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 arc4_i = arc4_j = 0; 73 74 /* Reset for next reseed cycle. */ 75 arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS; 76 arc4_numruns = 0; 77 78 /* 79 * Throw away the first N bytes of output, as suggested in the 80 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 81 * by Fluher, Mantin, and Shamir. N=768 is based on 82 * suggestions in the paper "(Not So) Random Shuffles of RC4" 83 * by Ilya Mironov. 84 */ 85 for (n = 0; n < 768; n++) 86 (void)arc4_randbyte(); 87 mtx_unlock(&arc4_mtx); 88 } 89 90 /* 91 * Initialize our S-box to its beginning defaults. 92 */ 93 static void 94 arc4_init(void) 95 { 96 int n; 97 98 mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF); 99 arc4_i = arc4_j = 0; 100 for (n = 0; n < 256; n++) 101 arc4_sbox[n] = (u_int8_t) n; 102 103 arc4_t_reseed = 0; 104 } 105 106 SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL); 107 108 /* 109 * Generate a random byte. 110 */ 111 static u_int8_t 112 arc4_randbyte(void) 113 { 114 u_int8_t arc4_t; 115 116 arc4_i = (arc4_i + 1) % 256; 117 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 118 119 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 120 121 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 122 return arc4_sbox[arc4_t]; 123 } 124 125 /* 126 * MPSAFE 127 */ 128 void 129 arc4rand(void *ptr, u_int len, int reseed) 130 { 131 u_char *p; 132 struct timeval tv; 133 134 getmicrouptime(&tv); 135 if (reseed || 136 (arc4_numruns > ARC4_RESEED_BYTES) || 137 (tv.tv_sec > arc4_t_reseed)) 138 arc4_randomstir(); 139 140 mtx_lock(&arc4_mtx); 141 arc4_numruns += len; 142 p = ptr; 143 while (len--) 144 *p++ = arc4_randbyte(); 145 mtx_unlock(&arc4_mtx); 146 } 147 148 uint32_t 149 arc4random(void) 150 { 151 uint32_t ret; 152 153 arc4rand(&ret, sizeof ret, 0); 154 return ret; 155 } 156