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Paper 2007/109

How to Enrich the Message Space of a Cipher

Thomas Ristenpart and 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.

Metadata
Available format(s)
PDF
Category
Secret-key cryptography
Publication info
Published elsewhere. Preliminary version appears in FSE 2007.
Keywords
Deterministic encryptionenciphering schemesymmetric encryptionlength-preserving encryptionmultipermutation
Contact author(s)
tristenp @ cs ucsd edu
History
2015-02-27: revised
2007-03-26: received
See all versions
Short URL
https://ia.cr/2007/109
License
Creative Commons Attribution
CC BY
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