Artifact Identifier:

ws-trust-1.3-spec-cs-01

Location:

Current: http://docs.oasis-open.org/ws-sx/ws-trust/200512/

This Version: http://docs.oasis-open.org/ws-sx/ws-trust/200512/ws-trust-1.3-spec-cs-01.doc

Previous Version: http://docs.oasis-open.org/ws-sx/ws-trust/200512/ws-trust-1.3-spec-cd-01.doc

Artifact Type:

specification

Technical Committee:

OASIS Web Service Secure Exchange TC

Chair(s):

Kelvin Lawrence, IBM

Chris Kaler, Microsoft

Editor(s):

Anthony Nadalin, IBM

Marc Goodner, Microsoft

Martin Gudgin, Microsoft

Abbie Barbir, Nortel

Hans Granqvist, VeriSign

OASIS Conceptual Model topic area:

Related work:

N/A

Abstract:

This specification defines extensions that build on [WS-Security] to provide a framework for requesting and issuing security tokens, and to broker trust relationships.

Status:

This document was last revised or approved by the WS-SX TC on the above date. The level of approval is also listed above. Check the current location noted above for possible later revisions of this document. This document is updated periodically on no particular schedule.

Technical Committee members should send comments on this specification to the Technical Committee’s email list. Others should send comments to the Technical Committee by using the “Send A Comment” button on the Technical Committee’s web page at http://www.oasis-open.org/committees/ws-sx.

For information on whether any patents have been disclosed that may be essential to implementing this specification, and any offers of patent licensing terms, please refer to the Intellectual Property Rights section of the Technical Committee web page (http://www.oasis-open.org/committees/ws-sx/ipr.php).

The non-normative errata page for this specification is located at http://www.oasis-open.org/committees/ws-sx.

Copyright © OASIS Open 2006. All Rights Reserved.

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1         Introduction. 5

1.1 Goals and Non-Goals. 5

1.2 Requirements. 6

1.3 Namespace. 6

1.4 Schema and WSDL Files. 7

1.5 Terminology. 7

1.5.1 Notational Conventions. 8

1.6 Normative References. 9

1.7 Non-Normative References. 10

2         Web Services Trust Model 11

2.1 Models for Trust Brokering and Assessment 12

2.2 Token Acquisition. 12

2.3 Out-of-Band Token Acquisition. 13

2.4 Trust Bootstrap. 13

3         Security Token Service Framework. 14

3.1 Requesting a Security Token. 14

3.2 Returning a Security Token. 15

3.3 Binary Secrets. 17

3.4 Composition. 17

4         Issuance Binding. 19

4.1 Requesting a Security Token. 19

4.2 Request Security Token Collection. 21

4.2.1       Processing Rules. 23

4.3 Returning a Security Token Collection. 23

4.4 Returning a Security Token. 24

4.4.1 wsp:AppliesTo in RST and RSTR. 25

4.4.2 Requested References. 26

4.4.3 Keys and Entropy. 26

4.4.4 Returning Computed Keys. 27

4.4.5 Sample Response with Encrypted Secret 28

4.4.6 Sample Response with Unencrypted Secret 28

4.4.7 Sample Response with Token Reference. 29

4.4.8 Sample Response without Proof-of-Possession Token. 29

4.4.9 Zero or One Proof-of-Possession Token Case. 29

4.4.10 More Than One Proof-of-Possession Tokens Case. 30

4.5 Returning Security Tokens in Headers. 31

5         Renewal Binding. 33

6         Cancel Binding. 36

6.1 STS-initiated Cancel Binding. 37

7         Validation Binding. 39

8         Negotiation and Challenge Extensions. 42

8.1 Negotiation and Challenge Framework. 43

8.2 Signature Challenges. 43

8.3 Binary Exchanges and Negotiations. 44

8.4 Key Exchange Tokens. 45

8.5 Custom Exchanges. 46

8.6 Signature Challenge Example. 46

8.7 Custom Exchange Example. 48

8.8 Protecting Exchanges. 49

8.9 Authenticating Exchanges. 50

9         Key and Token Parameter Extensions. 51

9.1 On-Behalf-Of Parameters. 51

9.2 Key and Encryption Requirements. 51

9.3 Delegation and Forwarding Requirements. 56

9.4 Policies. 57

9.5 Authorized Token Participants. 58

10       Key Exchange Token Binding. 59

11       Error Handling. 61

12       Security Considerations. 62

A.       Key Exchange. 64

A.1 Ephemeral Encryption Keys. 64

A.2 Requestor-Provided Keys. 64

A.3 Issuer-Provided Keys. 65

A.4 Composite Keys. 65

A.5 Key Transfer and Distribution. 66

A.5.1 Direct Key Transfer 66

A.5.2 Brokered Key Distribution. 66

A.5.3 Delegated Key Transfer 67

A.5.4 Authenticated Request/Reply Key Transfer 68

A.6 Perfect Forward Secrecy. 69

B.       WSDL. 70

C.       Acknowledgements. 72

D.       Revision History. 77

 

