330

Message Level Web Service Security

Workflow participants using HTTPS

authenticate

authenticate

authenticate

A

B

C

D

Figure 7.6

Authentication Between Point to Point Participants

Web service scenarios that pass messages to multiple participants lend them 

selves to using message level security. Since message level security is based on

data origin authentication, an application that passes messages to numerous inter 

mediary participants on the way to the target recipient can verify, at each interme 

diary point and at the final target recipient, that the initial message creator identity

associated with the message is as claimed. In other words, the initial message

content creator's identity moves with the message through the chain of recipients. 

7.4.2.3

Levels of Granularity

In addition to handling end to end use cases, message level security can provide

security at a more granular level than HTTPS. The ability to apply security at differ 

ent levels of granularity is important. Consider scenarios that handle XML docu 

ments, which are composed of a nested hierarchy of elements and subelements

making them inherently granular. Message level security, which is XML aware, can

be more flexible in applying security mechanisms to a message than HTTPS. 

For example, suppose you need to encrypt only certain elements or fragments

of an XML document to be sent as a SOAP message. If you use HTTPS, you

essentially encrypt the entire SOAP message since HTTPS encrypts everything

passed on the wire. If you use message level security, you can encrypt just a

portion of the XML document, then send a SOAP message that is partially

encrypted. Since encryption is computationally intensive, encrypting an entire

document (particularly a large one) can impact performance. 

Message level security's finer grained control in applying security protections

is useful in common Web service interactions, such as end to end scenarios. You

can apply different security to portions of a document so that participants in a

workflow may only access those fragments applicable to their separate functions.

For example, an application handling purchase orders may encrypt just credit card

information. As the order passes among numerous workflow participants cus