Natural Blogarithms

Enough with coding your own pseudo-random number generators, check out Random.org. Here’s a site that makes the claim of providing “true random numbers” to anyone on the internet.  If you need many numbers you can actually download pregenerated files or even write your own client that will access their server via HTTP, SOAP or CORBA. 

So what is “true randomness,” you ask?   From their own introduction:

Randomness and random numbers have traditionally been used for a variety of purposes, for example games such as dice games. With the advent of computers, people recognized the need for a means of introducing randomness into a computer program. Surprising as it may seem, however, it is difficult to get a computer to do something by chance. A computer running a program follows its instructions blindly and is therefore completely predictable.

Computer engineers chose to introduce randomness into computers in the form of pseudo-random number generators. As the name suggests, pseudo-random numbers are not truly random. Rather, they are computed from a mathematical formula or simply taken from a precalculated list. A lot of research has gone into pseudo-random number theory and modern algorithms for generating them are so good that the numbers look exactly like they were really random. Pseudo-random numbers have the characteristic that they are predictable, meaning they can be predicted if you know where in the sequence the first number is taken from. For some purposes, predictability is a good characteristic, for others it is not.

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True Random Numbers

True random numbers are typically generated by sampling and processing a source of entropy outside the computer. A source of entropy can be very simple, like the little variations in somebody’s mouse movements or in the amount of time between keystrokes. In practice, however, it can be tricky to use user input as a source of entropy. Keystrokes, for example, are often buffered by the computer’s operating system, meaning that several keystrokes are collected before they are sent to the program waiting for them. To the program, it will seem as though the keys were pressed almost simultaneously.

A really good source of entropy is a radioactive source. The points in time at which a radioactive source decays are completely unpredictable, and can be sampled and fed into a computer, avoiding any buffering mechanisms in the operating system. In fact, this is what the HotBits people at Fourmilab in Switzerland are doing. Another source of entropy could be atmospheric noise from a radio, like that used here at random.org, or even just background noise from an office or laboratory. The lavarand people at Silicon Graphics have been clever enough to use lava lamps to generate random numbers, so their entropy source not only gives them entropy, it also looks good! The latest random number generator to come online (both lavarand and HotBits precede random.org) is Damon Hart-Davis’ Java EntropyPool which gathers random bits from a variety of sources including HotBits and random.org, but also from web page hits received by the EntropyPool’s web server.

This is another one for my file, “I wish I thought of that.” A number of times in my research in stochastic partial differential equations or in variable knot splines algorithms I relied on fairly standard linear congruential pseudo random number generators. I often wondered in the back of my mind just how perturbed my results might have been have the lack of “true” randomness. I’d always resigned myself to not being able to attain true randomness. I might give this site a try.

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