arc4random.c revision 53893
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: head/sys/libkern/arc4random.c 53893 1999-11-29 19:23:35Z dan $ 11 */ 12 13#include <sys/libkern.h> 14 15#define ARC4_MAXRUNS 64 16 17static u_int8_t arc4_i, arc4_j; 18static int arc4_initialized = 0; 19static int arc4_numruns = 0; 20static u_int8_t arc4_sbox[256]; 21 22extern u_int read_random (void *, u_int); 23 24static __inline void 25arc4_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 */ 37static void 38arc4_randomstir (void) 39{ 40 u_int8_t key[256]; 41 int r, n; 42 43 r = read_random(key, sizeof(key)); 44 /* if r == 0 || -1, just use what was on the stack */ 45 if (r > 0) 46 { 47 for (n = r; n < sizeof(key); n++) 48 key[n] = key[n % r]; 49 } 50 51 for (n = 0; n < 256; n++) 52 { 53 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256; 54 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]); 55 } 56} 57 58/* 59 * Initialize our S-box to its beginning defaults. 60 */ 61static void 62arc4_init(void) 63{ 64 int n; 65 66 arc4_i = arc4_j = 0; 67 for (n = 0; n < 256; n++) 68 arc4_sbox[n] = (u_int8_t) n; 69 70 arc4_randomstir(); 71 arc4_initialized = 1; 72} 73 74/* 75 * Generate a random byte. 76 */ 77static u_int8_t 78arc4_randbyte(void) 79{ 80 u_int8_t arc4_t; 81 82 arc4_i = (arc4_i + 1) % 256; 83 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256; 84 85 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]); 86 87 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256; 88 return arc4_sbox[arc4_t]; 89} 90 91u_int32_t 92arc4random(void) 93{ 94 u_int32_t ret; 95 96 /* Initialize array if needed. */ 97 if (!arc4_initialized) 98 arc4_init(); 99 if (++arc4_numruns > ARC4_MAXRUNS) 100 { 101 arc4_randomstir(); 102 arc4_numruns = 0; 103 } 104 105 ret = arc4_randbyte(); 106 ret |= arc4_randbyte() << 8; 107 ret |= arc4_randbyte() << 16; 108 ret |= arc4_randbyte() << 24; 109 110 return ret; 111} 112