Linear Cryptanalysis of PRINTcipher - Trails and Samples Everywhere

PRINTcipher is a recent lightweight block cipher designed by Knudsen et al. Some noteworthy characteristics are a burnt-in key, a key-dependent permutation layer and identical round keys. Independent work on PRINTcipher has identified weak key classes that allow for a key recovery — the obvious countermeasure is to avoid these weak keys at the cost of a small loss of key entropy. This paper identifies several larger classes of weak keys. We show how to distinguish classes of keys and give a 28-round linear attack applicable to half the keys. We show that there are several similar attacks, each focusing on a specific class of keys. We also observe how some specific properties of PRINTcipher allow us to collect several samples from each plaintext–ciphertext pair. We use this property to construct an attack on 29-round PRINTcipher applicable to a fraction 2−5 of the keys.