1 /* $OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb 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 * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
8 *
9 * Permission to use, copy, modify, and distribute this software for any
10 * purpose with or without fee is hereby granted, provided that the above
11 * copyright notice and this permission notice appear in all copies.
12 *
13 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
14 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
15 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
16 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
17 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
18 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
19 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
20 */
21
22 /*
23 * ChaCha based random number generator for OpenBSD.
24 */
25
26 #define _DEFAULT_SOURCE
27 #include <fcntl.h>
28 #include <limits.h>
29 #include <signal.h>
30 #include <stdint.h>
31 #include <stdlib.h>
32 #include <string.h>
33 #include <unistd.h>
34 #include <sys/types.h>
35 #include <sys/time.h>
36
37 #define KEYSTREAM_ONLY
38 #include "chacha_private.h"
39
40 #define minimum(a, b) ((a) < (b) ? (a) : (b))
41
42 #if defined(__GNUC__) || defined(_MSC_VER)
43 #define inline __inline
44 #else /* __GNUC__ || _MSC_VER */
45 #define inline
46 #endif /* !__GNUC__ && !_MSC_VER */
47
48 #define KEYSZ 32
49 #define IVSZ 8
50 #define BLOCKSZ 64
51 #define RSBUFSZ (16*BLOCKSZ)
52
53 #if SIZE_MAX <= 65535
54 #define REKEY_BASE ((size_t) 32 * 1024) /* NB. should be a power of 2 */
55 #elif SIZE_MAX <= 1048575
56 #define REKEY_BASE ((size_t) 256 * 1024) /* NB. should be a power of 2 */
57 #else
58 #define REKEY_BASE ((size_t)1024 * 1024) /* NB. should be a power of 2 */
59 #endif
60
61 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
62 static struct _rs {
63 size_t rs_have; /* valid bytes at end of rs_buf */
64 size_t rs_count; /* bytes till reseed */
65 } *rs;
66
67 /* Maybe be preserved in fork children, if _rs_allocate() decides. */
68 static struct _rsx {
69 chacha_ctx rs_chacha; /* chacha context for random keystream */
70 unsigned char rs_buf[RSBUFSZ]; /* keystream blocks */
71 } *rsx;
72
73 static inline int _rs_allocate(struct _rs **, struct _rsx **);
74 static inline void _rs_forkdetect(void);
75 #include "arc4random.h"
76
77 static inline void _rs_rekey(unsigned char *dat, size_t datlen);
78
79 static inline void
_rs_init(unsigned char * buf,size_t n)80 _rs_init(unsigned char *buf, size_t n)
81 {
82 if (n < KEYSZ + IVSZ)
83 return;
84
85 if (rs == NULL) {
86 if (_rs_allocate(&rs, &rsx) == -1)
87 abort();
88 }
89
90 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8);
91 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
92 }
93
94 static void
_rs_stir(void)95 _rs_stir(void)
96 {
97 uint8_t rnd[KEYSZ + IVSZ];
98 uint32_t rekey_fuzz = 0;
99
100 memset(rnd, 0, (KEYSZ + IVSZ) * sizeof(u_char));
101
102 if (getentropy(rnd, sizeof rnd) == -1)
103 _getentropy_fail();
104
105 if (!rs)
106 _rs_init(rnd, sizeof(rnd));
107 else
108 _rs_rekey(rnd, sizeof(rnd));
109 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */
110
111 /* invalidate rs_buf */
112 rs->rs_have = 0;
113 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
114
115 /* rekey interval should not be predictable */
116 chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
117 (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
118 rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
119 }
120
121 static inline void
_rs_stir_if_needed(size_t len)122 _rs_stir_if_needed(size_t len)
123 {
124 _rs_forkdetect();
125 if (!rs || rs->rs_count <= len)
126 _rs_stir();
127 if (rs->rs_count <= len)
128 rs->rs_count = 0;
129 else
130 rs->rs_count -= len;
131 }
132
133 static inline void
_rs_rekey(unsigned char * dat,size_t datlen)134 _rs_rekey(unsigned char *dat, size_t datlen)
135 {
136 #ifndef KEYSTREAM_ONLY
137 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
138 #endif
139 /* fill rs_buf with the keystream */
140 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
141 rsx->rs_buf, sizeof(rsx->rs_buf));
142 /* mix in optional user provided data */
143 if (dat) {
144 size_t i, m;
145
146 m = minimum(datlen, KEYSZ + IVSZ);
147 for (i = 0; i < m; i++)
148 rsx->rs_buf[i] ^= dat[i];
149 }
150 /* immediately reinit for backtracking resistance */
151 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
152 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
153 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
154 }
155
156 static inline void
_rs_random_buf(void * _buf,size_t n)157 _rs_random_buf(void *_buf, size_t n)
158 {
159 unsigned char *buf = (unsigned char *)_buf;
160 unsigned char *keystream;
161 size_t m;
162
163 _rs_stir_if_needed(n);
164 while (n > 0) {
165 if (rs->rs_have > 0) {
166 m = minimum(n, rs->rs_have);
167 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
168 - rs->rs_have;
169 memcpy(buf, keystream, m);
170 memset(keystream, 0, m);
171 buf += m;
172 n -= m;
173 rs->rs_have -= m;
174 }
175 if (rs->rs_have == 0)
176 _rs_rekey(NULL, 0);
177 }
178 }
179
180 static inline void
_rs_random_u32(uint32_t * val)181 _rs_random_u32(uint32_t *val)
182 {
183 unsigned char *keystream;
184
185 _rs_stir_if_needed(sizeof(*val));
186 if (rs->rs_have < sizeof(*val))
187 _rs_rekey(NULL, 0);
188 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
189 memcpy(val, keystream, sizeof(*val));
190 memset(keystream, 0, sizeof(*val));
191 rs->rs_have -= sizeof(*val);
192 }
193
194 uint32_t
arc4random(void)195 arc4random(void)
196 {
197 uint32_t val;
198
199 #ifndef __SINGLE_THREAD__
200 _ARC4_LOCK();
201 #endif
202 _rs_random_u32(&val);
203 #ifndef __SINGLE_THREAD__
204 _ARC4_UNLOCK();
205 #endif
206 return val;
207 }
208
209 void
arc4random_buf(void * buf,size_t n)210 arc4random_buf(void *buf, size_t n)
211 {
212 #ifndef __SINGLE_THREAD__
213 _ARC4_LOCK();
214 #endif
215 _rs_random_buf(buf, n);
216 #ifndef __SINGLE_THREAD__
217 _ARC4_UNLOCK();
218 #endif
219 }
220
