On the Optimal Key Size of the Even-Mansour Cipher in the Random Function Oracle Model

Vol. 17, No. 3, pp. 35-42, Jun. 2007
10.13089/JKIISC.2007.17.3.35, Full Text:
Keywords: block cipher, Provable Security, Feistel Scheme, Even-Mansour Cipher, Pseudorandomness, Random Oracle
Abstract

We describe the problem of reducing the key material in the Even-Mansour cipher without security degradation. Even and Mansour proposed a block cipher based on XORing secret key material just prior to and after applying random oracle permutation P such that $C=k_2\bigoplus P(M\bigoplus k_1)$. Recently, Gentry and Ramzan showed that this scheme in the random permutation oracle can be replaced by the four-round Feistel network construction in the random function oracle and also proved that their scheme is super-pseudorandom. In this paper we reduce the key size from 2n to n, which is the optimal key size of Even-Mansour cipher in the random function oracle model and also give almost the same level of security.

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Cite this article
[IEEE Style]
J. Sung, "On the Optimal Key Size of the Even-Mansour Cipher in the Random Function Oracle Model," Journal of The Korea Institute of Information Security and Cryptology, vol. 17, no. 3, pp. 35-42, 2007. DOI: 10.13089/JKIISC.2007.17.3.35.

[ACM Style]
Jae-Chul Sung. 2007. On the Optimal Key Size of the Even-Mansour Cipher in the Random Function Oracle Model. Journal of The Korea Institute of Information Security and Cryptology, 17, 3, (2007), 35-42. DOI: 10.13089/JKIISC.2007.17.3.35.