| Re: How to generate cryptographically-secure random big-integers? [message #170215 is a reply to message #170213] |
Wed, 20 October 2010 09:29   |
alvaro.NOSPAMTHANX
Messages: 277
Registered: September 2010
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Senior Member |
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El 20/10/2010 8:57, Robert Maas, http://tinyurl.com/uh3t escribió/wrote:
> I need to generate a random integer uniformly distributed from 0 to
> 165704257009980305087908956205223296585688096305918417966291411066008093135 190411324365527113804568013399264982255120906812142560021321323875432044092 494966970218269418334085525290028472777766273110227504712320
> The following code:
> srand(time());
You only need to set a seed for PHP versions older than 4.2.0.
> $random = (rand()%9); ...etc...
As soon as you start using rand() you realize that its output is far
from random:
http://www.boallen.com/random-numbers.html
I've found mt_rand() quite more appropriate.
> :is no good because time returns 1287555603 currently, and it would
> be relatively easy for somebody who has access to my source code to
> try all possible values for the time seed, a 10-digit integer, and
> thus crack my cryptosystem. I'm doing personal research to try to
> find something that is truly random for two hundred and ten
> independently random cryptographically secure digits. My current
> idea is to call the microsecond-time function a moderately large
> number of times in succession, subtract adacent values (result
> usually 4, often 5, rarely any other value), build a Markovian
> model for the sequence, and then apply interval refinement directly
> to the interval where I want the value until the length of the
> interval is small enough to specify a single integer. But before I
> go to a lot of effort to develop this idea, maybe one of you has an
> idea for some method somebody else already did that I could use
> instead?
The rest of your message involve mathematical issues that go beyond my
reach, sorry <:-) However, why exactly are you building your own
cryptosystem when there're so many libraries out there?
--
-- http://alvaro.es - Álvaro G. Vicario - Burgos, Spain
-- Mi sitio sobre programación web: http://borrame.com
-- Mi web de humor satinado: http://www.demogracia.com
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