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From: Cristiano on 23 Dec 2009 05:47
Greg Rose wrote:
> In article <4b30b227(a)news.x-privat.org>,
> Cristiano <cristiano.pi(a)NSquipo.it> wrote:
>> Joseph Ashwood wrote:
>>> [...] Although it does increase the difficulty, it does not
>>> change an insecure PRNG to a cryptographically secure PRNG.
>>
>> If you decimate the output of a LFSR (which is "an insecure PRNG")
>> you get a cryptographically secure PRNG (self-shrinking LFSR).
>
> No you don't. There are attacks against the SSG.

There are attacks against many ciphers, but it doesn't mean that they are
not cryptographically secure.
Here:
http://en.wikipedia.org/wiki/Self-shrinking_generator#Cryptanalysis
I read that there is an attack against the SSG which requires 2^(0.7*L)
steps. If you take, say, L=256 or longer, the time needed to break that SSG
will be very big. I would call that SSG cryptographically secure PRNG.

Cristiano


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