A Semantics for Web Services Authentication

Karthikeyan Bhargavan and Cedric Fournet and Andrew D. Gordon

To appear at Principles of Programming Languages (POPL04), Venice, Italy, January 14-16, 2004


We consider the problem of specifying and verifying cryptographic security protocols for XML web services. The security specification WS-Security describes a range of XML security tokens, such as username tokens, public-key certificates, and digital signature blocks, amounting to a flexible vocabulary for expressing protocols. To describe the syntax of these tokens, we extend the usual XML data model with symbolic representations of cryptographic values. We use predicates on this data model to describe the semantics of security tokens and of sample protocols distributed with the WSE implementation of WS-Security. By embedding our data model within Abadi and Fournet's applied pi calculus, we formulate and prove security properties with respect to the standard Dolev-Yao threat model. Moreover, we informally discuss issues not addressed by the formal model. To the best of our knowledge, this is the first approach to the specification and verification of security protocols based on a faithful account of the XML wire format.

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