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#ifdef WIN32
54#include <wincrypt.h>
55#include <process.h>
56#else
57#include <fcntl.h>
58#include <unistd.h>
59#include <sys/param.h>
60#include <sys/time.h>
61#ifdef _EVENT_HAVE_SYS_SYSCTL_H
62#include <sys/sysctl.h>
63#endif
64#endif
65#include <limits.h>
66#include <stdlib.h>
67#include <string.h>
68#endif
69
70/* Add platform entropy 32 bytes (256 bits) at a time. */
71#define ADD_ENTROPY 32
72
73/* Re-seed from the platform RNG after generating this many bytes. */
74#define BYTES_BEFORE_RESEED 1600000
75
76struct arc4_stream {
77	unsigned char i;
78	unsigned char j;
79	unsigned char s[256];
80};
81
82#ifdef WIN32
83#define getpid _getpid
84#define pid_t int
85#endif
86
87static int rs_initialized;
88static struct arc4_stream rs;
89static pid_t arc4_stir_pid;
90static int arc4_count;
91static int arc4_seeded_ok;
92
93static inline unsigned char arc4_getbyte(void);
94
95static inline void
96arc4_init(void)
97{
98	int     n;
99
100	for (n = 0; n < 256; n++)
101		rs.s[n] = n;
102	rs.i = 0;
103	rs.j = 0;
104}
105
106static inline void
107arc4_addrandom(const unsigned char *dat, int datlen)
108{
109	int     n;
110	unsigned char si;
111
112	rs.i--;
113	for (n = 0; n < 256; n++) {
114		rs.i = (rs.i + 1);
115		si = rs.s[rs.i];
116		rs.j = (rs.j + si + dat[n % datlen]);
117		rs.s[rs.i] = rs.s[rs.j];
118		rs.s[rs.j] = si;
119	}
120	rs.j = rs.i;
121}
122
123#ifndef WIN32
124static ssize_t
125read_all(int fd, unsigned char *buf, size_t count)
126{
127	size_t numread = 0;
128	ssize_t result;
129
130	while (numread < count) {
131		result = read(fd, buf+numread, count-numread);
132		if (result<0)
133			return -1;
134		else if (result == 0)
135			break;
136		numread += result;
137	}
138
139	return (ssize_t)numread;
140}
141#endif
142
143#ifdef WIN32
144#define TRY_SEED_WIN32
145static int
146arc4_seed_win32(void)
147{
148	/* This is adapted from Tor's crypto_seed_rng() */
149	static int provider_set = 0;
150	static HCRYPTPROV provider;
151	unsigned char buf[ADD_ENTROPY];
152
153	if (!provider_set) {
154		if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
155		    CRYPT_VERIFYCONTEXT)) {
156			if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
157				return -1;
158		}
159		provider_set = 1;
160	}
161	if (!CryptGenRandom(provider, sizeof(buf), buf))
162		return -1;
163	arc4_addrandom(buf, sizeof(buf));
164	evutil_memclear_(buf, sizeof(buf));
165	arc4_seeded_ok = 1;
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
173static int
174arc4_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	arc4_seeded_ok = 1;
204	return 0;
205}
206#endif
207
208#if _EVENT_HAVE_DECL_CTL_KERN && _EVENT_HAVE_DECL_KERN_ARND
209#define TRY_SEED_SYSCTL_BSD
210static int
211arc4_seed_sysctl_bsd(void)
212{
213	/* Based on code from William Ahern and from OpenBSD, this function
214	 * tries to use the KERN_ARND syscall to get entropy from the kernel.
215	 * This can work even if /dev/urandom is inaccessible for some reason
216	 * (e.g., we're running in a chroot). */
217	int mib[] = { CTL_KERN, KERN_ARND };
218	unsigned char buf[ADD_ENTROPY];
219	size_t len, n;
220	int i, any_set;
221
222	memset(buf, 0, sizeof(buf));
223
224	len = sizeof(buf);
225	if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
226		for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
227			n = sizeof(unsigned);
228			if (n + len > sizeof(buf))
229			    n = len - sizeof(buf);
230			if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
231				return -1;
232		}
233	}
234	/* make sure that the buffer actually got set. */
235	for (i=any_set=0; i<sizeof(buf); ++i) {
236		any_set |= buf[i];
237	}
238	if (!any_set)
239		return -1;
240
241	arc4_addrandom(buf, sizeof(buf));
242	evutil_memclear_(buf, sizeof(buf));
243	arc4_seeded_ok = 1;
244	return 0;
245}
246#endif
247#endif /* defined(_EVENT_HAVE_SYS_SYSCTL_H) */
248
249#ifdef __linux__
250#define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
251static int
252arc4_seed_proc_sys_kernel_random_uuid(void)
253{
254	/* Occasionally, somebody will make /proc/sys accessible in a chroot,
255	 * but not /dev/urandom.  Let's try /proc/sys/kernel/random/uuid.
