J2EE™ Security for Servlets, EJBs and Web Services: Applying Theory and Standards to Practice

Message Digest

Message digests, also known as message fingerprints or secure hash, are computed by applying a one-way hash function over the data bits comprising the message. Any modification in the original message, either intentional or unintentional, will most certainly result in a change of the digest value. Also, it is computationally impossible to derive the original message from the digest value. These properties make digests ideal for detecting changes in a given message. Compute the digest before storing or transmitting the message and then compute the digest after loading or receiving the message. If the digest values match then one can be sure with good confidence that the message has not changed. However, this scheme fails if a malicious ...