1/*	$NetBSD: arc4random.c,v 1.1.1.4 2021/04/07 02:43:14 christos Exp $	*/
2/* Portable arc4random.c based on arc4random.c from OpenBSD.
3 * Portable version by Chris Davis, adapted for Libevent by Nick Mathewson
4 * Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson
5 * Copyright (c) 2010-2012 Niels Provos and Nick Mathewson
6 *
7 * Note that in Libevent, this file isn't compiled directly.  Instead,
8 * it's included from evutil_rand.c
9 */
10
11/*
12 * Copyright (c) 1996, David Mazieres <dm@uun.org>
13 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
14 *
15 * Permission to use, copy, modify, and distribute this software for any
16 * purpose with or without fee is hereby granted, provided that the above
17 * copyright notice and this permission notice appear in all copies.
18 *
19 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
20 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
21 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
22 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
23 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
24 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
25 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
26 */
27
28/*
29 * Arc4 random number generator for OpenBSD.
30 *
31 * This code is derived from section 17.1 of Applied Cryptography,
32 * second edition, which describes a stream cipher allegedly
33 * compatible with RSA Labs "RC4" cipher (the actual description of
34 * which is a trade secret).  The same algorithm is used as a stream
35 * cipher called "arcfour" in Tatu Ylonen's ssh package.
36 *
37 * Here the stream cipher has been modified always to include the time
38 * when initializing the state.  That makes it impossible to
39 * regenerate the same random sequence twice, so this can't be used
40 * for encryption, but will generate good random numbers.
41 *
42 * RC4 is a registered trademark of RSA Laboratories.
43 */
44
45#ifndef ARC4RANDOM_EXPORT
46#define ARC4RANDOM_EXPORT
47#endif
48
49#ifndef ARC4RANDOM_UINT32
50#define ARC4RANDOM_UINT32 uint32_t
51#endif
52
53#ifndef ARC4RANDOM_NO_INCLUDES
54#include "evconfig-private.h"
55#ifdef _WIN32
56#include <wincrypt.h>
57#include <process.h>
58#include <winerror.h>
59#else
60#include <fcntl.h>
61#include <unistd.h>
62#include <sys/param.h>
63#include <sys/time.h>
64#ifdef EVENT__HAVE_SYS_SYSCTL_H
65#include <sys/sysctl.h>
66#endif
67#ifdef EVENT__HAVE_SYS_RANDOM_H
68#include <sys/random.h>
69#endif
70#endif
71#include <limits.h>
72#include <stdlib.h>
73#include <string.h>
74#endif
75
76/* Add platform entropy 32 bytes (256 bits) at a time. */
77#define ADD_ENTROPY 32
78
79/* Re-seed from the platform RNG after generating this many bytes. */
80#define BYTES_BEFORE_RESEED 1600000
81
82struct arc4_stream {
83	unsigned char i;
84	unsigned char j;
85	unsigned char s[256];
86};
87
88#ifdef _WIN32
89#define getpid _getpid
90#define pid_t int
91#endif
92
93static int rs_initialized;
94static struct arc4_stream rs;
95static pid_t arc4_stir_pid;
96static int arc4_count;
97
98static inline unsigned char arc4_getbyte(void);
99
100static inline void
101arc4_init(void)
102{
103	int     n;
104
105	for (n = 0; n < 256; n++)
106		rs.s[n] = n;
107	rs.i = 0;
108	rs.j = 0;
109}
110
111static inline void
112arc4_addrandom(const unsigned char *dat, int datlen)
113{
114	int     n;
115	unsigned char si;
116
117	rs.i--;
118	for (n = 0; n < 256; n++) {
119		rs.i = (rs.i + 1);
120		si = rs.s[rs.i];
121		rs.j = (rs.j + si + dat[n % datlen]);
