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A Construction of a Cipher From a Single Pseudorandom Permutation

Shimon Even 1 and Yishay Mansour 2

Abstract We suggest a scheme for a block cipher which uses only one randomly chosen permutation, F . The key, consisting of two blocks, K 1 and K 2 is used in the following way: The message block is XORed with K 1 before applying F , and the outcome is XORed with K 2 , to produce the cryptogram block. We show that the resulting cipher is secure (when the permutation is random or pseudorandom). This removes the need to store, or generate a multitude of permutations.

1 Comp. Sci. Dept., Technion, Israel Institute of Technology,
Haifa, Israel 32000.