A true random number generator produces numeric sequences that are irregular (no recognizable patterns or periods), unpredictable, and irreproducible.

Pseudo-Random Sequences

“It looks random. This means that it passes all the statistical tests of randomness that we can find.” (Schneier)

Cryptographically Secure Pseudo-Random Sequences

“It is unpredictable. It must be computationally infeasible to predict what the next random bit will be, given complete knowledge of the algorithm or hardware generating the sequence and all of the previous bits in the stream.” (Schneier)

Real Random Sequences

It is irreproducible. “It cannot be reliably reproduced. If you run the sequence generator twice with the exact same input (at least as exact as humanly possible), you will get two completely unrelated random sequences.” (Schneier)


  • Bruce Schneier, Applied Cryptography: Protocols, Algorithms and Source Code in C,John Wiley & Sons, Inc.,1996

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