On 08/05/2017 02:01 AM, Jan Dušátko wrote:
And, the hardest one. What is exactly mean random number? Can choosing of numbers without any relations between them provide for us enought randomnes? How much of perfect random signal can be? This can lead to one crazy question - if the perfect random will be a small subset, can we be in risk use one of them?
That is a very tricky issue! A true random number generator will eventually output strings like "1234567890" that look anything but random to a human. So, does random mean "produced by an unpredictable physical process," or does it mean "I do not see a pattern in the output data"? The latter answer is perilous, because our perceptual systems seek patterns and happily impose them where none is present; faces seen in cracked ceiling plaster, etc., are not "there" until we put them there ourselves. I see two answers: A theoretical or abstract answer that says "As long as there is no way to predict the placement or content of 'orderly' outputs in a stream of data, that data is random." A pragmatic answer says "Depending on the application a random number generator is feeding into, it may be necessary to filter out strings that present as 'too easy to guess' where and as they appear." Does this kind of filtering make the remaining 'random' data less random? In the sense of "more predictable," yes it does. But only slightly, unless the pattern seeking filter is /very/ aggressive. Calculating the impact of a filter that excludes strings like "1234567890" from use as "random" data in applications like generating cipher keys should be simple enough. Increasing the length of the keys to compensate for this bias, in the unlikely event that this is considered worth doing, should be trivial in most cases.
Lot of people do hard work understanding, what is it random. How we test random. How we detect random. And, how we can use random. We all enjoy their hard work.
Definitely. Because of the close connection between the concept of "random" and concrete physical phenomena that are easy to visualize and manipulate in imagination, even I can understand and play with these ideas. :o)