256	 * Its format is stupid, so we need to decode it from hex.
257	 */
258	int fd;
259	char buf[128];
260	unsigned char entropy[64];
261	int bytes, n, i, nybbles;
262	for (bytes = 0; bytes<ADD_ENTROPY; ) {
263		fd = evutil_open_closeonexec("/proc/sys/kernel/random/uuid", O_RDONLY, 0);
264		if (fd < 0)
265			return -1;
266		n = read(fd, buf, sizeof(buf));
267		close(fd);
268		if (n<=0)
269			return -1;
270		memset(entropy, 0, sizeof(entropy));
271		for (i=nybbles=0; i<n; ++i) {
272			if (EVUTIL_ISXDIGIT(buf[i])) {
273				int nyb = evutil_hex_char_to_int(buf[i]);
274				if (nybbles & 1) {
275					entropy[nybbles/2] |= nyb;
276				} else {
277					entropy[nybbles/2] |= nyb<<4;
278				}
279				++nybbles;
280			}
281		}
282		if (nybbles < 2)
283			return -1;
284		arc4_addrandom(entropy, nybbles/2);
285		bytes += nybbles/2;
286	}
287	evutil_memclear_(entropy, sizeof(entropy));
288	evutil_memclear_(buf, sizeof(buf));
289	arc4_seeded_ok = 1;
290	return 0;
291}
292#endif
293
294#ifndef WIN32
295#define TRY_SEED_URANDOM
296static char *arc4random_urandom_filename = NULL;
297
298static int arc4_seed_urandom_helper_(const char *fname)
299{
300	unsigned char buf[ADD_ENTROPY];
301	int fd;
302	size_t n;
303
304	fd = evutil_open_closeonexec(fname, O_RDONLY, 0);
305	if (fd<0)
306		return -1;
307	n = read_all(fd, buf, sizeof(buf));
308	close(fd);
309	if (n != sizeof(buf))
310		return -1;
311	arc4_addrandom(buf, sizeof(buf));
312	evutil_memclear_(buf, sizeof(buf));
313	arc4_seeded_ok = 1;
314	return 0;
315}
316
317static int
318arc4_seed_urandom(void)
319{
320	/* This is adapted from Tor's crypto_seed_rng() */
321	static const char *filenames[] = {
322		"/dev/srandom", "/dev/urandom", "/dev/random", NULL
323	};
324	int i;
325	if (arc4random_urandom_filename)
326		return arc4_seed_urandom_helper_(arc4random_urandom_filename);
327
328	for (i = 0; filenames[i]; ++i) {
329		if (arc4_seed_urandom_helper_(filenames[i]) == 0) {
330			return 0;
331		}
332	}
333
334	return -1;
335}
336#endif
337
338static int
339arc4_seed(void)
340{
341	int ok = 0;
342	/* We try every method that might work, and don't give up even if one
343	 * does seem to work.  There's no real harm in over-seeding, and if
344	 * one of these sources turns out to be broken, that would be bad. */
345#ifdef TRY_SEED_WIN32
346	if (0 == arc4_seed_win32())
347		ok = 1;
348#endif
349#ifdef TRY_SEED_URANDOM
350	if (0 == arc4_seed_urandom())
351		ok = 1;
352#endif
353#ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
354	if (arc4random_urandom_filename == NULL &&
355	    0 == arc4_seed_proc_sys_kernel_random_uuid())
356		ok = 1;
357#endif
358#ifdef TRY_SEED_SYSCTL_LINUX
359	/* Apparently Linux is deprecating sysctl, and spewing warning
360	 * messages when you try to use it. */
361	if (!ok && 0 == arc4_seed_sysctl_linux())
362		ok = 1;
363#endif
364#ifdef TRY_SEED_SYSCTL_BSD
365	if (0 == arc4_seed_sysctl_bsd())
366		ok = 1;
367#endif
368	return ok ? 0 : -1;
369}
370
371static int
372arc4_stir(void)
373{
374	int     i;
375
376	if (!rs_initialized) {
377		arc4_init();
378		rs_initialized = 1;
379	}
380
381	arc4_seed();
382	if (!arc4_seeded_ok)
383		return -1;
384
385	/*
386	 * Discard early keystream, as per recommendations in
387	 * "Weaknesses in the Key Scheduling Algorithm of RC4" by
388	 * Scott Fluhrer, Itsik Mantin, and Adi Shamir.
