Cryptanalysis of Ladder-DES

Feistel ciphers are very common and very important in the design and analysis of blockciphers, especially due to four reasons: (1) Many (DES-like) ciphers are based on Feistel's construction. (2) Luby and Rackoo proved the security of a four-round Feistel construction when the round functions are random. (3) Recently several provably secure ciphers were suggested, which use other (assumed secure) ciphers as the round function. (4) Other such ciphers use this construction as attempts to improve the security of other ciphers (e.g., to improve the security of DES). In this paper we cryptanalyze Ladder-DES, a four-rounds Feistel cipher using DES in the round function, and show that its security is smaller than expected.