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Published in:
2011 | OriginalPaper | Chapter
Online Ciphers from Tweakable Blockciphers
Authors : Phillip Rogaway, Haibin Zhang
Published in: Topics in Cryptology – CT-RSA 2011
Publisher: Springer Berlin Heidelberg
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Online ciphers are deterministic length-preserving permutations
${\mathcal E}_K : (\{0. 1\}^n)^+\rightarrow(\{0. 1\}^n)^+$
where the
i
-th block of ciphertext depends only on the first
i
blocks of plaintext. Definitions, constructions, and applications for these objects were first given by Bellare, Boldyreva, Knudsen, and Namprempre. We simplify and generalize their work, showing that online ciphers are rather trivially constructed from tweakable blockciphers, a notion of Liskov, Rivest, and Wagner. We go on to show how to define and achieve online ciphers for settings in which messages need
not
be a multiple of
n
bits.