Boole is a hash function designed by Gregory Rose and was submitted to the NIST Hash competition. It is a stream cipher based hash function which produces digests up to 512 bits. Different variants exist, namely Boole16, Boole32 and Boole64 where the number refers to word size in bits. Boole64 is considered as the official submission. In this paper we demonstrate a collision attack with complexity 2
for the 64-bit variant and 2
for the 32-bit variant. The amount of memory required is negligible. Since the attack on Boole32 is practical, we present an example for a collision.