random.c revision 238106 
1/*
2 * util/random.c - thread safe random generator, which is reasonably secure.
3 *
4 * Copyright (c) 2007, NLnet Labs. All rights reserved.
5 *
6 * This software is open source.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 *
12 * Redistributions of source code must retain the above copyright notice,
13 * this list of conditions and the following disclaimer.
14 *
15 * Redistributions in binary form must reproduce the above copyright notice,
16 * this list of conditions and the following disclaimer in the documentation
17 * and/or other materials provided with the distribution.
18 *
19 * Neither the name of the NLNET LABS nor the names of its contributors may
20 * be used to endorse or promote products derived from this software without
21 * specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
24 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
25 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
26 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
27 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
28 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
29 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
30 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
31 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
32 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
33 * POSSIBILITY OF SUCH DAMAGE.
34 */
35
36/**
37 * \file
38 * Thread safe random functions. Similar to arc4random() with an explicit
39 * initialisation routine.
40 *
41 * The code in this file is based on arc4random from
42 * openssh-4.0p1/openbsd-compat/bsd-arc4random.c
43 * That code is also BSD licensed. Here is their statement:
44 *
45 * Copyright (c) 1996, David Mazieres <dm@uun.org>
46 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
47 *
48 * Permission to use, copy, modify, and distribute this software for any
49 * purpose with or without fee is hereby granted, provided that the above
50 * copyright notice and this permission notice appear in all copies.
51 *
52 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
53 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
54 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
55 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
56 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
57 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
58 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
59 */
60#include "config.h"
61#include "util/random.h"
62#include "util/log.h"
63#include <openssl/rand.h>
64#include <openssl/rc4.h>
65#include <openssl/err.h>
66
67/**
68 * Struct with per-thread random state.
69 * Keeps SSL types away from the header file.
70 */
71struct ub_randstate {
72	/** key used for arc4random generation */
73	RC4_KEY rc4;
74	/** keeps track of key usage */
75	int rc4_ready;
76};
77
78/** Size of key to use (must be multiple of 8) */
79#define SEED_SIZE 24
80
81/**
82 * Max random value.  Similar to RAND_MAX, but more portable
83 * (mingw uses only 15 bits random).
84 */
85#define MAX_VALUE 0x7fffffff
86
87/** Number of bytes to reseed after */
88#define REKEY_BYTES	(1 << 24)
89
90/* (re)setup system seed */
91void
92ub_systemseed(unsigned int seed)
93{
94	/* RAND_ is threadsafe, by the way */
95	if(!RAND_status()) {
96		/* try to seed it */
97		unsigned char buf[256];
98		unsigned int v = seed;
99		size_t i;
100		for(i=0; i<256/sizeof(seed); i++) {
101			memmove(buf+i*sizeof(seed), &v, sizeof(seed));
102			v = v*seed + (unsigned int)i;
103		}
104		RAND_seed(buf, 256);
105		if(!RAND_status()) {
106			log_err("Random generator has no entropy "
107				"(error %ld)", ERR_get_error());
108		} else {
109			verbose(VERB_OPS, "openssl has no entropy, "
110				"seeding with time and pid");
111		}
112	}
113}
114
115/** reseed random generator */
116static void
117ub_arc4random_stir(struct ub_randstate* s, struct ub_randstate* from)
118{
119	/* not as unsigned char, but longerint so that it is
120	   aligned properly on alignment sensitive platforms */
121	uint64_t rand_buf[SEED_SIZE/sizeof(uint64_t)];
122	int i;
123
124	memset(&s->rc4, 0, sizeof(s->rc4));
125	memset(rand_buf, 0xc, sizeof(rand_buf));
126	if (from) {
127		uint8_t* rbuf = (uint8_t*)rand_buf;
128		for(i=0; i<SEED_SIZE; i++)
129			rbuf[i] = (uint8_t)ub_random(from);
130	} else {
131		if(!RAND_status())
132			ub_systemseed((unsigned)getpid()^(unsigned)time(NULL));
133		if (RAND_bytes((unsigned char*)rand_buf,
134			(int)sizeof(rand_buf)) <= 0) {
135			/* very unlikely that this happens, since we seeded
136			 * above, if it does; complain and keep going */
137			log_err("Couldn't obtain random bytes (error %ld)",
138				    ERR_get_error());
139			s->rc4_ready = 256;
140			return;
141		}
142	}
143	RC4_set_key(&s->rc4, SEED_SIZE, (unsigned char*)rand_buf);
144
145	/*
146	 * Discard early keystream, as per recommendations in:
147	 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
148	 */
149	for(i = 0; i <= 256; i += sizeof(rand_buf))
150		RC4(&s->rc4, sizeof(rand_buf), (unsigned char*)rand_buf,
151			(unsigned char*)rand_buf);
152
153	memset(rand_buf, 0, sizeof(rand_buf));
154
155	s->rc4_ready = REKEY_BYTES;
156}
157
158struct ub_randstate*
159ub_initstate(unsigned int seed, struct ub_randstate* from)
160{
161	struct ub_randstate* s = (struct ub_randstate*)calloc(1, sizeof(*s));
162	if(!s) {
163		log_err("malloc failure in random init");
164		return NULL;
165	}
166	ub_systemseed(seed);
167	ub_arc4random_stir(s, from);
168	return s;
169}
170
171long int
172ub_random(struct ub_randstate* s)
173{
174	unsigned int r = 0;
175	if (s->rc4_ready <= 0) {
176		ub_arc4random_stir(s, NULL);
177	}
178
179	RC4(&s->rc4, sizeof(r),
180		(unsigned char *)&r, (unsigned char *)&r);
181	s->rc4_ready -= sizeof(r);
182	return (long int)((r) % (((unsigned)MAX_VALUE + 1)));
183}
184
185long int
186ub_random_max(struct ub_randstate* state, long int x)
187{
188	/* make sure we fetch in a range that is divisible by x. ignore
189	 * values from d .. MAX_VALUE, instead draw a new number */
190	long int d = MAX_VALUE - (MAX_VALUE % x); /* d is divisible by x */
191	long int v = ub_random(state);
192	while(d <= v)
193		v = ub_random(state);
194	return (v % x);
195}
196
197void
198ub_randfree(struct ub_randstate* s)
199{
200	if(s)
201		free(s);
202	/* user app must do RAND_cleanup(); */
203}
204