One particular notion introduced in Part 1 of this tutorial 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 the much narrower procedure involved in transforming 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 element of a strong protocol, but it is not sufficient by itself. Section 2 of this tutorial mostly addresses how cryptographic algorithms work; section 3 reviews the use of some algorithms in actual protocols, particularly protocols that combine multiple algorithms to accomplish complex goals.