XML Security 1.1 Requirements and Design Considerations

W3C Working Draft 03 March 2011

This version:
Latest published version:
Latest editor's draft:
Previous version:
Frederick Hirsch, Nokia
Thomas Roessler, W3C


This Note summarizes scenarios, design decisions, and requirements for the XML Signature and Canonical XML specifications, to guide ongoing W3C work to revise these specifications.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Changes since the previous publication include addition of a new section to record requirements to correct known issues and formatting changes due to conversion to use ReSpec source. Please review differences between this and the previous Working Draft.

This document was published by the XML Security Working Group as a Working Draft. If you wish to make comments regarding this document, please send them to public-xmlsec@w3.org (subscribe, archives). All feedback is welcome.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. The group does not expect this document to become a W3C Recommendation. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1. Introduction

This use case and requirements document is intended to summarize use cases and requirements driving revisions to XML Signature 2nd Edition [XMLDSIG-CORE], XML Encryption [XMLENC-CORE], and Canonical XML 1.1 [XML-C14N11]. It is not intended to define all possible use cases for these Recommendations, but rather to provide rationale for decisions leading to XML Signature 1.1, XML Encryption 1.1, XML Signature Properties and XML Security Generic Hybrid Ciphers.

This document outlines general principles and use cases leading to requirements and offers some design options. It elaborates on principles and updates requirements expressed for the original XML Security work including original requirements documents (e.g. [XML-CANONICAL-REQ], and [XMLDSIG-REQUIREMENTS]). This document also reflects material from a W3C workshop on next steps for XML Security [XMLSEC-NEXTSTEPS-2007] and position papers associated with the workshop, including [XMLDSIG-COMPLEXITY], [XMLDSIG-SEMANTICS], and [XMLDSIG-THOMPSON].

Design options were documented early on to provide a starting point with the expectation that specifications developed to meet the requirements could subsequently differ in design choices.Thus the design choices in this document should be viewed as historical information.

2. Principles

The following design principles will be used to guide further development of XML Security, including XML Signature, XML Encryption and Canonical XML. These principles are intended to encourage consistent design decisions, to provide insight into design rationale and to anchor discussions on requirements and design. This list includes items from the original requirements for XML Signature [XMLDSIG-REQUIREMENTS] as well as general principles from EXI [EXI]. Listed in alphabetical order:

Backward compatible:

Backward compatibility should not be broken unnecessarily. Versioning should be clearly considered. Consideration must be given, for example, for interoperability with the First and Second Editions of XML Signature [XMLDSIG-CORE].

Consistent with the Web Architecture:

XML Security must be consistent with the Web Architecture [WEBARCH].


XML Security should enable efficient implementations, in order to remove barriers to adoption and use.

Meet common requirements, enable extensibility:

One of primary objectives of XML Signature is to support a wide variety of use cases requiring digital signatures, including situations requiring multiple signatures, counter-signatures, and signatures including multiple items to be included in a signature. Extensibility should be possible, but by default options should be constrained when the flexibility is not needed.


To reach the broadest set of applications, reduce the security threat footprint and improve efficiency, simple, elegant approaches are preferred to large, analytical or complex ones.


Recognize pragmatic issues, including recognizing that software might be implemented in layers, with a security layer independent of an application layer.

Reuse Existing Open Standards

Existing open standards should be reused where possible, as long as other principles can be met.


XML Security should adhere to security best practices, and minimize the opportunities for threats based on XML Security mechanisms.

XML Interoperable:

XML Security must integrate well with existing XML technologies, be compatible with the XML Information Set [XML-INFOSET], in order to maintain interoperability with existing and prospective XML specifications.

XML Signatures are First Class Objects:

XML Signatures should themselves be self-describing first class XML objects [XMLDSIG-REQUIREMENTS] . This means that XML Signatures can be referenced via URI and used in other operations. For example, an XML Signature may be signed or encrypted, or referred to in a statement (such as an RDF statement).

3. Requirements and Design Options

This section outlines the motivation, requirements and design considerations for XML Security 1.1.

