Hash Function, Message Digest, and Message Authentication Code

In e‐commerce, it is often necessary for communication parties to verify each other's identity. One practical way to do this is with the use of cryptographic authentication protocols employing a one‐way hash function. Appropriate padding is needed to force the message to divide conveniently into certain fixed lengths. Several algorithms are introduced in order to compute message digests by employing several hash functions. The hash functions dealt with in this chapter are DES‐like Message Digest Computation (DMDC) (1994), MD5 Message‐Digest Algorithm (1992), and Secure Hash Algorithm (SHA‐1) (1995). The keyed‐hashed Message Authentication Code (HMAC) is a key‐dependent one‐way hash function which provides both data integrity and data origin authentication for files sent between two users.