random.c revision 75ecf5267604f166b85a7ee2cf0d9cb682966680 
1/*
2 * Random number generator
3 * Copyright (c) 2010-2011, Jouni Malinen <j@w1.fi>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 *
9 * Alternatively, this software may be distributed under the terms of BSD
10 * license.
11 *
12 * See README and COPYING for more details.
13 *
14 * This random number generator is used to provide additional entropy to the
15 * one provided by the operating system (os_get_random()) for session key
16 * generation. The os_get_random() output is expected to be secure and the
17 * implementation here is expected to provide only limited protection against
18 * cases where os_get_random() cannot provide strong randomness. This
19 * implementation shall not be assumed to be secure as the sole source of
20 * randomness. The random_get_bytes() function mixes in randomness from
21 * os_get_random() and as such, calls to os_get_random() can be replaced with
22 * calls to random_get_bytes() without reducing security.
23 *
24 * The design here follows partially the design used in the Linux
25 * drivers/char/random.c, but the implementation here is simpler and not as
26 * strong. This is a compromise to reduce duplicated CPU effort and to avoid
27 * extra code/memory size. As pointed out above, os_get_random() needs to be
28 * guaranteed to be secure for any of the security assumptions to hold.
29 */
30
31#include "utils/includes.h"
32#ifdef __linux__
33#include <fcntl.h>
34#endif /* __linux__ */
35
36#include "utils/common.h"
37#include "utils/eloop.h"
38#include "sha1.h"
39#include "random.h"
40
41#define POOL_WORDS 32
42#define POOL_WORDS_MASK (POOL_WORDS - 1)
43#define POOL_TAP1 26
44#define POOL_TAP2 20
45#define POOL_TAP3 14
46#define POOL_TAP4 7
47#define POOL_TAP5 1
48#define EXTRACT_LEN 16
49#define MIN_READY_MARK 2
50
51static u32 pool[POOL_WORDS];
52static unsigned int input_rotate = 0;
53static unsigned int pool_pos = 0;
54static u8 dummy_key[20];
55#ifdef __linux__
56static size_t dummy_key_avail = 0;
57static int random_fd = -1;
58#endif /* __linux__ */
59static unsigned int own_pool_ready = 0;
60#define RANDOM_ENTROPY_SIZE 20
61static char *random_entropy_file = NULL;
62static int random_entropy_file_read = 0;
63
64#define MIN_COLLECT_ENTROPY 1000
65static unsigned int entropy = 0;
66static unsigned int total_collected = 0;
67
68
69static void random_write_entropy(void);
70
71
72static u32 __ROL32(u32 x, u32 y)
73{
74	return (x << (y & 31)) | (x >> (32 - (y & 31)));
75}
76
77
78static void random_mix_pool(const void *buf, size_t len)
79{
80	static const u32 twist[8] = {
81		0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
82		0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278
83	};
84	const u8 *pos = buf;
85	u32 w;
86
87	wpa_hexdump_key(MSG_EXCESSIVE, "random_mix_pool", buf, len);
88
89	while (len--) {
90		w = __ROL32(*pos++, input_rotate & 31);
91		input_rotate += pool_pos ? 7 : 14;
92		pool_pos = (pool_pos - 1) & POOL_WORDS_MASK;
93		w ^= pool[pool_pos];
94		w ^= pool[(pool_pos + POOL_TAP1) & POOL_WORDS_MASK];
95		w ^= pool[(pool_pos + POOL_TAP2) & POOL_WORDS_MASK];
96		w ^= pool[(pool_pos + POOL_TAP3) & POOL_WORDS_MASK];
97		w ^= pool[(pool_pos + POOL_TAP4) & POOL_WORDS_MASK];
98		w ^= pool[(pool_pos + POOL_TAP5) & POOL_WORDS_MASK];
99		pool[pool_pos] = (w >> 3) ^ twist[w & 7];
100	}
101}
102
103
104static void random_extract(u8 *out)
105{
106	unsigned int i;
107	u8 hash[SHA1_MAC_LEN];
108	u32 *hash_ptr;
109	u32 buf[POOL_WORDS / 2];
110
111	/* First, add hash back to pool to make backtracking more difficult. */
112	hmac_sha1(dummy_key, sizeof(dummy_key), (const u8 *) pool,
113		  sizeof(pool), hash);
114	random_mix_pool(hash, sizeof(hash));
115	/* Hash half the pool to extra data */
116	for (i = 0; i < POOL_WORDS / 2; i++)
117		buf[i] = pool[(pool_pos - i) & POOL_WORDS_MASK];
118	hmac_sha1(dummy_key, sizeof(dummy_key), (const u8 *) buf,
119		  sizeof(buf), hash);
120	/*
121	 * Fold the hash to further reduce any potential output pattern.
122	 * Though, compromise this to reduce CPU use for the most common output
123	 * length (32) and return 16 bytes from instead of only half.