3.1 Widget Security

3.1.1 Use Cases

Widgets may require signing for integrity protection and source authentication. This signing of a Widget package may be provided using XML Signature.

3.1.2 Requirements

Provide the ability to sign and verify a widget package using XML Signature. Enable the use of SHA-256 to support sufficient security. Support the use of properties in a XML Signature, including Profile, Role, and Identifier properties to enable interoperable interpretation of signatures. See the Widget Signature specification for a summary of requirements [WIDGETS-DIGSIG] .

3.1.3 Design

Define generic widget properties. See XML Signature Properties [XMLDSIG-PROPERTIES] .

3.2 Derived Keys

3.2.1 Use Cases and Background

Several open specifications make use of derived keys, e.g. RSA Laboratories' PKCS #5 v2.0 [PKCS5] and OASIS' WS-SecureConversation Version 1.3 [WS-SECURECONVERSATION13] . These derived keys are used for a variety of purposes including encryption and message authentication, and the purpose of key derivation itself is typically a combination of a desire to expand a given, but limited, set of key material and prudent security practices of limiting use (exposure) of such key material.

Contrary to the situation in the ASN.1-based world (e.g. S/MIME [SMIME] ), there is currently a lack of general support in the core XML Security specifications, XML Signature and XML Encryption, for derived keys. Amendment 1 of the aforementioned PKCS #5 v2.0 Amendment 1 [PKCS5] adds support for derived keys only in the context of password-based cryptography. Other XML-based open specifications have similar limitations (see below). This means that an originator of an XML document or message cannot generally make use of key derivation in a standardized manner when performing cryptographic operations on that document.

3.2.2 Use Of Derived Keys in Existing WS-* Specifications

This section outlines the use of derived keys with Web Services specifications related to Web Services Security [WS-SECURITY11].

Web Services Security: UsernameToken Profile Version 1.1

This specification [WSS-USERNAME11] describes a key derivation technique for passwords using salt and iteration count (PKCS #5 PBKDF1). It does not allow use of PBKDF2, which is the recommended method to derive keys from passwords in PKCS #5 v2.0. Initial key material cannot be referenced other than with wsu:Id. The key length will always be 160 bits. WS-Trust Version 1.3:

Ws-Trust Version 1.3 [WS-TRUST13] describes key derivation through a combination of entropies from both parties. The key is never sent on the wire. The key is never referenced directly (but further key material is derived from it). WS-Trust provides one specific method to derive keys which builds on the P_hash (P_SHA-1) function from TLS. WS-SecurityPolicy 1.2:

WS-SecurityPolicy Version 1.2 [WS-SECURITYPOLICY12] really only specifies whether derived keys shall be used or not but may also specify the algorithm to derive keys. The specification also identifies when derived key tokens shall appear in message headers (header layout). WS-SecurityPolicy relies on WS-SecureConversation for the definition of derived keys, key derivation methods and derived key token format. WS-SecureConversation 1.3:

This specification [WS-SECURECONVERSATION13] defines the wsc:DerivedKeyTokenType token type. The derived key token can be used to derive keys from any other token that contains keys. The key derivation algorithm specified builds on the P_hash (P_SHA-1) function from TLS, just as the algorithm in the Web Service Security UsernameToken Profile document. Citing from the specification: "The <wsc:DerivedKeyToken> element is used to indicate that the key for a specific reference is generated from the function. This is so that explicit security tokens, secrets, or key material need not be exchanged as often." (This latter seems dubious since the DerivedKeyToken still needs to be exchanged.) Further: "Basically, a signature or encryption references a <wsc:DerivedKeyToken> in the <wsse:Security> header that, in turn, references the <wsc:SecurityContextToken>." The derived key token does not support references using key identifiers or key names. All references must use an ID (to a wsu:Id attribute) or a URI reference to the <wsc:Identifier> element in the Security Context Token.

3.2.3 Solution Requirements Use in existing specifications (R1)

A derived key type shall be possible to use in those situations where existing specifications make use of ad-hoc derived keys or needs a derived key type

The motivation for this requirement is that any XML Security definition shall be generic enough that there shall be no need to continue with "point" solutions for derived keys; i.e. it shall cover existing and foreseeable uses. No external dependencies (R2)

A derived key type shall enable the simple use of derived keys with XML Signature or XML Encryption -using applications, and shall not require import of non-W3C developed specifications with complex security tokens.