 

[WS-Security] defines the basic mechanisms for providing secure messaging.  This specification uses these base mechanisms and defines additional primitives and extensions for security token exchange to enable the issuance and dissemination of credentials within different trust domains.

 

In order to secure a communication between two parties, the two parties must exchange security credentials (either directly or indirectly).  However, each party needs to determine if they can "trust" the asserted credentials of the other party.

 

In this specification we define extensions to [WS-Security] that provide:

·         Methods for issuing, renewing, and validating security tokens.

·         Ways to establish assess the presence of, and broker trust relationships.

 

Using these extensions, applications can engage in secure communication designed to work with the general Web services framework, including WSDL service descriptions, UDDI businessServices and bindingTemplates, and [SOAP] [SOAP2] messages.

 

To achieve this, this specification introduces a number of elements that are used to request security tokens and broker trust relationships.

 

This specification defines a number of extensions; compliant services are NOT REQUIRED to implement everything defined in this specification.  However, if a service implements an aspect of the specification, it MUST comply with the requirements specified (e.g. related "MUST" statements).

 

Section 12 is non-normative.

1.1 Goals and Non-Goals

The goal of WS-Trust is to enable applications to construct trusted [SOAP] message exchanges. This trust is represented through the exchange and brokering of security tokens. This specification provides a protocol agnostic way to issue, renew, and validate these security tokens.

 

This specification is intended to provide a flexible set of mechanisms that can be used to support a range of security protocols; this specification intentionally does not describe explicit fixed security protocols.

 

As with every security protocol, significant efforts must be applied to ensure that specific profiles and message exchanges constructed using WS-Trust are not vulnerable to attacks (or at least that the attacks are understood).

 

The following are explicit non-goals for this document:

·         Password authentication

·         Token revocation

·         Management of trust policies

 

Additionally, the following topics are outside the scope of this document:

·         Establishing a security context token

·         Key derivation

1.2 Requirements

The Web services trust specification must support a wide variety of security models.  The following list identifies the key driving requirements for this specification:

·         Requesting and obtaining security tokens

·         Establishing, managing and assessing trust relationships

1.3 Namespace

The [URI] that MUST be used by implementations of this specification is:

Table 1 lists XML namespaces that are used in this specification. The choice of any namespace prefix is arbitrary and not semantically significant.

Table 1: Prefixes and XML Namespaces used in this specification.

Prefix	Namespace	Specification(s)
S11	http://schemas.xmlsoap.org/soap/envelope/	[SOAP]
S12	http://www.w3.org/2003/05/soap-envelope	[SOAP12]
wsu	http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd	[WS-Security]
wsse	http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd	[WS-Security]
wsse11	http://docs.oasis-open.org/wss/oasis-wss-wsecurity-secext-1.1.xsd	[WS-Security]
wst	http://docs.oasis-open.org/ws-sx/ws-trust/200512	This specification
ds	http://www.w3.org/2000/09/xmldsig#	[XML-Signature]
xenc	http://www.w3.org/2001/04/xmlenc#	[XML-Encrypt]
wsp	http://schemas.xmlsoap.org/ws/2004/09/policy	[WS-Policy]
wsa	http://www.w3.org/2005/08/addressing	[WS-Addressing]
xs	http://www.w3.org/2001/XMLSchema	[XML-Schema1] [XML-Schema2]

1.4 Schema and WSDL Files

The schema [XML-Schema1], [XML-Schema2]  for this specification can be located at:

 

The WSDL for this specification can be located in Appendix II of this document as well as at:

In this document, reference is made to the wsu:Id attribute, wsu:Created and wsu:Expires elements in the utility schema. These were added to the utility schema with the intent that other specifications requiring such an ID or timestamp could reference it (as is done here).

1.5 Terminology

Claim – A claim is a statement made about a client, service or other resource (e.g. name, identity, key, group, privilege, capability, etc.).

Security Token – A security token represents a collection of claims.