124	 */
125	hash_ptr = (u32 *) hash;
126	hash_ptr[0] ^= hash_ptr[4];
127	os_memcpy(out, hash, EXTRACT_LEN);
128}
129
130
131void random_add_randomness(const void *buf, size_t len)
132{
133	struct os_time t;
134	static unsigned int count = 0;
135
136	count++;
137	wpa_printf(MSG_MSGDUMP, "Add randomness: count=%u entropy=%u",
138		   count, entropy);
139	if (entropy > MIN_COLLECT_ENTROPY && (count & 0x3ff) != 0) {
140		/*
141		 * No need to add more entropy at this point, so save CPU and
142		 * skip the update.
143		 */
144		return;
145	}
146
147	os_get_time(&t);
148	wpa_hexdump_key(MSG_EXCESSIVE, "random pool",
149			(const u8 *) pool, sizeof(pool));
150	random_mix_pool(&t, sizeof(t));
151	random_mix_pool(buf, len);
152	wpa_hexdump_key(MSG_EXCESSIVE, "random pool",
153			(const u8 *) pool, sizeof(pool));
154	entropy++;
155	total_collected++;
156}
157
158
159int random_get_bytes(void *buf, size_t len)
160{
161	int ret;
162	u8 *bytes = buf;
163	size_t left;
164
165	wpa_printf(MSG_MSGDUMP, "Get randomness: len=%u entropy=%u",
166		   (unsigned int) len, entropy);
167
168	/* Start with assumed strong randomness from OS */
169	ret = os_get_random(buf, len);
170	wpa_hexdump_key(MSG_EXCESSIVE, "random from os_get_random",
171			buf, len);
172
173	/* Mix in additional entropy extracted from the internal pool */
174	left = len;
175	while (left) {
176		size_t siz, i;
177		u8 tmp[EXTRACT_LEN];
178		random_extract(tmp);
179		wpa_hexdump_key(MSG_EXCESSIVE, "random from internal pool",
180				tmp, sizeof(tmp));
181		siz = left > EXTRACT_LEN ? EXTRACT_LEN : left;
182		for (i = 0; i < siz; i++)
183			*bytes++ ^= tmp[i];
184		left -= siz;
185	}
186	wpa_hexdump_key(MSG_EXCESSIVE, "mixed random", buf, len);
187
188	if (entropy < len)
189		entropy = 0;
190	else
191		entropy -= len;
192
193	return ret;
194}
195
196
197int random_pool_ready(void)
198{
199#ifdef __linux__
200	int fd;
201	ssize_t res;
202
203	/*
204	 * Make sure that there is reasonable entropy available before allowing
205	 * some key derivation operations to proceed.
206	 */
207
208	if (dummy_key_avail == sizeof(dummy_key))
209		return 1; /* Already initialized - good to continue */
210
211	/*
212	 * Try to fetch some more data from the kernel high quality
213	 * /dev/random. There may not be enough data available at this point,
214	 * so use non-blocking read to avoid blocking the application
215	 * completely.
216	 */
217	fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
218	if (fd < 0) {
219#ifndef CONFIG_NO_STDOUT_DEBUG
220		int error = errno;
221		perror("open(/dev/random)");
222		wpa_printf(MSG_ERROR, "random: Cannot open /dev/random: %s",
223			   strerror(error));
224#endif /* CONFIG_NO_STDOUT_DEBUG */
225		return -1;
226	}
227
228	res = read(fd, dummy_key + dummy_key_avail,
229		   sizeof(dummy_key) - dummy_key_avail);
230	if (res < 0) {
231		wpa_printf(MSG_ERROR, "random: Cannot read from /dev/random: "
232			   "%s", strerror(errno));
233		res = 0;
234	}
235	wpa_printf(MSG_DEBUG, "random: Got %u/%u bytes from "
236		   "/dev/random", (unsigned) res,
237		   (unsigned) (sizeof(dummy_key) - dummy_key_avail));
238	dummy_key_avail += res;
239	close(fd);
240
241	if (dummy_key_avail == sizeof(dummy_key)) {
242		if (own_pool_ready < MIN_READY_MARK)
243			own_pool_ready = MIN_READY_MARK;
244		random_write_entropy();
245		return 1;
246	}
247
248	wpa_printf(MSG_INFO, "random: Only %u/%u bytes of strong "
249		   "random data available from /dev/random",
250		   (unsigned) dummy_key_avail, (unsigned) sizeof(dummy_key));
251
252	if (own_pool_ready >= MIN_READY_MARK ||
253	    total_collected + 10 * own_pool_ready > MIN_COLLECT_ENTROPY) {
254		wpa_printf(MSG_INFO, "random: Allow operation to proceed "
255			   "based on internal entropy");
256		return 1;
257	}
258
259	wpa_printf(MSG_INFO, "random: Not enough entropy pool available for "
260		   "secure operations");
261	return 0;
