one-way hash function

(Or "message digest function") A function which takes a variable-length message and produces a fixed-length

hash. Given the hash it is computationally impossible 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} 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/)}.

(1995-02-16)