Introduction
First, encryption is the process of taking some sort of message and concealing it by turning the meaningful message (the "plaintext") into something that, at first glance, looks meaningless (the "ciphertext"). Decryption is the process of taking the ciphertext and converting it back to the original plaintext. There are two sorts of decryption -- what we might call "hostile" and "friendly." Friendly decryption occurs if you are the intended recipient and have been told what you have to do to convert the message. The method used to convert it is known as "the key." A key usually consists of two parts: A method and a specific piece of data used to apply the key -- usually, in cryptography, a set of letters and numbers used to conceal the message. Think of a combination lock: To open it, you must know how all combination locks work (right to the first digit, left to the second, right to the third) and the combination (23-16-21, or whatever). Because cryptographic methods are fairly standard, it is common to refer to the "combination" alone as the "key," rather than applying that term both to method and specific data.