2 * Random number generator
3 * Copyright (c) 2010-2011, Jouni Malinen <j@w1.fi>
5 * This software may be distributed under the terms of the BSD license.
6 * See README for more details.
8 * This random number generator is used to provide additional entropy to the
9 * one provided by the operating system (os_get_random()) for session key
10 * generation. The os_get_random() output is expected to be secure and the
11 * implementation here is expected to provide only limited protection against
12 * cases where os_get_random() cannot provide strong randomness. This
13 * implementation shall not be assumed to be secure as the sole source of
14 * randomness. The random_get_bytes() function mixes in randomness from
15 * os_get_random() and as such, calls to os_get_random() can be replaced with
16 * calls to random_get_bytes() without reducing security.
18 * The design here follows partially the design used in the Linux
19 * drivers/char/random.c, but the implementation here is simpler and not as
20 * strong. This is a compromise to reduce duplicated CPU effort and to avoid
21 * extra code/memory size. As pointed out above, os_get_random() needs to be
22 * guaranteed to be secure for any of the security assumptions to hold.
25 #include "utils/includes.h"
28 #endif /* __linux__ */
30 #include "utils/common.h"
31 #include "utils/eloop.h"
32 #include "crypto/crypto.h"
37 #define POOL_WORDS_MASK (POOL_WORDS - 1)
43 #define EXTRACT_LEN 16
44 #define MIN_READY_MARK 2
46 static u32 pool[POOL_WORDS];
47 static unsigned int input_rotate = 0;
48 static unsigned int pool_pos = 0;
49 static u8 dummy_key[20];
51 static size_t dummy_key_avail = 0;
52 static int random_fd = -1;
53 #endif /* __linux__ */
54 static unsigned int own_pool_ready = 0;
55 #define RANDOM_ENTROPY_SIZE 20
56 static char *random_entropy_file = NULL;
57 static int random_entropy_file_read = 0;
59 #define MIN_COLLECT_ENTROPY 1000
60 static unsigned int entropy = 0;
61 static unsigned int total_collected = 0;
64 static void random_write_entropy(void);
67 static u32 __ROL32(u32 x, u32 y)
69 return (x << (y & 31)) | (x >> (32 - (y & 31)));
73 static void random_mix_pool(const void *buf, size_t len)
75 static const u32 twist[8] = {
76 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
77 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278
82 wpa_hexdump_key(MSG_EXCESSIVE, "random_mix_pool", buf, len);
85 w = __ROL32(*pos++, input_rotate & 31);
86 input_rotate += pool_pos ? 7 : 14;
87 pool_pos = (pool_pos - 1) & POOL_WORDS_MASK;
89 w ^= pool[(pool_pos + POOL_TAP1) & POOL_WORDS_MASK];
90 w ^= pool[(pool_pos + POOL_TAP2) & POOL_WORDS_MASK];
91 w ^= pool[(pool_pos + POOL_TAP3) & POOL_WORDS_MASK];
92 w ^= pool[(pool_pos + POOL_TAP4) & POOL_WORDS_MASK];
93 w ^= pool[(pool_pos + POOL_TAP5) & POOL_WORDS_MASK];
94 pool[pool_pos] = (w >> 3) ^ twist[w & 7];
99 static void random_extract(u8 *out)
102 u8 hash[SHA1_MAC_LEN];
104 u32 buf[POOL_WORDS / 2];
106 /* First, add hash back to pool to make backtracking more difficult. */
107 hmac_sha1(dummy_key, sizeof(dummy_key), (const u8 *) pool,
109 random_mix_pool(hash, sizeof(hash));
110 /* Hash half the pool to extra data */
111 for (i = 0; i < POOL_WORDS / 2; i++)
112 buf[i] = pool[(pool_pos - i) & POOL_WORDS_MASK];
113 hmac_sha1(dummy_key, sizeof(dummy_key), (const u8 *) buf,
116 * Fold the hash to further reduce any potential output pattern.
