ISAAC (cipher)

ISAAC, an acronym for indirection, shift, accumulate, add and count, is a cryptographically secure pseudorandom number generator that is also used as a stream cipher. Robert J. Jenkins Jr. designed it in 1993, and the reference implementation source code was dedicated to the public domain. Jenkins described his method as a loop between attack and defence: he developed statistical tests intended to break a random number generator, and then developed the generator so that it passed those tests, and that generator is ISAAC. In the atlas it sits with the stream ciphers, since it produces a keystream of pseudorandom values that can be combined with data, and it is a practical example of how a generator built for software speed and tested hard against bias can serve cryptographic work.