annotate random.c @ 224:1dbd2473482f DROPBEAR_0.46

* ... and a bit more for the CHANGES
author Matt Johnston <matt@ucc.asn.au>
date Fri, 08 Jul 2005 19:20:10 +0000
parents 65585699d980
children ca7e76d981d9 3be7ae2e8dfa
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1 /*
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2 * Dropbear - a SSH2 server
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3 *
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4 * Copyright (c) 2002,2003 Matt Johnston
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5 * All rights reserved.
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6 *
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7 * Permission is hereby granted, free of charge, to any person obtaining a copy
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8 * of this software and associated documentation files (the "Software"), to deal
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9 * in the Software without restriction, including without limitation the rights
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10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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11 * copies of the Software, and to permit persons to whom the Software is
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12 * furnished to do so, subject to the following conditions:
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13 *
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14 * The above copyright notice and this permission notice shall be included in
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15 * all copies or substantial portions of the Software.
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16 *
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17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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20 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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23 * SOFTWARE. */
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24
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25 #include "includes.h"
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26 #include "buffer.h"
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27 #include "dbutil.h"
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28 #include "bignum.h"
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29
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30 static int donerandinit = 0;
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31
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32 /* this is used to generate unique output from the same hashpool */
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33 static unsigned int counter = 0;
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34 #define MAX_COUNTER 1000000/* the max value for the counter, so it won't loop */
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36 static unsigned char hashpool[SHA1_HASH_SIZE];
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37
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38 #define INIT_SEED_SIZE 32 /* 256 bits */
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39
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40 static void readrand(unsigned char* buf, unsigned int buflen);
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41
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42 /* The basic setup is we read some data from /dev/(u)random or prngd and hash it
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43 * into hashpool. To read data, we hash together current hashpool contents,
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44 * and a counter. We feed more data in by hashing the current pool and new
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45 * data into the pool.
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46 *
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47 * It is important to ensure that counter doesn't wrap around before we
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48 * feed in new entropy.
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49 *
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50 */
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51
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52 static void readrand(unsigned char* buf, unsigned int buflen) {
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53
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54 static int already_blocked = 0;
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55 int readfd;
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56 unsigned int readpos;
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57 int readlen;
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58 #ifdef DROPBEAR_PRNGD_SOCKET
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59 struct sockaddr_un egdsock;
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60 char egdcmd[2];
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61 #endif
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62
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63 #ifdef DROPBEAR_RANDOM_DEV
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64 readfd = open(DROPBEAR_RANDOM_DEV, O_RDONLY);
70
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65 if (readfd < 0) {
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66 dropbear_exit("couldn't open random device");
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67 }
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68 #endif
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69
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70 #ifdef DROPBEAR_PRNGD_SOCKET
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71 memset((void*)&egdsock, 0x0, sizeof(egdsock));
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72 egdsock.sun_family = AF_UNIX;
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73 strlcpy(egdsock.sun_path, DROPBEAR_PRNGD_SOCKET,
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74 sizeof(egdsock.sun_path));
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75
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76 readfd = socket(PF_UNIX, SOCK_STREAM, 0);
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77 if (readfd < 0) {
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78 dropbear_exit("couldn't open random device");
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79 }
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80 /* todo - try various common locations */
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81 if (connect(readfd, (struct sockaddr*)&egdsock,
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82 sizeof(struct sockaddr_un)) < 0) {
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83 dropbear_exit("couldn't open random device");
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84 }
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85
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86 if (buflen > 255)
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87 dropbear_exit("can't request more than 255 bytes from egd");
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88 egdcmd[0] = 0x02; /* blocking read */
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89 egdcmd[1] = (unsigned char)buflen;
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90 if (write(readfd, egdcmd, 2) < 0)
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91 dropbear_exit("can't send command to egd");
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92 #endif
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93
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94 /* read the actual random data */
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95 readpos = 0;
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96 do {
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97 if (!already_blocked)
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98 {
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99 int ret;
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100 struct timeval timeout;
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101 fd_set read_fds;
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102
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103 timeout.tv_sec = 2; /* two seconds should be enough */
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104 timeout.tv_usec = 0;
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105
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106 FD_ZERO(&read_fds);
