Page 122 - CISSO_Prep_ Guide
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Hashing algorithms are a very good and accurate integrity check
tool. Much more accurate than a checksum or parity bit, the hash
will detect changes of even a single bit in a message. A hash
algorithm will calculate a hash value (also known as a digest,
fingerprint, or thumbprint) from the entire input message. The
output digest itself is a fixed length, so even though the input
message can be of variable length, then output is always the
same length. The length depends on the hash algorithm used.
MD5, for example, generates a digest length of 128 bits' SHA1,
a digest of 160 bits, and SHA512, a 512-bit digest length. Those
are the most common hash algorithms in use today.
When Alice wants to send a message to Bob and ensure that the
message has not been affected by noise or network problems,
Alice can, first of all, compute the digest of the message and
send it along with the message to Bob. When Bob receives the
message, he will compute the digest of the received message and
ensure that the digest he computes is the same as the digest
Alice sent him. As seen in the diagram below:
