How Can I Reliably Seed mt19937 in C for High-Quality Random Number Generation?

Addressing PRNG Seeding Issues in C

Despite the widespread use of for random number generation, the approach often relies on std::random_device, which suffers from several limitations. Recognizing these issues, this discussion explores how to seed the mt19937 PRNG thoroughly, portably, and succinctly.

Avoid Sole Reliance on std::random_device and time(NULL)

Using std::random_device or time(NULL) alone is insufficient for seeding mt19937 due to low entropy and non-uniform distribution.

Solution: Using a CSPRNG Wrapper

A minimal solution is to use a wrapper around a CSPRNG, such as sysrandom defined below. This wrapper provides access to cryptographic-grade random bytes:

size_t sysrandom(void* dst, size_t dstlen);

Platform-Specific Implementations

For Windows, we can utilize CryptGenRandom:

size_t sysrandom(void* dst, size_t dstlen)
{
    HCRYPTPROV ctx;
    ... // Acquire and release cryptographic context
    CryptGenRandom(ctx, dstlen, dst);
    return dstlen;
}

On Unix-like systems, we can employ /dev/urandom:

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

Seeding mt19937

Using the sysrandom wrapper, we can seed mt19937 with sufficient bits:

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

Comparison with Boost

This approach parallels boost::random_device, which utilizes secure CSPRNGs on various platforms.

Additional Considerations

On Linux, getrandom provides a more secure alternative to /dev/urandom. OpenBSD lacks /dev/urandom; instead, use getentropy.

Conclusion

This article provides a comprehensive guide to effectively seeding the mt19937 PRNG, ensuring high-quality random number generation in C

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