The motivation for this is that basic use of XML Signature or XML Encryption should not require use of externally defined security tokens or other security specification elements. Continued use of existing derivation methods (R3)

An XML Security derived key type shall allow for existing methods to derive keys; i.e. it shall be possible to use already specified key derivation methods with the new derived key type.

This requirement is based on the assumptions that implementations may want to continue with already chosen key derivation schemes. Future-proof with regards to key lengths (R4)

A derived key type shall allow for arbitrary derived key lengths. Referential flexibility (R5)

A derived key type shall allow for referencing using any referencing method in use today for other key types used in XMLDsig or XMLEnc.

A derived key type shall allow for forward referencing with reference lists as recommended by WS-I BSP [WSI-BSP10] .

3.2.4 Existing Specifications vs. Requirements

Evaluating the existing specifications against the requirements gives the following result:

UsernameToken Profile:

  • R1: Not met (method specified in UsernameToken profile is ad-hoc for UsernameToken specifically)

  • R2: Not met (method requires use of UsernameToken profile)

  • R3: Not met (UsernameToken profile mandates use of specified mechanism)

  • R4: Not met (Only accept length of 160 bits)

  • R5: Not met (No referencing with KeyName or KeyIdentifier and no <referenceList> element)


  • R1: N/A (WS-Trust does not define a derived key type per se; only a method to derive keys)

  • R2: N/A

  • R3: Meets (Through use of URI to identify method and extensibility)

  • R4: Meets

  • R5: Meets (Choice of STS on how to identify key)


  • R1: N/A (WS-SecurityPolicy does not define a derived key type)

  • R2: N/A

  • R3: Meets (Through the use of URIs to identify key derivation methods and schema extensibility)

  • R4: Meets

  • R5: N/A


  • R1: Meets

  • R2: Does not meet.

  • R3: Meets (may use the <Properties> element to carry parameters for other key derivation methods.

  • R4: Meets

  • R5: Does not meet as referencing can only be done to a <wsse:SecurityTokenReference>

3.2.5 Design Options Create a ds:DerivedKeyType type modeled after the xenc:EncryptedKeyType.

In this design option, the new DerivedKeyType is modeled after the xenc:EncryptedKeyType. A *possible* outline of such a type could be:

Outline of possible DerivedKeyType schema definition

<element name="DerivedKey" type="xmlsec:DerivedKeyType"/>
<complexType name="DerivedKeyType">
<element name="KeyDerivationMethod" 
type="xmlsec:KeyDerivationMethodType" minOccurs="0"/>
<element ref="xenc:ReferenceList" minOccurs="0"/>
<element name="CarriedKeyName" type="string" minOccurs="0"/>
<attribute name="Id" type="ID" use="optional"/>
<attribute name="Type" type="anyURI" use="optional"/>

<complexType name="KeyDerivationMethodType">
<any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
<attribute name="Algorithm" type="anyURI" use="required"/>

The proposal immediately meets requirements R2, R3 (any key derivation method may be used, including the ones specified, e.g., in WS-SecureConversation), R4 and R5. For R1 we have:

Username Token Profile: As the UsernameToken Profile requires use of an existing procedure to derive keys, the proposal cannot formally meet requirement R1. However, since the UsernameTokenType is extensible, syntactically the requirement can be met since a <ds:DerivedKey> element could be placed in lieu of the current <salt> and <iteration> elements.

WS-Trust: Use of derived keys in WS-Trust is _implicit_, since the derived key is never sent. The derived keys may be referenced by any available means in issued tokens and the requester is only required to identify particular key derivation methods. Since URIs are used for this (the <wst:ComputedKey> element), any other key derivation method with a well-known URI may be used. Specifically, one can also envision an STS returning a proof token containing a <DerivedKey> element when there already is a shared key between the STS and a token requester. And so, R1 is met.

WS-SecurityPolicy: Not affected by a new key type. R1 is met.

