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("$FreeBSD$");
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
27int arc4rand_iniseed_state = ARC4_ENTR_NONE;
28
29static u_int8_t arc4_i, arc4_j;
30static int arc4_numruns = 0;
31static u_int8_t arc4_sbox[256];
32static time_t arc4_t_reseed;
33static struct mtx arc4_mtx;
34
35static u_int8_t arc4_randbyte(void);
36
37static __inline void
38arc4_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 */
50static void
51arc4_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 */
93static void
94arc4_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
106SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
107
108/*
109 * Generate a random byte.
110 */
111static u_int8_t
112arc4_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 */
128void
129arc4rand(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
149uint32_t
150arc4random(void)
151{
152	uint32_t ret;
153
154	arc4rand(&ret, sizeof ret, 0);
155	return ret;
156}
157