Unbalanced Feistel Networks and Block Cipher Design

Published: Feb 27, 2000
Updated: Feb 27, 2000
Section: Network Security Library :: Cryptography
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Company: Counterpane Internet Security, Inc.
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We examine a generalization of the concept of Feistel networks, which we call Unbalanced Feistel Networks (UFNs). Like conventional Feistel networks, UFNs consist of a series of rounds in which one part of the block operates on the rest of the block. However, in a UFN the two parts need not be of equal size. Removing this limitation on Feistel networks has interesting implications for designing ciphers secure against linear and differential attacks. We describe UFNs and a terminology for discussing their properties, present and analyze some UFN constructions, and make some initial observations about their security.

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