1/*	$OpenBSD: arc4random.c,v 1.50 2014/07/21 18:13:12 deraadt Exp $	*/
2
3/*
4 * Copyright (c) 1996, David Mazieres <dm@uun.org>
5 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
6 * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
7 *
8 * Permission to use, copy, modify, and distribute this software for any
9 * purpose with or without fee is hereby granted, provided that the above
10 * copyright notice and this permission notice appear in all copies.
11 *
12 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
13 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
14 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
15 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
16 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
17 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
18 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
19 */
20
21/*
22 * ChaCha based random number generator for OpenBSD.
23 */
24
25#include <fcntl.h>
26#include <limits.h>
27#include <signal.h>
28#include <stdint.h>
29#include <stdlib.h>
30#include <string.h>
31#include <unistd.h>
32#include <sys/types.h>
33#include <sys/param.h>
34#include <sys/time.h>
35
36#define KEYSTREAM_ONLY
37#include "chacha_private.h"
38
39#define min(a, b) ((a) < (b) ? (a) : (b))
40#ifdef __GNUC__
41#define inline __inline
42#else				/* !__GNUC__ */
43#define inline
44#endif				/* !__GNUC__ */
45
46#define KEYSZ	32
47#define IVSZ	8
48#define BLOCKSZ	64
49#define RSBUFSZ	(16*BLOCKSZ)
50
51/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
52static struct _rs {
53	size_t		rs_have;	/* valid bytes at end of rs_buf */
54	size_t		rs_count;	/* bytes till reseed */
55} *rs;
56
57/* Maybe be preserved in fork children, if _rs_allocate() decides. */
58static struct _rsx {
59	chacha_ctx	rs_chacha;	/* chacha context for random keystream */
60	u_char		rs_buf[RSBUFSZ];	/* keystream blocks */
61} *rsx;
62
63static inline int _rs_allocate(struct _rs **, struct _rsx **);
64static inline void _rs_forkdetect(void);
65#include "arc4random.h"
66
67static inline void _rs_rekey(u_char *dat, size_t datlen);
68
69static inline void
70_rs_init(u_char *buf, size_t n)
71{
72	if (n < KEYSZ + IVSZ)
73		return;
74
75	if (rs == NULL) {
76		if (_rs_allocate(&rs, &rsx) == -1)
77			abort();
78	}
79
80	chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
81	chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
82}
83
84static void
85_rs_stir(void)
86{
87	u_char rnd[KEYSZ + IVSZ];
88
89	if (getentropy(rnd, sizeof rnd) == -1)
90		_getentropy_fail();
91
92	if (!rs)
93		_rs_init(rnd, sizeof(rnd));
94	else
95		_rs_rekey(rnd, sizeof(rnd));
96	explicit_bzero(rnd, sizeof(rnd));	/* discard source seed */
97
98	/* invalidate rs_buf */
99	rs->rs_have = 0;
100	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
101
102	rs->rs_count = 1600000;
103}
104
105static inline void
106_rs_stir_if_needed(size_t len)
107{
108	_rs_forkdetect();
109	if (!rs || rs->rs_count <= len)
110		_rs_stir();
111	if (rs->rs_count <= len)
112		rs->rs_count = 0;
113	else
114		rs->rs_count -= len;
115}
116
117static inline void
118_rs_rekey(u_char *dat, size_t datlen)
119{
120#ifndef KEYSTREAM_ONLY
121	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
122#endif
123	/* fill rs_buf with the keystream */
124	chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
125	    rsx->rs_buf, sizeof(rsx->rs_buf));
126	/* mix in optional user provided data */
127	if (dat) {
128		size_t i, m;
129
130		m = min(datlen, KEYSZ + IVSZ);
131		for (i = 0; i < m; i++)
132			rsx->rs_buf[i] ^= dat[i];
133	}
134	/* immediately reinit for backtracking resistance */
135	_rs_init(rsx->rs_buf, KEYSZ + IVSZ);
136	memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
137	rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
138}
139
140static inline void
141_rs_random_buf(void *_buf, size_t n)
142{
143	u_char *buf = (u_char *)_buf;
144	u_char *keystream;
145	size_t m;
146
147	_rs_stir_if_needed(n);
148	while (n > 0) {
149		if (rs->rs_have > 0) {
150			m = min(n, rs->rs_have);
151			keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
152			    - rs->rs_have;
153			memcpy(buf, keystream, m);
154			memset(keystream, 0, m);
155			buf += m;
156			n -= m;
157			rs->rs_have -= m;
158		}
159		if (rs->rs_have == 0)
160			_rs_rekey(NULL, 0);
161	}
162}
163
164static inline void
165_rs_random_u32(uint32_t *val)
166{
167	u_char *keystream;
168
169	_rs_stir_if_needed(sizeof(*val));
170	if (rs->rs_have < sizeof(*val))
171		_rs_rekey(NULL, 0);
172	keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
173	memcpy(val, keystream, sizeof(*val));
174	memset(keystream, 0, sizeof(*val));
175	rs->rs_have -= sizeof(*val);
176}
177
178uint32_t
179arc4random(void)
180{
181	uint32_t val;
182
183	_ARC4_LOCK();
184	_rs_random_u32(&val);
185	_ARC4_UNLOCK();
186	return val;
187}
188
189void
190arc4random_buf(void *buf, size_t n)
191{
192	_ARC4_LOCK();
193	_rs_random_buf(buf, n);
194	_ARC4_UNLOCK();
195}
196