WS-SecureConversation: Use of derived keys in WS-SecureConversation is typically based on the establishment of a session context, from which specific keys are derived. The proposed <xmlsec:DerivedKeyType> type may be used in a similar fashion, although the interactive nature of WS-SecureConversation (exchange of Nonces, Labels) may still favor use of the existing DerivedKeyToken in this context. But as a counterexample, a party that wishes to send data authenticated with a key derived from a key established in the session, may do so using the <xmlsec:DerivedKey> element in the <ds:KeyInfo> element, and the element may refer to a SecurityContextToken that identifies the base key. This would, it seems, eliminate an absolute need for a <wsc:DerivedKeyToken> (and should be similar in nature as the "Implied Derived Key" option in WS-SecureConversation). Also, the <wsc:DerivedKeyToken> implies use of a particular key derivation algorithm (the <Label> and <Nonce> elements) although it does not require them.

In summary, WS-Trust and WS-SecurityPolicy are not directly affected by this proposal. UsernameToken profile could use the proposal if the (artificial) requirement to only use the key derivation method specified in the UsernameToken Profile document was relaxed. WS-SecureConversation comes close in establishing an alternative but the specification defines a token primarily for use in interactive sessions based on a security context and which is designed for a particular key derivation method. It also seems strange to require use of such a token in more basic XMLDsig or XMLEnc situations. Finally, the proposal seems to be able to replace the DerivedKeyToken currently used in WS-SecureConversation.

3.3 Algorithm security and interoperability

3.3.1 Fundamentals

XML Signature specifies algorithm identifiers and implementation requirements for algorithms related to various aspects of signature processing, including digest and signature algorithms. The algorithms listed in XML Signature, Second Edition date from the original XML Signature Recommendation, published in 2002. Since that time there have been new algorithms introduced to address security risks associated with earlier algorithms (e.g. SHA-256 versus SHA-1), changes in patent status related to algorithms (e.g. RSA signing no longer has licensing requirements), and additional algorithms introduced to meet additional requirements (Suite B algorithms [SUITEB], [ECC-ALGS] ).

In order to meet the principle of "Secure" and "Pragmatic", new algorithm requirements should be met.

3.3.2 Requirements Address SHA security concerns, recognize RSA de-facto use.

In order to address concerns related to potential risks associated with SHA-1 [SHA-1-Collisions], the following algorithm requirements that update the SHA algorithm should be met in XML Signature 1.1 and XML Encryption 1.1:

  • Digest:

    SHA256 be required.

    SHA384 and SHA512 optional.

  • Mac:

    HMAC-SHA256 recommended.

    HMAC-SHA384 and HMAC-SHA512 optional. (Note these are Recommended in XML Signature 1.1.)

  • Signature:

    RSAwithSHA256 required.

    RSAwithSHA384, RSAwithSHA512 optional. Revise guidance for DSAwithSHA1

In order to discourage the use of DSAwithSHA1 but to continue to enable interoperability, the following algorithm changes are requirements;

  • Signature:

    Continue to require DSAwithSHA1 for signature verification, but change DSAwithSHA1 to optional (from required) for signature generation. Add Suite B algorithm support

In order to:

  1. enable long term security for digital signatures (including in commercial contexts),

  2. ensure that the XML Signature standard is cryptographically secure and makes use of the best current practices for digital signature algorithms, and

  3. enable use of XML Signature technology in a wide variety of commercial and government applications, including those that require Suite B

elliptic curve algorithms are to be added to XML Signature.

The additional algorithm requirements are as follows:

  • Signature:

    Require ECDSAwithSHA256.

    ECDSAwithSHA1, ECDSAwithSHA384, ECDSAwithSHA512 optional. (Note ECDSAwithSHA1 is Discouraged in XML Signature 1.1 due to concerns with SHA-1.)

  • Define ECKeyValue element to enable interoperable exchange of EC public key values in XML Signature context.

  • Provide profile guidance for use of RFC 4050 [RFC4050] when it continues to be used in XML Signature context but indicate preference for mechanism defined in XML Signature.

