Talk:Random number generator (device)

From Rosetta Code

Primer notes[edit]

On Linux, reading from /dev/urandom pulls from the system entropy pool (which may contributed to by HRNGs, among other sources), but provides psuedorandom numbers if that entropy pool dries up. reading from /dev/random, on the other hand, pulls from the same entropy pool, but blocks whenever the entropy pool dries up. --Michael Mol 14:03, 11 January 2011 (UTC)

I guess that a solution may use either /dev/random or /dev/urandom. The entropy pool probably has enough entropy for a 32-bit integer. I prefer to use /dev/urandom. Many kernels use a secure hash, like SHA1, to convert the entropy pool to random numbers. (NetBSD uses SHA1.) Even if the entropy pool is dry, the random numbers should remain secure. I guess that you would have to reverse or defeat SHA1 to replicate the pseudorandom numbers from a dry pool; but SHA1 is a secure hash so difficult to reverse.
OpenBSD 4.8 and before had /dev/urandom giving random numbers, but /dev/random giving only errors. (This was because /dev/random was a reserved device, and /dev/srandom of OpenBSD was like /dev/random of Linux.) So /dev/urandom was better than /dev/random for OpenBSD. This has changed with OpenBSD 4.9 (from May 2011); now /dev/random also gives random numbers. So if some example on Rosetta Code uses /dev/random, I will not care to change it to /dev/urandom. --Kernigh 04:47, 8 May 2011 (UTC)

Libraries and features[edit]

Is it within the scope of this task to use libraries and language features which provide random numbers derived from both hardware and software sources, or is the intent here to show a more low-level access to the underlying operating system itself? --Michael Mol 14:03, 11 January 2011 (UTC)

I would say yes, if there is some hardware involved, so that the random numbers are not 100% "pseudo". The stress should be on random numbers. Just showing how to read from an arbitrary device is perhaps not very interesting. --Abu 14:25, 11 January 2011 (UTC)
To be certain, the task's fundamental drive is to obtain numbers which are not deterministically-generated, even with an unknown seed? --Michael Mol 14:44, 11 January 2011 (UTC)
Er. I was unclear. Clarification handy, though: http://irclog.perlgeek.de/rosettacode/2011-01-11#i_3175701 --Michael Mol 15:21, 11 January 2011 (UTC)
OK: So let's say, it should involve real-world generated entropy during each step, and define the scope of this task to what is covered by the Wikipedia article. --Abu 15:26, 11 January 2011 (UTC)