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#if !defined(SOLARIS2)
11# include <sys/cdefs.h>
12#endif
13
14#include <sys/types.h>
15#include <sys/param.h>
16#ifdef __FreeBSD__
17# include <sys/kernel.h>
18#endif
19# include <sys/random.h>
20#ifdef __FreeBSD__
21# include <sys/libkern.h>
22#endif
23#include <sys/lock.h>
24# include <sys/mutex.h>
25#include <sys/time.h>
26
27#include <sys/socket.h>
28#include <net/if.h>
29#include <netinet/in.h>
30#include <netinet/ip.h>
31#include "netinet/ip_compat.h"
32#ifdef HAS_SYS_MD5_H
33# include <sys/md5.h>
34#else
35# include "md5.h"
36#endif
37
38#ifdef NEED_LOCAL_RAND
39#if !defined(__GNUC__)
40# define __inline
41#endif
42
43#define	ARC4_RESEED_BYTES 65536
44#define	ARC4_RESEED_SECONDS 300
45#define	ARC4_KEYBYTES (256 / 8)
46
47static u_int8_t arc4_i, arc4_j;
48static int arc4_numruns = 0;
49static u_int8_t arc4_sbox[256];
50static time_t arc4_t_reseed;
51static ipfmutex_t arc4_mtx;
52static MD5_CTX md5ctx;
53
54static u_int8_t arc4_randbyte(void);
55static int ipf_read_random(void *dest, int length);
56
57static __inline void
58arc4_swap(u_int8_t *a, u_int8_t *b)
59{
60	u_int8_t c;
61
62	c = *a;
63	*a = *b;
64	*b = c;
65}
66
67/*
68 * Stir our S-box.
69 */
70static void
71arc4_randomstir (void)
72{
73	u_int8_t key[256];
74	int r, n;
75	struct timeval tv_now;
76
77	/*
78	 * XXX read_random() returns unsafe numbers if the entropy
79	 * device is not loaded -- MarkM.
80	 */
81	r = ipf_read_random(key, ARC4_KEYBYTES);
82	GETKTIME(&tv_now);
83	MUTEX_ENTER(&arc4_mtx);
84	/* If r == 0 || -1, just use what was on the stack. */
85	if (r > 0) {
86		for (n = r; n < sizeof(key); n++)
87			key[n] = key[n % r];
88	}
89
90	for (n = 0; n < 256; n++) {
91		arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
92		arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
93	}
94
95	/* Reset for next reseed cycle. */
96	arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS;
97	arc4_numruns = 0;
98
99	/*
100	 * Throw away the first N words of output, as suggested in the
101	 * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
102	 * by Fluher, Mantin, and Shamir.  (N = 768 in our case.)
103	 */
104	for (n = 0; n < 768*4; n++)
105		arc4_randbyte();
106	MUTEX_EXIT(&arc4_mtx);
107}
108
109/*
110 * Initialize our S-box to its beginning defaults.
111 */
112static void
113arc4_init(void)
114{
115	int n;
116
117	MD5Init(&md5ctx);
118
119	MUTEX_INIT(&arc4_mtx, "arc4_mtx");
120	arc4_i = arc4_j = 0;
121	for (n = 0; n < 256; n++)
122		arc4_sbox[n] = (u_int8_t) n;
123
124	arc4_t_reseed = 0;
125}
126
127
128/*
129 * Generate a random byte.
130 */
131static u_int8_t
132arc4_randbyte(void)
133{
134	u_int8_t arc4_t;
135
136	arc4_i = (arc4_i + 1) % 256;
137	arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
138
139	arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
140
141	arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
142	return arc4_sbox[arc4_t];
143}
144
145/*
146 * MPSAFE
147 */
148void
149arc4rand(void *ptr, u_int len, int reseed)
150{
151	u_int8_t *p;
152	struct timeval tv;
153
154	GETKTIME(&tv);
155	if (reseed ||
156	   (arc4_numruns > ARC4_RESEED_BYTES) ||
157	   (tv.tv_sec > arc4_t_reseed))
158		arc4_randomstir();
159
160	MUTEX_ENTER(&arc4_mtx);
161	arc4_numruns += len;
162	p = ptr;
163	while (len--)
164		*p++ = arc4_randbyte();
165	MUTEX_EXIT(&arc4_mtx);
166}
167
168uint32_t
169ipf_random(void)
170{
171	uint32_t ret;
172
173	arc4rand(&ret, sizeof ret, 0);
174	return ret;
175}
176
177
178static u_char pot[ARC4_RESEED_BYTES];
179static u_char *pothead = pot, *pottail = pot;
180static int inpot = 0;
181
182/*
183 * This is not very strong, and this is understood, but the aim isn't to
184 * be cryptographically strong - it is just to make up something that is
185 * pseudo random.
186 */
187void
188ipf_rand_push(void *src, int length)
189{
190	static int arc4_inited = 0;
191	u_char *nsrc;
192	int mylen;
193
194	if (arc4_inited == 0) {
195		arc4_init();
196		arc4_inited = 1;
197	}
198
199	if (length < 64) {
200		MD5Update(&md5ctx, src, length);
201		return;
202	}
203
204	nsrc = src;
205	mylen = length;
206
207#if defined(_SYS_MD5_H) && defined(SOLARIS2)
208# define	buf	buf_un.buf8
209#endif
210	MUTEX_ENTER(&arc4_mtx);
211	while ((mylen > 64)  && (sizeof(pot) - inpot > sizeof(md5ctx.buf))) {
212		MD5Update(&md5ctx, nsrc, 64);
213		mylen -= 64;
214		nsrc += 64;
215		if (pottail + sizeof(md5ctx.buf) > pot + sizeof(pot)) {
216			int left, numbytes;
217
218			numbytes = pot + sizeof(pot) - pottail;
219			bcopy(md5ctx.buf, pottail, numbytes);
220			left = sizeof(md5ctx.buf) - numbytes;
221			pottail = pot;
222			bcopy(md5ctx.buf + sizeof(md5ctx.buf) - left,
223			      pottail, left);
224			pottail += left;
225		} else {
226			bcopy(md5ctx.buf, pottail, sizeof(md5ctx.buf));
227			pottail += sizeof(md5ctx.buf);
228		}
229		inpot += 64;
230	}
231	MUTEX_EXIT(&arc4_mtx);
232#if defined(_SYS_MD5_H) && defined(SOLARIS2)
233# undef buf
234#endif
235}
236
237
238static int
239ipf_read_random(void *dest, int length)
240{
241	if (length > inpot)
242		return 0;
243
244	MUTEX_ENTER(&arc4_mtx);
245	if (pothead + length > pot + sizeof(pot)) {
246		int left, numbytes;
247
248		left = length;
249		numbytes = pot + sizeof(pot) - pothead;
250		bcopy(pothead, dest, numbytes);
251		left -= numbytes;
252		pothead = pot;
253		bcopy(pothead, dest + length - left, left);
254		pothead += left;
255	} else {
256		bcopy(pothead, dest, length);
257		pothead += length;
258	}
259	inpot -= length;
260	if (inpot == 0)
261		pothead = pottail = pot;
262	MUTEX_EXIT(&arc4_mtx);
263
264	return length;
265}
266
267#endif /* NEED_LOCAL_RAND */
268