The last two requirements are discussed in more detail in the following design section.

3.3.3 Suite B Elliptic Curve Key Value Design (ECKeyValue) RFC 4050 issues in XML Signature context

RFC 4050 is an informational RFC that defines a method of representing ECDSA public keys and ECC curve parameters for use with XML Signature, but it has some issues related to XML Signature:

  • The RFC 4050 definition of an ECDSAKeyValue is larger than necessary.

    An ECDSAKeyValue is defined by the type ECPointType, which has subelements X and Y. X and Y are defined as FieldParamsType which is an abstract type. Separate derived types are defined for prime fields, trinomial base fields, pentanomial base fields, and odd characteristic extension fields. In order to validate against the 4050 schema, one must include the type attribute from the XML schema instance namespace. This is not a significant problem but it does make the public key larger than necessary.

  • ECPointType definition is inconsistent with ANSI X9.62 and RFC 3279.

    ECPointType is reused in the definition of the ExplicitParamsType to describe the base point of a curve. The field parameters are already included in the FieldParams element. The use of the FieldParamsType in the ECPointType definition appears to be a mistake in 4050. If you look at the ASN.1 definition for ECC public keys in RFC 3279 [RFC3279] , ECPoint simply references the Point to Octet String conversion function in ANSI X9.62 (section A.5.6 in the 2005 version, section 4.3.6 in the 1998 version). The conversion functions in X9.62 are not ASN.1 specific and it appears they would be implemented as part of any ECC crypto library. It appears that RFC 4050 tried to avoid using any of the conversion functions in X9.62 but somehow mixed up the definitions between a field type and a field element.

  • Limitation of the decimal type in XSD

    RFC 4050 defines X and Y (at least for prime and odd characteristic extension fields) as xs:nonNegativeInteger which derives from the xs:decimal primitive type. However, XSD requires implementations to support only a maximum of 18 digits (see section 3.2.3 in [XMLSCHEMA11-2] ). It is possible to create an example requiring 77 and 78 digits for X and Y respectively. This means that there is no guarantee that an RFC 4050 compliant ECDSAKeyValue element will actually validate against the RFC 4050 schema.

  • Collision between the RFC 4050 DTD and the XMLDSIG DTD

    Merging the RFC 4050 DTD into the XMLDSIG DTD is a problem due to conflicting DTD definitions. In ECDSAKeyValue, Y is defined as follows:

    Definition of Y in ECDSAKeyValue
    <!ATTLIST Y Value CDATA #required>

    However, DSAKeyValue defines Y as follows:

    Definition of Y in DSAKeyValue

    ECDSAKeyValue also contains identical definition for elements SEED and P as DSAKeyValue.

    It does not seem possible to scope the definition of Y under a specific element in DTD. Proposed Solution to RFC 4050 issues in XML Signature context

Because of these issues, a possible proposed solution is for XML Signature 1.1 to define a new ECPublicKey element in the ds namespace rather than attempt to reuse the RFC 4050 ECDSAPublicKey elements. This new element will be based on the ASN.1 definition ANSI X9.62 and RFC 3279. Changing the name of the element to ECPublicKey means it can be also used in XML Encryption to support ECDH. (Note, XML Signature 1.1 defined ECKeyValue instead).

To maximize interoperability with existing RFC 4050 implementations, we should also put a note in 1.1 to recommend implementations to support a profile of RFC 4050. The profile will support only named prime curves.

3.4 Correct known issues

This section summarizes the motivation for new features designed to address known issues. (This section of the requirements document was written after the XML Signature 1.1 specification was updated in order to record the rationale for the changes.)

3.4.1 Limitations associated with X509IssueSerial

The X509IssuerSerialNumber child element of the X509IssuerSerialType XML Schema type was defined to be an integer holding an X.509 certificate serial number. XML Schema validators may not support integer types with decimal data exceeding 18 decimal digits [XMLSCHEMA-2] and this maximum length has proven insufficient as many Certificate Authorities issue certificates with large random serial numbers that exceed this limit. A new element is defined in XML Signature 1.1 with a different type definition, the sig11:X509Digest element, and a warning that deployments that make use of the X509IssuerSerial element should take care if schema validation is involved.

