TwoCats is sequential memory and compute time hard password hashing scheme that maximizes an attackers time*memory cost for guessing passwords. Christian Forler and Alexander Peslyak (aka SolarDesigner) provided most of the ideas that I have combined in TwoCats. While they may not want credit for this work, it belongs to them more than me.

SkinnyCat is a compatible stripped-down version of TwoCats supporting only a memory cost. It is meant to be simple to implement, yet provide fast memory-hard password security.

Pebble is a tool for estimating decent upper bounds on pebbling difficulty for various DAG architectures. It was useful in selecting the sliding-reverse pattern for cache-timing attack resistance.

Please read TwoCats.odt for a description of the algorithm and credits for ideas.

This stuff is free, as in freedom. I place what I wrote into the public domain. Bits of twocats-tests.c are borrowed and are under BSD/MIT-like licenses.