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

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Table of Contents

1 Introduction. 6

1.1 Goals and Non-Goals. 6

1.2 Requirements. 7

1.3 Namespace. 7

1.4 Schema and WSDL Files. 8

1.5 Terminology. 8

1.5.1 Notational Conventions. 9

1.6 Normative References. 10

1.7 Non-Normative References. 11

2 Web Services Trust Model 12

2.1 Models for Trust Brokering and Assessment 13

2.2 Token Acquisition. 13

2.3 Out-of-Band Token Acquisition. 14

2.4 Trust Bootstrap. 14

3 Security Token Service Framework. 15

3.1 Requesting a Security Token. 15

3.2 Returning a Security Token. 16

3.3 Binary Secrets. 18

3.4 Composition. 18

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

1 Introduction

[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:

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

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:

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

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

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

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 (n