Special Edition Using Java™ 2 Enterprise Edition

Digital Signatures

Many times, you want to verify that a document hasn't been tampered with, but you don't necessarily need to encrypt the document. A digital signature is essentially a way to verify that a document hasn't been changed and that the document comes from the party you think it does.

There are two basic components to a digital signature: a secure hash function and public key encryption. A secure hash algorithm takes a block of data and boils it down into a smaller block of bits. The algorithm should produce the same hash value for a particular pattern of bit every time it runs. That is, when you compute the hash value before you send the document, you want the receiver to compute the same hash value. A good hash algorithm also changes ...