Security analysis of the full-round DDO-64 block cipher

Abstract

DDO-64 is a 64-bit Feistel-like block cipher based on data-dependent operations (DDOs). It is composed of 8 rounds and uses a 128-bit key. There are two versions of DDO-64, named DDO-64V(1) and DDO-64V(2), according to the key schedule. They were designed under an attempt for improving the security and performance of DDP-based ciphers. In this paper, however, we show that like most of the existing DDP-based ciphers, DDO-64V(1) and DDO-64V(2) are also vulnerable to related-key attacks. The attack on DDO-64V(1) requires 2(35.5) related-key chosen plaintexts and 2(63.5) encryptions while the attack on DDO-64V(2) only needs 8 related-key chosen plaintexts and 2(31) encryptions: our attacks are both mainly due to their simple key schedules and structural weaknesses. These works are the first known cryptanalytic results on DDO-64V(1) and DDO-64V(2) so far. (C) 2008 Elsevier Inc. All rights reserved.