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 
29 int	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  */
36 int
37 getentropy(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