ISAAC (Indirection, Shift, Accumulate, Add, and Count) is a cryptographically secure pseudo random number generator. With an average cycle length of 2 to the 8295th power its output is uniformly distributed and unpredictable. ISAAC has been developed by Bob Jenkins and placed into the public domain in 1996. See Acknowledgements for legal information on ISAAC.
ISAAC is at the heart of SecExMail's entropy collection system and comprises the stream cipher subsystem of the SecExMail cipher.