122		rs.s[rs.i] = rs.s[rs.j];
123		rs.s[rs.j] = si;
124	}
125	rs.j = rs.i;
126}
127
128#ifndef _WIN32
129static ssize_t
130read_all(int fd, unsigned char *buf, size_t count)
131{
132	size_t numread = 0;
133	ssize_t result;
134
135	while (numread < count) {
136		result = read(fd, buf+numread, count-numread);
137		if (result<0)
138			return -1;
139		else if (result == 0)
140			break;
141		numread += result;
142	}
143
144	return (ssize_t)numread;
145}
146#endif
147
148#ifdef _WIN32
149#define TRY_SEED_WIN32
150static int
151arc4_seed_win32(void)
152{
153	/* This is adapted from Tor's crypto_seed_rng() */
154	static int provider_set = 0;
155	static HCRYPTPROV provider;
156	unsigned char buf[ADD_ENTROPY];
157
158	if (!provider_set) {
159		if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
160		    CRYPT_VERIFYCONTEXT)) {
161			if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
162				return -1;
163		}
164		provider_set = 1;
165	}
166	if (!CryptGenRandom(provider, sizeof(buf), buf))
167		return -1;
168	arc4_addrandom(buf, sizeof(buf));
169	evutil_memclear_(buf, sizeof(buf));
170	return 0;
171}
172#endif
173
174#if defined(EVENT__HAVE_GETRANDOM)
175#define TRY_SEED_GETRANDOM
176static int
177arc4_seed_getrandom(void)
178{
179	unsigned char buf[ADD_ENTROPY];
180	size_t len, n;
181	unsigned i;
182	int any_set;
183
184	memset(buf, 0, sizeof(buf));
185
186	for (len = 0; len < sizeof(buf); len += n) {
187		n = sizeof(buf) - len;
188
189		if (0 == getrandom(&buf[len], n, 0))
190			return -1;
191	}
192	/* make sure that the buffer actually got set. */
193	for (i=0,any_set=0; i<sizeof(buf); ++i) {
194		any_set |= buf[i];
195	}
196	if (!any_set)
197		return -1;
198
199	arc4_addrandom(buf, sizeof(buf));
200	evutil_memclear_(buf, sizeof(buf));
201	return 0;
202}
203#endif /* EVENT__HAVE_GETRANDOM */
204
205#if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
206#if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND
207#define TRY_SEED_SYSCTL_BSD
208static int
209arc4_seed_sysctl_bsd(void)
210{
211	/* Based on code from William Ahern and from OpenBSD, this function
212	 * tries to use the KERN_ARND syscall to get entropy from the kernel.
213	 * This can work even if /dev/urandom is inaccessible for some reason
214	 * (e.g., we're running in a chroot). */
215	int mib[] = { CTL_KERN, KERN_ARND };
216	unsigned char buf[ADD_ENTROPY];
217	size_t len, n;
218	int i, any_set;
219
220	memset(buf, 0, sizeof(buf));
221
222	len = sizeof(buf);
223	if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
224		for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
225			n = sizeof(unsigned);
226			if (n + len > sizeof(buf))
227			    n = len - sizeof(buf);
228			if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
229				return -1;
230		}
231	}
232	/* make sure that the buffer actually got set. */
233	for (i=any_set=0; i<sizeof(buf); ++i) {
234		any_set |= buf[i];
235	}
236	if (!any_set)
237		return -1;
238
239	arc4_addrandom(buf, sizeof(buf));
240	evutil_memclear_(buf, sizeof(buf));
241	return 0;
242}
243#endif
244#endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */
245
246#ifdef __linux__
247#define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
248static int
249arc4_seed_proc_sys_kernel_random_uuid(void)
250{
251	/* Occasionally, somebody will make /proc/sys accessible in a chroot,
252	 * but not /dev/urandom.  Let's try /proc/sys/kernel/random/uuid.
253	 * Its format is stupid, so we need to decode it from hex.
