(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 aNeNcryptioN 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-key digital 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)
