RdRand is an instruction for returning random number

Random number

Random number may refer to:* A number generated for or part of a set exhibiting statistical randomness.* A random sequence obtained from a stochastic process.* An algorithmically random sequence in algorithmic information theory....

s from an on-chip random number generator that will be available in Ivy Bridge processors. It is part of the Intel 64 instruction set architecture

Instruction set

An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...

. The random number generator is NIST SP800-90A, FIPS 140-2

FIPS 140-2

The Federal Information Processing Standard Publication 140-2, , is a U.S. government computer security standard used to accredit cryptographic modules. The title is Security Requirements for Cryptographic Modules...

, and ANSI

Ansi

Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....

 X9.82 compliant.

Bull Mountain

Bull Mountain is Intel's code name for both the RdRand instruction and the underlying random number generator (RNG). Intel calls their RNG a "digital random number generator". The generator uses an on-processor entropy

Entropy

Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...

 source, which passes the randomly generated bits to an AES

Advanced Encryption Standard

Advanced Encryption Standard is a specification for the encryption of electronic data. It has been adopted by the U.S. government and is now used worldwide. It supersedes DES...

(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.