Signed Security Token – A signed security token is a security token that is cryptographically endorsed by a specific authority (e.g. an X.509 certificate or a Kerberos ticket).

Proof-of-Possession Token – A proof-of-possession (POP) token is a security token that contains secret data that can be used to demonstrate authorized use of an associated security token. Typically, although not exclusively, the proof-of-possession information is encrypted with a key known only to the recipient of the POP token.

Digest – A digest is a cryptographic checksum of an octet stream.

Signature – A signature is a value computed with a cryptographic algorithm and bound to data in such a way that intended recipients of the data can use the signature to verify that the data has not been altered and/or has originated from the signer of the message, providing message integrity and authentication. The signature can be computed and verified with symmetric key algorithms, where the same key is used for signing and verifying, or with asymmetric key algorithms, where different keys are used for signing and verifying (a private and public key pair are used).

Trust Engine– The trust engine of a Web service is a conceptual component that evaluates the security-related aspects of a message as described in section 2 below.

Security Token Service – A security token service (STS) is a Web service that issues security tokens (see [WS-Security]).  That is, it makes assertions based on evidence that it trusts, to whoever trusts it (or to specific recipients).  To communicate trust, a service requires proof, such as a signature to prove knowledge of a security token or set of security tokens. A service itself can generate tokens or it can rely on a separate STS to issue a security token with its own trust statement (note that for some security token formats this can just be a re-issuance or co-signature).  This forms the basis of trust brokering.

Trust – Trust is the characteristic that one entity is willing to rely upon a second entity to execute a set of actions and/or to make set of assertions about a set of subjects and/or scopes.

Direct Trust – Direct trust is when a relying party accepts as true all (or some subset of) the claims in the token sent by the requestor.

Direct Brokered Trust – Direct Brokered Trust is when one party trusts a second party who, in turn, trusts or vouches for, a third party.

Indirect Brokered Trust – Indirect Brokered Trust is a variation on direct brokered trust where the second party negotiates with the third party, or additional parties, to assess the trust of the third party.

Message Freshness– Message freshness is the process of verifying that the message has not been replayed and is currently valid.

We provide basic definitions for the security terminology used in this specification.  Note that readers should be familiar with the [WS-Security] specification.

1.5.1 Notational Conventions

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

 

Namespace URIs of the general form "some-URI" represents some application-dependent or context-dependent URI as defined in [URI ].

 

This specification uses the following syntax to define outlines for messages:

·         The syntax appears as an XML instance, but values in italics indicate data types instead of literal values.

·         Characters are appended to elements and attributes to indicate cardinality:

o    "?" (0 or 1)

o    "*" (0 or more)

o    "+" (1 or more)

·         The character "|" is used to indicate a choice between alternatives.

·         The characters "(" and ")" are used to indicate that contained items are to be treated as a group with respect to cardinality or choice.

·         The characters "[" and "]" are used to call out references and property names.

·         Ellipses (i.e., "...") indicate points of extensibility. Additional children and/or attributes MAY be added at the indicated extension points but MUST NOT contradict the semantics of the parent and/or owner, respectively. By default, if a receiver does not recognize an extension, the receiver SHOULD ignore the extension; exceptions to this processing rule, if any, are clearly indicated below.

·         XML namespace prefixes (see Table 1) are used to indicate the namespace of the element being defined.

 

Elements and Attributes defined by this specification are referred to in the text of this document using XPath 1.0 expressions. Extensibility points are referred to using an extended version of this syntax:

• An element extensibility point is referred to using {any} in place of the element name. This indicates that any element name can be used, from any namespace other than the namespace of this specification.
• An attribute extensibility point is referred to using @{any} in place of the attribute name. This indicates that any attribute name can be used, from any namespace other than the namespace of this specification.

 

In this document reference is made to the wsu:Idattribute and the wsu:Created and wsu:Expires elements in a utility schema ( http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd). The wsu:Id attribute and the wsu:Created and wsu:Expires elements were added to the utility schema with the intent that other specifications requiring such an ID type attribute or timestamp element could reference it (as is done here).

 

1.6 Normative References

[RFC2119]                    S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997.

