Differential Cryptanalysis of 18-Round PRIDE

The rapid growth of the Internet of Things together with the increasing popularity of connected objects have created a need for secure, efficient and lightweight ciphers. Among the multitude of candidates, the block cipher PRIDE is, to this day, one of the most efficient solutions for 8-bit micro-controllers. In this paper, we provide new insights and a better understanding of differential attacks of PRIDE. First, we show that two previous attacks are incorrect, and describe (new and old) properties of the cipher that make such attacks intricate. Based on this understanding, we show how to properly mount a differential attack. Our proposal is the first single key differential attack that reaches 18 rounds out of 20. It requires 261 chosen plaintexts and recovers the 128-bit key with a final time complexity of 263.3 encryptions, while requiring a memory of about 235 blocks of 64 bits.