Description:

The Digest:: modules calculate digests, also called "fingerprints" or
"hashes", of some data, called a message. The digest is (usually) some
small/fixed size string. The actual size of the digest depend of the a
lgorithm used. The message is simply a sequence of arbitrary bytes or bits.
An important property of the digest algorithms is that the digest is likely
to change if the message change in some way. Another property is that
digest functions are one-way functions, that is it should be hard to find
a message that correspond to some given digest. Algorithms differ in how
"likely" and how "hard", as well as how efficient they are to compute.
Note that the properties of the algorithms change over time, as the
algorithms are analyzed and machines grow faster. If your application
for instance depends on it being "impossible" to generate the same digest
for a different message it is wise to make it easy to plug in stronger
algorithms as the one used grow weaker. Using the interface documented
here should make it easy to change algorithms later.