In Symmetrical Key Cryptography, both parties must possess a secret key which they must exchange prior to using any encryption. Distribution of the secret key has always been problematic, because it involved face-to-face meeting, use of a trusted courier or sending the key through an existing encryption channel. None of these methods was very practical or safe.

In Public Key Cryptography the Key distribution is done through public key servers. When a person creates a key-pair, he keeps one key private and the other, public-key, is uploaded to a server where it can be accessed by anyone to send the user a private, encrypted, message.