1/*
2 * rand_source.c
3 *
4 * implements a random source based on /dev/random
5 *
6 * David A. McGrew
7 * Cisco Systems, Inc.
8 */
9/*
10 *
11 * Copyright(c) 2001-2006 Cisco Systems, Inc.
12 * All rights reserved.
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 *
18 *   Redistributions of source code must retain the above copyright
19 *   notice, this list of conditions and the following disclaimer.
20 *
21 *   Redistributions in binary form must reproduce the above
22 *   copyright notice, this list of conditions and the following
23 *   disclaimer in the documentation and/or other materials provided
24 *   with the distribution.
25 *
26 *   Neither the name of the Cisco Systems, Inc. nor the names of its
27 *   contributors may be used to endorse or promote products derived
28 *   from this software without specific prior written permission.
29 *
30 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
31 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
32 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
33 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
34 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
35 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
36 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
37 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
38 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
41 * OF THE POSSIBILITY OF SUCH DAMAGE.
42 *
43 */
44
45#include "config.h"
46
47#ifdef DEV_URANDOM
48# include <fcntl.h>          /* for open()  */
49# include <unistd.h>         /* for close() */
50#elif defined(HAVE_RAND_S)
51# define _CRT_RAND_S
52# include <stdlib.h>
53#else
54# include <stdio.h>
55#endif
56
57#include "rand_source.h"
58
59
60/*
61 * global dev_rand_fdes is file descriptor for /dev/random
62 *
63 * This variable is also used to indicate that the random source has
64 * been initialized.  When this variable is set to the value of the
65 * #define RAND_SOURCE_NOT_READY, it indicates that the random source
66 * is not ready to be used.  The value of the #define
67 * RAND_SOURCE_READY is for use whenever that variable is used as an
68 * indicator of the state of the random source, but not as a file
69 * descriptor.
70 */
71
72#define RAND_SOURCE_NOT_READY (-1)
73#define RAND_SOURCE_READY     (17)
74
75static int dev_random_fdes = RAND_SOURCE_NOT_READY;
76
77
78err_status_t
79rand_source_init(void) {
80  if (dev_random_fdes >= 0) {
81    /* already open */
82    return err_status_ok;
83  }
84#ifdef DEV_URANDOM
85  /* open random source for reading */
86  dev_random_fdes = open(DEV_URANDOM, O_RDONLY);
87  if (dev_random_fdes < 0)
88    return err_status_init_fail;
89#elif defined(HAVE_RAND_S)
90  dev_random_fdes = RAND_SOURCE_READY;
91#else
92  /* no random source available; let the user know */
93  fprintf(stderr, "WARNING: no real random source present!\n");
94  dev_random_fdes = RAND_SOURCE_READY;
95#endif
96  return err_status_ok;
97}
98
99err_status_t
100rand_source_get_octet_string(void *dest, uint32_t len) {
101
102  /*
103   * read len octets from /dev/random to dest, and
104   * check return value to make sure enough octets were
105   * written
106   */
107#ifdef DEV_URANDOM
108  uint8_t *dst = (uint8_t *)dest;
109  while (len)
110  {
111    ssize_t num_read = read(dev_random_fdes, dst, len);
112    if (num_read <= 0 || num_read > len)
113      return err_status_fail;
114    len -= num_read;
115    dst += num_read;
116  }
117#elif defined(HAVE_RAND_S)
118  uint8_t *dst = (uint8_t *)dest;
119  while (len)
120  {
121    unsigned int val;
122    errno_t err = rand_s(&val);
123
124    if (err != 0)
125      return err_status_fail;
126
127    *dst++ = val & 0xff;
128    len--;
129  }
130#else
131  /* Generic C-library (rand()) version */
132  /* This is a random source of last resort */
133  uint8_t *dst = (uint8_t *)dest;
134  while (len)
135  {
136	  int val = rand();
137	  /* rand() returns 0-32767 (ugh) */
138	  /* Is this a good enough way to get random bytes?
139	     It is if it passes FIPS-140... */
140	  *dst++ = val & 0xff;
141	  len--;
142  }
143#endif
144  return err_status_ok;
145}
146
147err_status_t
148rand_source_deinit(void) {
149  if (dev_random_fdes < 0)
150    return err_status_dealloc_fail;  /* well, we haven't really failed, *
151				      * but there is something wrong    */
152#ifdef DEV_URANDOM
153  close(dev_random_fdes);
154#endif
155  dev_random_fdes = RAND_SOURCE_NOT_READY;
156
157  return err_status_ok;
158}
159