Chapter 4 - Message Digests, Message Authentication Codes, and Digital Signatures

Abstract

Message digests, message authentication codes, and digital signatures are all based on a notion of “hashing.” Hashing is one of those 50-cent words that simply means convert. An important property of the one-way hash function is that it must be collision-free. The strength of a one-way hash lies in the underlying hash function itself. A Message Digest is a more commonly used term used to represent a “one-way hash function,” and the hash value result is simply referred to as the digest. The Java Cryptography Architecture (JCA) introduced an engine specific for working with cryptographic one-way hash functions, the MessageDigest engine. The SUN provider supports MD5 and SHA-1 natively, and other providers may offer their alternative message digest algorithms. A MAC combines the use of a message digest with a secret key known only to two users. Before the calculation of the digest, the Mac engine must be initialized. Initialization is completed once the secret key is provided to the engine. The robust design means that the SecretKey could originate from either a KeyGenerator or from a KeyAgreement operation. The JCA includes an implementation of the digital signature algorithm (DSA), which provides all of the mechanisms necessary to accomplish the overall signature process.