(*Test with a truncation of output to 128 bits, ie the first 16 bytes*)
Definition checkHexTrunc password text digest := 
  bytelist_eq (firstn 16 (HMACHex text password)) (hexstring_to_bytelist digest) = true.

Lemma RFC6868_example4_2hex: checkHex "4a656665" "7768617420646f2079612077616e7420666f72206e6f7468696e673f" "5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843".