Adding the nonce for confidentiality to generator security constraints with an XPath expression

The following information explains the difference between using an XPath expression and using keywords to specify which part of the message to sign:

XPath expression: Specify any part of the message using an XPath expression. XPath is a language that is used to address parts of an XML document. You can find information on XPath syntax at the following Web site: http://www.w3.org/TR/1999/REC-xpath-19991116.
Keywords: Specify only elements within the message using predefined keywords.

Nonce for confidentiality is used to specify that the nonce is embedded in a particular element within the message and that the element is encrypted. Nonce is a randomly generated, cryptographic token. When you add a nonce to a specific part of a message, it can prevent theft and replay attacks because a generated nonce is unique. For example, without a nonce, the token might be intercepted and used in a replay attack when a user name token is passed from one machine to another machine using a non-secure transport, such as HTTP. The user name token can be stolen even if you use XML digital signature and XML encryption. This situation might be prevented by adding a nonce.

Complete the following steps to specify a nonce for confidentiality using an XPath expression when you configure the generator security constraints for either the request generator or the response generator. The request generator is configured for the client and the response generator is configured for the server. In the following steps, you must configure either the client-side extensions in step 2 or the server-side extensions in step 3.

Click Window > Open Perspective > J2EE.
Optional: Locate the client-side extensions using the Project Explorer window. The Client Deployment Descriptor window is displayed. This Web service contains the extensions that you need to configure. Complete the following steps to locate the client-side extensions:
1. Expand the Web Services > Client section and double-click the name of the Web service.
2. Click the WS Extension tab and expand the Request Generator Configuration section.
Optional: Locate the server-side extensions using the Project Explorer window. The Web Services Editor window is displayed. This Web service contains the extensions that you need to configure. Complete the following steps to locate the server-side extensions:
1. Expand the Web Services > Services section and double-click the name of the Web service.
2. Click the Extensions tab and expand the Response Generator Service Configuration Details section.
Expand the Confidentiality section. Confidentiality refers to encryption while integrity refers to digital signing. Confidentiality reduces the risk of someone intercepting the message as it moves across a network. With confidentiality specifications, the message is encrypted before it is sent and decrypted when it is received at the intended target. For more information on encryption, see XML encryption.
Click Add to specify a nonce for integrity. The Confidentiality Dialog window is displayed. Complete the following steps to specify a configuration:
1. Specify a name for the confidentiality element in the Confidentiality Name field. For example, you might specify conf_nonce.
2. Specify an order in the Order field. The value, which must be a positive integer value, specifies the order in which the encryption is processed. An order value of 1 specifies that the encryption is done first.
Click Add under the Nonce section of the Confidentiality Dialog window. Complete the following steps to specify the none dialect and the message part:
1. Select the nonce dialect from the Nonce section. The http://www.w3.org/TR/1999/REC-xpath-19991116 dialect specifies the message part to which a nonce is added and encrypted using an XPath expression.
2. Specify the message part to which a nonce is added and encrypted using an XPath expression in the Nonce keyword field. For example, to specify that a nonce is added to the bodycontent element and it is encrypted, you might add the following expression in the Nonce keyword field as one continuous line:
```
/*[namespace-uri()='http://schemas.xmlsoap.org/soap/envelope/' and local-name()='Envelope']/*
[namespace-uri()='http://schemas.xmlsoap.org/soap/envelope/' and local-name()='Bodycontent']
```
In the Message Parts section, click Add and select http://www.w3.org/TR/1999/REC-xpath-19991116 in the Message parts dialect field.
In the Message Parts section, select the message parts keyword.
Important: You must define at least one message part in Message Parts section in order to specify nonce for Confidentiality. The selection of message part here is for encrypting a message part in addition to the parent element of the nonce.
Click OK to save the configuration changes.
Note: These configurations for the consumer and the generator must match.
In addition to the nonce, you can specify that the timestamp element is signed. For more information, see the following articles:
- Adding time stamps for confidentiality to generator security constraints with keywords
- Adding time stamps for confidentiality to generator security constraints with an XPath expression

After you specify which message parts to encrypt, you must specify which method is used to encrypt sign the message. For more information, see Configuring encryption information for the generator binding.