Cracking random number generators (xoroshiro128+)

Re:Cracking random number generators (xoroshiro128+) by imaginenore on Tuesday August 22, 2017 @10:58AM (#15073026)

Can you crack this PRNG without knowing the seed?

    f(1) = 1 // seed

    f(n) = sha512(f(n-1) . f(1))

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Re:Cracking random number generators (xoroshiro128+) by mdpopescu on Tuesday August 22, 2017 @03:38PM (#15075682)

This is similar to Yarrow / Fortuna (internal state is a counter, output is the hash of the state) so I'm guessing it's not breakable, at least not trivially.

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Re:Cracking random number generators (xoroshiro128+) by sdevlin on Tuesday August 22, 2017 @11:48AM (#15073539)

I guess it depends what you mean by “crack”. Given f(1), which I assume is public, you can predict all future outputs.

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Re:Cracking random number generators (xoroshiro128+) by imaginenore on Tuesday August 22, 2017 @01:13PM (#15074423)

I said without knowing the seed, so f(1) is not public, only f(n) formula is.

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Re:Cracking random number generators (xoroshiro128+) by benchaney on Tuesday August 22, 2017 @05:34PM (#15076588)

f(1) is the first batch of output.

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Re:Cracking random number generators (xoroshiro128+) by IshKebab on Tuesday August 22, 2017 @12:00PM (#15073679)

That is not what we mean by "crack". Read the article.

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