note 52555 added to function.uniqid
| From: | tommiboy at osu1 dot php dot net | Date: | Thu, 05 May 2005 15:18:08 +0000 |
| Subject: | note 52555 added to function.uniqid | ||
| Groups: | php.notes | ||
| Request: | Send a blank email to php-notes+get-88967@lists.php.net to get a copy of this message | ||
"It seems intuitively likely that at least 2 people somewhere in the world over the past 12
years have already got back exactly the same hash because of what they fed in to be digested."
Really?
12 years = 86400 * 365 *12 seconds = 3,7 * 10^8 seconds
2^128 = 3,4 * 10^38, thus approximately 10^38 samples are needed to find a collison (1.7* 10^38,
more exactly)
Consequently, this means:
--> MD5 calculations per second during last 12 years = 10^30 (worldwide)
Approx. number of PCs worldwide: 820 million (2004), this is <= 10^9
--> MD5 calculations per PC per second >= 10^21
An optimized MD5 implementation takes around 400-450 clock cycles on Pentium-class hardware.
--> During the past 12 years, the average PC had a clock frequency of 10^23 Hertz.
That is about a quadrillion times faster than the PC which I bought last week :)
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