xref: /freebsd/contrib/libevent/arc4random.c (revision b59017c5cad90d0f09a59e68c00457b7faf93e7c) 
1 /* Portable arc4random.c based on arc4random.c from OpenBSD.
2  * Portable version by Chris Davis, adapted for Libevent by Nick Mathewson
3  * Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson
4  * Copyright (c) 2010-2012 Niels Provos and Nick Mathewson
5  *
6  * Note that in Libevent, this file isn't compiled directly.  Instead,
7  * it's included from evutil_rand.c
8  */
9 
10 /*
11  * Copyright (c) 1996, David Mazieres <dm@uun.org>
12  * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
13  *
14  * Permission to use, copy, modify, and distribute this software for any
15  * purpose with or without fee is hereby granted, provided that the above
16  * copyright notice and this permission notice appear in all copies.
17  *
18  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
19  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
20  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
21  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
22  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
23  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
24  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
25  */
26 
27 /*
28  * Arc4 random number generator for OpenBSD.
29  *
30  * This code is derived from section 17.1 of Applied Cryptography,
31  * second edition, which describes a stream cipher allegedly
32  * compatible with RSA Labs "RC4" cipher (the actual description of
33  * which is a trade secret).  The same algorithm is used as a stream
34  * cipher called "arcfour" in Tatu Ylonen's ssh package.
35  *
36  * Here the stream cipher has been modified always to include the time
37  * when initializing the state.  That makes it impossible to
38  * regenerate the same random sequence twice, so this can't be used
39  * for encryption, but will generate good random numbers.
40  *
41  * RC4 is a registered trademark of RSA Laboratories.
42  */
43 
44 #ifndef ARC4RANDOM_EXPORT
45 #define ARC4RANDOM_EXPORT
46 #endif
47 
48 #ifndef ARC4RANDOM_UINT32
49 #define ARC4RANDOM_UINT32 uint32_t
50 #endif
51 
52 #ifndef ARC4RANDOM_NO_INCLUDES
53 #include "evconfig-private.h"
54 #ifdef _WIN32
55 #include <wincrypt.h>
56 #include <process.h>
57 #include <winerror.h>
58 #else
59 #include <fcntl.h>
60 #include <unistd.h>
61 #include <sys/param.h>
62 #include <sys/time.h>
63 #ifdef EVENT__HAVE_SYS_SYSCTL_H
64 #include <sys/sysctl.h>
65 #endif
66 #ifdef EVENT__HAVE_SYS_RANDOM_H
67 #include <sys/random.h>
68 #endif
69 #endif
70 #include <limits.h>
71 #include <stdlib.h>
72 #include <string.h>
73 #endif
74 
75 /* Add platform entropy 32 bytes (256 bits) at a time. */
76 #define ADD_ENTROPY 32
77 
78 /* Re-seed from the platform RNG after generating this many bytes. */
79 #define BYTES_BEFORE_RESEED 1600000
80 
81 struct arc4_stream {
82 	unsigned char i;
83 	unsigned char j;
84 	unsigned char s[256];
85 };
86 
87 #ifdef _WIN32
88 #define getpid _getpid
89 #define pid_t int
90 #endif
91 
92 static int rs_initialized;
93 static struct arc4_stream rs;
94 static pid_t arc4_stir_pid;
95 static int arc4_count;
96 
97 static inline unsigned char arc4_getbyte(void);
98 
99 static inline void
100 arc4_init(void)
101 {
102 	int     n;
103 
104 	for (n = 0; n < 256; n++)
105 		rs.s[n] = n;
106 	rs.i = 0;
107 	rs.j = 0;
108 }
109 
110 static inline void
111 arc4_addrandom(const unsigned char *dat, int datlen)
112 {
113 	int     n;
114 	unsigned char si;
115 
116 	rs.i--;
117 	for (n = 0; n < 256; n++) {
118 		rs.i = (rs.i + 1);
119 		si = rs.s[rs.i];
120 		rs.j = (rs.j + si + dat[n % datlen]);
