Power of a Public Random Permutation and Its Application to Authenticated Encryption

This paper shows that many independent pseudorandom permutations over {0,1}ⁿ can be obtained from a single public random permutation and secret n bits. It is then proved that a slightly modified IAPM (an authenticated-encryption scheme) is secure even if the underlying block cipher F is publicly accessible (as a blackbox). A similar result is derived for OCB mode, too. The security proofs are based on our first result, and they are extremely simple. Finally, it is shown that our security bound is tight within a constant factor.