1 /*- 2 * THE BEER-WARE LICENSE 3 * 4 * <dan@FreeBSD.ORG> wrote this file. As long as you retain this notice you 5 * can do whatever you want with this stuff. If we meet some day, and you 6 * think this stuff is worth it, you can buy me a beer in return. 7 * 8 * Dan Moschuk 9 * 10 * $FreeBSD: src/sys/libkern/arc4random.c,v 1.3.2.2 2001/09/17 07:06:50 silby Exp $ 11 * $DragonFly: src/sys/libkern/arc4random.c,v 1.3 2006/09/03 17:31:55 dillon Exp $ 12 */ 13 14 #include <sys/types.h> 15 #include <sys/random.h> 16 #include <sys/libkern.h> 17 #include <sys/time.h> 18 19 #define ARC4_MAXRUNS 16384 20 #define ARC4_RESEED_SECONDS 300 21 #define ARC4_KEYBYTES 32 /* 256 bit key */ 22 23 static u_int8_t arc4_i, arc4_j; 24 static int arc4_initialized = 0; 25 static int arc4_numruns = 0; 26 static u_int8_t arc4_sbox[256]; 27 static struct timeval arc4_tv_nextreseed; 28 29 static u_int8_t arc4_randbyte(void); 30 31 static __inline void 32 arc4_swap(u_int8_t *a, u_int8_t *b) 33 { 34 u_int8_t c; 35 36 c = *a; 37 *a = *b; 38 *b = c; 39 } 40 41 /* 42 * Stir our S-box. 43 */ 44 static void 45 arc4_randomstir (void) 46 { 47 u_int8_t key[256]; 48 int r, n; 49 50 /* 51 * XXX read_random() returns unsafe numbers if the entropy 52 * device is not loaded -- MarkM. 53 */ 54 r = read_random_unlimited(key, ARC4_KEYBYTES); 55 /* If r == 0 || -1, just use what was on the stack. */ 56 if (r > 0) 57 { 58 for (n = r; n < sizeof(key); n++) 59 key[n] = key[n % r]; 60 } 61 62 for (n = 0; n < 256; n++) { 63 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256; 64 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]); 65 } 66 67 /* 68 * Discard early keystream, as per recommendations in: 69 * "(Not So) Random Shuffles of RC4" by Ilya Mironov. 70 */ 71 for (n = 0; n < 768*4; n++) 72 arc4_randbyte(); 73 74 /* Reset for next reseed cycle. */ 75 getmicrotime(&arc4_tv_nextreseed); 76 arc4_tv_nextreseed.tv_sec += ARC4_RESEED_SECONDS; 77 arc4_numruns = 0; 78 } 79 80 /* 81 * Initialize our S-box to its beginning defaults. 82 */ 83 static void 84 arc4_init(void) 85 { 86 int n; 87 88 arc4_i = arc4_j = 0; 89 for (n = 0; n < 256; n++) 90 arc4_sbox[n] = (u_int8_t) n; 91 92 arc4_randomstir(); 93 arc4_initialized = 1; 94 95 /* 96 * Discard early keystream, as per recommendations in: 97 * "(Not So) Random Shuffles of RC4" by Ilya Mironov. 98 */ 99 for (n = 0; n < 768*4; n++) 100 arc4_randbyte(); 101 } 102 103 /* 104 * Generate a random byte. 105 */ 106 static u_int8_t 107 arc4_randbyte(void) 108 { 109 u_int8_t arc4_t; 110 111 arc4_i = (arc4_i + 1) % 256; 112 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 113 114 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 115 116 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 117 return arc4_sbox[arc4_t]; 118 } 119 120 u_int32_t 121 karc4random(void) 122 { 123 u_int32_t ret; 124 struct timeval tv_now; 125 126 /* Initialize array if needed. */ 127 if (!arc4_initialized) 128 arc4_init(); 129 130 getmicrotime(&tv_now); 131 if ((++arc4_numruns > ARC4_MAXRUNS) || 132 (tv_now.tv_sec > arc4_tv_nextreseed.tv_sec)) 133 { 134 arc4_randomstir(); 135 } 136 137 ret = arc4_randbyte(); 138 ret |= arc4_randbyte() << 8; 139 ret |= arc4_randbyte() << 16; 140 ret |= arc4_randbyte() << 24; 141 142 return ret; 143 } 144 145 void 146 karc4rand(void *ptr, size_t len) 147 { 148 uint8_t *p; 149 struct timeval tv_now; 150 151 p = ptr; 152 153 /* Initialize array if needed. */ 154 if (!arc4_initialized) 155 arc4_init(); 156 157 getmicrotime(&tv_now); 158 if ((++arc4_numruns > ARC4_MAXRUNS) || 159 (tv_now.tv_sec > arc4_tv_nextreseed.tv_sec)) 160 { 161 arc4_randomstir(); 162 } 163 164 while (len--) 165 *p++ = arc4_randbyte(); 166 } 167