121 		rs.s[rs.i] = rs.s[rs.j];
122 		rs.s[rs.j] = si;
123 	}
124 	rs.j = rs.i;
125 }
126 
127 #ifndef _WIN32
128 static ssize_t
129 read_all(int fd, unsigned char *buf, size_t count)
130 {
131 	size_t numread = 0;
132 	ssize_t result;
133 
134 	while (numread < count) {
135 		result = read(fd, buf+numread, count-numread);
136 		if (result<0)
137 			return -1;
138 		else if (result == 0)
139 			break;
140 		numread += result;
141 	}
142 
143 	return (ssize_t)numread;
144 }
145 #endif
146 
147 #ifdef _WIN32
148 #define TRY_SEED_WIN32
149 static int
150 arc4_seed_win32(void)
151 {
152 	/* This is adapted from Tor's crypto_seed_rng() */
153 	static int provider_set = 0;
154 	static HCRYPTPROV provider;
155 	unsigned char buf[ADD_ENTROPY];
156 
157 	if (!provider_set) {
158 		if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
159 		    CRYPT_VERIFYCONTEXT)) {
160 			if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
161 				return -1;
162 		}
163 		provider_set = 1;
164 	}
165 	if (!CryptGenRandom(provider, sizeof(buf), buf))
166 		return -1;
167 	arc4_addrandom(buf, sizeof(buf));
168 	evutil_memclear_(buf, sizeof(buf));
169 	return 0;
170 }
171 #endif
172 
173 #if defined(EVENT__HAVE_GETRANDOM)
174 #define TRY_SEED_GETRANDOM
175 static int
176 arc4_seed_getrandom(void)
177 {
178 	unsigned char buf[ADD_ENTROPY];
179 	size_t len, n;
180 	unsigned i;
181 	int any_set;
182 
183 	memset(buf, 0, sizeof(buf));
184 
185 	for (len = 0; len < sizeof(buf); len += n) {
186 		n = sizeof(buf) - len;
187 
188 		if (0 == getrandom(&buf[len], n, 0))
189 			return -1;
190 	}
191 	/* make sure that the buffer actually got set. */
192 	for (i=0,any_set=0; i<sizeof(buf); ++i) {
193 		any_set |= buf[i];
194 	}
195 	if (!any_set)
196 		return -1;
197 
198 	arc4_addrandom(buf, sizeof(buf));
199 	evutil_memclear_(buf, sizeof(buf));
200 	return 0;
201 }
202 #endif /* EVENT__HAVE_GETRANDOM */
203 
204 #if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
205 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND
206 #define TRY_SEED_SYSCTL_BSD
207 static int
208 arc4_seed_sysctl_bsd(void)
209 {
210 	/* Based on code from William Ahern and from OpenBSD, this function
211 	 * tries to use the KERN_ARND syscall to get entropy from the kernel.
212 	 * This can work even if /dev/urandom is inaccessible for some reason
213 	 * (e.g., we're running in a chroot). */
214 	int mib[] = { CTL_KERN, KERN_ARND };
215 	unsigned char buf[ADD_ENTROPY];
216 	size_t len, n;
217 	int i, any_set;
218 
219 	memset(buf, 0, sizeof(buf));
220 
221 	len = sizeof(buf);
222 	if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
223 		for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
224 			n = sizeof(unsigned);
225 			if (n + len > sizeof(buf))
226 			    n = len - sizeof(buf);
227 			if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
228 				return -1;
229 		}
230 	}
231 	/* make sure that the buffer actually got set. */
232 	for (i=any_set=0; i<sizeof(buf); ++i) {
233 		any_set |= buf[i];
234 	}
235 	if (!any_set)
236 		return -1;
237 
238 	arc4_addrandom(buf, sizeof(buf));
239 	evutil_memclear_(buf, sizeof(buf));
240 	return 0;
241 }
242 #endif
243 #endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */
244 
245 #ifdef __linux__
246 #define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
247 static int
248 arc4_seed_proc_sys_kernel_random_uuid(void)
249 {
250 	/* Occasionally, somebody will make /proc/sys accessible in a chroot,
251 	 * but not /dev/urandom.  Let's try /proc/sys/kernel/random/uuid.
252 	 * Its format is stupid, so we need to decode it from hex.