3.4.2 Simplify access to ds:KeyInfo

The RetrievalMethod is ambiguous about whether the result is an element within KeyInfo or the KeyInfo element itself. It also supports the use of ds:Transform adding complexity. The new KeyInfoReference element removes the ambiguity by always referencing the KeyInfo element itself. It also is simpler in that it does not allow any ds:Transform children.

3.4.3 XML KeyValue type interoperability

XML Signature 1.1 defines XML formats to convey key information in the KeyValue element. There are scenarios where at least one of signer and/or verifier are not able to serialize keys in those XML formats. The DEREncodedKeyValue element has been added to XML Signature 1.1 to support use of other binary encodings.

3.4.4 Support OCSP use case

It is sometimes useful to provide an OCSP response along with an X.509 certificate. The OCSPResponse element was added to X509Data to support this use case.

4. Acknowledgments

Contributions received from the members of the XML Security Working Group: Scott Cantor, Juan Carlos Cruellas, Pratik Datta, Gerald Edgar, Ken Graf, Phillip Hallam-Baker, Brad Hill, Frederick Hirsch, Brian LaMacchia, Konrad Lanz, Hal Lockhart, Cynthia Martin, Rob Miller, Sean Mullan, Shivaram Mysore, Magnus Nyström, Bruce Rich, Thomas Roessler, Ed Simon, Chris Solc, John Wray, Kelvin Yiu.

A. References

Dated references below are to the latest known or appropriate edition of the referenced work. The referenced works may be subject to revision, and conformant implementations may follow, and are encouraged to investigate the appropriateness of following, some or all more recent editions or replacements of the works cited. It is in each case implementation-defined which editions are supported.

A.1 Normative references

No normative references.

