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/random.h> 16 #include <sys/libkern.h> 17 #include <sys/time.h> 18 19 #define ARC4_RESEED_BYTES 65536 20 #define ARC4_RESEED_SECONDS 300 21 #define ARC4_KEYBYTES (256 / 8) 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 time_t arc4_t_reseed; 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 struct timeval tv_now; 50 51 /* 52 * XXX read_random() returns unsafe numbers if the entropy 53 * device is not loaded -- MarkM. 54 */ 55 r = read_random(key, ARC4_KEYBYTES); 56 /* If r == 0 || -1, just use what was on the stack. */ 57 if (r > 0) { 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 /* Reset for next reseed cycle. */ 68 getmicrouptime(&tv_now); 69 arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS; 70 arc4_numruns = 0; 71 } 72 73 /* 74 * Initialize our S-box to its beginning defaults. 75 */ 76 static void 77 arc4_init(void) 78 { 79 int n; 80 81 arc4_i = arc4_j = 0; 82 for (n = 0; n < 256; n++) 83 arc4_sbox[n] = (u_int8_t) n; 84 85 arc4_randomstir(); 86 arc4_initialized = 1; 87 88 /* 89 * Throw away the first N words of output, as suggested in the 90 * paper "Weaknesses in the Key Scheduling Algorithm of RC4" 91 * by Fluher, Mantin, and Shamir. (N = 256 in our case.) 92 */ 93 for (n = 0; n < 256*4; n++) 94 arc4_randbyte(); 95 } 96 97 /* 98 * Generate a random byte. 99 */ 100 static u_int8_t 101 arc4_randbyte(void) 102 { 103 u_int8_t arc4_t; 104 105 arc4_i = (arc4_i + 1) % 256; 106 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 107 108 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 109 110 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 111 return arc4_sbox[arc4_t]; 112 } 113 114 void 115 arc4rand(void *ptr, u_int len, int reseed) 116 { 117 u_char *p; 118 struct timeval tv; 119 120 /* Initialize array if needed. */ 121 if (!arc4_initialized) 122 arc4_init(); 123 124 getmicrouptime(&tv); 125 arc4_numruns += len; 126 if (reseed || 127 (arc4_numruns > ARC4_RESEED_BYTES) || 128 (tv.tv_sec > arc4_t_reseed)) 129 arc4_randomstir(); 130 131 p = ptr; 132 while (len--) 133 *p++ = arc4_randbyte(); 134 } 135 136 uint32_t 137 arc4random(void) 138 { 139 uint32_t ret; 140 141 arc4rand(&ret, sizeof ret, 0); 142 return ret; 143 } 144