arc4random.c revision 62072
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 62072 2000-06-25 10:15:58Z markm $ 11 */ 12 13#include <sys/types.h> 14#include <sys/random.h> 15#include <sys/libkern.h> 16 17#define ARC4_MAXRUNS 64 18 19static u_int8_t arc4_i, arc4_j; 20static int arc4_initialized = 0; 21static int arc4_numruns = 0; 22static u_int8_t arc4_sbox[256]; 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 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 */ 62static void 63arc4_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 */ 78static u_int8_t 79arc4_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 92u_int32_t 93arc4random(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