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[REBOL] Re: How to generate a UUID? (was possible data format... Re:Re: dbms3.r

From: joel:neely:fedex at: 16-Jan-2002 20:16

Hi, again, Gregg, Gregg Irwin wrote:
> I don't know if "cryptographically secure" equates to > "universally unique", but I'd be glad if it did. :) >
(Should have checked before the previous note...) CHECKSUM/SECURE is represented as being SHA, which does produce a 160-bit "secure" hash of its input. According to the _Federal_Register_ ["Proposed Federal Information Processing Standard for Secure Hash Standard", v. 57, n. 21, 31 Jan 1992, pp. 3747-3749] The SHA is called secure because it is designed to be compu- tationally infeasible to recover a message corresponding to a given message digest, or to find two different messages which will produce the same message digest. Any change to a message in transit will, with a very high probability, result in a different message digest, and the signature will fail to verify. According to Bruce Schneier in _Applied_Cryptography_ (2d edition, John Wiley & Sons, 1996) There are no known cryptographic attacks against SHA. Because it produces a 160-bit hash, it is more resistant to brute-force attacks (including birthday attacks) than 128-bit hash functions... Needless to say, none of this implies that synonyms fail to exist (see previous note), but simply that it should be infeasibly hard to construct a synonym for a given input. -jn- -- ; sub REBOL {}; sub head ($) {@_[0]} REBOL [] # despam: func [e] [replace replace/all e ":" "." "#" "@"] ; sub despam {my ($e) = @_; $e =~ tr/:#/.@/; return "\n$e"} print head reverse despam "moc:xedef#yleen:leoj" ;