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 * $FreeBSD$ 11 */ 12 13 #include <sys/types.h> 14 #include <sys/random.h> 15 #include <sys/libkern.h> 16 17 #define ARC4_MAXRUNS 64 18 19 static u_int8_t arc4_i, arc4_j; 20 static int arc4_initialized = 0; 21 static int arc4_numruns = 0; 22 static u_int8_t arc4_sbox[256]; 23 24 static __inline void 25 arc4_swap(u_int8_t *a, u_int8_t *b) 26 { 27 u_int8_t c; 28 29 c = *a; 30 *a = *b; 31 *b = c; 32 } 33 34 /* 35 * Stir our S-box. 36 */ 37 static void 38 arc4_randomstir (void) 39 { 40 u_int8_t key[256]; 41 int r, n; 42 43 /* XXX read_random() returns unsafe numbers if the entropy 44 * devce is not loaded - MarkM 45 */ 46 r = read_random(key, sizeof(key)); 47 /* if r == 0 || -1, just use what was on the stack */ 48 if (r > 0) 49 { 50 for (n = r; n < sizeof(key); n++) 51 key[n] = key[n % r]; 52 } 53 54 for (n = 0; n < 256; n++) 55 { 56 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256; 57 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]); 58 } 59 } 60 61 /* 62 * Initialize our S-box to its beginning defaults. 63 */ 64 static void 65 arc4_init(void) 66 { 67 int n; 68 69 arc4_i = arc4_j = 0; 70 for (n = 0; n < 256; n++) 71 arc4_sbox[n] = (u_int8_t) n; 72 73 arc4_randomstir(); 74 arc4_initialized = 1; 75 } 76 77 /* 78 * Generate a random byte. 79 */ 80 static u_int8_t 81 arc4_randbyte(void) 82 { 83 u_int8_t arc4_t; 84 85 arc4_i = (arc4_i + 1) % 256; 86 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 87 88 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 89 90 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 91 return arc4_sbox[arc4_t]; 92 } 93 94 u_int32_t 95 arc4random(void) 96 { 97 u_int32_t ret; 98 99 /* Initialize array if needed. */ 100 if (!arc4_initialized) 101 arc4_init(); 102 if (++arc4_numruns > ARC4_MAXRUNS) 103 { 104 arc4_randomstir(); 105 arc4_numruns = 0; 106 } 107 108 ret = arc4_randbyte(); 109 ret |= arc4_randbyte() << 8; 110 ret |= arc4_randbyte() << 16; 111 ret |= arc4_randbyte() << 24; 112 113 return ret; 114 } 115