How Can I Securely Seed the Mt19937 PRNG in C Across Different Platforms?

Succinct, Portable, and Thorough Seeding of Mt19937 PRNG in C

Despite the shortcomings of using std::random_device and time(NULL) for seeding, it's possible to achieve a robust and portable solution:

CSPRNG-Based Seeding

To avoid the limitations of std::random_device, we can utilize a CSPRNG such as:

• Windows: CryptGenRandom
• Unix-Like: /dev/urandom
• Last Resort (Optional): std::random_device (can be problematic)

Minimal Seeding Function:

The following cross-platform function provides a minimal wrapper around various OS-specific CSPRNGs:

size_t sysrandom(void* dst, size_t dstlen) {
  #ifdef _WIN32
    // Windows CSPRNG implementation
  #elif defined(__linux__)
    // Linux CSPRNG implementation
  #else
    // POSIX CSPRNG implementation
  #endif
}

Efficient Seeding:

With sysrandom available, seeding the mt19937 PRNG becomes:

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

Additional Notes:

• For enhanced security on Linux (3.17 ), consider using getrandom with a fallback to /dev/urandom.
• On OpenBSD, use getentropy instead of /dev/urandom.
• For cryptographic security, I/O buffering should be disabled when using sysrandom.

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