Paper 2007/317

Improving Upon the TET Mode of Operation

Palash Sarkar

Abstract

Naor and Reingold had proposed the construction of a strong pseudo-random permutation (SPRP) by using a layer of ECB encryption between two layers of invertible block-wise universal hash functions. At Crypto 2007, Halevi presented constructions of invertible block-wise universal hash functions and a new mode of operation (called TET) based on them. In this paper, we present a new mode of operation called {\heh} using the Naor-Reingold approach. This is built using a new construction of invertible block-wise universal hash function. The new construction improves over Halevi's construction by removing restrictions on the hashing key. This in turn, leads to {\heh} improving over TET by allowing more efficient encryption and decryption of variable length messages as well as supporting better key agility. For the important application of disk encryption, we present a variant called {\hehfp} which has better key agility than TET.