transforms>

<DigestMethod

Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>

</Reference>

</SignedInfo>

</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:

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:

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. 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]. The

XSL style sheet or transform to be evaluated appears as the character

content of a transform parameter child element named XSLT. The root

element of a XSLT style sheet SHOULD be <xsl:stylesheet>.

This transform requires an octet stream as input. If the actual

input is an XPath node-set, then the signature application should

attempt to covert 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 transformauthors

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 transformafter the XSLT

transformto perform 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].

7.0 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 three 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. And, 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.

Any canonicalization algorithm should yield output in a specific

fixed coded character set. For both the minimal canonicalization

defined in this specification and Canonical XML [XML-C14N] that coded

character set is UTF-8 (without a byte order mark (BOM)).Neither the

minimal canonicalization nor the Canonical XML [XML-C14N] algorithms

provide character normalization. We RECOMMEND that signature

applications create XML content (Signature elements and their

descendents/content) in Normalization Form C [NFC] 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

A. replacing character and entity references as above,

B. replacing occurrences of #x9, #xA, and #xD with #x20 (space)

except that the sequence #xD#xA is replaced by a single space,

and

C. 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 (5C) 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 XML1.0 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 octect stream that was signed.

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

application 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.

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 it "sees," persons and automated

mechanisms 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 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 'accented-e'). An

adversary could introduce changes that are normalized and

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. Consequently, while we RECOMMEND all documents

operated upon and generated by signature applications be in [NFC]

(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.

9.0 Schema, DTD, Data Model, and Valid Examples

XML Signature Schema Instance

http://www.w3.org/TR/2000/CR-xmldsig-core-20001031/xmldsig-

core-schema.xsd Valid XML schema instance based on the

20000922 Schema/DTD [XML-Schema].

XML Signature DTD

http://www.w3.org/TR/2000/CR-xmldsig-core-20001031/xmldsig-

core-schema.dtd

RDF Data Model

http://www.w3.org/TR/2000/CR-xmldsig-core-20001031/xmldsig-

datamodel-20000112.gif

XML Signature Object Example

http://www.w3.org/TR/2000/CR-xmldsig-core-20001031/signature-

example.xml A cryptographical invalid XML example that

includes foreign content and validates under the schema. (It

validates under the DTD when the foreign content is removed or

the DTD is modified accordingly).

RSA XML Signature Example

http://www.w3.org/TR/2000/CR-xmldsig-core-20001031/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/TR/2000/CR-xmldsig-core-20001031/signature-

example-dsa.xml Similar to above but uses DSA.

10.0 Definitions

Authentication Code

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 (integrity) but not signer

authentication

Authentication, Message

"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

"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]

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 inability to change a message without also changing the

signature value. See message authentication.

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 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 signer authentication and message

authentication (integrity). (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

An application that implements the MANDATORY (REQUIRED/MUST)

portions of this specification; these conformance requirements

are over the structure of the Signature element type and its

children (including SignatureValue) and mandatory to support

algorithms.

Signature, Detached

The signature is over content external to the Signature

element, and can be identified via a URI or transform.

Consequently, the signature is "detached" from the content it

signs. This 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 octet stream from source content to derived

content. 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.

11.0 References

ABA Digital Signature Guidelines.

http://www.abanet.org/scitech/ec/isc/dsgfree.html

Bourret Declaring Elements and Attributes in an XML DTD.

Ron Bourret. http://www.informatik.tu-

darmstadt.de/DVS1/staff/bourret/xml/xmldtd.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 186-1. Digital Signature Standard (DSS).

U.S. Department of Commerce/National Institute of

Standards and Technology.

http://csrc.nist.gov/fips/fips1861.pdf

HMAC Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:

Keyed-Hashing for Message Authentication", RFC

2104, February 1997.

http://www.ietf.org/rfc/rfc2104.txt

HTTP Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,

Masinter, L., Leach, P. and T. Berners-Lee,

"Hypertext Transfer Protocol -- HTTP/1.1", RFC

2616, June 1999.

http://www.ietf.org/rfc/rfc2616.txt

KEYWORDS Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC2119, March 1997.

http://www.ietf.org/rfc/rfc2119.txt

LDAP-DN Wahl, M., Kille, S. and T. Howes, "Lightweight

Directory Access Protocol (v3): UTF-8 String

Representation of Distinguished Names", RFC2253,

December 1997. http://www.ietf.org/rfc/rfc2253.txt

MD5 Rivest, R., "The MD5 Message-Digest Algorithm", RFC

1321, April 1992.

http://www.ietf.org/rfc/rfc1321.txt

MIME Freed, N. and N. Borenstein, "Multipurpose Internet

Mail Extensions (MIME) Part One: Format of Internet

Message Bodies", RFC2045, November 1996.

http://www.ietf.org/rfc/rfc2045.txt

NFC TR15. Unicode Normalization Forms. M. Davis, M.

Drst. Revision 18: November 1999.

PGP Callas, J., Donnerhacke, L., Finney, H. and R.

Thayer, "OpenPGP Message Format", November 1998.

http://www.ietf.org/rfc/rfc2440.txt

RANDOM Eastlake, D., Crocker, S. and J. Schiller,

"Randomness Recommendations for Security", RFC

1750, December 1994.

http://www.ietf.org/rfc/rfc1750.txt

RDF RDF Schema W3C Candidate Recommendation. D.

