crypt-isaac

https://github.com/wyhaines/crypt-isaac

ISAAC is a fast, cryptographically secure pseudo random number generator with strong statistical properties. This gem provides both a pure Ruby and a C extension based implementation which conforms to the Ruby 2 api for Random, with some enhancements. So, you should be able to use it as a drop in replacement for Ruby's (Mersenne Twister based) PRNG.