Fast pseudorandom number generator for cryptography in C

Question

I was using the following code to generate sequence of pseudo-random numbers that was used for cryptographic purposes, but then I read somewhere that it may not be very secure. Can someone give me C implementation of a better generator -- the main goal is for this method to be fast. For instance, I did some research and came across Blum Blum Shub method, which would totally kill performance by doing pow(N) calculations.

PS. And please don't quote Wikipedia articles w/o C/C++ code. I'm looking for C or C++ code sample of what I'm showing below.

#define ROL(v, shift) ((((v) >> ((sizeof(v) * 8) - (shift))) | ((v) << (shift))))

ULONGLONG uiPSN = doSeed();   //64-bit unsigned integer

for(int i = 0; i < sizeOfArray; i++)
{
    uiPSN = uiPSN * 214013L + 2531011L;
    uiPSN = ROL(uiPSN, 16);

    //Apply 'uiPSN'
}

Answer 1

ISAAC (http://www.burtleburtle.net/bob/rand/isaacafa.html) is probably one of the fastest cryptographically secure PRNGs (code at site). Another approach is to use a block cipher in counter mode. Something like TwoFish, which is reasonably fast and freely available, would be effective.

If you don't need a lot of numbers, all modern operating systems have built-in RNGs suitable for cryptographic use, though they typically can't produce lots of numbers because they rely on accumulating entropy from sources like input timings. Unix-like systems (Linux, OSX) have /dev/random, Windows has CryptGenRandom. Even if these aren't suitable for your needs, you probably should use them to seed the PRNG you do end up using.