117 * Though, compromise this to reduce CPU use for the most common output
118 * length (32) and return 16 bytes from instead of only half.
120 hash_ptr = (u32 *) hash;
121 hash_ptr[0] ^= hash_ptr[4];
122 os_memcpy(out, hash, EXTRACT_LEN);
126 void random_add_randomness(const void *buf, size_t len)
129 static unsigned int count = 0;
132 if (entropy > MIN_COLLECT_ENTROPY && (count & 0x3ff) != 0) {
134 * No need to add more entropy at this point, so save CPU and
139 wpa_printf(MSG_EXCESSIVE, "Add randomness: count=%u entropy=%u",
143 wpa_hexdump_key(MSG_EXCESSIVE, "random pool",
144 (const u8 *) pool, sizeof(pool));
145 random_mix_pool(&t, sizeof(t));
146 random_mix_pool(buf, len);
147 wpa_hexdump_key(MSG_EXCESSIVE, "random pool",
148 (const u8 *) pool, sizeof(pool));
154 int random_get_bytes(void *buf, size_t len)
160 wpa_printf(MSG_MSGDUMP, "Get randomness: len=%u entropy=%u",
161 (unsigned int) len, entropy);
163 /* Start with assumed strong randomness from OS */
164 ret = os_get_random(buf, len);
165 wpa_hexdump_key(MSG_EXCESSIVE, "random from os_get_random",
168 /* Mix in additional entropy extracted from the internal pool */
174 wpa_hexdump_key(MSG_EXCESSIVE, "random from internal pool",
176 siz = left > EXTRACT_LEN ? EXTRACT_LEN : left;
177 for (i = 0; i < siz; i++)
183 /* Mix in additional entropy from the crypto module */
189 if (crypto_get_random(tmp, sizeof(tmp)) < 0) {
190 wpa_printf(MSG_ERROR, "random: No entropy available "
191 "for generating strong random bytes");
194 wpa_hexdump_key(MSG_EXCESSIVE, "random from crypto module",
196 siz = left > EXTRACT_LEN ? EXTRACT_LEN : left;
197 for (i = 0; i < siz; i++)
201 #endif /* CONFIG_FIPS */
203 wpa_hexdump_key(MSG_EXCESSIVE, "mixed random", buf, len);
214 int random_pool_ready(void)
221 * Make sure that there is reasonable entropy available before allowing
222 * some key derivation operations to proceed.
225 if (dummy_key_avail == sizeof(dummy_key))
226 return 1; /* Already initialized - good to continue */
229 * Try to fetch some more data from the kernel high quality
230 * /dev/random. There may not be enough data available at this point,
231 * so use non-blocking read to avoid blocking the application
234 fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
236 wpa_printf(MSG_ERROR, "random: Cannot open /dev/random: %s",
241 res = read(fd, dummy_key + dummy_key_avail,
242 sizeof(dummy_key) - dummy_key_avail);
244 wpa_printf(MSG_ERROR, "random: Cannot read from /dev/random: "
245 "%s", strerror(errno));
248 wpa_printf(MSG_DEBUG, "random: Got %u/%u bytes from "
249 "/dev/random", (unsigned) res,
250 (unsigned) (sizeof(dummy_key) - dummy_key_avail));
251 dummy_key_avail += res;
254 if (dummy_key_avail == sizeof(dummy_key)) {
255 if (own_pool_ready < MIN_READY_MARK)
256 own_pool_ready = MIN_READY_MARK;
257 random_write_entropy();
261 wpa_printf(MSG_INFO, "random: Only %u/%u bytes of strong "
262 "random data available from /dev/random",
263 (unsigned) dummy_key_avail, (unsigned) sizeof(dummy_key));
265 if (own_pool_ready >= MIN_READY_MARK ||
266 total_collected + 10 * own_pool_ready > MIN_COLLECT_ENTROPY) {
