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LCE: Don't play dice with random numbers

LWN.net LogoH. Peter Anvin has been involved with Linux for more than 20 years, and is currently one of the x86 architecture maintainers. During his work on Linux, one of his areas of interest has been the generation and use of random numbers, and his talk at LinuxCon Europe 2012 was designed to address a lot of misunderstandings that he has encountered regarding random numbers. The topic is complex, and so, for the benefit of experts in the area, he noted that "I will be making some simplifications". (In addition, your editor has attempted to fill out some details that Peter mentioned only briefly, and so may have added some "simplifications" of his own.)

Random numbers

Possibly the first use of random numbers in computer programs was for games. Later, random numbers were used in Monte Carlo simulations, where randomness can be used to mimic physical processes. More recently, random numbers have become an essential component in security protocols.

Randomness is a subtle property. To illustrate this, Peter displayed a photograph of three icosahedral dice that he'd thrown at home, saying "here, if you need a random number, you can use 846". Why doesn't this work, he asked. First of all, a random number is only random once. In addition, it is only random until we know what it is. These facts are not the same thing. Peter noted that it is possible to misuse a random number by reusing it; this can lead to breaches in security protocols.

There are no tests for randomness. Indeed, there is a yet-to-be-proved mathematical conjecture that there are no tractable tests of randomness. On the other hand, there are tests...Read more at LWN

 

 

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