Welcome to the resource topic for 2007/109
Title:
How to Enrich the Message Space of a Cipher
Authors: Thomas Ristenpart, Phillip Rogaway
Abstract:Given (deterministic) ciphers \calE and~E that can encipher messages of \el and n bits, respectively, we construct a cipher~\calE^*=XLS[\calE,E] that can encipher messages of \el+s bits for any s<n. Enciphering such a string will take one call to~\calE and two calls to~E. We prove that~\calE^* is a strong pseudorandom permutation as long as~\calE and~E are. Our construction works even in the tweakable and VIL (variable-input-length) settings. It makes use of a multipermutation (a pair of orthogonal Latin squares), a combinatorial object not previously used to get a provable-security result.
ePrint: https://eprint.iacr.org/2007/109
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