Security Analysis of the Lightweight Block Ciphers XTEA, LED and Piccolo

In this paper, we investigate the security of the lightweight block ciphers against the meet-in-the-middle (MITM) attack. Since the MITM attack mainly exploits low key-dependency in a key expanding function, the block ciphers having a simple key expanding function are likely to be vulnerable to the MITM attack. On the other hand, such a simple key expanding function leads compact implementation, and thus is utilized in several lightweight block ciphers. However, the security of such lightweight block ciphers against the MITM attack has not been studied well so far. We apply the MITM attack to the ciphers, then give more accurate security analysis for them. Specifically, combining thorough analysis with new techniques, we present the MITM attacks on 29, 8, 16, 14 and 21 rounds of XTEA, LED-64, LED-128, Piccolo-80 and Piccolo-128, respectively. Consequently, it is demonstrated that the MITM attack is the most powerful attack in the single-key setting on those ciphers with respect to the number of attacked rounds. Moreover, we consider the possibility of applying the recent speed-up keysearch based on MITM attack to those ciphers.