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 #endif
67 #include <limits.h>
68 #include <stdlib.h>
69 #include <string.h>
70 #endif
71
72 /* Add platform entropy 32 bytes (256 bits) at a time. */
73 #define ADD_ENTROPY 32
74
75 /* Re-seed from the platform RNG after generating this many bytes. */
76 #define BYTES_BEFORE_RESEED 1600000
77
78 struct arc4_stream {
79 unsigned char i;
80 unsigned char j;
81 unsigned char s[256];
82 };
83
84 #ifdef _WIN32
85 #define getpid _getpid
86 #define pid_t int
87 #endif
88
89 static int rs_initialized;
90 static struct arc4_stream rs;
91 static pid_t arc4_stir_pid;
92 static int arc4_count;
93
94 static inline unsigned char arc4_getbyte(void);
95
96 static inline void
arc4_init(void)97 arc4_init(void)
98 {
99 int n;
100
101 for (n = 0; n < 256; n++)
102 rs.s[n] = n;
103 rs.i = 0;
104 rs.j = 0;
105 }
106
107 static inline void
arc4_addrandom(const unsigned char * dat,int datlen)108 arc4_addrandom(const unsigned char *dat, int datlen)
109 {
110 int n;
111 unsigned char si;
112
113 rs.i--;
114 for (n = 0; n < 256; n++) {
115 rs.i = (rs.i + 1);
116 si = rs.s[rs.i];
117 rs.j = (rs.j + si + dat[n % datlen]);
118 rs.s[rs.i] = rs.s[rs.j];
119 rs.s[rs.j] = si;
120 }
121 rs.j = rs.i;
122 }
123
124 #ifndef _WIN32
125 static ssize_t
read_all(int fd,unsigned char * buf,size_t count)126 read_all(int fd, unsigned char *buf, size_t count)
127 {
128 size_t numread = 0;
129 ssize_t result;
130
131 while (numread < count) {
132 result = read(fd, buf+numread, count-numread);
133 if (result<0)
134 return -1;
135 else if (result == 0)
136 break;
137 numread += result;
138 }
139
140 return (ssize_t)numread;
141 }
142 #endif
143
144 #ifdef _WIN32
145 #define TRY_SEED_WIN32
146 static int
arc4_seed_win32(void)147 arc4_seed_win32(void)
148 {
149 /* This is adapted from Tor's crypto_seed_rng() */
150 static int provider_set = 0;
151 static HCRYPTPROV provider;
152 unsigned char buf[ADD_ENTROPY];
153
154 if (!provider_set) {
155 if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
156 CRYPT_VERIFYCONTEXT)) {
157 if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
158 return -1;
159 }
160 provider_set = 1;
161 }
162 if (!CryptGenRandom(provider, sizeof(buf), buf))
163 return -1;
164 arc4_addrandom(buf, sizeof(buf));
165 evutil_memclear_(buf, sizeof(buf));
166 return 0;
167 }
168 #endif
169
170 #if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
171 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_RANDOM && EVENT__HAVE_DECL_RANDOM_UUID
172 #define TRY_SEED_SYSCTL_LINUX
173 static int
arc4_seed_sysctl_linux(void)174 arc4_seed_sysctl_linux(void)
175 {
176 /* Based on code by William Ahern, this function tries to use the
177 * RANDOM_UUID sysctl to get entropy from the kernel. This can work
178 * even if /dev/urandom is inaccessible for some reason (e.g., we're
179 * running in a chroot). */
180 int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
181 unsigned char buf[ADD_ENTROPY];
182 size_t len, n;
183 unsigned i;
184 int any_set;
185
186 memset(buf, 0, sizeof(buf));
187
188 for (len = 0; len < sizeof(buf); len += n) {
189 n = sizeof(buf) - len;
190
191 if (0 != sysctl(mib, 3, &buf[len], &n, NULL, 0))
192 return -1;
193 }
194 /* make sure that the buffer actually got set. */
195 for (i=0,any_set=0; i<sizeof(buf); ++i) {
196 any_set |= buf[i];
197 }
198 if (!any_set)
199 return -1;
200
201 arc4_addrandom(buf, sizeof(buf));
202 evutil_memclear_(buf, sizeof(buf));
203 return 0;
204 }
205 #endif
206
207 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND
208 #define TRY_SEED_SYSCTL_BSD
209 static int
arc4_seed_sysctl_bsd(void)210 arc4_seed_sysctl_bsd(void)
211 {
212 /* Based on code from William Ahern and from OpenBSD, this function
213 * tries to use the KERN_ARND syscall to get entropy from the kernel.
