# Re: CPRNG

*From*: Ilmari Karonen <usenet2@xxxxxxxxxxxxxx>*Date*: 7 Jun 2009 20:32:34 GMT

On 2009-06-07, Phoenix <ribeiroalvo@xxxxxxxxx> wrote:

Is this algorithm, cryptographically secure pseudo-random number

generator?

http://www.number.com.pt/index.html

No, I don't think so. For one thing, it seems it should be possible

to recover the cipher state (and thereby predict future outputs) with

high probability by observing just three consecutive outputs.

(Call the outputs x, y and z. By definition, we have y = frac(ax) for

some a, and z = frac(by) = frac((a+x)y) = frac(frac(ay) + xy). Let w

= frac(ay) = frac(z - xy + 1). Then we have a = (y + r)/x = (w + s)/y

for some integers r and s, which we should be able to solve for using

a form of Euclid's algorithm. There may be some issues with roundoff,

but I do believe the basic idea should work.)

--

Ilmari Karonen

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**Follow-Ups**:**Re: CPRNG***From:*Maaartin

**References**:**CPRNG***From:*Phoenix

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