1/*	$OpenBSD: getentropy_win.c,v 1.6 2020/11/11 10:41:24 bcook Exp $	*/
2
3/*
4 * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
5 * Copyright (c) 2014, Bob Beck <beck@obtuse.com>
6 *
7 * Permission to use, copy, modify, and distribute this software for any
8 * purpose with or without fee is hereby granted, provided that the above
9 * copyright notice and this permission notice appear in all copies.
10 *
11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18 *
19 * Emulation of getentropy(2) as documented at:
20 * http://man.openbsd.org/getentropy.2
21 */
22
23#include <windows.h>
24#include <bcrypt.h>
25#include <errno.h>
26#include <stdint.h>
27#include <sys/types.h>
28
29int	getentropy(void *buf, size_t len);
30
31/*
32 * On Windows, BCryptGenRandom with BCRYPT_USE_SYSTEM_PREFERRED_RNG is supposed
33 * to be a well-seeded, cryptographically strong random number generator.
34 * https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
35 */
36int
37getentropy(void *buf, size_t len)
38{
39	if (len > 256) {
40		errno = EIO;
41		return (-1);
42	}
43
44	if (FAILED(BCryptGenRandom(NULL, buf, len, BCRYPT_USE_SYSTEM_PREFERRED_RNG))) {
45		errno = EIO;
46		return (-1);
47	}
48
49	return (0);
50}
51