New Results on the Pseudorandomness of Some Blockcipher Constructions

In this paper, we describe new results on the security, in the Luby-Rackoff paradigm, of two modified Feistel constructions, namely the L-scheme, a construction used at various levels of the MISTY blockcipher which allows to derive a 2n-bit permutation from several n-bit permutations, and a slightly different construction named the R-scheme. We obtain pseudorandomness and super-pseudorandomness proofs for Lschemes and R-schemes with a sufficient number of rounds, which extend the pseudorandomness and non superpseudorandomness results on the 4-round L-scheme previously established by Sugita [Su96] and Sakurai et al. [Sa97]. In particular, we show that unlike the 3-round L-scheme, the 3-round R-scheme is pseudorandom, and that both the 5-round L scheme and the 5-round R scheme are super pseudorandom (whereas the 4 round versions of both schemes are not super pseudorandom). The security bounds obtained here are close to those established by Luby and Rackoff for the three round version...

• Type: Conference
• Year: 2001
• Where: FSE
• Authors: Henri Gilbert, Marine Minier
• Keywords: Cryptology, Feistel Constructions, FSE 2001, Original Feistel Scheme, Super Pseudorandom