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

[RFC2246]                    IETF Standard, "The TLS Protocol", January 1999.

http://www.ietf.org/rfc/rfc2246.txt

[SOAP]                        W3C Note, "SOAP: Simple Object Access Protocol 1.1", 08 May 2000.

http://www.w3.org/TR/2000/NOTE-SOAP-20000508/

[SOAP12]                     W3C Recommendation, "SOAP 1.2 Part 1: Messaging Framework", 24 June 2003.

http://www.w3.org/TR/2003/REC-soap12-part1-20030624/

[URI]                            T. Berners-Lee, R. Fielding, L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 3986, MIT/LCS, Day Software, Adobe Systems, January 2005.

http://www.ietf.org/rfc/rfc3986.txt

[WS-Addressing]          W3C Recommendation, "Web Services Addressing (WS-Addressing)", 9 May 2006.

http://www.w3.org/TR/2006/REC-ws-addr-core-20060509

[WS-Policy]                  W3C Member Submission, "Web Services Policy 1.2 - Framework", 25 April 2006.

http://www.w3.org/Submission/2006/SUBM-WS-Policy-20060425/

[WS-PolicyAttachment] W3C Member Submission, "Web Services Policy 1.2 - Attachment", 25 April 2006.

http://www.w3.org/Submission/2006/SUBM-WS-PolicyAttachment-20060425/

[WS-Security]               OASIS Standard, "OASIS Web Services Security: SOAP Message Security 1.0 (WS-Security 2004)", March 2004.

                                    http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-soap-message-security-1.0.pdf

OASIS Standard, "OASIS Web Services Security: SOAP Message Security 1.1 (WS-Security 2004)", February 2006.

http://www.oasis-open.org/committees/download.php/16790/wss-v1.1-spec-os-SOAPMessageSecurity.pdf

[XML-C14N]                  W3C Recommendation, "Canonical XML Version 1.0", 15 March 2001.

http://www.w3.org/TR/2001/REC-xml-c14n-20010315

[XML-Encrypt]              W3C Recommendation, "XML Encryption Syntax and Processing", 10 December 2002.

http://www.w3.org/TR/2002/REC-xmlenc-core-20021210/

[XML-Schema1]             W3C Recommendation, "XML Schema Part 1: Structures Second Edition", 28 October 2004.

http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/

[XML-Schema2]            W3C Recommendation, "XML Schema Part 2: Datatypes Second Edition", 28 October 2004.

http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/

[XML-Signature]            W3C Recommendation, "XML-Signature Syntax and Processing", 12 February 2002.

http://www.w3.org/TR/2002/REC-xmlenc-core-20021210/

                                   

1.7 Non-Normative References

[Kerberos]                   J. Kohl and C. Neuman, "The Kerberos Network 149 Authentication Service (V5)," RFC 1510, September 1993.

http://www.ietf.org/rfc/rfc1510.txt

[WS-Federation]            "Web Services Federation Language," BEA, IBM, Microsoft, RSA Security, VeriSign, July 2003.

[WS-SecurityPolicy]      OASIS Committee Draft, “WS-SecurityPolicy 1.2”, September 2006

                                    http://docs.oasis-open.org/ws-sx/ws-securitypolicy/200512

[X509]                          S. Santesson, et al,"Internet X.509 Public Key Infrastructure Qualified Certificates Profile."

http://www.itu.int/rec/recommendation.asp?type=items&lang=e&parent=T-REC-X.509-200003-I

The Web service security model defined in WS-Trust is based on a process in which a Web service can require that an incoming message prove a set of claims (e.g., name, key, permission, capability, etc.).  If a message arrives without having the required proof of claims, the service SHOULD ignore or reject the message.  A service can indicate its required claims and related information in its policy as described by [WS-Policy] and [WS-PolicyAttachment] specifications.

 

Authentication of requests is based on a combination of optional network and transport-provided security and information (claims) proven in the message.  Requestors can authenticate recipients using network and transport-provided security, claims proven in messages, and encryption of the request using a key known to the recipient.

 

One way to demonstrate authorized use of a security token is to include a digital signature using the associated secret key (from a proof-of-possession token).  This allows a requestor to prove a required set of claims by associating security tokens (e.g., PKIX, X.509 certificates) with the messages.

·         If the requestor does not have the necessary token(s) to prove required claims to a service, it can contact appropriate authorities (as indicated in the service's policy) and request the needed tokens with the proper claims.  These "authorities", which we refer to as security token services, may in turn require their own set of claims for authenticating and authorizing the request for security tokens.  Security token services form the basis of trust by issuing a range of security tokens that can be used to broker trust relationships between different trust domains.

·         This specification also defines a general mechanism for multi-message exchanges during token acquisition.  One example use of this is a challenge-response protocol that is also defined in this specification. This is used by a Web service for additional challenges to a requestor to ensure message freshness and verification of authorized use of a security token.