There's another problem, if the author tells us that this is crc, while it's a MAC (not particularly strong tbh), it shows that we, as developers and users, cannot trust that cryptographic decisions of the author are of any consideration. For reference, crc is not a signature, its full name is "cyclic redundancy check", which is a really simple mathematical operation, that computes a specific remainder that comes from polynomial long division (of polynomials decided from the message). It is not any kind of cryptographic signature and given a string, it's crc and target crc, we can find another string that differs in one byte only, that has the target crc, all of this in time faster than computing whole original crc.