1/*	$OpenBSD: arc4random.c,v 1.24 2013/06/11 16:59:50 deraadt Exp $	*/
2
3/*
4 * Copyright (c) 1996, David Mazieres <dm@uun.org>
5 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
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
20/*
21 * Arc4 random number generator for OpenBSD.
22 *
23 * This code is derived from section 17.1 of Applied Cryptography,
24 * second edition, which describes a stream cipher allegedly
25 * compatible with RSA Labs "RC4" cipher (the actual description of
26 * which is a trade secret).  The same algorithm is used as a stream
27 * cipher called "arcfour" in Tatu Ylonen's ssh package.
28 *
29 * RC4 is a registered trademark of RSA Laboratories.
30 */
31
32#include <sys/cdefs.h>
33__FBSDID("$FreeBSD: stable/10/lib/libc/gen/arc4random.c 315227 2017-03-14 06:12:51Z delphij $");
34
35#include "namespace.h"
36#include <fcntl.h>
37#include <limits.h>
38#include <stdlib.h>
39#include <unistd.h>
40#include <sys/types.h>
41#include <sys/param.h>
42#include <sys/sysctl.h>
43#include <sys/time.h>
44#include <pthread.h>
45
46#include "libc_private.h"
47#include "un-namespace.h"
48
49#ifdef __GNUC__
50#define inline __inline
51#else				/* !__GNUC__ */
52#define inline
53#endif				/* !__GNUC__ */
54
55struct arc4_stream {
56	u_int8_t i;
57	u_int8_t j;
58	u_int8_t s[256];
59};
60
61static pthread_mutex_t	arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
62
63#define	RANDOMDEV	"/dev/random"
64#define	KEYSIZE		128
65#define	_ARC4_LOCK()						\
66	do {							\
67		if (__isthreaded)				\
68			_pthread_mutex_lock(&arc4random_mtx);	\
69	} while (0)
70
71#define	_ARC4_UNLOCK()						\
72	do {							\
73		if (__isthreaded)				\
74			_pthread_mutex_unlock(&arc4random_mtx);	\
75	} while (0)
76
77static int rs_initialized;
78static struct arc4_stream rs;
79static pid_t arc4_stir_pid;
80static int arc4_count;
81
82extern int __sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp,
83    void *newp, size_t newlen);
84
85static inline u_int8_t arc4_getbyte(void);
86static void arc4_stir(void);
87
88static inline void
89arc4_init(void)
90{
91	int     n;
92
93	for (n = 0; n < 256; n++)
94		rs.s[n] = n;
95	rs.i = 0;
96	rs.j = 0;
97}
98
99static inline void
100arc4_addrandom(u_char *dat, int datlen)
101{
102	int     n;
103	u_int8_t si;
104
105	rs.i--;
106	for (n = 0; n < 256; n++) {
107		rs.i = (rs.i + 1);
108		si = rs.s[rs.i];
109		rs.j = (rs.j + si + dat[n % datlen]);
110		rs.s[rs.i] = rs.s[rs.j];
111		rs.s[rs.j] = si;
112	}
113	rs.j = rs.i;
114}
115
116static size_t
117arc4_sysctl(u_char *buf, size_t size)
118{
119	int mib[2];
120	size_t len, done;
121
122	mib[0] = CTL_KERN;
123	mib[1] = KERN_ARND;
124	done = 0;
125
126	do {
127		len = size;
128		if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1)
129			return (done);
130		done += len;
131		buf += len;
132		size -= len;
133	} while (size > 0);
134
135	return (done);
136}
137
138static void
139arc4_stir(void)
140{
141	int done, fd, i;
142	struct {
143		struct timeval	tv;
144		pid_t		pid;
145		u_char	 	rnd[KEYSIZE];
146	} rdat;
147
148	if (!rs_initialized) {
149		arc4_init();
150		rs_initialized = 1;
151	}
152	done = 0;
153	if (arc4_sysctl((u_char *)&rdat, KEYSIZE) == KEYSIZE)
154		done = 1;
155	if (!done) {
156		fd = _open(RANDOMDEV, O_RDONLY | O_CLOEXEC, 0);
157		if (fd >= 0) {
158			if (_read(fd, &rdat, KEYSIZE) == KEYSIZE)
159				done = 1;
160			(void)_close(fd);
161		}
162	}
163	if (!done) {
164		(void)gettimeofday(&rdat.tv, NULL);
165		rdat.pid = getpid();
166		/* We'll just take whatever was on the stack too... */
167	}
168
169	arc4_addrandom((u_char *)&rdat, KEYSIZE);
170
171	/*
172	 * Discard early keystream, as per recommendations in:
173	 * "(Not So) Random Shuffles of RC4" by Ilya Mironov.
