(*******Injectivity of pad_inc*************************)

Lemma xor_equiv_byte: forall xpad XPAD k K, isbyteZ XPAD ->
bytes_bits_lists xpad (HP.HMAC_SHA256.sixtyfour XPAD) ->
bytes_bits_lists k (map Byte.unsigned K) ->
bytes_bits_lists (BLxor k xpad) (HP.HMAC_SHA256.mkArgZ K (Byte.repr XPAD)).