Brickley, R.V. Guha. March 2000.

http://www.w3.org/TR/2000/CR-rdf-schema-20000327/

RDF Model and Syntax 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 Kaliski, B. and J. Staddon, "PKCS #1: RSA

Cryptography Specifications Version 2.0", RFC2437,

October 1998. http://www.ietf.org/rfc/rfc2437.txt

SAX SAX: The Simple API for XML David Megginson et. al.

May 1998. http://www.megginson.com/SAX/index.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/fips/fip180-1.pdf

Unicode The Unicode Consortium. The Unicode Standard.

http://www.unicode.org/unicode/standard/standard.html

UTF-16 Hoffman, P. and F. Yergeau, "UTF-16, an encoding of

ISO 10646", RFC2781, February 2000.

http://www.ietf.org/rfc/rfc2781.txt

UTF-8 Yergeau, F., "UTF-8, a transformation format of ISO

10646", RFC2279, January 1998.

http://www.ietf.org/rfc/rfc2279.txt

URI Berners-Lee, T., Fielding, R. and L. Masinter,

"Uniform Resource Identifiers (URI): Generic

Syntax", RFC2396, August 1998.

http://www.ietf.org/rfc/rfc2396.txt

URI-Literal Hinden, R., Carpenter, B. and L. Masinter, "Format

for Literal IPv6 Addresses in URL's", RFC2732,

December 1999. http://www.ietf.org/rfc/rfc2732.txt

URL Berners-Lee, T., Masinter, L. and M. McCahill,

"Uniform Resource Locators (URL)", RFC1738,

December 1994. http://www.ietf.org/rfc/rfc1738.txt

URN Moats, R., "URN Syntax" RFC2141, May 1997.

http://www.ietf.org/rfc/rfc2141.txt

Daigle, L., van Gulik, D., Iannella, R. and P.

Faltstrom, "URN Namespace Definition Mechanisms",

RFC2611, June 1999.

http://www.ietf.org/rfc/rfc2611.txt

X509v3 ITU-T Recommendation X.509 version 3 (1997).

"Information Technology - Open Systems

Interconnection - The Directory Authentication

Framework" ISO/IEC 9594-8:1997.

XHTML 1.0 XHTML(tm) 1.0: The Extensible Hypertext Markup

Language Recommendation. S. Pemberton, D. Raggett,

et. al. January 2000.

http://www.w3.org/TR/2000/REC-xhtml1-20000126/

XLink XML Linking Language. Working Draft. S. DeRose, D.

Orchard, B. Trafford. July 1999.

http://www.w3.org/1999/07/WD-xlink-19990726

XML Extensible Markup Language (XML) 1.0

Recommendation. T. Bray, J. Paoli, C. M. Sperberg-

McQueen. February 1998.

http://www.w3.org/TR/1998/REC-xml-19980210

XML-C14N J. Boyer, "Canonical XML Version 1.0", RFC3076,

September 2000. http://www.w3.org/TR/2000/CR-xml-

c14n-20001026

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 Whitehead, E. and M. Murata, "XML Media Types",

July 1998. http://www.ietf.org/rfc/rfc2376.txt

XML-ns Namespaces in XML Recommendation. T. Bray, D.

Hollander, A. Layman. Janury 1999.

http://www.w3.org/TR/1999/REC-xml-names-19990114

XML-schema XML Schema Part 1: Structures Working Draft. D.

Beech, M. Maloney, N. Mendelshohn. September 2000.

http://www.w3.org/TR/2000/WD-xmlschema-1-20000922/

XML Schema Part 2: Datatypes Working Draft. P.

Biron, A. Malhotra. September 2000.

http://www.w3.org/TR/2000/WD-xmlschema-2-20000922/

XML-Signature-RD Reagle, J., "XML Signature Requirements", RFC2907,

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.

Recommendation. J. Clark, S. DeRose. October 1999.

http://www.w3.org/TR/1999/REC-xpath-19991116

XPointer XML Pointer Language (XPointer). Candidate

Recommendation. S. DeRose, R. Daniel, E. Maler.

http://www.w3.org/TR/2000/CR-xptr-20000607

XSL Extensible Stylesheet Language (XSL) Working Draft.

S. Adler, A. Berglund, J. Caruso, S. Deach, P.

Grosso, E. Gutentag, A. Milowski, S. Parnell, J.

Richman, S. Zilles. March 2000.

http://www.w3.org/TR/2000/WD-xsl-

20000327/xslspec.html

XSLT XSL Transforms (XSLT) Version 1.0. Recommendation.

J. Clark. November 1999.

http://www.w3.org/TR/1999/REC-xslt-19991116.html

12. Authors' Addresses

Donald E. Eastlake 3rd

Motorola, Mail Stop: M2-450

20 Forbes Boulevard

Mansfield, MA 02048 USA

Phone: 1-508-261-5434

EMail: Donald.Eastlake@motorola.com

Joseph M. Reagle Jr., W3C

Massachusetts Institute of Technology

Laboratory for Computer Science

NE43-350, 545 Technology Square

Cambridge, MA 02139

Phone: 1.617.258.7621

EMail: reagle@w3.org

David Solo

Citigroup

909 Third Ave, 16th Floor

NY, NY 10043 USA

Phone: +1-212-559-2900

EMail: dsolo@alum.mit.edu

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