Paper 2006/062

A New Mode of Encryption Secure Against Symmetric Nonce Respecting Adversaries

Debrup Chakraborty and Palash Sarkar

Abstract

We present MEM, which is a new mode of encryption using a block cipher. MEM is proved to be a strong pseudo-random permutation (SPRP) against {\em symmetric} nonce respecting adversaries, where a symmetric nonce respecting adversary is one which does not repeat nonces to either the encryption or the decryption oracle. Against such adversaries, MEM provides a secure, length preserving, tagless mode of encryption. In our construction, the number of block cipher calls is approximately half that of the earlier known more general constructions CMC, EME and EME${}^{\ast }$ of tweakable SPRPs. In situations where the appropriate adversary can be assumed, and where a tagless mode of encryption is required, our construction is the most efficient solution till date.