254	 */
255	int fd;
256	char buf[128];
257	unsigned char entropy[64];
258	int bytes, n, i, nybbles;
259	for (bytes = 0; bytes<ADD_ENTROPY; ) {
260		fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0);
261		if (fd < 0)
262			return -1;
263		n = read(fd, buf, sizeof(buf));
264		close(fd);
265		if (n<=0)
266			return -1;
267		memset(entropy, 0, sizeof(entropy));
268		for (i=nybbles=0; i<n; ++i) {
269			if (EVUTIL_ISXDIGIT_(buf[i])) {
270				int nyb = evutil_hex_char_to_int_(buf[i]);
271				if (nybbles & 1) {
272					entropy[nybbles/2] |= nyb;
273				} else {
274					entropy[nybbles/2] |= nyb<<4;
275				}
276				++nybbles;
277			}
278		}
279		if (nybbles < 2)
280			return -1;
281		arc4_addrandom(entropy, nybbles/2);
282		bytes += nybbles/2;
283	}
284	evutil_memclear_(entropy, sizeof(entropy));
285	evutil_memclear_(buf, sizeof(buf));
286	return 0;
287}
288#endif
289
290#ifndef _WIN32
291#define TRY_SEED_URANDOM
292static char *arc4random_urandom_filename = NULL;
293
294static int arc4_seed_urandom_helper_(const char *fname)
295{
296	unsigned char buf[ADD_ENTROPY];
297	int fd;
298	size_t n;
299
300	fd = evutil_open_closeonexec_(fname, O_RDONLY, 0);
301	if (fd<0)
302		return -1;
303	n = read_all(fd, buf, sizeof(buf));
304	close(fd);
305	if (n != sizeof(buf))
306		return -1;
307	arc4_addrandom(buf, sizeof(buf));
308	evutil_memclear_(buf, sizeof(buf));
309	return 0;
310}
311
312static int
313arc4_seed_urandom(void)
314{
315	/* This is adapted from Tor's crypto_seed_rng() */
316	static const char *filenames[] = {
317		"/dev/srandom", "/dev/urandom", "/dev/random", NULL
318	};
319	int i;
320	if (arc4random_urandom_filename)
321		return arc4_seed_urandom_helper_(arc4random_urandom_filename);
322
323	for (i = 0; filenames[i]; ++i) {
324		if (arc4_seed_urandom_helper_(filenames[i]) == 0) {
325			return 0;
326		}
327	}
328
329	return -1;
330}
331#endif
332
333static int
334arc4_seed(void)
335{
336	int ok = 0;
337	/* We try every method that might work, and don't give up even if one
338	 * does seem to work.  There's no real harm in over-seeding, and if
339	 * one of these sources turns out to be broken, that would be bad. */
340#ifdef TRY_SEED_WIN32
341	if (0 == arc4_seed_win32())
342		ok = 1;
343#endif
344#ifdef TRY_SEED_GETRANDOM
345	if (0 == arc4_seed_getrandom())
346		ok = 1;
347#endif
348#ifdef TRY_SEED_URANDOM
349	if (0 == arc4_seed_urandom())
350		ok = 1;
351#endif
352#ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
353	if (arc4random_urandom_filename == NULL &&
354	    0 == arc4_seed_proc_sys_kernel_random_uuid())
355		ok = 1;
356#endif
357#ifdef TRY_SEED_SYSCTL_BSD
358	if (0 == arc4_seed_sysctl_bsd())
359		ok = 1;
360#endif
361	return ok ? 0 : -1;
362}
363
364static int
365arc4_stir(void)
366{
367	int     i;
368
369	if (!rs_initialized) {
370		arc4_init();
371		rs_initialized = 1;
372	}
373
374	if (0 != arc4_seed())
375		return -1;
376
377	/*
378	 * Discard early keystream, as per recommendations in
379	 * "Weaknesses in the Key Scheduling Algorithm of RC4" by
380	 * Scott Fluhrer, Itsik Mantin, and Adi Shamir.
381	 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
382	 *
383	 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
384	 * we drop at least 2*256 bytes, with 12*256 as a conservative
385	 * value.
386	 *
387	 * RFC4345 says to drop 6*256.
388	 *
389	 * At least some versions of this code drop 4*256, in a mistaken
390	 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers
391	 * to processor words.
392	 *
393	 * We add another sect to the cargo cult, and choose 12*256.
