2 * THE BEER-WARE LICENSE
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.
10 * $FreeBSD: src/sys/libkern/arc4random.c,v 1.3.2.2 2001/09/17 07:06:50 silby Exp $
11 * $DragonFly: src/sys/libkern/arc4random.c,v 1.3 2006/09/03 17:31:55 dillon Exp $
14 #include <sys/types.h>
15 #include <sys/random.h>
16 #include <sys/libkern.h>
19 #define ARC4_MAXRUNS 16384
20 #define ARC4_RESEED_SECONDS 300
21 #define ARC4_KEYBYTES 32 /* 256 bit key */
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 struct timeval arc4_tv_nextreseed;
29 static u_int8_t arc4_randbyte(void);
32 arc4_swap(u_int8_t *a, u_int8_t *b)
45 arc4_randomstir (void)
51 * XXX read_random() returns unsafe numbers if the entropy
52 * device is not loaded -- MarkM.
54 r = read_random_unlimited(key, ARC4_KEYBYTES);
55 /* If r == 0 || -1, just use what was on the stack. */
58 for (n = r; n < sizeof(key); n++)
62 for (n = 0; n < 256; n++)
64 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
65 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
68 /* Reset for next reseed cycle. */
69 getmicrotime(&arc4_tv_nextreseed);
70 arc4_tv_nextreseed.tv_sec += ARC4_RESEED_SECONDS;
75 * Initialize our S-box to its beginning defaults.
83 for (n = 0; n < 256; n++)
84 arc4_sbox[n] = (u_int8_t) n;
90 * Throw away the first N words of output, as suggested in the
91 * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
92 * by Fluher, Mantin, and Shamir. (N = 256 in our case.)
94 for (n = 0; n < 256*4; n++)
99 * Generate a random byte.
106 arc4_i = (arc4_i + 1) % 256;
107 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
109 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
111 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
112 return arc4_sbox[arc4_t];
119 struct timeval tv_now;
121 /* Initialize array if needed. */
122 if (!arc4_initialized)
125 getmicrotime(&tv_now);
126 if ((++arc4_numruns > ARC4_MAXRUNS) ||
127 (tv_now.tv_sec > arc4_tv_nextreseed.tv_sec))
132 ret = arc4_randbyte();
133 ret |= arc4_randbyte() << 8;
134 ret |= arc4_randbyte() << 16;
135 ret |= arc4_randbyte() << 24;
141 karc4rand(void *ptr, size_t len)
144 struct timeval tv_now;
148 /* Initialize array if needed. */
149 if (!arc4_initialized)
152 getmicrotime(&tv_now);
153 if ((++arc4_numruns > ARC4_MAXRUNS) ||
154 (tv_now.tv_sec > arc4_tv_nextreseed.tv_sec))
160 *p++ = arc4_randbyte();