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
11 #include <sys/cdefs.h>
12 __FBSDID("$FreeBSD: releng/9.2/sys/libkern/arc4random.c 249915 2013-04-26 01:56:58Z ache $");
13
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>
19 #include <sys/lock.h>
20 #include <sys/mutex.h>
21 #include <sys/time.h>
22
23 #define ARC4_RESEED_BYTES 65536
24 #define ARC4_RESEED_SECONDS 300
25 #define ARC4_KEYBYTES (256 / 8)
26
27 int arc4rand_iniseed_state = ARC4_ENTR_NONE;
28
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;
34
35 static u_int8_t arc4_randbyte(void);
36
37 static __inline void
38 arc4_swap(u_int8_t *a, u_int8_t *b)
39 {
40 u_int8_t c;
41
42 c = *a;
43 *a = *b;
44 *b = c;
45 }
46
47 /*
48 * Stir our S-box.
49 */
50 static void
51 arc4_randomstir (void)
52 {
53 u_int8_t key[256];
54 int r, n;
55 struct timeval tv_now;
56
57 /*
58 * XXX read_random() returns unsafe numbers if the entropy
59 * device is not loaded -- MarkM.
60 */
61 r = read_random(key, ARC4_KEYBYTES);
62 getmicrouptime(&tv_now);
63 mtx_lock(&arc4_mtx);
64 /* If r == 0 || -1, just use what was on the stack. */
65 if (r > 0) {
66 for (n = r; n < sizeof(key); n++)
67 key[n] = key[n % r];
68 }
69
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]);
73 }
74 arc4_i = arc4_j = 0;
75
76 /* Reset for next reseed cycle. */
77 arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS;
78 arc4_numruns = 0;
79
80 /*
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 = 256 in our case.)
84 */
85 for (n = 0; n < 256*4; n++)
86 arc4_randbyte();
87 mtx_unlock(&arc4_mtx);
88 }
89
90 /*
91 * Initialize our S-box to its beginning defaults.
92 */
93 static void
94 arc4_init(void)
95 {
96 int n;
97
98 mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF);
99 arc4_i = arc4_j = 0;
100 for (n = 0; n < 256; n++)
101 arc4_sbox[n] = (u_int8_t) n;
102
103 arc4_t_reseed = 0;
104 }
105
106 SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
107
108 /*
109 * Generate a random byte.
110 */
111 static u_int8_t
112 arc4_randbyte(void)
113 {
114 u_int8_t arc4_t;
115
116 arc4_i = (arc4_i + 1) % 256;
117 arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
118
119 arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
120
121 arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
122 return arc4_sbox[arc4_t];
123 }
124
125 /*
126 * MPSAFE
127 */
128 void
129 arc4rand(void *ptr, u_int len, int reseed)
130 {
131 u_char *p;
132 struct timeval tv;
133
134 getmicrouptime(&tv);
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))
139 arc4_randomstir();
140
141 mtx_lock(&arc4_mtx);
142 arc4_numruns += len;
143 p = ptr;
144 while (len--)
145 *p++ = arc4_randbyte();
146 mtx_unlock(&arc4_mtx);
147 }
148
149 uint32_t
150 arc4random(void)
151 {
152 uint32_t ret;
153
154 arc4rand(&ret, sizeof ret, 0);
155 return ret;
156 }
Cache object: 2d32f9e838bb4fbda1c38b84559f5628
|