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 int arc4rand_iniseed_state = ARC4_ENTR_NONE;
29 static u_int8_t arc4_i, arc4_j;
30 static int arc4_numruns = 0;
31 static u_int8_t arc4_sbox[256];
32 static time_t arc4_t_reseed;
33 static struct mtx arc4_mtx;
35 static u_int8_t arc4_randbyte(void);
38 arc4_swap(u_int8_t *a, u_int8_t *b)
51 arc4_randomstir (void)
55 struct timeval tv_now;
58 * XXX read_random() returns unsafe numbers if the entropy
59 * device is not loaded -- MarkM.
61 r = read_random(key, ARC4_KEYBYTES);
62 getmicrouptime(&tv_now);
64 /* If r == 0 || -1, just use what was on the stack. */
66 for (n = r; n < sizeof(key); n++)
70 for (n = 0; n < 256; n++) {
71 arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
72 arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
76 /* Reset for next reseed cycle. */
77 arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS;
81 * Throw away the first N words of output, as suggested in the
82 * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
83 * by Fluher, Mantin, and Shamir. (N = 768 in our case.)
85 for (n = 0; n < 768*4; n++)
87 mtx_unlock(&arc4_mtx);
91 * Initialize our S-box to its beginning defaults.
98 mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF);
100 for (n = 0; n < 256; n++)
101 arc4_sbox[n] = (u_int8_t) n;
106 SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
109 * Generate a random byte.
116 arc4_i = (arc4_i + 1) % 256;
117 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
119 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
121 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
122 return arc4_sbox[arc4_t];
129 arc4rand(void *ptr, u_int len, int reseed)
135 if (atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE,
136 ARC4_ENTR_SEED) || reseed ||
137 (arc4_numruns > ARC4_RESEED_BYTES) ||
138 (tv.tv_sec > arc4_t_reseed))
145 *p++ = arc4_randbyte();
146 mtx_unlock(&arc4_mtx);
154 arc4rand(&ret, sizeof ret, 0);