Cryptology ePrint Archive: Report 2007/197

On-Line Ciphers and the Hash-CBC Constructions

Mihir Bellare and Alexandra Boldyreva and Lars Knudsen and Chanathip Namprempre

Abstract: We initiate a study of on-line ciphers. These are ciphers that can take input plaintexts of large and varying lengths and will output the i-th block of the ciphertext after having processed only the first i blocks of the plaintext. Such ciphers permit length-preserving encryption of a data stream with only a single pass through the data. We provide security definitions for this primitive and study its basic properties. We then provide attacks on some possible candidates, including CBC with fixed IV. We then provide two constructions, HCBC1 and HCBC2, based on a given block cipher E and a family of computationally AXU functions. HCBC1 is proven secure against chosen-plaintext attacks assuming that E is a PRP secure against chosen-plaintext attacks, while HCBC2 is proven secure against chosen-ciphertext attacks assuming that E is a PRP secure against chosen-ciphertext attacks.

Category / Keywords: secret-key cryptography / block cipher, PRP, disk-sector encryption

Publication Info: Preliminary version appeared in CRYPTO 2001. This is the full version.

Date: received 25 May 2007, last revised 29 Jun 2007

Contact author: nchanath at engr tu ac th

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Version: 20070629:071325 (All versions of this report)

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