RdRand (also RDRAND) is an instruction for returning random numbers from an on-chip random number generator[1] that will be available in Ivy Bridge processors. It is part of the Intel 64 instruction set architecture. The random number generator is NIST SP800-90A, FIPS 140-2, and ANSI X9.82 compliant.[2]
Bull Mountain is Intel's code name for both the RdRand instruction and the underlying random number generator (RNG).[1] Intel calls their RNG a "digital random number generator". The generator uses an on-processor entropy source, which passes the randomly generated bits to an AES (in CBC-MAC mode) conditioner to distill the entropy into non-deterministic random numbers. A deterministic random bit generator is seeded by the output from the conditioner, providing cryptographically secure random numbers to applications requesting them via the RdRand instruction.[2][3]