On generalized Feistel networks

  • Authors:
  • Viet Tung Hoang;Phillip Rogaway

  • Affiliations:
  • Dept. of Computer Science, University of California, Davis;Dept. of Computer Science, University of California, Davis

  • Venue:
  • CRYPTO'10 Proceedings of the 30th annual conference on Advances in cryptology
  • Year:
  • 2010

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Abstract

We prove beyond-birthday-bound security for most of the well-known types of generalized Feistel networks: (1) unbalanced Feistel networks, where the n-bit to m-bit round functions may have n ≠ m; (2) alternating Feistel networks, where the round functions alternate between contracting and expanding; (3) type-1, type-2, and type-3 Feistel networks, where n-bit to n-bit round functions are used to encipher kn-bit strings for some k ≥ 2; and (4) numeric variants of any of the above, where one enciphers numbers in some given range rather than strings of some given size. Using a unified analytic framework, we show that, in any of these settings, for any ε 0, with enough rounds, the subject scheme can tolerate CCA attacks of up to q ∼ N1-ε adversarial queries, where N is the size of the round functions' domain (the larger domain for alternating Feistel). Prior analyses for most generalized Feistel networks established security to only q ∼ N0.5 queries.