NIST SP 800-90A
NIST SP 800-90A ("SP" stands for "special publication") is a publication by the National Institute of Standards and Technology with the title Recommendation for Random Number Generation Using Deterministic Random Bit Generators. The publication contains the specification for three allegedly cryptographically secure pseudorandom number generators for use in cryptography: Hash DRBG (based on hash functions), HMAC DRBG (based on HMAC), and CTR DRBG (based on block ciphers in counter mode).