From Open Tibia Wiki

RSA is an assymetric cryptosystem used widely to secure communication between clients and servers.

Open Tibia version > 7.6 uses 128bytes RSA to secure account information and XTEA keys during character list retrieval and game login, after which XTEA is used instead.

To generate a new RSA key-pair and PEM file you can use our PEM generator tool. The tool does not output errors, but will generate new prime numbers for P,Q if either is invalid. The requirements for primes P,Q are that P and Q are both 512 bits in size, are prime numbers, and P != Q.