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.
11 #include <sys/cdefs.h>
12 __FBSDID("$FreeBSD$");
14 #include <sys/types.h>
15 #include <sys/param.h>
16 #include <sys/kernel.h>
17 #include <sys/random.h>
18 #include <sys/libkern.h>
20 #include <sys/mutex.h>
23 #define ARC4_RESEED_BYTES 65536
24 #define ARC4_RESEED_SECONDS 300
25 #define ARC4_KEYBYTES (256 / 8)
27 static u_int8_t arc4_i, arc4_j;
28 static int arc4_numruns = 0;
29 static u_int8_t arc4_sbox[256];
30 static time_t arc4_t_reseed;
31 static struct mtx arc4_mtx;
33 static u_int8_t arc4_randbyte(void);
36 arc4_swap(u_int8_t *a, u_int8_t *b)
49 arc4_randomstir (void)
53 struct timeval tv_now;
56 * XXX read_random() returns unsafe numbers if the entropy
57 * device is not loaded -- MarkM.
59 r = read_random(key, ARC4_KEYBYTES);
60 getmicrouptime(&tv_now);
62 /* If r == 0 || -1, just use what was on the stack. */
64 for (n = r; n < sizeof(key); n++)
68 for (n = 0; n < 256; n++) {
69 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
70 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
73 /* Reset for next reseed cycle. */
74 arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS;
78 * Throw away the first N words of output, as suggested in the
79 * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
80 * by Fluher, Mantin, and Shamir. (N = 256 in our case.)
82 for (n = 0; n < 256*4; n++)
84 mtx_unlock(&arc4_mtx);
88 * Initialize our S-box to its beginning defaults.
95 mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF);
97 for (n = 0; n < 256; n++)
98 arc4_sbox[n] = (u_int8_t) n;
103 SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
106 * Generate a random byte.
113 arc4_i = (arc4_i + 1) % 256;
114 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
116 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
118 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
119 return arc4_sbox[arc4_t];
126 arc4rand(void *ptr, u_int len, int reseed)
133 (arc4_numruns > ARC4_RESEED_BYTES) ||
134 (tv.tv_sec > arc4_t_reseed))
141 *p++ = arc4_randbyte();
142 mtx_unlock(&arc4_mtx);
150 arc4rand(&ret, sizeof ret, 0);