
Security • Chapter 12 603
One-way means that you cannot derive the source data by examining only the
digest.Another important feature of the hash algorithm is that it generates a hash
that is unique for each piece of data, even if just one bit of data is changed.You
can see a hash value as the fingerprint of a piece of data. Let’s say, for example,
you send somebody a plain text e-mail. How do you and the receiver of the e-
mail know that the message has not been altered while it was sent? Here is where
the message digest comes in. Before you send your e-mail, you apply a hash algo-
rithm on that message, and you send the message and message digest to ...