Need FIX protocol Description

[yudxp]

    result = ActionPacket(
        timestamp=int.from_bytes(data[2:6], "big"),
        unlock_mode=UnlockMode(data[6]),
        signature=data[7:20]

in the code "signature = data[7:20]" isn't the HMAC only 13 bytes? and in time packet 14 bytes
so the length of the data only 20bytes.