Cryptology ePrint Archive: Report 2004/059

Symmetric Encryption in a Simulatable Dolev-Yao Style Cryptographic Library

Michael Backes and Birgit Pfitzmann

Abstract: Recently we solved the long-standing open problem of justifying a Dolev-Yao type model of cryptography as used in virtually all automated protocol provers under active attacks. The justification was done by defining an ideal system handling Dolev-Yao-style terms and a cryptographic realization with the same user interface, and by showing that the realization is as secure as the ideal system in the sense of reactive simulatability. This definition encompasses arbitrary active attacks and enjoys general composition and property-preservation properties. Security holds in the standard model of cryptography and under standard assumptions of adaptively secure primitives.

A major primitive missing in that library so far is symmetric encryption. We show why symmetric encryption is harder to idealize in a way that allows general composition than existing primitives in this library. We discuss several approaches to overcome these problems. For our favorite approach we provide a detailed provably secure idealization of symmetric encryption within the given framework for constructing nested terms.

Category / Keywords: foundations / cryptographic protocols, security analysis of protocols, formal methods, Dolev-Yao, symmetric encryption, cryptographically composable operators

Date: received 23 Feb 2004

Contact author: mbc at zurich ibm com

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Version: 20040223:215329 (All versions of this report)

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