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 #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 #define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */ 53 54 /* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */ 55 static struct _rs { 56 size_t rs_have; /* valid bytes at end of rs_buf */ 57 size_t rs_count; /* bytes till reseed */ 58 } *rs; 59 60 /* Maybe be preserved in fork children, if _rs_allocate() decides. */ 61 static struct _rsx { 62 chacha_ctx rs_chacha; /* chacha context for random keystream */ 63 u_char rs_buf[RSBUFSZ]; /* keystream blocks */ 64 } *rsx; 65 66 static inline int _rs_allocate(struct _rs **, struct _rsx **); 67 static inline void _rs_forkdetect(void); 68 #include "arc4random.h" 69 70 static inline void _rs_rekey(u_char *dat, size_t datlen); 71 72 static inline void 73 _rs_init(u_char *buf, size_t n) 74 { 75 if (n < KEYSZ + IVSZ) 76 return; 77 78 if (rs == NULL) { 79 if (_rs_allocate(&rs, &rsx) == -1) 80 _exit(1); 81 } 82 83 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8); 84 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ); 85 } 86 87 static void 88 _rs_stir(void) 89 { 90 u_char rnd[KEYSZ + IVSZ]; 91 uint32_t rekey_fuzz = 0; 92 93 if (getentropy(rnd, sizeof rnd) == -1) 94 _getentropy_fail(); 95 96 if (!rs) 97 _rs_init(rnd, sizeof(rnd)); 98 else 99 _rs_rekey(rnd, sizeof(rnd)); 100 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */ 101 102 /* invalidate rs_buf */ 103 rs->rs_have = 0; 104 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 105 106 /* rekey interval should not be predictable */ 107 chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz, 108 (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz)); 109 rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE); 110 } 111 112 static inline void 113 _rs_stir_if_needed(size_t len) 114 { 115 _rs_forkdetect(); 116 if (!rs || rs->rs_count <= len) 117 _rs_stir(); 118 if (rs->rs_count <= len) 119 rs->rs_count = 0; 120 else 121 rs->rs_count -= len; 122 } 123 124 static inline void 125 _rs_rekey(u_char *dat, size_t datlen) 126 { 127 #ifndef KEYSTREAM_ONLY 128 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 129 #endif 130 /* fill rs_buf with the keystream */ 131 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 132 rsx->rs_buf, sizeof(rsx->rs_buf)); 133 /* mix in optional user provided data */ 134 if (dat) { 135 size_t i, m; 136 137 m = minimum(datlen, KEYSZ + IVSZ); 138 for (i = 0; i < m; i++) 139 rsx->rs_buf[i] ^= dat[i]; 140 } 141 /* immediately reinit for backtracking resistance */ 142 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 143 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 144 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 145 } 146 147 static inline void 148 _rs_random_buf(void *_buf, size_t n) 149 { 150 u_char *buf = (u_char *)_buf; 151 u_char *keystream; 152 size_t m; 153 154 _rs_stir_if_needed(n); 155 while (n > 0) { 156 if (rs->rs_have > 0) { 157 m = minimum(n, rs->rs_have); 158 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 159 - rs->rs_have; 160 memcpy(buf, keystream, m); 161 memset(keystream, 0, m); 162 buf += m; 163 n -= m; 164 rs->rs_have -= m; 165 } 166 if (rs->rs_have == 0) 167 _rs_rekey(NULL, 0); 168 } 169 } 170 171 static inline void 172 _rs_random_u32(uint32_t *val) 173 { 174 u_char *keystream; 175 176 _rs_stir_if_needed(sizeof(*val)); 177 if (rs->rs_have < sizeof(*val)) 178 _rs_rekey(NULL, 0); 179 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 180 memcpy(val, keystream, sizeof(*val)); 181 memset(keystream, 0, sizeof(*val)); 182 rs->rs_have -= sizeof(*val); 183 } 184 185 uint32_t 186 arc4random(void) 187 { 188 uint32_t val; 189 190 _ARC4_LOCK(); 191 _rs_random_u32(&val); 192 _ARC4_UNLOCK(); 193 return val; 194 } 195 DEF_WEAK(arc4random); 196 197 void 198 arc4random_buf(void *buf, size_t n) 199 { 200 _ARC4_LOCK(); 201 _rs_random_buf(buf, n); 202 _ARC4_UNLOCK(); 203 } 204 DEF_WEAK(arc4random_buf); 205