HKDF

RU: HKDF

HMAC-based Extract-and-Expand Key Derivation Function (RFC 5869): a two-step KDF that first extracts a fixed-length pseudorandom key from potentially weak or non-uniform input keying material (using HMAC with an optional salt), then expands it into one or more output keys of any desired length. Used in TLS 1.3, Signal protocol, and ECIES.