389	 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
390	 *
391	 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
392	 * we drop at least 2*256 bytes, with 12*256 as a conservative
393	 * value.
394	 *
395	 * RFC4345 says to drop 6*256.
396	 *
397	 * At least some versions of this code drop 4*256, in a mistaken
398	 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers
399	 * to processor words.
400	 *
401	 * We add another sect to the cargo cult, and choose 12*256.
402	 */
403	for (i = 0; i < 12*256; i++)
404		(void)arc4_getbyte();
405
406	arc4_count = BYTES_BEFORE_RESEED;
407
408	return 0;
409}
410
411
412static void
413arc4_stir_if_needed(void)
414{
415	pid_t pid = getpid();
416
417	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
418	{
419		arc4_stir_pid = pid;
420		arc4_stir();
421	}
422}
423
424static inline unsigned char
425arc4_getbyte(void)
426{
427	unsigned char si, sj;
428
429	rs.i = (rs.i + 1);
430	si = rs.s[rs.i];
431	rs.j = (rs.j + si);
432	sj = rs.s[rs.j];
433	rs.s[rs.i] = sj;
434	rs.s[rs.j] = si;
435	return (rs.s[(si + sj) & 0xff]);
436}
437
438static inline unsigned int
439arc4_getword(void)
440{
441	unsigned int val;
442
443	val = arc4_getbyte() << 24;
444	val |= arc4_getbyte() << 16;
445	val |= arc4_getbyte() << 8;
446	val |= arc4_getbyte();
447
448	return val;
449}
450
451#ifndef ARC4RANDOM_NOSTIR
452ARC4RANDOM_EXPORT int
453arc4random_stir(void)
454{
455	int val;
456	_ARC4_LOCK();
457	val = arc4_stir();
458	_ARC4_UNLOCK();
459	return val;
460}
461#endif
462
463#ifndef ARC4RANDOM_NOADDRANDOM
464ARC4RANDOM_EXPORT void
465arc4random_addrandom(const unsigned char *dat, int datlen)
466{
467	int j;
468	_ARC4_LOCK();
469	if (!rs_initialized)
470		arc4_stir();
471	for (j = 0; j < datlen; j += 256) {
472		/* arc4_addrandom() ignores all but the first 256 bytes of
473		 * its input.  We want to make sure to look at ALL the
474		 * data in 'dat', just in case the user is doing something
475		 * crazy like passing us all the files in /var/log. */
476		arc4_addrandom(dat + j, datlen - j);
477	}
478	_ARC4_UNLOCK();
479}
480#endif
481
482#ifndef ARC4RANDOM_NORANDOM
483ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
484arc4random(void)
485{
486	ARC4RANDOM_UINT32 val;
487	_ARC4_LOCK();
488	arc4_count -= 4;
489	arc4_stir_if_needed();
490	val = arc4_getword();
491	_ARC4_UNLOCK();
492	return val;
493}
494#endif
495
496ARC4RANDOM_EXPORT void
497arc4random_buf(void *_buf, size_t n)
498{
499	unsigned char *buf = _buf;
500	_ARC4_LOCK();
501	arc4_stir_if_needed();
502	while (n--) {
503		if (--arc4_count <= 0)
504			arc4_stir();
505		buf[n] = arc4_getbyte();
506	}
507	_ARC4_UNLOCK();
508}
509
510#ifndef ARC4RANDOM_NOUNIFORM
511/*
512 * Calculate a uniformly distributed random number less than upper_bound
513 * avoiding "modulo bias".
514 *
515 * Uniformity is achieved by generating new random numbers until the one
516 * returned is outside the range [0, 2**32 % upper_bound).  This
517 * guarantees the selected random number will be inside
518 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
519 * after reduction modulo upper_bound.
520 */
521ARC4RANDOM_EXPORT unsigned int
522arc4random_uniform(unsigned int upper_bound)
523{
524	ARC4RANDOM_UINT32 r, min;
525
526	if (upper_bound < 2)
527		return 0;
528
529#if (UINT_MAX > 0xffffffffUL)
530	min = 0x100000000UL % upper_bound;
531#else
532	/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
533	if (upper_bound > 0x80000000)
534		min = 1 + ~upper_bound;		/* 2**32 - upper_bound */
535	else {
536		/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
537		min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
538	}
539#endif
540
541	/*
542	 * This could theoretically loop forever but each retry has
543	 * p > 0.5 (worst case, usually far better) of selecting a
544	 * number inside the range we need, so it should rarely need
545	 * to re-roll.
546	 */
547	for (;;) {
548		r = arc4random();
549		if (r >= min)
550			break;
551	}
552
553	return r % upper_bound;
554}
555#endif
556