From: Eugene Salamin <gene_salamin@yahoo.com> For cryptosecure, I don't see how you can do better than a physical noise or quantum source.? Why do computer science people so disdain physical RNG's; it is because they don't involve fun things like algorithm analysis?? This annoys me so much that I've made it into a litmus test.? When I pick up a book that discusses random number generation, I immediately look to see if physical RNG's are discussed, not necessarily praised, and if not, I ignore the entire book.
Now, there is a place for pseudo-RNG's, and that is if the same sequence of random numbers must be generated again since then the initial seed can represent the entire lengthy sequence.
--well, you've answered your own question. PRNGs are better than true-random in the sense you can re-run your program with exact same results, which is needed to be able to debug it. Also PRNGs are probably faster and also higher quality randomness (paradoxically) than true random RNGs in many cases, albeit by algorithms applied to true random bits they could be made excellent too. True random RNGs are essential for cryptographic purposes, i.e. generating something secret. A way I invented a long time ago to generate true random bits, is this. Let F(x) be a continuous function of x with |slope|=2, which maps some real interval to itself, for example if |x|<1 then F(x)=2+2x for -1<x<-1/2, -2x for |x|<1/2, 2-2x for 1/2<x<1. Build an analog circuit to compute F(x) on some voltage interval. (A circuit made of ideal op-amps and ideal diodes can do that.) Use it cyclically to compute x0=x, x1=F(x), x2=F(F(x)), x3=F(F(F(x))), etc forever. Each new analog value will contain 1 new bit of randomness. If we output the sequence sign(x_k) of bits, they will be random bits. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)