An implementation of HKDF in Erlang.
OKM = hkdf:derive(sha384, <<"Never gonna give you up">>, 42).
PRK = hkdf:extract(sha384, <<"Never gonna give you up">>).
PRK = hkdf:extract(sha384, <<"Never gonna give you up">>).
OKM = hkdf:expand(sha384, PRK, 42).