Science and Development Network (SciDev.Net)
Any message authentication or digital signature mechanism can be viewed as having fundamentally two levels. At the lower level, there must be some sort of function that produces an authenticator: a value to be used to authenticate a message. This lower-level function is then used as primitive in a higher-level authentication protocol that enables a receiver to verify the authenticity of a message. Cryptographic hash functions play an important role in modern cryptography. The basic idea of cryptographic hash functions is that a hash-value serves as a compact representative image (sometimes called an imprint, digital fingerprint, or massage digest) of an input string, and can be used as if it was uniquely identifiable with that string.