RdRand

RdRand is an instruction for returning random numbers from an Intel on-chip hardware random number generator.RdRand is available in Ivy Bridge and later processors. It uses cascade construction, combining a HW RNG operating at 3Gbps with CSPRNG with all components sealed on CPU. The entropy source is a meta-stable circuit, with unpredictable behavior based on thermal noise. The entropy is fed into a 3:1 compression ratio entropy extractor (whitener) based on AES-CBC-MAC. Online statistical tests are performed at this stage and only high quality random data are used as the seed for cryptographically secure SP800-90 AES-CTR DRBG compliant PRNG. This generator is producing maximum of 512 128-bit AES blocks before it's reseeded. According to documentation the 512 blocks is a upper limit for reseed, in practice it reseeds much more frequently.

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