arc4random.c (4553B)
1 /* $OpenBSD: arc4random.c,v 1.49 2014/07/20 20:51:13 bcook 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. */ 52 static 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. */ 58 static struct _rsx { 59 chacha_ctx rs_chacha; /* chacha context for random keystream */ 60 u_char rs_buf[RSBUFSZ]; /* keystream blocks */ 61 } *rsx; 62 63 static inline int _rs_allocate(struct _rs **, struct _rsx **); 64 static inline void _rs_forkdetect(void); 65 #include "arc4random.h" 66 67 static inline void _rs_rekey(u_char *dat, size_t datlen); 68 69 static 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 84 static 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 } 104 105 static 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 } 116 117 static 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 } 139 140 static 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 } 163 164 static 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 } 177 178 uint32_t 179 arc4random(void) 180 { 181 uint32_t val; 182 183 _ARC4_LOCK(); 184 _rs_random_u32(&val); 185 _ARC4_UNLOCK(); 186 return val; 187 } 188 189 void 190 arc4random_buf(void *buf, size_t n) 191 { 192 _ARC4_LOCK(); 193 _rs_random_buf(buf, n); 194 _ARC4_UNLOCK(); 195 }