How Can I Generate Thoroughly Random Seeds for mt19937 in C ?

Thorough Random Seed Generation for mt19937 in C

Problem:

Recent answers often suggest using with std::random_device to seed the mt19937 PRNG, which is flawed as it doesn't provide sufficient randomness, can be predictable, and may use a PRNG with fixed seed.

Portable and Thorough Seeding:

A portable and thorough approach to seeding mt19937 involves using a CSPRNG, such as:

• Windows: sysrandom utilizing CryptGenRandom
• Unix-Like: sysrandom utilizing /dev/urandom (or getrandom if available on Linux 3.17 or higher)
• OpenBSD: sysrandom utilizing getentropy

Code Example:

#include <cstdint>
#include <cstdlib>
#include <fstream>

size_t sysrandom(void* dst, size_t dstlen);

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

Linux Specialization with getrandom:

#if defined(HAVE_GETRANDOM)
size_t sysrandom(void* dst, size_t dstlen) {
  int bytes = syscall(SYS_getrandom, dst, dstlen, 0);
  if (bytes != dstlen) {
    throw std::runtime_error("Unable to read N bytes from CSPRNG.");
  }
  return dstlen;
}
#endif

OpenBSD Special Case:

#if defined(HAVE_GETENTROPY)
size_t sysrandom(void* dst, size_t dstlen) {
  int bytes = getentropy(dst, dstlen);
  if (bytes != dstlen) {
    throw std::runtime_error("Unable to read N bytes from CSPRNG.");
  }
  return dstlen;
}
#endif

Other Thoughts:

• Use an unbuffered read/write approach for cryptographically secure random bytes.
• Specialized functions (e.g., for Linux or OpenBSD) can be added for improved efficiency.

The above is the detailed content of How Can I Generate Thoroughly Random Seeds for mt19937 in C ?. For more information, please follow other related articles on the PHP Chinese website!