Paper 2007/197

On-Line Ciphers and the Hash-CBC Constructions

Mihir Bellare, Alexandra Boldyreva, Lars Knudsen, and Chanathip Namprempre


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.

Available format(s)
Secret-key cryptography
Publication info
Published elsewhere. Preliminary version appeared in CRYPTO 2001. This is the full version.
block cipherPRPdisk-sector encryption
Contact author(s)
nchanath @ engr tu ac th
2007-06-29: last of 3 revisions
2007-05-25: received
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Creative Commons Attribution


      author = {Mihir Bellare and Alexandra Boldyreva and Lars Knudsen and Chanathip Namprempre},
      title = {On-Line Ciphers and the Hash-CBC Constructions},
      howpublished = {Cryptology ePrint Archive, Paper 2007/197},
      year = {2007},
      note = {\url{}},
      url = {}
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