267 wpa_printf(MSG_INFO, "random: Allow operation to proceed "
268 "based on internal entropy");
272 wpa_printf(MSG_INFO, "random: Not enough entropy pool available for "
273 "secure operations");
275 #else /* __linux__ */
276 /* TODO: could do similar checks on non-Linux platforms */
278 #endif /* __linux__ */
282 void random_mark_pool_ready(void)
285 wpa_printf(MSG_DEBUG, "random: Mark internal entropy pool to be "
286 "ready (count=%u/%u)", own_pool_ready, MIN_READY_MARK);
287 random_write_entropy();
293 static void random_close_fd(void)
295 if (random_fd >= 0) {
296 eloop_unregister_read_sock(random_fd);
303 static void random_read_fd(int sock, void *eloop_ctx, void *sock_ctx)
307 if (dummy_key_avail == sizeof(dummy_key)) {
312 res = read(sock, dummy_key + dummy_key_avail,
313 sizeof(dummy_key) - dummy_key_avail);
315 wpa_printf(MSG_ERROR, "random: Cannot read from /dev/random: "
316 "%s", strerror(errno));
320 wpa_printf(MSG_DEBUG, "random: Got %u/%u bytes from /dev/random",
322 (unsigned) (sizeof(dummy_key) - dummy_key_avail));
323 dummy_key_avail += res;
325 if (dummy_key_avail == sizeof(dummy_key)) {
327 if (own_pool_ready < MIN_READY_MARK)
328 own_pool_ready = MIN_READY_MARK;
329 random_write_entropy();
333 #endif /* __linux__ */
336 static void random_read_entropy(void)
341 if (!random_entropy_file)
344 buf = os_readfile(random_entropy_file, &len);
346 return; /* entropy file not yet available */
348 if (len != 1 + RANDOM_ENTROPY_SIZE) {
349 wpa_printf(MSG_DEBUG, "random: Invalid entropy file %s",
350 random_entropy_file);
355 own_pool_ready = (u8) buf[0];
356 random_add_randomness(buf + 1, RANDOM_ENTROPY_SIZE);
357 random_entropy_file_read = 1;
359 wpa_printf(MSG_DEBUG, "random: Added entropy from %s "
360 "(own_pool_ready=%u)",
361 random_entropy_file, own_pool_ready);
365 static void random_write_entropy(void)
367 char buf[RANDOM_ENTROPY_SIZE];
372 if (!random_entropy_file)
375 if (random_get_bytes(buf, RANDOM_ENTROPY_SIZE) < 0)
378 f = fopen(random_entropy_file, "wb");
380 wpa_printf(MSG_ERROR, "random: Could not open entropy file %s "
381 "for writing", random_entropy_file);
385 opr = own_pool_ready > 0xff ? 0xff : own_pool_ready;
386 if (fwrite(&opr, 1, 1, f) != 1 ||
387 fwrite(buf, RANDOM_ENTROPY_SIZE, 1, f) != 1)
391 wpa_printf(MSG_ERROR, "random: Could not write entropy data "
392 "to %s", random_entropy_file);
396 wpa_printf(MSG_DEBUG, "random: Updated entropy file %s "
397 "(own_pool_ready=%u)",
398 random_entropy_file, own_pool_ready);
402 void random_init(const char *entropy_file)
404 os_free(random_entropy_file);
406 random_entropy_file = os_strdup(entropy_file);
408 random_entropy_file = NULL;
409 random_read_entropy();
415 random_fd = open("/dev/random", O_RDONLY | O_NONBLOCK);
417 wpa_printf(MSG_ERROR, "random: Cannot open /dev/random: %s",
421 wpa_printf(MSG_DEBUG, "random: Trying to read entropy from "
424 eloop_register_read_sock(random_fd, random_read_fd, NULL, NULL);
425 #endif /* __linux__ */
427 random_write_entropy();
431 void random_deinit(void)
435 #endif /* __linux__ */
436 random_write_entropy();
437 os_free(random_entropy_file);
438 random_entropy_file = NULL;