Biclique cryptanalysis of reduced-round Piccolo block cipher

Abstract

Piccolo is a lightweight block cipher, with a fixed 64-bit block size and variable key length 80- or 128-bit, which was proposed at CHES 2011. The iterative structure of Piccolo is a variant of Generalized Feistel Network. The transformation utilizing different-size-word based permutation improves diffusion property of Piccolo and the simple key schedule algorithm reduces hardware costs. By analyzing the distribution of the subkeys, we present a biclique cryptanalysis of full round Piccolo-80 without postwhitening keys and 28-round Piccolo-128 without prewhitening keys. The attacks are respectively with data complexity of 2 48 and 2 24 chosen ciphertexts, and with time complexity of 2 78.95 and 2 126.79 encryptions. © 2012 Springer-Verlag.