Cryptanalysis of Reduced Round ChaCha- New Attack and Deeper Analysis

ePrint Report: Cryptanalysis of Reduced Round ChaCha- New Attack and Deeper Analysis

Sabyasachi Dey, Hirenra Kumar Garai, Subhamoy Maitra

In this paper we present several analyses on ChaCha, a software stream cipher. First, we consider a divide-and-conquer approach on the secret key bits by partitioning them. The partitions are based on multiple input-output differentials to obtain a significantly improved attack on 6-round ChaCha256 with a complexity of 2^{99.48}. It is 2^{40} times faster than the currently best known attack. Note …

analysis attack bits cipher complexity cryptanalysis eprint report input key report secret secret key software stream stream cipher