How Can I Properly Seed the MT19937 PRNG in C for Secure Random Number Generation?

How to Thoroughly Seed the MT19937 PRNG in C

Typically, std::random_device is used to generate random numbers, as seen in the following code:

std::random_device rd;  
std::mt19937 gen(rd());
std::uniform_int_distribution<> dis(0, 5);
dis(gen);

However, this method is flawed because:

• std::random_device() returns insufficient entropy.
• std::mt19937 gen(rd());gen() may not produce a good output distribution.
• std::random_device can be implemented as a PRNG with a fixed seed.

A more reliable approach is to use a CSPRNG, such as CryptGenRandom on Windows or /dev/urandom on Unix-like systems, to generate high-quality random bytes to seed the PRNG. For example:

#include <bit>
#include <iostream>
#include <string>

size_t sysrandom(void* dst, size_t dstlen) {
    std::ifstream stream("/dev/urandom", std::ios_base::binary | std::ios_base::in);
    stream.read((char*)dst, dstlen);
    return dstlen;
}

int main() {
    std::uint_least32_t seed;
    sysrandom(&seed, sizeof(seed));
    std::mt19937 gen(seed);

    // Your code to use the generator here...
    return 0;
}

This code uses /dev/urandom as the CSPRNG and seeds the PRNG using a 32-bit value, which should be increased for better security. This approach is portable, well-tested, and easy to use, providing a solid foundation for generating random numbers in C .

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