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 11 #include <sys/cdefs.h> 12 __FBSDID("$FreeBSD$"); 13 14 #include <sys/types.h> 15 #include <sys/param.h> 16 #include <sys/kernel.h> 17 #include <sys/random.h> 18 #include <sys/libkern.h> 19 #include <sys/lock.h> 20 #include <sys/mutex.h> 21 #include <sys/time.h> 22 23 #define ARC4_RESEED_BYTES 65536 24 #define ARC4_RESEED_SECONDS 300 25 #define ARC4_KEYBYTES (256 / 8) 26 27 static u_int8_t arc4_i, arc4_j; 28 static int arc4_numruns = 0; 29 static u_int8_t arc4_sbox[256]; 30 static time_t arc4_t_reseed; 31 static struct mtx arc4_mtx; 32 33 static u_int8_t arc4_randbyte(void); 34 35 static __inline void 36 arc4_swap(u_int8_t *a, u_int8_t *b) 37 { 38 u_int8_t c; 39 40 c = *a; 41 *a = *b; 42 *b = c; 43 } 44 45 /* 46 * Stir our S-box. 47 */ 48 static void 49 arc4_randomstir (void) 50 { 51 u_int8_t key[256]; 52 int r, n; 53 struct timeval tv_now; 54 55 /* 56 * XXX read_random() returns unsafe numbers if the entropy 57 * device is not loaded -- MarkM. 58 */ 59 r = read_random(key, ARC4_KEYBYTES); 60 getmicrouptime(&tv_now); 61 mtx_lock(&arc4_mtx); 62 /* If r == 0 || -1, just use what was on the stack. */ 63 if (r > 0) { 64 for (n = r; n < sizeof(key); n++) 65 key[n] = key[n % r]; 66 } 67 68 for (n = 0; n < 256; n++) { 69 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256; 70 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]); 71 } 72 73 /* Reset for next reseed cycle. */ 74 arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS; 75 arc4_numruns = 0; 76 77 /* 78 * Throw away the first N words of output, as suggested in the 79 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 80 * by Fluher, Mantin, and Shamir. (N = 256 in our case.) 81 */ 82 for (n = 0; n < 256*4; n++) 83 arc4_randbyte(); 84 mtx_unlock(&arc4_mtx); 85 } 86 87 /* 88 * Initialize our S-box to its beginning defaults. 89 */ 90 static void 91 arc4_init(void) 92 { 93 int n; 94 95 mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF); 96 arc4_i = arc4_j = 0; 97 for (n = 0; n < 256; n++) 98 arc4_sbox[n] = (u_int8_t) n; 99 100 arc4_t_reseed = 0; 101 } 102 103 SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL); 104 105 /* 106 * Generate a random byte. 107 */ 108 static u_int8_t 109 arc4_randbyte(void) 110 { 111 u_int8_t arc4_t; 112 113 arc4_i = (arc4_i + 1) % 256; 114 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 115 116 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 117 118 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 119 return arc4_sbox[arc4_t]; 120 } 121 122 /* 123 * MPSAFE 124 */ 125 void 126 arc4rand(void *ptr, u_int len, int reseed) 127 { 128 u_char *p; 129 struct timeval tv; 130 131 getmicrouptime(&tv); 132 if (reseed || 133 (arc4_numruns > ARC4_RESEED_BYTES) || 134 (tv.tv_sec > arc4_t_reseed)) 135 arc4_randomstir(); 136 137 mtx_lock(&arc4_mtx); 138 arc4_numruns += len; 139 p = ptr; 140 while (len--) 141 *p++ = arc4_randbyte(); 142 mtx_unlock(&arc4_mtx); 143 } 144 145 uint32_t 146 arc4random(void) 147 { 148 uint32_t ret; 149 150 arc4rand(&ret, sizeof ret, 0); 151 return ret; 152 } 153