<algorithm> (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-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.
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Nearby terms: One-Time Password « One Time Programmable Read-Only Memory « one-way function « one-way hash function » on-line » On-Line Analytical Processing » Online Computer Library Center, Inc.