Practical cryptanalysis of ARMADILLO2

Abstract

The ARMADILLO2 primitive is a very innovative hardware-oriented multi-purpose design published at CHES 2010 and based on data-dependent bit transpositions. In this paper, we first show a very unpleasant property of the internal permutation that allows for example to obtain a cheap distinguisher on ARMADILLO2 when instantiated as a stream-cipher. Then, we exploit the very weak diffusion properties of the internal permutation when the attacker can control the Hamming weight of the input values, leading to a practical free-start collision attack on the ARMADILLO2 compression function. Moreover, we describe a new attack so-called local-linearization that seems to be very efficient on data-dependent bit transpositions designs and we obtain a practical semi-free-start collision attack on the ARMADILLO2 hash function. Finally, we provide a related-key recovery attack when ARMADILLO2 is instantiated as a stream cipher. All collision attacks have been verified experimentally, they require negligible memory and a very small number of computations (less than one second on an average computer), even for the high security versions of the scheme. © 2012 Springer-Verlag.