A Cryptographically-Secure Pseudo-Random Number Generator that uses system APIs as its source of secure random bytes. In the case of Windows, it uses the $(MONO BCryptGenRandom), $(MONO CryptGenRandom), and $(MONO RtlGenRandom) libraries in that order of fallback. On POSIX-ish systems, it uses the pseudo-device, $(MONO /dev/random), as its source of secure random bytes.