One fundamental notion introduced in the earlier tutorials is worth emphasizing again before we get underway: It is important to make the distinction between protocols and algorithms.

A protocol is a specification of the complete set of steps involved in carrying out a cryptographic activity, including explicit specification of how to proceed in every contingency. An algorithm is a much narrower procedure used to transform some digital data into some other digital data. Cryptographic protocols inevitably involve using one or more cryptographic algorithms, but security (and other cryptographic goals) is a product of a total protocol.

Clearly, using a strong and appropriate algorithm is an important part of creating a strong protocol, but it is not sufficient by itself. The first sections of this tutorial mostly address how cryptographic algorithms work; the later sections take a look at the use of some algorithms in actual protocols, particularly protocols that combine multiple algorithms to accomplish complex goals.