1 /* $OpenBSD: arc4random.c,v 1.55 2019/03/24 17:56:54 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 * 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 #include <fcntl.h>
27 #include <limits.h>
28 #include <signal.h>
29 #include <stdint.h>
30 #include <stdlib.h>
31 #include <string.h>
32 #include <unistd.h>
33 #include <sys/types.h>
34 #include <sys/time.h>
35
36 #define KEYSTREAM_ONLY
37 #include "chacha_private.h"
38
39 #define minimum(a, b) ((a) < (b) ? (a) : (b))
40
41 #if defined(__GNUC__) || defined(_MSC_VER)
42 #define inline __inline
43 #else /* __GNUC__ || _MSC_VER */
44 #define inline
45 #endif /* !__GNUC__ && !_MSC_VER */
46
47 #define KEYSZ 32
48 #define IVSZ 8
49 #define BLOCKSZ 64
50 #define RSBUFSZ (16*BLOCKSZ)
51
52 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
53 static struct _rs {
54 size_t rs_have; /* valid bytes at end of rs_buf */
55 size_t rs_count; /* bytes till reseed */
56 } *rs;
57
58 /* Maybe be preserved in fork children, if _rs_allocate() decides. */
59 static struct _rsx {
60 chacha_ctx rs_chacha; /* chacha context for random keystream */
61 u_char rs_buf[RSBUFSZ]; /* keystream blocks */
62 } *rsx;
63
64 static inline int _rs_allocate(struct _rs **, struct _rsx **);
65 static inline void _rs_forkdetect(void);
66 #include "arc4random.h"
67
68 static inline void _rs_rekey(u_char *dat, size_t datlen);
69
70 static inline void
_rs_init(u_char * buf,size_t n)71 _rs_init(u_char *buf, size_t n)
72 {
73 if (n < KEYSZ + IVSZ)
74 return;
75
76 if (rs == NULL) {
77 if (_rs_allocate(&rs, &rsx) == -1)
78 _exit(1);
79 }
80
81 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
82 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
83 }
84
85 static void
_rs_stir(void)86 _rs_stir(void)
87 {
88 u_char rnd[KEYSZ + IVSZ];
89
90 if (getentropy(rnd, sizeof rnd) == -1)
91 _getentropy_fail();
92
93 if (!rs)
94 _rs_init(rnd, sizeof(rnd));
95 else
96 _rs_rekey(rnd, sizeof(rnd));
97 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */
98
99 /* invalidate rs_buf */
100 rs->rs_have = 0;
101 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
102
103 rs->rs_count = 1600000;
104 }
105
106 static inline void
_rs_stir_if_needed(size_t len)107 _rs_stir_if_needed(size_t len)
108 {
109 _rs_forkdetect();
110 if (!rs || rs->rs_count <= len)
111 _rs_stir();
112 if (rs->rs_count <= len)
113 rs->rs_count = 0;
114 else
115 rs->rs_count -= len;
116 }
117
118 static inline void
_rs_rekey(u_char * dat,size_t datlen)119 _rs_rekey(u_char *dat, size_t datlen)
120 {
121 #ifndef KEYSTREAM_ONLY
122 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
123 #endif
124 /* fill rs_buf with the keystream */
125 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
126 rsx->rs_buf, sizeof(rsx->rs_buf));
127 /* mix in optional user provided data */
128 if (dat) {
129 size_t i, m;
130
131 m = minimum(datlen, KEYSZ + IVSZ);
132 for (i = 0; i < m; i++)
133 rsx->rs_buf[i] ^= dat[i];
134 }
135 /* immediately reinit for backtracking resistance */
136 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
137 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
138 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
139 }
140
141 static inline void
_rs_random_buf(void * _buf,size_t n)142 _rs_random_buf(void *_buf, size_t n)
143 {
144 u_char *buf = (u_char *)_buf;
145 u_char *keystream;
146 size_t m;
147
148 _rs_stir_if_needed(n);
149 while (n > 0) {
150 if (rs->rs_have > 0) {
151 m = minimum(n, rs->rs_have);
152 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
153 - rs->rs_have;
154 memcpy(buf, keystream, m);
155 memset(keystream, 0, m);
156 buf += m;
157 n -= m;
158 rs->rs_have -= m;
159 }
160 if (rs->rs_have == 0)
161 _rs_rekey(NULL, 0);
162 }
163 }
164
165 static inline void
_rs_random_u32(uint32_t * val)166 _rs_random_u32(uint32_t *val)
167 {
168 u_char *keystream;
169
170 _rs_stir_if_needed(sizeof(*val));
171 if (rs->rs_have < sizeof(*val))
172 _rs_rekey(NULL, 0);
173 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
174 memcpy(val, keystream, sizeof(*val));
175 memset(keystream, 0, sizeof(*val));
176 rs->rs_have -= sizeof(*val);
177 }
178
179 uint32_t
arc4random(void)180 arc4random(void)
181 {
182 uint32_t val;
183
184 _ARC4_LOCK();
185 _rs_random_u32(&val);
186 _ARC4_UNLOCK();
187 return val;
188 }
189
190 void
arc4random_buf(void * buf,size_t n)191 arc4random_buf(void *buf, size_t n)
192 {
193 _ARC4_LOCK();
194 _rs_random_buf(buf, n);
195 _ARC4_UNLOCK();
196 }
197