ABSTRACT
The basic idea of a message digest is that a set of bits
produced by a cryptographic hash function serves as a
compact representation of the original message (i.e., the
input string to the hash function) and can be used to identify
that message uniquely. Any change in the original message
has a very high probability of resulting in a different message
digest. This makes the message digest useful in detecting
errors or unauthorized changes in a message. Additionally,
because the hash function creates a mapping of a variable
length string into a smaller, fixed-length string, information
is lost. This makes it a one-way function. The message digest
can therefore be used to prove the existence of a message
without permitting its reconstruction. This has value in
authentication applications.