214 * This can work even if /dev/urandom is inaccessible for some reason
215 * (e.g., we're running in a chroot). */
216 int mib[] = { CTL_KERN, KERN_ARND };
217 unsigned char buf[ADD_ENTROPY];
218 size_t len, n;
219 int i, any_set;
220
221 memset(buf, 0, sizeof(buf));
222
223 len = sizeof(buf);
224 if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
225 for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
226 n = sizeof(unsigned);
227 if (n + len > sizeof(buf))
228 n = len - sizeof(buf);
229 if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
230 return -1;
231 }
232 }
233 /* make sure that the buffer actually got set. */
234 for (i=any_set=0; i<sizeof(buf); ++i) {
235 any_set |= buf[i];
236 }
237 if (!any_set)
238 return -1;
239
240 arc4_addrandom(buf, sizeof(buf));
241 evutil_memclear_(buf, sizeof(buf));
242 return 0;
243 }
244 #endif
245 #endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */
246
247 #ifdef __linux__
248 #define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
249 static int
arc4_seed_proc_sys_kernel_random_uuid(void)250 arc4_seed_proc_sys_kernel_random_uuid(void)
251 {
252 /* Occasionally, somebody will make /proc/sys accessible in a chroot,
253 * but not /dev/urandom. Let's try /proc/sys/kernel/random/uuid.
254 * Its format is stupid, so we need to decode it from hex.
255 */
256 int fd;
257 char buf[128];
258 unsigned char entropy[64];
259 int bytes, n, i, nybbles;
260 for (bytes = 0; bytes<ADD_ENTROPY; ) {
261 fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0);
262 if (fd < 0)
263 return -1;
264 n = read(fd, buf, sizeof(buf));
265 close(fd);
266 if (n<=0)
267 return -1;
268 memset(entropy, 0, sizeof(entropy));
269 for (i=nybbles=0; i<n; ++i) {
270 if (EVUTIL_ISXDIGIT_(buf[i])) {
271 int nyb = evutil_hex_char_to_int_(buf[i]);
272 if (nybbles & 1) {
273 entropy[nybbles/2] |= nyb;
274 } else {
275 entropy[nybbles/2] |= nyb<<4;
276 }
277 ++nybbles;
278 }
279 }
280 if (nybbles < 2)
281 return -1;
282 arc4_addrandom(entropy, nybbles/2);
283 bytes += nybbles/2;
284 }
285 evutil_memclear_(entropy, sizeof(entropy));
286 evutil_memclear_(buf, sizeof(buf));
287 return 0;
288 }
289 #endif
290
291 #ifndef _WIN32
292 #define TRY_SEED_URANDOM
293 static char *arc4random_urandom_filename = NULL;
294
arc4_seed_urandom_helper_(const char * fname)295 static int arc4_seed_urandom_helper_(const char *fname)
296 {
297 unsigned char buf[ADD_ENTROPY];
298 int fd;
299 size_t n;
300
301 fd = evutil_open_closeonexec_(fname, O_RDONLY, 0);
302 if (fd<0)
303 return -1;
304 n = read_all(fd, buf, sizeof(buf));
305 close(fd);
306 if (n != sizeof(buf))
307 return -1;
308 arc4_addrandom(buf, sizeof(buf));
309 evutil_memclear_(buf, sizeof(buf));
310 return 0;
311 }
312
313 static int
arc4_seed_urandom(void)314 arc4_seed_urandom(void)
315 {
316 /* This is adapted from Tor's crypto_seed_rng() */
317 static const char *filenames[] = {
318 "/dev/srandom", "/dev/urandom", "/dev/random", NULL
319 };
320 int i;
321 if (arc4random_urandom_filename)
322 return arc4_seed_urandom_helper_(arc4random_urandom_filename);
323
324 for (i = 0; filenames[i]; ++i) {
325 if (arc4_seed_urandom_helper_(filenames[i]) == 0) {
326 return 0;
327 }
328 }
329
330 return -1;
331 }
332 #endif
333
334 static int
arc4_seed(void)335 arc4_seed(void)
336 {
337 int ok = 0;
338 /* We try every method that might work, and don't give up even if one
339 * does seem to work. There's no real harm in over-seeding, and if
340 * one of these sources turns out to be broken, that would be bad. */
341 #ifdef TRY_SEED_WIN32
342 if (0 == arc4_seed_win32())
343 ok = 1;
344 #endif
345 #ifdef TRY_SEED_URANDOM
346 if (0 == arc4_seed_urandom())
347 ok = 1;
348 #endif
349 #ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
350 if (arc4random_urandom_filename == NULL &&
351 0 == arc4_seed_proc_sys_kernel_random_uuid())
352 ok = 1;
353 #endif
354 #ifdef TRY_SEED_SYSCTL_LINUX
355 /* Apparently Linux is deprecating sysctl, and spewing warning
356 * messages when you try to use it. */
357 if (!ok && 0 == arc4_seed_sysctl_linux())
358 ok = 1;
359 #endif
360 #ifdef TRY_SEED_SYSCTL_BSD
361 if (0 == arc4_seed_sysctl_bsd())
362 ok = 1;
363 #endif
364 return ok ? 0 : -1;
365 }
366
367 static int
arc4_stir(void)368 arc4_stir(void)
369 {
370 int i;
371
372 if (!rs_initialized) {
373 arc4_init();
374 rs_initialized = 1;
375 }
376
377 if (0 != arc4_seed())
378 return -1;
379
380 /*
381 * Discard early keystream, as per recommendations in
382 * "Weaknesses in the Key Scheduling Algorithm of RC4" by
383 * Scott Fluhrer, Itsik Mantin, and Adi Shamir.
