Abstract

This paper describes BEAST, a new blockcipher for arbitrary size blocks. It is a Luby-Rackoff cipher and fast when the blocks are large. BEAST is assembled from cryptographic hash functions and stream ciphers. It is provably secure if these building blocks are secure. For smartcard applications, a variant BEAST-RK is proposed, where the bulk operations can be done by the smartcard's host without knowing the key. Only fast key-dependent operations remain to be done by the smartcard. 1 INTRODUCTION Based on random functions, Luby and Rackoff (1988) described provably secure block ciphers. This theoretical break-through is of practical interest, since it enables us to assemble a secure cipher from secure components. Components are known, which we can reasonably expect to be secure. In this paper, the hash function SHA-1 (see Schneier, 1995) and the stream cipher SEAL (Rogaway and Coppersmith, 1993) are considered as components, though other choices would do, as well (Lucks, 1996). SHA-1 ...

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