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 /* r = read_random(key, sizeof(key)); */ 44 r = 0; /* XXX MarkM - revisit this when /dev/random is done */ 45 /* if r == 0 || -1, just use what was on the stack */ 46 if (r > 0) 47 { 48 for (n = r; n < sizeof(key); n++) 49 key[n] = key[n % r]; 50 } 51 52 for (n = 0; n < 256; n++) 53 { 54 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256; 55 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]); 56 } 57 } 58 59 /* 60 * Initialize our S-box to its beginning defaults. 61 */ 62 static void 63 arc4_init(void) 64 { 65 int n; 66 67 arc4_i = arc4_j = 0; 68 for (n = 0; n < 256; n++) 69 arc4_sbox[n] = (u_int8_t) n; 70 71 arc4_randomstir(); 72 arc4_initialized = 1; 73 } 74 75 /* 76 * Generate a random byte. 77 */ 78 static u_int8_t 79 arc4_randbyte(void) 80 { 81 u_int8_t arc4_t; 82 83 arc4_i = (arc4_i + 1) % 256; 84 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 85 86 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 87 88 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 89 return arc4_sbox[arc4_t]; 90 } 91 92 u_int32_t 93 arc4random(void) 94 { 95 u_int32_t ret; 96 97 /* Initialize array if needed. */ 98 if (!arc4_initialized) 99 arc4_init(); 100 if (++arc4_numruns > ARC4_MAXRUNS) 101 { 102 arc4_randomstir(); 103 arc4_numruns = 0; 104 } 105 106 ret = arc4_randbyte(); 107 ret |= arc4_randbyte() << 8; 108 ret |= arc4_randbyte() << 16; 109 ret |= arc4_randbyte() << 24; 110 111 return ret; 112 } 113