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107 FD_SET(readfd, &read_fds);
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108 ret = select(readfd + 1, &read_fds, NULL, NULL, &timeout);
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109 if (ret == 0)
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110 {
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111 dropbear_log(LOG_INFO, "Warning: Reading the random source seems to have blocked.\nIf you experience problems, you probably need to find a better entropy source.");
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112 already_blocked = 1;
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113 }
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114 }
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115 readlen = read(readfd, &buf[readpos], buflen - readpos);
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116 if (readlen <= 0) {
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117 if (readlen < 0 && errno == EINTR) {
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118 continue;
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119 }
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120 dropbear_exit("error reading random source");
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121 }
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122 readpos += readlen;
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123 } while (readpos < buflen);
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124
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125 close (readfd);
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126 }
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127
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128 /* initialise the prng from /dev/(u)random or prngd */
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129 void seedrandom() {
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130
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131 unsigned char readbuf[INIT_SEED_SIZE];
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132
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133 hash_state hs;
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134
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135 /* initialise so compilers will be happy about hashing it */
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136 if (!donerandinit) {
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137 m_burn(hashpool, sizeof(hashpool));
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138 }
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139
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140 /* get the seed data */
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141 readrand(readbuf, sizeof(readbuf));
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142
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143 /* hash in the new seed data */
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144 sha1_init(&hs);
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145 sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
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146 sha1_process(&hs, (void*)readbuf, sizeof(readbuf));
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147 sha1_done(&hs, hashpool);
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148
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149 counter = 0;
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150 donerandinit = 1;
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151 }
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152
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153 /* return len bytes of pseudo-random data */
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154 void genrandom(unsigned char* buf, unsigned int len) {
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155
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156 hash_state hs;
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157 unsigned char hash[SHA1_HASH_SIZE];
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158 unsigned int copylen;
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159
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160 if (!donerandinit) {
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161 dropbear_exit("seedrandom not done");
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162 }
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163
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164 while (len > 0) {
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165 sha1_init(&hs);
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166 sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
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167 sha1_process(&hs, (void*)&counter, sizeof(counter));
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168 sha1_done(&hs, hash);
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169
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170 counter++;
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171 if (counter > MAX_COUNTER) {
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172 seedrandom();
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173 }
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174
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175 copylen = MIN(len, SHA1_HASH_SIZE);
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176 memcpy(buf, hash, copylen);
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177 len -= copylen;
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178 buf += copylen;
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179 }
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180 m_burn(hash, sizeof(hash));
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181 }
188
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182
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183 /* Generates a random mp_int.
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184 * max is a *mp_int specifying an upper bound.
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185 * rand must be an initialised *mp_int for the result.
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186 * the result rand satisfies: 0 < rand < max
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187 * */
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188 void gen_random_mpint(mp_int *max, mp_int *rand) {
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189
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190 unsigned char *randbuf = NULL;
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191 unsigned int len = 0;
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192 const char masks[] = {0xff, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f};
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193
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194 const int size_bits = mp_count_bits(max);
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195
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196 len = size_bits / 8;
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197 if ((size_bits % 8) != 0) {
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198 len += 1;
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199 }
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200
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201 randbuf = (unsigned char*)m_malloc(len);
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202 do {
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203 genrandom(randbuf, len);
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204 /* Mask out the unrequired bits - mp_read_unsigned_bin expects
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205 * MSB first.*/
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206 randbuf[0] &= masks[size_bits % 8];
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207
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208 bytes_to_mp(rand, randbuf, len);
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209
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210 /* keep regenerating until we get one satisfying
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211 * 0 < rand < max */
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212 } while ( ( (max != NULL) && (mp_cmp(rand, max) != MP_LT) )
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213 || (mp_cmp_d(rand, 0) != MP_GT) );
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214 m_burn(randbuf, len);
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215 m_free(randbuf);
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216 }