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	memset(buf, 0, 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	memset(buf, 0, 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	memset(buf, 0, 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	memset(entropy, 0, sizeof(entropy));
288	memset(buf, 0, sizeof(buf));
289	return 0;
290}
291#endif
292
293#ifndef WIN32
294#define TRY_SEED_URANDOM
295static int
296arc4_seed_urandom(void)
297{
298	/* This is adapted from Tor's crypto_seed_rng() */
299	static const char *filenames[] = {
300		"/dev/srandom", "/dev/urandom", "/dev/random", NULL
301	};
302	unsigned char buf[ADD_ENTROPY];
303	int fd, i;
304	size_t n;
305
306	for (i = 0; filenames[i]; ++i) {
307		fd = evutil_open_closeonexec(filenames[i], O_RDONLY, 0);
308		if (fd<0)
309			continue;
310		n = read_all(fd, buf, sizeof(buf));
311		close(fd);
312		if (n != sizeof(buf))
313			return -1;
314		arc4_addrandom(buf, sizeof(buf));
315		memset(buf, 0, sizeof(buf));
316		arc4_seeded_ok = 1;
317		return 0;
318	}
319
320	return -1;
321}
322#endif
323
324static int
325arc4_seed(void)
326{
327	int ok = 0;
328	/* We try every method that might work, and don't give up even if one
329	 * does seem to work.  There's no real harm in over-seeding, and if
330	 * one of these sources turns out to be broken, that would be bad. */
331#ifdef TRY_SEED_WIN32
332	if (0 == arc4_seed_win32())
333		ok = 1;
334#endif
335#ifdef TRY_SEED_URANDOM
336	if (0 == arc4_seed_urandom())
337		ok = 1;
338#endif
339#ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
340	if (0 == arc4_seed_proc_sys_kernel_random_uuid())
341		ok = 1;
342#endif
343#ifdef TRY_SEED_SYSCTL_LINUX
344	/* Apparently Linux is deprecating sysctl, and spewing warning
345	 * messages when you try to use it. */
346	if (!ok && 0 == arc4_seed_sysctl_linux())
347		ok = 1;
348#endif
349#ifdef TRY_SEED_SYSCTL_BSD
350	if (0 == arc4_seed_sysctl_bsd())
351		ok = 1;
352#endif
353	return ok ? 0 : -1;
354}
355
356static int
357arc4_stir(void)
358{
359	int     i;
360
361	if (!rs_initialized) {
362		arc4_init();
363		rs_initialized = 1;
364	}
365
366	arc4_seed();
367	if (!arc4_seeded_ok)
368		return -1;
369
370	/*
371	 * Discard early keystream, as per recommendations in
372	 * "Weaknesses in the Key Scheduling Algorithm of RC4" by
373	 * Scott Fluhrer, Itsik Mantin, and Adi Shamir.
374	 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
375	 *
376	 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
377	 * we drop at least 2*256 bytes, with 12*256 as a conservative
378	 * value.
379	 *
380	 * RFC4345 says to drop 6*256.
381	 *
382	 * At least some versions of this code drop 4*256, in a mistaken
383	 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers
384	 * to processor words.
385	 *
386	 * We add another sect to the cargo cult, and choose 12*256.
387	 */
388	for (i = 0; i < 12*256; i++)
389		(void)arc4_getbyte();
390	arc4_count = BYTES_BEFORE_RESEED;
391
392	return 0;
393}
394
395
396static void
397arc4_stir_if_needed(void)
398{
399	pid_t pid = getpid();
400
401	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
402	{
403		arc4_stir_pid = pid;
404		arc4_stir();
405	}
406}
407
408static inline unsigned char
409arc4_getbyte(void)
410{
411	unsigned char si, sj;
412
413	rs.i = (rs.i + 1);
414	si = rs.s[rs.i];
415	rs.j = (rs.j + si);
416	sj = rs.s[rs.j];
417	rs.s[rs.i] = sj;
418	rs.s[rs.j] = si;
419	return (rs.s[(si + sj) & 0xff]);
420}
421
422static inline unsigned int
423arc4_getword(void)
424{
425	unsigned int val;
426
427	val = arc4_getbyte() << 24;
428	val |= arc4_getbyte() << 16;
429	val |= arc4_getbyte() << 8;
430	val |= arc4_getbyte();
431
432	return val;
433}
434
435#ifndef ARC4RANDOM_NOSTIR
436ARC4RANDOM_EXPORT int
437arc4random_stir(void)
438{
439	int val;
440	_ARC4_LOCK();
441	val = arc4_stir();
442	_ARC4_UNLOCK();
443	return val;
444}
445#endif
446
447#ifndef ARC4RANDOM_NOADDRANDOM
448ARC4RANDOM_EXPORT void
449arc4random_addrandom(const unsigned char *dat, int datlen)
450{
451	int j;
452	_ARC4_LOCK();
453	if (!rs_initialized)
454		arc4_stir();
455	for (j = 0; j < datlen; j += 256) {
456		/* arc4_addrandom() ignores all but the first 256 bytes of
457		 * its input.  We want to make sure to look at ALL the
458		 * data in 'dat', just in case the user is doing something
459		 * crazy like passing us all the files in /var/log. */
460		arc4_addrandom(dat + j, datlen - j);
461	}
462	_ARC4_UNLOCK();
463}
464#endif
465
466#ifndef ARC4RANDOM_NORANDOM
467ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
468arc4random(void)
469{
470	ARC4RANDOM_UINT32 val;
471	_ARC4_LOCK();
472	arc4_count -= 4;
473	arc4_stir_if_needed();
474	val = arc4_getword();
475	_ARC4_UNLOCK();
476	return val;
477}
478#endif
479
480ARC4RANDOM_EXPORT void
481arc4random_buf(void *_buf, size_t n)
482{
483	unsigned char *buf = _buf;
484	_ARC4_LOCK();
485	arc4_stir_if_needed();
486	while (n--) {
487		if (--arc4_count <= 0)
488			arc4_stir();
489		buf[n] = arc4_getbyte();
490	}
491	_ARC4_UNLOCK();
492}
493
494#ifndef ARC4RANDOM_NOUNIFORM
495/*
496 * Calculate a uniformly distributed random number less than upper_bound
497 * avoiding "modulo bias".
498 *
499 * Uniformity is achieved by generating new random numbers until the one
500 * returned is outside the range [0, 2**32 % upper_bound).  This
501 * guarantees the selected random number will be inside
502 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
503 * after reduction modulo upper_bound.
504 */
505ARC4RANDOM_EXPORT unsigned int
506arc4random_uniform(unsigned int upper_bound)
507{
508	ARC4RANDOM_UINT32 r, min;
509
510	if (upper_bound < 2)
511		return 0;
512
513#if (UINT_MAX > 0xffffffffUL)
514	min = 0x100000000UL % upper_bound;
515#else
516	/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
517	if (upper_bound > 0x80000000)
518		min = 1 + ~upper_bound;		/* 2**32 - upper_bound */
519	else {
520		/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
521		min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
522	}
523#endif
524
525	/*
526	 * This could theoretically loop forever but each retry has
527	 * p > 0.5 (worst case, usually far better) of selecting a
528	 * number inside the range we need, so it should rarely need
529	 * to re-roll.
530	 */
531	for (;;) {
532		r = arc4random();
533		if (r >= min)
534			break;
535	}
536
537	return r % upper_bound;
538}
539#endif
540