[kwlug-disc] Hash functions.

John Van Ostrand john at netdirect.ca
Sun Jan 2 12:39:59 EST 2011



----- Original Message -----
> ----- Original Message -----
> > Yes.. thank you CRC is exactly what I'm looking for.
> 
> Keep in mind that a CRC will not guarantee uniqueness, there may be
> two messages that generate the same CRC. In cases like yours I'd look
> for things that naturally make it unique. If you have the phone number
> of the SMS source and the date/time in seconds or microseconds, that
> alone could make a unique number. Reduce the size by doing some coding
> with the numbers, "pack digits" or convert the phone number to an
> integer and the date/time to another. A final check to see if there
> was a duplicate message in the last second and few bits for a count
> and you should have uniqueness.
> 
> For something a little different than that try a GUID or UUID. You
> should be able to find a function to generate one. The number is so
> large that randomly generating GUID should not result in a duplicate
> GUID for a long time.
> 
> Also mentioned was predictabilty. If there is a chance predicable IDs
> could result in a security issue you should go with GUIDs.

http://php.net/manual/en/function.uniqid.php

http://www.shapeshifter.se/2008/09/29/uuid-generator-for-php/

-- 
John Van Ostrand 
CTO, co-CEO 
Net Direct Inc. 
564 Weber St. N. Unit 12, Waterloo, ON N2L 5C6 
Ph: 866-883-1172 x5102 
Fx: 519-883-8533 

Linux Solutions / IBM Hardware 




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