First of all, virtually all rand functions do not provide true randomness, rather they provide so-called pseudo-random numbers. So, how do pseudo-random number generators work? Basically in the same way that encryption works: You have a function a hash that takes some input, and produces some output in such a complex manner that it's impossible from the output to guess the input or vice versa. That is, every cypher can be used to create a rather good pseudo-random generator.
However, while you could use any pseudo-random generator to do encryption in principle, most pseudo-random number generators are primarily developed for speed, not cryptographic security, so they won't give hackers any headaches. For a pseudo-random generator, the hashing function is applied to some hidden internal state of the generator, and its output is used to a modify that internal state, and b to compute the output of the rand function.
The next invocation of rand will use that changed internal state, and thus produce a different result. The better the hash function, the less easily the results are distinguishable from true random numbers. As a matter of fact, computers nowadays have access to real random numbers: They stem from jitter in the timing of interrupts produced by external devices.
Linux uses these values of small uncertainty to constantly stir an "entropy pool", which is just a few kilobytes of internal state.
So, access to some really really good random numbers is as simple as opening one of these two devices and reading some bytes from them. Random Numbers are numbers generated by the process whose output is unpredictable.
We can take some simple example outcome of the dice. What is going to be output when we throw a dice is unpredictable. How Random numbers are genrated. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. How do random number generators work? Ask Question. Asked 10 years, 1 month ago.
Active 4 years, 8 months ago. Viewed k times. Improve this question. On the information provided for this game, they assure you the outcome of all spins on the slot machine are dependent upon the in-built random number generator RNG algorithm.
These RNGs are a mixture of technology and well-established mathematical systems which work in tandem to produce random number sequences in a reliable, accurate way. Before the advancements in digital and computer technology, the traditional random number generator was the simple and humble dice.
From there, technology advanced to the production of traditional mechanical slots, where the pull of a lever sends a group of reels in motion. The reels spin independently and usually come to a stop after one or two seconds.
This is a must-read text for anyone who uses random number generators for any serious work. One of the things to keep in mind is that there are no 'true' random number generators. They just generate numbers that look random to us mere mortals. One of the easiest examples of this to implement, as well is the Linear congruential generator.
Sure, the numbers look unpredictable to you and me, but they're actually evenly spaced within a finite field. Of course, some generators, like Blum Blum Shub aren't predictable for an outsider even if he applies serious mathematical skills and computing power to the task, but at the fundamental level, random number generators aren't random; they're regular and predictable. How I made them in the old days was by getting some value from the system that changes really rapidly, for example the system millisecond timer.
The next thing you have to do is to apply some formula that will generate a new number from this "input" number and clip it to the range you need, eg Update: I realize that this formula is a very bad one, it generates a pretty predictable set of numbers. Also, the system timer is too predictable as a source. So for most applications, this does not suffice. If you need better randomness, use more sources than just the system timer and better formulas to combine them.
I'm sure the answer is language-specific, but you can try altering my Google query for the language of your choice. There is a lot of information available about how they are working Why would you like to write a new random generator? You probably should not try to do so For example in a game you could use a shuffle bag which produces 'fair' random values - have a look at this interesting question on SO.
I post this here, because I really liked the idea and implementation when I read about it the first time :. It's also common to seed these types of generators by using something like the fifth decimal of the current clock time which also appears random to us. Add together inputs from a few chaotic systems, e. Quality: random. So, if you also maintain a pool of true random numbers, you have all of speed, quality and security. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
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