92 lines
3.4 KiB
C
92 lines
3.4 KiB
C
/*************************************************************************
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* Copyright (c) 2020-2021 Elichai Turkel *
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* Distributed under the CC0 software license, see the accompanying file *
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* EXAMPLES_COPYING or https://creativecommons.org/publicdomain/zero/1.0 *
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*************************************************************************/
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/*
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* This file is an attempt at collecting best practice methods for obtaining randomness with different operating systems.
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* It may be out-of-date. Consult the documentation of the operating system before considering to use the methods below.
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*
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* Platform randomness sources:
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* Linux -> `getrandom(2)`(`sys/random.h`), if not available `/dev/urandom` should be used. http://man7.org/linux/man-pages/man2/getrandom.2.html, https://linux.die.net/man/4/urandom
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* macOS -> `getentropy(2)`(`sys/random.h`), if not available `/dev/urandom` should be used. https://www.unix.com/man-page/mojave/2/getentropy, https://opensource.apple.com/source/xnu/xnu-517.12.7/bsd/man/man4/random.4.auto.html
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* FreeBSD -> `getrandom(2)`(`sys/random.h`), if not available `kern.arandom` should be used. https://www.freebsd.org/cgi/man.cgi?query=getrandom, https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
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* OpenBSD -> `getentropy(2)`(`unistd.h`), if not available `/dev/urandom` should be used. https://man.openbsd.org/getentropy, https://man.openbsd.org/urandom
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* Windows -> `BCryptGenRandom`(`bcrypt.h`). https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
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*/
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#if defined(_WIN32)
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#include <windows.h>
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#include <ntstatus.h>
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#include <bcrypt.h>
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#elif defined(__ANDROID__)
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#include <fcntl.h>
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#include <unistd.h>
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#include <errno.h>
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#elif defined(__linux__) || defined(__FreeBSD__)
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#include <sys/random.h>
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#elif defined(__OpenBSD__)
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#include <unistd.h>
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#elif defined(__APPLE__)
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#include <Security/SecRandom.h>
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#else
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#error "Couldn't identify the OS"
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#endif
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#include <stddef.h>
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#include <limits.h>
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#include <stdio.h>
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/* Returns 1 on success, and 0 on failure. */
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static int fill_random(unsigned char* data, size_t size) {
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#if defined(_WIN32)
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NTSTATUS res = BCryptGenRandom(NULL, data, size, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
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if (res != STATUS_SUCCESS || size > ULONG_MAX) {
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return 0;
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} else {
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return 1;
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}
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#elif defined(__ANDROID__)
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int fd = open("/dev/urandom", O_RDONLY);
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if (fd < 0) {
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return 0; // Failed to open /dev/urandom
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}
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ssize_t read_bytes = 0;
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while (size > 0) {
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read_bytes = read(fd, data, size);
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if (read_bytes <= 0) {
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if (errno == EINTR) {
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continue; // If interrupted by signal, try again
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}
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close(fd);
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return 0; // Failed to read
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}
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data += read_bytes;
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size -= read_bytes;
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}
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close(fd);
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return 1;
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#elif defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__)
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/* If `getrandom(2)` is not available you should fallback to /dev/urandom */
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ssize_t res = getrandom(data, size, 0);
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if (res < 0 || (size_t)res != size ) {
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return 0;
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} else {
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return 1;
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}
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#elif defined(__APPLE__)
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/* If `getentropy(2)` is not available you should fallback to either
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* `SecRandomCopyBytes` or /dev/urandom */
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int res = SecRandomCopyBytes(kSecRandomDefault, size, data);
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if (res == 0) {
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return 1;
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} else {
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return 0;
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}
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#endif
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return 0;
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}
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