Cryptology ePrint Archive: Report 2007/158

A Simple Security Analysis of Hash-CBC and a New Efficient One-Key Online Cipher

Mridul Nandi

Abstract: In Crypto 2001, Bellare {\em et al.} introduced {\em online cipher} (or online permutation) and proposed two Hash-CBC mode constructions, namely {\bf HCBC} and {\bf HPCBC} along with security proofs. We observe that, the security proofs in their paper are {\em wrong} and it may not be fixed easily. In this paper, we provide a {\em simple} security analysis of these online ciphers. Moreover, we propose two variants of HPCBC, namely {\bf MHCBC-1} and {\bf MHCBC-2}. The first variant, MHCBC-1, is a slight modification of HPCBC so that it is more efficient in performance as well as in memory compare to HPCBC. The other one, MHCBC-2 requires only {\em one-key} (note that, HCBC and HPCBC require at least two and three keys respectively) and does not require any $\varepsilon$-$\mathrm{\Delta}$Universal Hash Family (which is costly in general).

Category / Keywords: secret-key cryptography / random permutation, pseudo random permutation, Online function, Online permutation, $\varepsilon$-$\mathrm{\Delta}$Universal Hash Family, Hash-CBC.

Date: received 30 Apr 2007, last revised 7 May 2007

Contact author: mridul nandi at gmail com

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Version: 20070507:212644 (All versions of this report)

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