262#else /* __linux__ */
263	/* TODO: could do similar checks on non-Linux platforms */
264	return 1;
265#endif /* __linux__ */
266}
267
268
269void random_mark_pool_ready(void)
270{
271	own_pool_ready++;
272	wpa_printf(MSG_DEBUG, "random: Mark internal entropy pool to be "
273		   "ready (count=%u/%u)", own_pool_ready, MIN_READY_MARK);
274	random_write_entropy();
275}
276
277
278#ifdef __linux__
279
280static void random_close_fd(void)
281{
282	if (random_fd >= 0) {
283		eloop_unregister_read_sock(random_fd);
284		close(random_fd);
285		random_fd = -1;
286	}
287}
288
289
290static void random_read_fd(int sock, void *eloop_ctx, void *sock_ctx)
291{
292	ssize_t res;
293
294	if (dummy_key_avail == sizeof(dummy_key)) {
295		random_close_fd();
296		return;
297	}
298
299	res = read(sock, dummy_key + dummy_key_avail,
300		   sizeof(dummy_key) - dummy_key_avail);
301	if (res < 0) {
302		wpa_printf(MSG_ERROR, "random: Cannot read from /dev/random: "
303			   "%s", strerror(errno));
304		return;
305	}
306
307	wpa_printf(MSG_DEBUG, "random: Got %u/%u bytes from /dev/random",
308		   (unsigned) res,
309		   (unsigned) (sizeof(dummy_key) - dummy_key_avail));
310	dummy_key_avail += res;
311
312	if (dummy_key_avail == sizeof(dummy_key)) {
313		random_close_fd();
314		if (own_pool_ready < MIN_READY_MARK)
315			own_pool_ready = MIN_READY_MARK;
316		random_write_entropy();
317	}
318}
319
320#endif /* __linux__ */
321
322
323static void random_read_entropy(void)
324{
325	char *buf;
326	size_t len;
327
328	if (!random_entropy_file)
329		return;
330
331	buf = os_readfile(random_entropy_file, &len);
332	if (buf == NULL)
333		return; /* entropy file not yet available */
334
335	if (len != 1 + RANDOM_ENTROPY_SIZE) {
336		wpa_printf(MSG_DEBUG, "random: Invalid entropy file %s",
337			   random_entropy_file);
338		os_free(buf);
339		return;
340	}
341
342	own_pool_ready = (u8) buf[0];
343	random_add_randomness(buf + 1, RANDOM_ENTROPY_SIZE);
344	random_entropy_file_read = 1;
345	os_free(buf);
346	wpa_printf(MSG_DEBUG, "random: Added entropy from %s "
347		   "(own_pool_ready=%u)",
348		   random_entropy_file, own_pool_ready);
349}
350
351
352static void random_write_entropy(void)
353{
354	char buf[RANDOM_ENTROPY_SIZE];
355	FILE *f;
356	u8 opr;
357
358	if (!random_entropy_file)
359		return;
360
361	random_get_bytes(buf, RANDOM_ENTROPY_SIZE);
362
363	f = fopen(random_entropy_file, "wb");
364	if (f == NULL) {
365		wpa_printf(MSG_ERROR, "random: Could not write %s",
366			   random_entropy_file);
367		return;
368	}
369
370	opr = own_pool_ready > 0xff ? 0xff : own_pool_ready;
371	fwrite(&opr, 1, 1, f);
372	fwrite(buf, RANDOM_ENTROPY_SIZE, 1, f);
373	fclose(f);
374
375	wpa_printf(MSG_DEBUG, "random: Updated entropy file %s "
376		   "(own_pool_ready=%u)",
377		   random_entropy_file, own_pool_ready);
378}
379
380
381void random_init(const char *entropy_file)
382{
383	os_free(random_entropy_file);
384	if (entropy_file)
385		random_entropy_file = os_strdup(entropy_file);
386	else
387		random_entropy_file = NULL;
388	random_read_entropy();
389
390#ifdef __linux__
391	if (random_fd >= 0)
392		return;
393
394	random_fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
395	if (random_fd < 0) {
396#ifndef CONFIG_NO_STDOUT_DEBUG
397		int error = errno;
398		perror("open(/dev/random)");
399		wpa_printf(MSG_ERROR, "random: Cannot open /dev/random: %s",
400			   strerror(error));
401#endif /* CONFIG_NO_STDOUT_DEBUG */
402		return;
403	}
404	wpa_printf(MSG_DEBUG, "random: Trying to read entropy from "
405		   "/dev/random");
406
407	eloop_register_read_sock(random_fd, random_read_fd, NULL, NULL);
408#endif /* __linux__ */
409
410	random_write_entropy();
411}
412
413
414void random_deinit(void)
415{
416#ifdef __linux__
417	random_close_fd();
418#endif /* __linux__ */
419	random_write_entropy();
420	os_free(random_entropy_file);
421	random_entropy_file = NULL;
422}
423