okup to see whether it recognizes the password. If the values match, the authentication is acknowledged; if the values do not match, the connection is ter- minated. Because a different token is provided each time a remote user dials in, CHAP provides robust authentication. A newer protocol, called DIAMETER, serves as a replacement for RADIUS. DIAMETER is also an AAA protocol for the same applications of network access and IP mobility. The major change is that DIAMETER extends RADIUS to provide AAA services to new access technologies. Encryption The best way to protect electronic data is to use encryption-that is, to encode the data SO as to render a document unreadable by all except those who are authorized to have access to it. Encryption and decryption are performed by using a cipher, which is an algorithm, or a series of well-defined steps that can be followed as a procedure. The content of an original document is referred to as plaintext. When Chapter 9 IP Services encryption is applied to the document, the plaintext is scrambled, through the use of an algorithm and a variable, or key; the result is called ciphertext. The key is a randomly selected string of numbers. Generally, the longer the string, the stronger the security. Although encryption may ensure privacy, other techniques are required for full communications security, including a message authentication code or digital signa- tures, both used to verify the authenticity and integrity of the message. The message authentication code is a tag, or short piece of information, used to authenticate a message. Using a secret key and an arbitrary-length message, a message authentica- tion code algorithm calculates a hash value, which protects the message's integrity and authenticity by allowing those who also have the secret key to detect any changes that may have been made to the message content. The same secret key is used to both generate and verify the message authentication code values. Digital signatures, on the other hand, use two complementary algorit