A construction of a cipher from a single pseudorandom permutation
We suggest a scheme for a block cipher which uses only one randomly chosen permutation,F. The key, consisting of two blocks,K1 andK2, is used in the following way. The message block is XORed withK1 before applyingF, and the outcome is XORed withK2, 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.