1 /* $OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb Exp $ */
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>
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.
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.
23 * ChaCha based random number generator for OpenBSD.
26 #include <sys/cdefs.h>
27 __FBSDID("$FreeBSD$");
29 #include "namespace.h"
30 #if defined(__FreeBSD__)
41 #include <sys/types.h>
44 #include "libc_private.h"
45 #include "un-namespace.h"
48 #define KEYSTREAM_ONLY
49 #if defined(__FreeBSD__)
50 #define ARC4RANDOM_FXRNG 1
52 #define ARC4RANDOM_FXRNG 0
56 #define minimum(a, b) ((a) < (b) ? (a) : (b))
58 #if defined(__GNUC__) || defined(_MSC_VER)
59 #define inline __inline
60 #else /* __GNUC__ || _MSC_VER */
62 #endif /* !__GNUC__ && !_MSC_VER */
67 #define RSBUFSZ (16*BLOCKSZ)
69 #define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */
71 /* Marked INHERIT_ZERO, so zero'd out in fork children. */
73 size_t rs_have; /* valid bytes at end of rs_buf */
74 size_t rs_count; /* bytes till reseed */
77 /* Maybe be preserved in fork children, if _rs_allocate() decides. */
79 chacha_ctx rs_chacha; /* chacha context for random keystream */
80 u_char rs_buf[RSBUFSZ]; /* keystream blocks */
82 uint32_t rs_seed_generation; /* 32-bit userspace RNG version */
86 static inline int _rs_allocate(struct _rs **, struct _rsx **);
87 static inline void _rs_forkdetect(void);
88 #include "arc4random.h"
90 static inline void _rs_rekey(u_char *dat, size_t datlen);
93 _rs_init(u_char *buf, size_t n)
99 if (_rs_allocate(&rs, &rsx) == -1)
103 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8);
104 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ, NULL);
110 u_char rnd[KEYSZ + IVSZ];
111 uint32_t rekey_fuzz = 0;
113 #if defined(__FreeBSD__)
117 * De-couple allocation (which locates the vdso_fxrngp pointer in
118 * auxinfo) from initialization. This allows us to read the root seed
119 * version before we fetch system entropy, maintaining the invariant
120 * that the PRF was seeded with entropy from rs_seed_generation or a
121 * later generation. But never seeded from an earlier generation.
122 * This invariant prevents us from missing a root reseed event.
126 if (_rs_allocate(&rs, &rsx) == -1)
131 * Transition period: new userspace on old kernel. This should become
132 * a hard error at some point, if the scheme is adopted.
134 if (vdso_fxrngp != NULL)
135 rsx->rs_seed_generation =
136 fxrng_load_acq_generation(&vdso_fxrngp->fx_generation32);
139 if (getentropy(rnd, sizeof rnd) == -1)
142 #if !defined(__FreeBSD__)
144 _rs_init(rnd, sizeof(rnd));
145 #else /* __FreeBSD__ */
148 _rs_init(rnd, sizeof(rnd));
151 _rs_rekey(rnd, sizeof(rnd));
152 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */
154 /* invalidate rs_buf */
156 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
158 /* rekey interval should not be predictable */
159 chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
160 (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
161 rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
165 _rs_stir_if_needed(size_t len)
168 if (!rs || rs->rs_count <= len)
170 if (rs->rs_count <= len)
177 _rs_rekey(u_char *dat, size_t datlen)
179 #ifndef KEYSTREAM_ONLY
180 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
182 /* fill rs_buf with the keystream */
183 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
184 rsx->rs_buf, sizeof(rsx->rs_buf));
185 /* mix in optional user provided data */
189 m = minimum(datlen, KEYSZ + IVSZ);
190 for (i = 0; i < m; i++)
191 rsx->rs_buf[i] ^= dat[i];
193 /* immediately reinit for backtracking resistance */
194 _rs_init(rsx->rs_buf, KEYSZ + IVSZ);
195 memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
196 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
200 _rs_random_buf(void *_buf, size_t n)
202 u_char *buf = (u_char *)_buf;
206 _rs_stir_if_needed(n);
208 if (rs->rs_have > 0) {
209 m = minimum(n, rs->rs_have);
210 keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
212 memcpy(buf, keystream, m);
213 memset(keystream, 0, m);
218 if (rs->rs_have == 0)
224 _rs_random_u32(uint32_t *val)
228 _rs_stir_if_needed(sizeof(*val));
229 if (rs->rs_have < sizeof(*val))
231 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
232 memcpy(val, keystream, sizeof(*val));
233 memset(keystream, 0, sizeof(*val));
234 rs->rs_have -= sizeof(*val);
243 _rs_random_u32(&val);
249 arc4random_buf(void *buf, size_t n)
252 _rs_random_buf(buf, n);