Public key cryptography algorithms are based on number theory laws and principles. For every cryptography system one of the most important is-sues is the user’s key which he/she uses to encrypt the messages. That is the reason the key generation process is always fundamental for data protection and, since cryptography takes up more space in our daily lives, the public key generation principles are so important. In this article the authors discuss the Miller–Rabin primality test in its relation to the key generation process.