Cryptology ePrint Archive: Report 2003/148

A Tweakable Enciphering Mode

Shai Halevi and Phillip Rogaway

Abstract: We describe a block-cipher mode of operation, CMC, that turns an n-bit block cipher into a tweakable enciphering scheme that acts on strings of mn bits, where m>=2. When the underlying block cipher is secure in the sense of a strong pseudorandom permutation (PRP), our scheme is secure in the sense of tweakable, strong PRP. Such an object can be used to encipher the sectors of a disk, in-place, offering security as good as can be obtained in this setting. CMC makes a pass of CBC encryption, xors in a mask, and then makes a pass of CBC decryption; no universal hashing, nor any other non-trivial operation beyond the block-cipher calls, is employed.

Besides proving the security of CMC we initiate a more general investigation of tweakable enciphering schemes, considering issues like the non-malleability of these objects.

Category / Keywords: secret-key cryptography / Block-cipher usage, cryptographic standards, disk encryption, modes of operation, provable security, sector-level encryption, symmetric encryption.

Publication Info: CRYPTO'03, LNCS, vol. 2729, Springer-Verlag, 2003

Date: received 28 Jul 2003

Contact author: shaih at watson ibm com

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Version: 20030728:190640 (All versions of this report)

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