Abstract. This paper presents a definition of secure information flow. It is not based on noninterference, but on computational indistinguishability of the secret inputs, when the public outputs are observed. This definition allows cryptographic primitives to be handled. This paper also presents a Denning-style information-flow analysis for programs that use encryption as a primitive operation. The proof of the correctness of the analysis is sketched.

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We state the basic requirements for time-stamping systems applicable as the necessary support to the legal use of electronic documents. We analyze the main drawbacks of the time-stamping systems proposed to date and present a new system that meets all the stated requirements. We prove that these requirements cannot be significantly tightened.

We present a type system for checking secrecy of messages handled by protocols that use the Backes-Pfitzmann-Waidner library for cryptographic operations. A secure realization of this library exists, therefore we obtain for the first time a cryptographically sound analysis for a full language for expressing protocols, particularly handling symmetric encryption and unbounded number of sessions. The language is similar to the spi-calculus, but has a completely deterministic semantics. The type system is similar to the Abadi-Blanchet type system for asymmetric communication.