Abstract

. This paper deals with a generalization of Luby's and Rackoff 's results [9] on the construction of block ciphers and their consequences for block cipher implementations. Based on dedicated hash functions, block ciphers are proposed which are more efficient and operate on larger blocks than their original Luby-Rackoff counterparts. 1 Introduction One usually demands a block cipher to be secure and efficient. Other not-socommon demands are to be simple and to cope with large blocks. Consider a cipher being provably secure if another cryptographic primitive is secure. This reduces the number of security assumptions a cryptographic application has to depend on---and thus the application's chance to be broken. Based on pseudorandom functions, Luby and Rackoff [9] described provably secure block ciphers. This theoretical break-through is also of practical interest--- pseudorandomness is a design goal for today's dedicated hash functions. E.g. the authors of RIPE-MD write [14]: "It is the...

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