To get cryptographically grade randomness you can use one of these C functions: *BSD, newer macOS, and GNU libc: int getentropy(void *buffer, size_t length);

To get cryptographically grade randomness you can use one of these C functions: *BSD, newer macOS, and GNU libc: int getentropy(void *buffer, size_t length); Linux 3.19+: ssize_t getrandom(void *buf, size_t buflen, unsigned int flags); iOS and macOS 10.7+: int SecRandomCopyBytes(SecRandomRef, size_t, uint8_t *); Fuchsia: void zx_cprng_draw(void* buffer, size_t buffer_size); Any *nix: Read from "/dev/random" (or "/dev/urandom" under the assumption that your system has already enough entropy). Windows: There are different functions/libraries depending on the Windows version and some of them are a complicated multi-step mess. Some time ago I wrote a C library that abstracts that away just for fun: https://github.com/panzi/portable_get_random https://github.com/panzi/portable_get_random*