| Bob wants to send information to Alice providing authentication and non-repudiation. Since they have already exchanged keys, Bob simply creates his message, encrypts it with his private key, and sends the cipher text to Alice. Alice receives the illegible text, decrypts it with Bob's public key, thus authenticating that Bob was the sender. If something is deciphered with Bob's public key, then his private key is the only one that could have encrypted the message.