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 { 64 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256; 65 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]); 66 } 67 68 /* Reset for next reseed cycle. */ 69 getmicrotime(&arc4_tv_nextreseed); 70 arc4_tv_nextreseed.tv_sec += ARC4_RESEED_SECONDS; 71 arc4_numruns = 0; 72 } 73 74 /* 75 * Initialize our S-box to its beginning defaults. 76 */ 77 static void 78 arc4_init(void) 79 { 80 int n; 81 82 arc4_i = arc4_j = 0; 83 for (n = 0; n < 256; n++) 84 arc4_sbox[n] = (u_int8_t) n; 85 86 arc4_randomstir(); 87 arc4_initialized = 1; 88 89 /* 90 * Throw away the first N words of output, as suggested in the 91 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 92 * by Fluher, Mantin, and Shamir. (N = 256 in our case.) 93 */ 94 for (n = 0; n < 256*4; n++) 95 arc4_randbyte(); 96 } 97 98 /* 99 * Generate a random byte. 100 */ 101 static u_int8_t 102 arc4_randbyte(void) 103 { 104 u_int8_t arc4_t; 105 106 arc4_i = (arc4_i + 1) % 256; 107 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 108 109 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 110 111 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 112 return arc4_sbox[arc4_t]; 113 } 114 115 u_int32_t 116 karc4random(void) 117 { 118 u_int32_t ret; 119 struct timeval tv_now; 120 121 /* Initialize array if needed. */ 122 if (!arc4_initialized) 123 arc4_init(); 124 125 getmicrotime(&tv_now); 126 if ((++arc4_numruns > ARC4_MAXRUNS) || 127 (tv_now.tv_sec > arc4_tv_nextreseed.tv_sec)) 128 { 129 arc4_randomstir(); 130 } 131 132 ret = arc4_randbyte(); 133 ret |= arc4_randbyte() << 8; 134 ret |= arc4_randbyte() << 16; 135 ret |= arc4_randbyte() << 24; 136 137 return ret; 138 } 139 140 void 141 karc4rand(void *ptr, size_t len) 142 { 143 uint8_t *p; 144 struct timeval tv_now; 145 146 p = ptr; 147 148 /* Initialize array if needed. */ 149 if (!arc4_initialized) 150 arc4_init(); 151 152 getmicrotime(&tv_now); 153 if ((++arc4_numruns > ARC4_MAXRUNS) || 154 (tv_now.tv_sec > arc4_tv_nextreseed.tv_sec)) 155 { 156 arc4_randomstir(); 157 } 158 159 while (len--) 160 *p++ = arc4_randbyte(); 161 } 162