Generating totally random numbers without random function?

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True random number generator

I was talking to a friend the other day and we were trying to figure out if it is possible to generate completely random numbers without the help of a random function? In C for example "rand" generates pseudo-random numbers. Or we can use something like "srand( time( NULL ) );" This will allow the computer to read numbers from its clock as seed values. So if I understand everything I have read so far right, then I am pretty sure that no random function actually produces truely random numbers. How would one write a program that generates numbers that are completely random and what would code look like?

Answer 1

Check out this question: http://stackoverflow.com/questions/37702/true-random-number-generator

Also, from wikipedia's entry on pseudorandom numbers

As John von Neumann joked, "Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin."

Answer 2

This is more of a physics question I think. If you think about it nothing is random, it just occurs due to events the complexity of which make them unpredictable to us. A computer is a subsystem just like any other in the universe and by giving it unpredictable external inputs (RTC, I/O garbage) we can get the same kind of randomness that that a roulette wheel gets from varying friction, air resistance, initial impulse and millions of factors that I can't wrap my head around.

Answer 3

The excellent random.org website provides hardware-based random numbers as well as a number of software interfaces to retrieve these.

This can be used e.g. for genuinely unpredictable seeds or for 'true' random numbers. Being a web service, there are limits on the number of draws you can make, so don't try to use this for your graduate school monte carlo simulation.

FWIW, I wrapped one of those interface in the R package random.

Answer 4

easy way to do it is using digits of PI number,

check this articles if you are interested:

http://www.lbl.gov/Science-Articles/Archive/pi-random.html

http://news.uns.purdue.edu/html4ever/2005/050426.Fischbach.pi.html

note that it's easy method, but it has some disadvantages (there are some known patterns in the digits of pi)

Answer 5

It would look like:

int random = CallHardwareRandomGenerator();

Even with hardware, randomness is tricky. There are things which are physically random (atomic decay is random, but with predictable average amounts, so that can be used as a source of random information) there are things that are physically random enough to make prediction impractical (this is how casinos make money).

There are things that are largely indeterminate (mix up information from key-stroke rate, mouse-movements, and a few things like that), which are a good-enough source of "randomness" for many uses.

Mathematically, we cannot produce randomness, but we can improve distribution and make something harder to predict. Cryptographic PRNGs do a stronger job at this than most, but are more expensive in terms of resources.

Answer 6

There's room for a fair amount of philosophical debate about what "truly random" really even means. From a practical viewpoint, even sources we know aren't truly random can be used in ways that produce what are probably close enough for almost any practical purpose though (in particular, that at least with current technology, full knowledge of the previously produced bitstream appears to be insufficient to predict the next bit accurately). Most of those do involve a bit of extra hardware though -- for example, it's pretty easy to put a source together from a little bit of Americium out of a smoke detector.

There are quite a few more sources as well, though they're mostly pretty low bandwidth (e.g., collect one bit for each keystroke, based on whether the interval between keystrokes was an even or odd number of CPU clocks -- assuming the CPU clock and keyboard clock are derived from separate crystals). OTOH, you have to be really careful with this -- a fair number of security holes (e.g., in Netscape around v. 4.0 or so) have stemmed from people believing that such sources were a lot more random than they really were.

While there are a number of web sites that produce random numbers from hardware sources, most of them are useless from a viewpoint of encryption. Even at best, you're just trusting your SSL (or TLS) connection to be secure so nobody captured the data you got from the site.