384 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
385 *
386 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
387 * we drop at least 2*256 bytes, with 12*256 as a conservative
388 * value.
389 *
390 * RFC4345 says to drop 6*256.
391 *
392 * At least some versions of this code drop 4*256, in a mistaken
393 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers
394 * to processor words.
395 *
396 * We add another sect to the cargo cult, and choose 12*256.
397 */
398 for (i = 0; i < 12*256; i++)
399 (void)arc4_getbyte();
400
401 arc4_count = BYTES_BEFORE_RESEED;
402
403 return 0;
404 }
405
406
407 static void
arc4_stir_if_needed(void)408 arc4_stir_if_needed(void)
409 {
410 pid_t pid = getpid();
411
412 if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
413 {
414 arc4_stir_pid = pid;
415 arc4_stir();
416 }
417 }
418
419 static inline unsigned char
arc4_getbyte(void)420 arc4_getbyte(void)
421 {
422 unsigned char si, sj;
423
424 rs.i = (rs.i + 1);
425 si = rs.s[rs.i];
426 rs.j = (rs.j + si);
427 sj = rs.s[rs.j];
428 rs.s[rs.i] = sj;
429 rs.s[rs.j] = si;
430 return (rs.s[(si + sj) & 0xff]);
431 }
432
433 static inline unsigned int
arc4_getword(void)434 arc4_getword(void)
435 {
436 unsigned int val;
437
438 val = arc4_getbyte() << 24;
439 val |= arc4_getbyte() << 16;
440 val |= arc4_getbyte() << 8;
441 val |= arc4_getbyte();
442
443 return val;
444 }
445
446 #ifndef ARC4RANDOM_NOSTIR
447 ARC4RANDOM_EXPORT int
arc4random_stir(void)448 arc4random_stir(void)
449 {
450 int val;
451 ARC4_LOCK_();
452 val = arc4_stir();
453 ARC4_UNLOCK_();
454 return val;
455 }
456 #endif
457
458 #ifndef ARC4RANDOM_NOADDRANDOM
459 ARC4RANDOM_EXPORT void
arc4random_addrandom(const unsigned char * dat,int datlen)460 arc4random_addrandom(const unsigned char *dat, int datlen)
461 {
462 int j;
463 ARC4_LOCK_();
464 if (!rs_initialized)
465 arc4_stir();
466 for (j = 0; j < datlen; j += 256) {
467 /* arc4_addrandom() ignores all but the first 256 bytes of
468 * its input. We want to make sure to look at ALL the
469 * data in 'dat', just in case the user is doing something
470 * crazy like passing us all the files in /var/log. */
471 arc4_addrandom(dat + j, datlen - j);
472 }
473 ARC4_UNLOCK_();
474 }
475 #endif
476
477 #ifndef ARC4RANDOM_NORANDOM
478 ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
arc4random(void)479 arc4random(void)
480 {
481 ARC4RANDOM_UINT32 val;
482 ARC4_LOCK_();
483 arc4_count -= 4;
484 arc4_stir_if_needed();
485 val = arc4_getword();
486 ARC4_UNLOCK_();
487 return val;
488 }
489 #endif
490
491 ARC4RANDOM_EXPORT void
arc4random_buf(void * buf_,size_t n)492 arc4random_buf(void *buf_, size_t n)
493 {
494 unsigned char *buf = buf_;
495 ARC4_LOCK_();
496 arc4_stir_if_needed();
497 while (n--) {
498 if (--arc4_count <= 0)
499 arc4_stir();
500 buf[n] = arc4_getbyte();
501 }
502 ARC4_UNLOCK_();
503 }
504
505 #ifndef ARC4RANDOM_NOUNIFORM
506 /*
507 * Calculate a uniformly distributed random number less than upper_bound
508 * avoiding "modulo bias".
509 *
510 * Uniformity is achieved by generating new random numbers until the one
511 * returned is outside the range [0, 2**32 % upper_bound). This
512 * guarantees the selected random number will be inside
513 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
514 * after reduction modulo upper_bound.
515 */
516 ARC4RANDOM_EXPORT unsigned int
arc4random_uniform(unsigned int upper_bound)517 arc4random_uniform(unsigned int upper_bound)
518 {
519 ARC4RANDOM_UINT32 r, min;
520
521 if (upper_bound < 2)
522 return 0;
523
524 #if (UINT_MAX > 0xffffffffUL)
525 min = 0x100000000UL % upper_bound;
526 #else
527 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */
528 if (upper_bound > 0x80000000)
529 min = 1 + ~upper_bound; /* 2**32 - upper_bound */
530 else {
531 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
532 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
533 }
534 #endif
535
536 /*
537 * This could theoretically loop forever but each retry has
538 * p > 0.5 (worst case, usually far better) of selecting a
539 * number inside the range we need, so it should rarely need
540 * to re-roll.
541 */
542 for (;;) {
543 r = arc4random();
544 if (r >= min)
545 break;
546 }
547
548 return r % upper_bound;
549 }
550 #endif
551