Definition checkHex password text digest :=
  bytelist_eq (HMACHex text password) (hexstring_to_bytelist digest) = true.

Lemma RFC4231_Section4_4_hex: (*called PRF-3 in RFC4868*) checkHex "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" "dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd" "773ea91e36800e46854db8ebd09181a72959098b3ef8c122d9635514ced565fe".