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 26 27 int arc4rand_iniseed_state = ARC4_ENTR_NONE; 28 29 static u_int8_t arc4_i, arc4_j; 30 static int arc4_numruns = 0; 31 static u_int8_t arc4_sbox[256]; 32 static time_t arc4_t_reseed; 33 static struct mtx arc4_mtx; 34 35 static u_int8_t arc4_randbyte(void); 36 37 static __inline void 38 arc4_swap(u_int8_t *a, u_int8_t *b) 39 { 40 u_int8_t c; 41 42 c = *a; 43 *a = *b; 44 *b = c; 45 } 46 47 /* 48 * Stir our S-box. 49 */ 50 static void 51 arc4_randomstir(void) 52 { 53 u_int8_t key[ARC4_KEYBYTES]; 54 int n; 55 struct timeval tv_now; 56 57 /* 58 * XXX: FIX!! This isn't brilliant. Need more confidence. 59 * This returns zero entropy before random(4) is seeded. 60 */ 61 (void)read_random(key, ARC4_KEYBYTES); 62 getmicrouptime(&tv_now); 63 mtx_lock(&arc4_mtx); 64 for (n = 0; n < 256; n++) { 65 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256; 66 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]); 67 } 68 arc4_i = arc4_j = 0; 69 /* Reset for next reseed cycle. */ 70 arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS; 71 arc4_numruns = 0; 72 /* 73 * Throw away the first N words of output, as suggested in the 74 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 75 * by Fluher, Mantin, and Shamir. (N = 256 in our case.) 76 * 77 * http://dl.acm.org/citation.cfm?id=646557.694759 78 */ 79 for (n = 0; n < 256*4; n++) 80 arc4_randbyte(); 81 mtx_unlock(&arc4_mtx); 82 } 83 84 /* 85 * Initialize our S-box to its beginning defaults. 86 */ 87 static void 88 arc4_init(void) 89 { 90 int n; 91 92 mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF); 93 arc4_i = arc4_j = 0; 94 for (n = 0; n < 256; n++) 95 arc4_sbox[n] = (u_int8_t) n; 96 97 arc4_t_reseed = 0; 98 } 99 100 SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL); 101 102 /* 103 * Generate a random byte. 104 */ 105 static u_int8_t 106 arc4_randbyte(void) 107 { 108 u_int8_t arc4_t; 109 110 arc4_i = (arc4_i + 1) % 256; 111 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 112 113 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 114 115 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 116 return arc4_sbox[arc4_t]; 117 } 118 119 /* 120 * MPSAFE 121 */ 122 void 123 arc4rand(void *ptr, u_int len, int reseed) 124 { 125 u_char *p; 126 struct timeval tv; 127 128 getmicrouptime(&tv); 129 if (atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE, 130 ARC4_ENTR_SEED) || reseed || 131 (arc4_numruns > ARC4_RESEED_BYTES) || 132 (tv.tv_sec > arc4_t_reseed)) 133 arc4_randomstir(); 134 135 mtx_lock(&arc4_mtx); 136 arc4_numruns += len; 137 p = ptr; 138 while (len--) 139 *p++ = arc4_randbyte(); 140 mtx_unlock(&arc4_mtx); 141 } 142 143 uint32_t 144 arc4random(void) 145 { 146 uint32_t ret; 147 148 arc4rand(&ret, sizeof ret, 0); 149 return ret; 150 } 151