Security of Random Feistel Schemes with 5 or More Rounds

We study cryptographic attacks on random Feistel schemes. We denote by m the number of plaintext/ciphertext pairs, and by k the number of rounds. In their famous paper [3], M. Luby and C. Rackoff have completely solved the cases m 2n/2 : the schemes are secure against all adaptive chosen plaintext attacks (CPA-2) when k ≥ 3 and against all adaptive chosen plaintext and chosen ciphertext attacks (CPCA-2) when k ≥ 4 (for this second result a proof is given in [9]). In this paper we study the cases m 2n . We will use the “coefficients H technique” of proof to analyze known plaintext attacks (KPA), adaptive or non-adaptive chosen plaitext attacks (CPA-1 and CPA-2) and adaptive or non-adaptive chosen plaitext and chosen ciphertext attacks (CPCA-1 and CPCA-2). In the first part of this paper, we will show that when m 2n the schemes are secure against all KPA when k ≥ 4, against all CPA-2 when k ≥ 5 and against all CPCA-2 attacks when k ≥ 6. This solves an open problem of [1],...

• Type: Conference
• Year: 2004
• Where: CRYPTO
• Authors: Jacques Patarin
• Keywords: Adaptive Chosen Plaintext, Chosen Plaintext Attack, CRYPTO 2004, Plaintext Attack