174	 */
175	for (i = 0; i < 3072; i++)
176		(void)arc4_getbyte();
177	arc4_count = 1600000;
178}
179
180static void
181arc4_stir_if_needed(void)
182{
183	pid_t pid = getpid();
184
185	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) {
186		arc4_stir_pid = pid;
187		arc4_stir();
188	}
189}
190
191static inline u_int8_t
192arc4_getbyte(void)
193{
194	u_int8_t si, sj;
195
196	rs.i = (rs.i + 1);
197	si = rs.s[rs.i];
198	rs.j = (rs.j + si);
199	sj = rs.s[rs.j];
200	rs.s[rs.i] = sj;
201	rs.s[rs.j] = si;
202	return (rs.s[(si + sj) & 0xff]);
203}
204
205static inline u_int32_t
206arc4_getword(void)
207{
208	u_int32_t val;
209	val = arc4_getbyte() << 24;
210	val |= arc4_getbyte() << 16;
211	val |= arc4_getbyte() << 8;
212	val |= arc4_getbyte();
213	return val;
214}
215
216void
217arc4random_stir(void)
218{
219	_ARC4_LOCK();
220	arc4_stir();
221	_ARC4_UNLOCK();
222}
223
224void
225arc4random_addrandom(u_char *dat, int datlen)
226{
227	_ARC4_LOCK();
228	if (!rs_initialized)
229		arc4_stir();
230	arc4_addrandom(dat, datlen);
231	_ARC4_UNLOCK();
232}
233
234u_int32_t
235arc4random(void)
236{
237	u_int32_t val;
238	_ARC4_LOCK();
239	arc4_count -= 4;
240	arc4_stir_if_needed();
241	val = arc4_getword();
242	_ARC4_UNLOCK();
243	return val;
244}
245
246void
247arc4random_buf(void *_buf, size_t n)
248{
249	u_char *buf = (u_char *)_buf;
250	_ARC4_LOCK();
251	arc4_stir_if_needed();
252	while (n--) {
253		if (--arc4_count <= 0)
254			arc4_stir();
255		buf[n] = arc4_getbyte();
256	}
257	_ARC4_UNLOCK();
258}
259
260/*
261 * Calculate a uniformly distributed random number less than upper_bound
262 * avoiding "modulo bias".
263 *
264 * Uniformity is achieved by generating new random numbers until the one
265 * returned is outside the range [0, 2**32 % upper_bound).  This
266 * guarantees the selected random number will be inside
267 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
268 * after reduction modulo upper_bound.
269 */
270u_int32_t
271arc4random_uniform(u_int32_t upper_bound)
272{
273	u_int32_t r, min;
274
275	if (upper_bound < 2)
276		return 0;
277
278	/* 2**32 % x == (2**32 - x) % x */
279	min = -upper_bound % upper_bound;
280	/*
281	 * This could theoretically loop forever but each retry has
282	 * p > 0.5 (worst case, usually far better) of selecting a
283	 * number inside the range we need, so it should rarely need
284	 * to re-roll.
285	 */
286	for (;;) {
287		r = arc4random();
288		if (r >= min)
289			break;
290	}
291
292	return r % upper_bound;
293}
294
295#if 0
296/*-------- Test code for i386 --------*/
297#include <stdio.h>
298#include <machine/pctr.h>
299int
300main(int argc, char **argv)
301{
302	const int iter = 1000000;
303	int     i;
304	pctrval v;
305
306	v = rdtsc();
307	for (i = 0; i < iter; i++)
308		arc4random();
309	v = rdtsc() - v;
310	v /= iter;
311
312	printf("%qd cycles\n", v);
313}
314#endif
315