253 	 */
254 	int fd;
255 	char buf[128];
256 	unsigned char entropy[64];
257 	int bytes, n, i, nybbles;
258 	for (bytes = 0; bytes<ADD_ENTROPY; ) {
259 		fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0);
260 		if (fd < 0)
261 			return -1;
262 		n = read(fd, buf, sizeof(buf));
263 		close(fd);
264 		if (n<=0)
265 			return -1;
266 		memset(entropy, 0, sizeof(entropy));
267 		for (i=nybbles=0; i<n; ++i) {
268 			if (EVUTIL_ISXDIGIT_(buf[i])) {
269 				int nyb = evutil_hex_char_to_int_(buf[i]);
270 				if (nybbles & 1) {
271 					entropy[nybbles/2] |= nyb;
272 				} else {
273 					entropy[nybbles/2] |= nyb<<4;
274 				}
275 				++nybbles;
276 			}
277 		}
278 		if (nybbles < 2)
279 			return -1;
280 		arc4_addrandom(entropy, nybbles/2);
281 		bytes += nybbles/2;
282 	}
283 	evutil_memclear_(entropy, sizeof(entropy));
284 	evutil_memclear_(buf, sizeof(buf));
285 	return 0;
286 }
287 #endif
288 
289 #ifndef _WIN32
290 #define TRY_SEED_URANDOM
291 static char *arc4random_urandom_filename = NULL;
292 
293 static int arc4_seed_urandom_helper_(const char *fname)
294 {
295 	unsigned char buf[ADD_ENTROPY];
296 	int fd;
297 	size_t n;
298 
299 	fd = evutil_open_closeonexec_(fname, O_RDONLY, 0);
300 	if (fd<0)
301 		return -1;
302 	n = read_all(fd, buf, sizeof(buf));
303 	close(fd);
304 	if (n != sizeof(buf))
305 		return -1;
306 	arc4_addrandom(buf, sizeof(buf));
307 	evutil_memclear_(buf, sizeof(buf));
308 	return 0;
309 }
310 
311 static int
312 arc4_seed_urandom(void)
313 {
314 	/* This is adapted from Tor's crypto_seed_rng() */
315 	static const char *filenames[] = {
316 		"/dev/srandom", "/dev/urandom", "/dev/random", NULL
317 	};
318 	int i;
319 	if (arc4random_urandom_filename)
320 		return arc4_seed_urandom_helper_(arc4random_urandom_filename);
321 
322 	for (i = 0; filenames[i]; ++i) {
323 		if (arc4_seed_urandom_helper_(filenames[i]) == 0) {
324 			return 0;
325 		}
326 	}
327 
328 	return -1;
329 }
330 #endif
331 
332 static int
333 arc4_seed(void)
334 {
335 	int ok = 0;
336 	/* We try every method that might work, and don't give up even if one
337 	 * does seem to work.  There's no real harm in over-seeding, and if
338 	 * one of these sources turns out to be broken, that would be bad. */
339 #ifdef TRY_SEED_WIN32
340 	if (0 == arc4_seed_win32())
341 		ok = 1;
342 #endif
343 #ifdef TRY_SEED_GETRANDOM
344 	if (0 == arc4_seed_getrandom())
345 		ok = 1;
346 #endif
347 #ifdef TRY_SEED_URANDOM
348 	if (0 == arc4_seed_urandom())
349 		ok = 1;
350 #endif
351 #ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
352 	if (arc4random_urandom_filename == NULL &&
353 	    0 == arc4_seed_proc_sys_kernel_random_uuid())
354 		ok = 1;
355 #endif
356 #ifdef TRY_SEED_SYSCTL_BSD
357 	if (0 == arc4_seed_sysctl_bsd())
358 		ok = 1;
359 #endif
360 	return ok ? 0 : -1;
361 }
362 
363 static int
364 arc4_stir(void)
365 {
366 	int     i;
367 
368 	if (!rs_initialized) {
369 		arc4_init();
370 		rs_initialized = 1;
371 	}
372 
373 	if (0 != arc4_seed())
374 		return -1;
375 
376 	/*
377 	 * Discard early keystream, as per recommendations in
378 	 * "Weaknesses in the Key Scheduling Algorithm of RC4" by
379 	 * Scott Fluhrer, Itsik Mantin, and Adi Shamir.
380 	 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
381 	 *
382 	 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
383 	 * we drop at least 2*256 bytes, with 12*256 as a conservative
384 	 * value.
385 	 *
386 	 * RFC4345 says to drop 6*256.
387 	 *
388 	 * At least some versions of this code drop 4*256, in a mistaken
389 	 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers
390 	 * to processor words.
391 	 *
392 	 * We add another sect to the cargo cult, and choose 12*256.
