  To analyse cryptographic properties of distributed systems in a systematic
way, a formal theory is required. In this paper, we present a theory that
allows (1) to specify distributed systems formally, (2) to verify their
cryptographic wrt. composition properties, and (3) to demonstrate the
correctness of syntactic interfaces for specified system components
automatically. To demonstrate the feasibility of the approach we use a typical
example from the domain of crypto-based systems: a variant of the Internet
security protocol TLS. A security flaw in the initial version of TLS
specification was revealed using a semi-automatic theorem prover, Isabelle/HOL.
