summaryrefslogtreecommitdiffstats
path: root/libc/bionic/arc4random.c
blob: d70580aff49a07a2bbbc8370b7968e1427a552cb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
/*      $OpenBSD: arc4random.c,v 1.19 2008/06/04 00:50:23 djm Exp $        */

/*
 * Copyright (c) 1996, David Mazieres <dm@uun.org>
 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * Arc4 random number generator for OpenBSD.
 *
 * This code is derived from section 17.1 of Applied Cryptography,
 * second edition, which describes a stream cipher allegedly
 * compatible with RSA Labs "RC4" cipher (the actual description of
 * which is a trade secret).  The same algorithm is used as a stream
 * cipher called "arcfour" in Tatu Ylonen's ssh package.
 *
 * Here the stream cipher has been modified always to include the time
 * when initializing the state.  That makes it impossible to
 * regenerate the same random sequence twice, so this can't be used
 * for encryption, but will generate good random numbers.
 *
 * RC4 is a registered trademark of RSA Laboratories.
 */

#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include "thread_private.h"

/* BIONIC-BEGIN */
/* this lock should protect the global variables in this file */
static pthread_mutex_t  _arc4_lock = PTHREAD_MUTEX_INITIALIZER;
#define  _ARC4_LOCK()      pthread_mutex_lock(&_arc4_lock)
#define  _ARC4_UNLOCK()    pthread_mutex_unlock(&_arc4_lock)
/* BIONIC-END */

#ifdef __GNUC__
#define inline __inline
#else                           /* !__GNUC__ */
#define inline
#endif                          /* !__GNUC__ */

struct arc4_stream {
        u_int8_t i;
        u_int8_t j;
        u_int8_t s[256];
};

static int rs_initialized;
static struct arc4_stream rs;
static pid_t arc4_stir_pid;
static int arc4_count;

static inline u_int8_t arc4_getbyte(void);

static inline void
arc4_init(void)
{
        int     n;

        for (n = 0; n < 256; n++)
                rs.s[n] = n;
        rs.i = 0;
        rs.j = 0;
}

static inline void
arc4_addrandom(u_char *dat, int datlen)
{
        int     n;
        u_int8_t si;

        rs.i--;
        for (n = 0; n < 256; n++) {
                rs.i = (rs.i + 1);
                si = rs.s[rs.i];
                rs.j = (rs.j + si + dat[n % datlen]);
                rs.s[rs.i] = rs.s[rs.j];
                rs.s[rs.j] = si;
        }
        rs.j = rs.i;
}

static void
arc4_stir(void)
{
#if 1  /* BIONIC-BEGIN */
	int     i, fd;
	union {
		struct timeval tv;
		u_int rnd[128 / sizeof(u_int)];
	}       rdat;
	int	n;

        if (!rs_initialized) {
                arc4_init();
                rs_initialized = 1;
        }

	fd = open("/dev/urandom", O_RDONLY);
	if (fd != -1) {
		read(fd, rdat.rnd, sizeof(rdat.rnd));
		close(fd);
	}
        else
        {
	    /* fd < 0 ?  Ah, what the heck. We'll just take
	     * whatever was on the stack. just add a little more
             * time-based randomness though
             */
            gettimeofday(&rdat.tv, NULL);
        }

        arc4_stir_pid = getpid();
	arc4_addrandom((void *) &rdat, sizeof(rdat));
#else  /* BIONIC-END */
        int     i, mib[2];
        size_t        len;
        u_char rnd[128];

        if (!rs_initialized) {
                arc4_init();
                rs_initialized = 1;
        }

        mib[0] = CTL_KERN;
        mib[1] = KERN_ARND;

        len = sizeof(rnd);
        sysctl(mib, 2, rnd, &len, NULL, 0);

        arc4_stir_pid = getpid();
        arc4_addrandom(rnd, sizeof(rnd));
#endif
        /*
         * Discard early keystream, as per recommendations in:
         * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
         */
        for (i = 0; i < 256; i++)
                (void)arc4_getbyte();
        arc4_count = 1600000;
}

static inline u_int8_t
arc4_getbyte(void)
{
        u_int8_t si, sj;

        rs.i = (rs.i + 1);
        si = rs.s[rs.i];
        rs.j = (rs.j + si);
        sj = rs.s[rs.j];
        rs.s[rs.i] = sj;
        rs.s[rs.j] = si;
        return (rs.s[(si + sj) & 0xff]);
}

u_int8_t
__arc4_getbyte(void)
{
        u_int8_t val;

        _ARC4_LOCK();
        if (--arc4_count == 0 || !rs_initialized)
                arc4_stir();
        val = arc4_getbyte();
        _ARC4_UNLOCK();
        return val;
}

static inline u_int32_t
arc4_getword(void)
{
        u_int32_t val;
        val = arc4_getbyte() << 24;
        val |= arc4_getbyte() << 16;
        val |= arc4_getbyte() << 8;
        val |= arc4_getbyte();
        return val;
}

void
arc4random_stir(void)
{
        _ARC4_LOCK();
        arc4_stir();
        _ARC4_UNLOCK();
}

void
arc4random_addrandom(u_char *dat, int datlen)
{
        _ARC4_LOCK();
        if (!rs_initialized)
                arc4_stir();
        arc4_addrandom(dat, datlen);
        _ARC4_UNLOCK();
}

u_int32_t
arc4random(void)
{
        u_int32_t val;
        _ARC4_LOCK();
        arc4_count -= 4;
        if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != getpid())
                arc4_stir();
        val = arc4_getword();
        _ARC4_UNLOCK();
        return val;
}

void
arc4random_buf(void *_buf, size_t n)
{
        u_char *buf = (u_char *)_buf;
        _ARC4_LOCK();
        if (!rs_initialized || arc4_stir_pid != getpid())
                arc4_stir();
        while (n--) {
                if (--arc4_count <= 0)
                        arc4_stir();
                buf[n] = arc4_getbyte();
        }
        _ARC4_UNLOCK();
}

/*
 * Calculate a uniformly distributed random number less than upper_bound
 * avoiding "modulo bias".
 *
 * Uniformity is achieved by generating new random numbers until the one
 * returned is outside the range [0, 2**32 % upper_bound).  This
 * guarantees the selected random number will be inside
 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
 * after reduction modulo upper_bound.
 */
u_int32_t
arc4random_uniform(u_int32_t upper_bound)
{
        u_int32_t r, min;

        if (upper_bound < 2)
                return 0;

#if (ULONG_MAX > 0xffffffffUL)
        min = 0x100000000UL % upper_bound;
#else
        /* Calculate (2**32 % upper_bound) avoiding 64-bit math */
        if (upper_bound > 0x80000000)
                min = 1 + ~upper_bound;                /* 2**32 - upper_bound */
        else {
                /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
                min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
        }
#endif

        /*
         * This could theoretically loop forever but each retry has
         * p > 0.5 (worst case, usually far better) of selecting a
         * number inside the range we need, so it should rarely need
         * to re-roll.
         */
        for (;;) {
                r = arc4random();
                if (r >= min)
                        break;
        }

        return r % upper_bound;
}

#if 0
/*-------- Test code for i386 --------*/
#include <stdio.h>
#include <machine/pctr.h>
int
main(int argc, char **argv)
{
        const int iter = 1000000;
        int     i;
        pctrval v;

        v = rdtsc();
        for (i = 0; i < iter; i++)
                arc4random();
        v = rdtsc() - v;
        v /= iter;

        printf("%qd cycles\n", v);
}
#endif