A.2 Informative references

D. McGrew, K. Igoe, M. Salter. RFC 6090: Fundamental Elliptic Curve Cryptography Algorithms, IETF Informational RFC, February 2011, URL: http://www.rfc-editor.org/rfc/rfc6090.txt
Takuki Kamiya; John Schneider. Efficient XML Interchange (EXI) Format 1.0. 8 December 2009. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2009/CR-exi-20091208/
B. Kaliski. PKCS #5 v2.0: Password-Based Cryptography Standard IETF RFC 2898. September 2000. URL: http://www.ietf.org/rfc/rfc2898.txt
W. Polk, R. Housley, L. Bassham. Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile. April 2002. Internet RFC 3279. URL: http://www.ietf.org/rfc/rfc3279.txt
S. Blake-Wilson, G. Karlinger, T. Kobayashi, Y. Wang. Using the Elliptic Curve Signature Algorithm (ECDSA) for XML Digital Signatures. IETF RFC 4050. April 2005. URL: http://www.ietf.org/rfc/rfc4050.txt
X. Wang, Y.L. Yin, H. Yu. Finding Collisions in the Full SHA-1. In Shoup, V., editor, Advances in Cryptology - CRYPTO 2005, 25th Annual International Cryptology Conference, Santa Barbara, California, USA, August 14-18, 2005, Proceedings, volume 3621 of LNCS, pages 17–36. Springer, 2005. URL: http://people.csail.mit.edu/yiqun/SHA1AttackProceedingVersion.pdf (also published in http://www.springerlink.com/content/26vljj3xhc28ux5m/)
B. Ramsdell. S/MIME Version 3 Message Specification. June 1999. Internet RFC 2633. URL: http://www.ietf.org/rfc/rfc2633.txt
NSA Suite B Cryptography, http://www.nsa.gov/ia/programs/suiteb_cryptography/
Norman Walsh; Ian Jacobs. Architecture of the World Wide Web, Volume One. 15 December 2004. W3C Recommendation. URL: http://www.w3.org/TR/2004/REC-webarch-20041215
M. Caceres,F Hirsch, M Priestley Digital Signatures for Widgets. 24 June 2010. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2010/CR-widgets-digsig-20100624
A. Nadalin, M. Goodner, M. Gudgin, A. Barbir, H. Granqvist. WS-SecureConversation 1.3,OASIS Standard, 1 March 2007. URL: http://www.oasis-open.org/specs/index.php#wssecconv1.3
A. Nadalin, C. Kaler, R. Monzillo, P. Hallam-Baker. Web Services Security: SOAP Message Security 1.1 (WS-Security 2004),, OASIS Standard, 1 February 2006. URL: http://www.oasis-open.org/specs/index.php#wssv1.1
A. Nadalin, M. Goodner, M. Gudgin, A. Barbir, H. Granqvist. WS-SecurityPolicy 1.2, OASIS Standard,, 1 July 2007. URL: http://www.oasis-open.org/specs/index.php#wssecpolv1.2
A. Nadalin, M. Goodner, M. Gudgin, A. Barbir, H. Granqvist. WS-Trust 1.3,,OASIS Standard, 19 March 2007. URL: http://www.oasis-open.org/specs/index.php#wstrustv1.3
M. McIntosh, M. Gudgin, K. S. Morrison, A. Barbir. Basic Security Profile Version 1.0, WS-I Final Material, 30 March 2007. URL: http://www.ws-i.org/Profiles/BasicSecurityProfile-1.0.html
A. Nadalin, C. Kaler, R. Monzillo, P. Hallam-Baker. Web Services Security UsernameToken Profile 1.1, OASIS Standard Specification, 1 February 2006. URL: http://www.oasis-open.org/committees/download.php/16782/wss-v1.1-spec-os-UsernameTokenProfile.pdf
John Boyer, Glenn Marcy. Canonical XML Version 1.1. 2 May 2008. W3C Recommendation. URL: http://www.w3.org/TR/2008/REC-xml-c14n11-20080502/
James Tauber; Joel Nava. XML Canonicalization Requirements. 5 June 1999. W3C Note. URL: http://www.w3.org/TR/1999/NOTE-xml-canonical-req-19990605
John Cowan; Richard Tobin. XML Information Set (Second Edition). 4 February 2004. W3C Recommendation. URL: http://www.w3.org/TR/2004/REC-xml-infoset-20040204/
Brad Hill. Complexity as the Enemy of Security: Position Paper for W3C Workshop on Next Steps for XML Signature and XML Encryption.. 25-26 September 2007. W3C Workshop. URL: http://www.w3.org/2007/xmlsec/ws/papers/04-hill-isecpartners/
Joseph Reagle; et al. XML Signature Syntax and Processing (Second Edition). 10 June 2008. W3C Recommendation. URL: http://www.w3.org/TR/2008/REC-xmldsig-core-20080610
Frederick Hirsch. XML Signature Properties. 3 March 2011. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2011/CR-xmldsig-properties-20110303/
Joseph Reagle Jr. XML-Signature Requirements. 14 October 1999. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/1999/WD-xmldsig-requirements-19991014
Sebastian Gajek, Lijun Liao, and Jörg Schwenk. Towards a Semantic of XML Signature: Position Paper for W3C Workshop on Next Steps for XML Signature and XML Encryption 25-26 September 2007. W3C Workshop. URL: http://www.w3.org/2007/xmlsec/ws/papers/07-gajek-rub/
Henry Thompson. Radical proposal for Vnext of XML Signature: Position Paper for W3C Workshop on Next Steps for XML Signature and XML Encryption 26 September 2007. W3C Workshop. URL: http://www.w3.org/2007/xmlsec/ws/papers/20-thompson/
Donald Eastlake; Joseph Reagle. XML Encryption Syntax and Processing. 10 December 2002. W3C Recommendation. URL: http://www.w3.org/TR/2002/REC-xmlenc-core-20021210/
Paul V. Biron; Ashok Malhotra. XML Schema Part 2: Datatypes Second Edition. 28 October 2004. W3C Recommendation. URL: http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/
Henry S. Thompson; et al. W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes. 30 January 2009. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2009/WD-xmlschema11-2-20090130
Workshop Report W3C Workshop on Next Steps for XML Signature and XML Encryption 25-26 September 2007. W3C Workshop Report. URL: http://www.w3.org/2007/xmlsec/ws/report.html