393 	 */
394 	for (i = 0; i < 12*256; i++)
395 		(void)arc4_getbyte();
396 
397 	arc4_count = BYTES_BEFORE_RESEED;
398 
399 	return 0;
400 }
401 
402 
403 static void
404 arc4_stir_if_needed(void)
405 {
406 	pid_t pid = getpid();
407 
408 	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
409 	{
410 		arc4_stir_pid = pid;
411 		arc4_stir();
412 	}
413 }
414 
415 static inline unsigned char
416 arc4_getbyte(void)
417 {
418 	unsigned char si, sj;
419 
420 	rs.i = (rs.i + 1);
421 	si = rs.s[rs.i];
422 	rs.j = (rs.j + si);
423 	sj = rs.s[rs.j];
424 	rs.s[rs.i] = sj;
425 	rs.s[rs.j] = si;
426 	return (rs.s[(si + sj) & 0xff]);
427 }
428 
429 static inline unsigned int
430 arc4_getword(void)
431 {
432 	unsigned int val;
433 
434 	val = arc4_getbyte() << 24;
435 	val |= arc4_getbyte() << 16;
436 	val |= arc4_getbyte() << 8;
437 	val |= arc4_getbyte();
438 
439 	return val;
440 }
441 
442 #ifndef ARC4RANDOM_NOSTIR
443 ARC4RANDOM_EXPORT int
444 arc4random_stir(void)
445 {
446 	int val;
447 	ARC4_LOCK_();
448 	val = arc4_stir();
449 	ARC4_UNLOCK_();
450 	return val;
451 }
452 #endif
453 
454 #ifndef ARC4RANDOM_NOADDRANDOM
455 ARC4RANDOM_EXPORT void
456 arc4random_addrandom(const unsigned char *dat, int datlen)
457 {
458 	int j;
459 	ARC4_LOCK_();
460 	if (!rs_initialized)
461 		arc4_stir();
462 	for (j = 0; j < datlen; j += 256) {
463 		/* arc4_addrandom() ignores all but the first 256 bytes of
464 		 * its input.  We want to make sure to look at ALL the
465 		 * data in 'dat', just in case the user is doing something
466 		 * crazy like passing us all the files in /var/log. */
467 		arc4_addrandom(dat + j, datlen - j);
468 	}
469 	ARC4_UNLOCK_();
470 }
471 #endif
472 
473 #ifndef ARC4RANDOM_NORANDOM
474 ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
475 arc4random(void)
476 {
477 	ARC4RANDOM_UINT32 val;
478 	ARC4_LOCK_();
479 	arc4_count -= 4;
480 	arc4_stir_if_needed();
481 	val = arc4_getword();
482 	ARC4_UNLOCK_();
483 	return val;
484 }
485 #endif
486 
487 ARC4RANDOM_EXPORT void
488 arc4random_buf(void *buf_, size_t n)
489 {
490 	unsigned char *buf = buf_;
491 	ARC4_LOCK_();
492 	arc4_stir_if_needed();
493 	while (n--) {
494 		if (--arc4_count <= 0)
495 			arc4_stir();
496 		buf[n] = arc4_getbyte();
497 	}
498 	ARC4_UNLOCK_();
499 }
500 
501 #ifndef ARC4RANDOM_NOUNIFORM
502 /*
503  * Calculate a uniformly distributed random number less than upper_bound
504  * avoiding "modulo bias".
505  *
506  * Uniformity is achieved by generating new random numbers until the one
507  * returned is outside the range [0, 2**32 % upper_bound).  This
508  * guarantees the selected random number will be inside
509  * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
510  * after reduction modulo upper_bound.
511  */
512 ARC4RANDOM_EXPORT unsigned int
513 arc4random_uniform(unsigned int upper_bound)
514 {
515 	ARC4RANDOM_UINT32 r, min;
516 
517 	if (upper_bound < 2)
518 		return 0;
519 
520 #if (UINT_MAX > 0xffffffffUL)
521 	min = 0x100000000UL % upper_bound;
522 #else
523 	/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
524 	if (upper_bound > 0x80000000)
525 		min = 1 + ~upper_bound;		/* 2**32 - upper_bound */
526 	else {
527 		/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
528 		min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
529 	}
530 #endif
531 
532 	/*
533 	 * This could theoretically loop forever but each retry has
534 	 * p > 0.5 (worst case, usually far better) of selecting a
535 	 * number inside the range we need, so it should rarely need
536 	 * to re-roll.
537 	 */
538 	for (;;) {
539 		r = arc4random();
540 		if (r >= min)
541 			break;
542 	}
543 
544 	return r % upper_bound;
545 }
546 #endif
547