How shall we accomplish our collection of goals? We have examined all the building blocks in this tutorial; let's put them together.

Suppose that Alice wishes to send a private message to Bob, and that she has obtained Bob's public key in a way that reliably links Bob to that key. Let's call Bob's public key PUB_B. Further, let us refer to RSA encryption by the name E_RSA, and to our favorite fast and secure symmetric key algorithms as E_SYM. While we are at it, let us call our favorite pseudo-random number generator PRN. For Alice's message M that she wishes to send to Bob, she calculates and sends:

		    [ E_RSA{PUB_B}(PRN), E_SYM{PRN}(M) ]
		    

That is to say, Alice: (1) Generates a pseudo-random "session key," which is of a moderate length (e.g. 64, 96, or 128 bits); (2) Encrypts the moderate-sized session key using (slow) RSA encryption and Bob's public key; (3) Encrypts the longer plain text M using a fast symmetric algorithm. Only a little bit of encryption with RSA is necessary: Bob is able to recover the session key because he has his own private key for RSA. And Bob is able to recover M because the protocol specifies the symmetric algorithm used to encrypt it once the session key is known.

We obtain the advantage of RSA in avoiding a requirement for externally-secured key exchange, and we also obtain the speed advantages of symmetric algorithms.