MFRC522 RFID Project - Cryptography

Gentlemen,

I want to make a RFID access project for a small company. The project is not hard, I think.
Every employee will receive a RFID tag, with his ID number written in it, cryptographed.

I just want to make a first step, just like this: cryptograph and write a number (like 824576) in a RFID tag. I downloaded some cipher libraries, but couldn't make them work like I want.

Any ideas? Thank you!
Fabio.

Well you didnt state what you didn’t like about what you have tried so far so......

But if I actually cared about access, it would be at least 2 parts, RFID coupled with additive keypad code.

Otherwise really no point in bothering with crypto, just beep them and call it a day because you have no idea who is actually holding the card anyways.

Slumpert:
But if I actually cared about access, it would be at least 2 parts, RFID coupled with additive keypad code.
Otherwise really no point in bothering with crypto, just beep them and call it a day because you have no idea who is actually holding the card anyways.

Thanks for the reply.
I really just want to make a cryptography on the ID number and write them to the tags, and later decrypt them in order to grant access. I know this is a too weak security implementation, but it is more than enough to where I am putting it.
Honestly, I have more places to apply this ideia (not exactly like that), so the point is how to apply crypto on it.

Best regards,
Fabio.