394	 */
395	for (i = 0; i < 12*256; i++)
396		(void)arc4_getbyte();
397
398	arc4_count = BYTES_BEFORE_RESEED;
399
400	return 0;
401}
402
403
404static void
405arc4_stir_if_needed(void)
406{
407	pid_t pid = getpid();
408
409	if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
410	{
411		arc4_stir_pid = pid;
412		arc4_stir();
413	}
414}
415
416static inline unsigned char
417arc4_getbyte(void)
418{
419	unsigned char si, sj;
420
421	rs.i = (rs.i + 1);
422	si = rs.s[rs.i];
423	rs.j = (rs.j + si);
424	sj = rs.s[rs.j];
425	rs.s[rs.i] = sj;
426	rs.s[rs.j] = si;
427	return (rs.s[(si + sj) & 0xff]);
428}
429
430static inline unsigned int
431arc4_getword(void)
432{
433	unsigned int val;
434
435	val = arc4_getbyte() << 24;
436	val |= arc4_getbyte() << 16;
437	val |= arc4_getbyte() << 8;
438	val |= arc4_getbyte();
439
440	return val;
441}
442
443#ifndef ARC4RANDOM_NOSTIR
444ARC4RANDOM_EXPORT int
445arc4random_stir(void)
446{
447	int val;
448	ARC4_LOCK_();
449	val = arc4_stir();
450	ARC4_UNLOCK_();
451	return val;
452}
453#endif
454
455#ifndef ARC4RANDOM_NOADDRANDOM
456ARC4RANDOM_EXPORT void
457arc4random_addrandom(const unsigned char *dat, int datlen)
458{
459	int j;
460	ARC4_LOCK_();
461	if (!rs_initialized)
462		arc4_stir();
463	for (j = 0; j < datlen; j += 256) {
464		/* arc4_addrandom() ignores all but the first 256 bytes of
465		 * its input.  We want to make sure to look at ALL the
466		 * data in 'dat', just in case the user is doing something
467		 * crazy like passing us all the files in /var/log. */
468		arc4_addrandom(dat + j, datlen - j);
469	}
470	ARC4_UNLOCK_();
471}
472#endif
473
474#ifndef ARC4RANDOM_NORANDOM
475ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
476arc4random(void)
477{
478	ARC4RANDOM_UINT32 val;
479	ARC4_LOCK_();
480	arc4_count -= 4;
481	arc4_stir_if_needed();
482	val = arc4_getword();
483	ARC4_UNLOCK_();
484	return val;
485}
486#endif
487
488ARC4RANDOM_EXPORT void
489arc4random_buf(void *buf_, size_t n)
490{
491	unsigned char *buf = buf_;
492	ARC4_LOCK_();
493	arc4_stir_if_needed();
494	while (n--) {
495		if (--arc4_count <= 0)
496			arc4_stir();
497		buf[n] = arc4_getbyte();
498	}
499	ARC4_UNLOCK_();
500}
501
502#ifndef ARC4RANDOM_NOUNIFORM
503/*
504 * Calculate a uniformly distributed random number less than upper_bound
505 * avoiding "modulo bias".
506 *
507 * Uniformity is achieved by generating new random numbers until the one
508 * returned is outside the range [0, 2**32 % upper_bound).  This
509 * guarantees the selected random number will be inside
510 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
511 * after reduction modulo upper_bound.
512 */
513ARC4RANDOM_EXPORT unsigned int
514arc4random_uniform(unsigned int upper_bound)
515{
516	ARC4RANDOM_UINT32 r, min;
517
518	if (upper_bound < 2)
519		return 0;
520
521#if (UINT_MAX > 0xffffffffUL)
522	min = 0x100000000UL % upper_bound;
523#else
524	/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
525	if (upper_bound > 0x80000000)
526		min = 1 + ~upper_bound;		/* 2**32 - upper_bound */
527	else {
528		/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
529		min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
530	}
531#endif
532
533	/*
534	 * This could theoretically loop forever but each retry has
535	 * p > 0.5 (worst case, usually far better) of selecting a
536	 * number inside the range we need, so it should rarely need
537	 * to re-roll.
538	 */
539	for (;;) {
540		r = arc4random();
541		if (r >= min)
542			break;
543	}
544
545	return r % upper_bound;
546}
547#endif
548