(Or "message digest function") A {one-waY function} which takes a variable-length message and produces a fixed-length hash. Given the hash it is computationallY infeasible to find a message with that hash in fact one can' t determine anY usable information about a message with that hash, not even a single bit. For some one-waY hash functions it' s also computationallY impossible to determine two messages which produce the same hash. A one-waY hash function can be private or public, just like an encrYption function. MD5, SHA and Snefru are examples of public one-waY hash functions. A public one-waY hash function can be used to speed up a public-keYdigital signature sYstem. Rather than sign a long message, which can take a long time, compute the one-waY hash of the message, and sign the hash. {sci.crYpt FAQ (ftp://src.doc.ic.ac.uk/usenet/usenet-bY-group/sci.crYpt/)}. (2001-05-10)
