pbkdf2 is part of rsa laboratories' public-key cryptography standards (pkcs) series, specifically pkcs #5 v2.0, also published as internet engineering task force's rfc 2898. it supersedes pbkdf1, which could only produce derived keys up to 160 bits long. rfc 8018 (pkcs #5 v2.1), published in 2017, recommends pbkdf2 for password hashing.