source4/lib/genrand.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    Functions to create reasonable random numbers for crypto use.
   5
   6    Copyright (C) Jeremy Allison 2001
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 2 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  21 */
  22
  23 #include "includes.h"
  24 #include "system/iconv.h"
  25 #include "system/filesys.h"
  26 #include "lib/crypto/crypto.h"
  27
  28 static unsigned char hash[258];
  29 static uint32_t counter;
  30
  31 static BOOL done_reseed = False;
  32 static void (*reseed_callback)(int *newseed);
  33
  34 /****************************************************************
  35  Copy any user given reseed data.
  36 *****************************************************************/
  37
  38 void set_rand_reseed_callback(void (*fn)(int *))
  39 {
  40         reseed_callback = fn;
  41         set_need_random_reseed();
  42 }
  43
  44 void set_need_random_reseed(void)
  45 {
  46         done_reseed = False;
  47 }
  48
  49 static void get_rand_reseed_data(int *reseed_data)
  50 {
  51         if (reseed_callback) {
  52                 reseed_callback(reseed_data);
  53         } else {
  54                 *reseed_data = 0;
  55         }
  56 }
  57
  58 /****************************************************************
  59  Setup the seed.
  60 *****************************************************************/
  61
  62 static void seed_random_stream(unsigned char *seedval, size_t seedlen)
  63 {
  64         unsigned char j = 0;
  65         size_t ind;
  66
  67         for (ind = 0; ind < 256; ind++)
  68                 hash[ind] = (unsigned char)ind;
  69
  70         for( ind = 0; ind < 256; ind++) {
  71                 unsigned char tc;
  72
  73                 j += (hash[ind] + seedval[ind%seedlen]);
  74
  75                 tc = hash[ind];
  76                 hash[ind] = hash[j];
  77                 hash[j] = tc;
  78         }
  79
  80         hash[256] = 0;
  81         hash[257] = 0;
  82 }
  83
  84 /****************************************************************
  85  Get datasize bytes worth of random data.
  86 *****************************************************************/
  87
  88 static void get_random_stream(unsigned char *data, size_t datasize)
  89 {
  90         unsigned char index_i = hash[256];
  91         unsigned char index_j = hash[257];
  92         size_t ind;
  93
  94         for( ind = 0; ind < datasize; ind++) {
  95                 unsigned char tc;
  96                 unsigned char t;
  97
  98                 index_i++;
  99                 index_j += hash[index_i];
 100
 101                 tc = hash[index_i];
 102                 hash[index_i] = hash[index_j];
 103                 hash[index_j] = tc;
 104
 105                 t = hash[index_i] + hash[index_j];
 106                 data[ind] = hash[t];
 107         }
 108
 109         hash[256] = index_i;
 110         hash[257] = index_j;
 111 }
 112
 113 /****************************************************************
 114  Get a 16 byte hash from the contents of a file.
 115
 116  Note that the hash is initialised, because the extra entropy is not
 117  worth the valgrind pain.
 118 *****************************************************************/
 119
 120 static void do_filehash(const char *fname, unsigned char *the_hash)
 121 {
 122         unsigned char buf[1011]; /* deliberate weird size */
 123         unsigned char tmp_md4[16];
 124         int fd, n;
 125
 126         ZERO_STRUCT(tmp_md4);
 127
 128         fd = open(fname,O_RDONLY,0);
 129         if (fd == -1)
 130                 return;
 131
 132         while ((n = read(fd, (char *)buf, sizeof(buf))) > 0) {
 133                 mdfour(tmp_md4, buf, n);
 134                 for (n=0;n<16;n++)
 135                         the_hash[n] ^= tmp_md4[n];
 136         }
 137         close(fd);
 138 }
 139
 140 /**************************************************************
 141  Try and get a good random number seed. Try a number of
 142  different factors. Firstly, try /dev/urandom - use if exists.
 143
 144  We use /dev/urandom as a read of /dev/random can block if
 145  the entropy pool dries up. This leads clients to timeout
 146  or be very slow on connect.
 147
 148  If we can't use /dev/urandom then seed the stream random generator
 149  above...
 150 **************************************************************/
 151
 152 static int do_reseed(BOOL use_fd, int fd)
 153 {
 154         unsigned char seed_inbuf[40];
 155         uint32_t v1, v2; struct timeval tval; pid_t mypid;
 156         int reseed_data = 0;
 157
 158         if (use_fd) {
 159                 if (fd != -1)
 160                         return fd;
 161
 162                 fd = open( "/dev/urandom", O_RDONLY,0);
 163                 if(fd >= 0)
 164                         return fd;
 165         }
 166
 167         /* Add in some secret file contents */
 168
 169         do_filehash("/etc/shadow", &seed_inbuf[0]);
 170
 171         /*
 172          * Add the counter, time of day, and pid.
 173          */
 174
 175         GetTimeOfDay(&tval);
 176         mypid = getpid();
 177         v1 = (counter++) + mypid + tval.tv_sec;
 178         v2 = (counter++) * mypid + tval.tv_usec;
 179
 180         SIVAL(seed_inbuf, 32, v1 ^ IVAL(seed_inbuf, 32));
 181         SIVAL(seed_inbuf, 36, v2 ^ IVAL(seed_inbuf, 36));
 182
 183         /*
 184          * Add any user-given reseed data.
 185          */
 186
 187         get_rand_reseed_data(&reseed_data);
 188         if (reseed_data) {
 189                 size_t i;
 190                 for (i = 0; i < sizeof(seed_inbuf); i++)
 191                         seed_inbuf[i] ^= ((char *)(&reseed_data))[i % sizeof(reseed_data)];
 192         }
 193
 194         seed_random_stream(seed_inbuf, sizeof(seed_inbuf));
 195
 196         return -1;
 197 }
 198
 199 /*
 200  Interface to the (hopefully) good crypto random number generator.
 201 */
 202 void generate_random_buffer(uint8_t *out, int len)
 203 {
 204         static int urand_fd = -1;
 205         unsigned char md4_buf[64];
 206         unsigned char tmp_buf[16];
 207         unsigned char *p;
 208
 209         if(!done_reseed) {
 210                 urand_fd = do_reseed(True, urand_fd);
 211                 done_reseed = True;
 212         }
 213
 214         if (urand_fd != -1 && len > 0) {
 215
 216                 if (read(urand_fd, out, len) == len)
 217                         return; /* len bytes of random data read from urandom. */
 218
 219                 /* Read of urand error, drop back to non urand method. */
 220                 close(urand_fd);
 221                 urand_fd = -1;
 222                 do_reseed(False, -1);
 223                 done_reseed = True;
 224         }
 225
 226         /*
 227          * Generate random numbers in chunks of 64 bytes,
 228          * then md4 them & copy to the output buffer.
 229          * This way the raw state of the stream is never externally
 230          * seen.
 231          */
 232
 233         p = out;
 234         while(len > 0) {
 235                 int copy_len = len > 16 ? 16 : len;
 236
 237                 get_random_stream(md4_buf, sizeof(md4_buf));
 238                 mdfour(tmp_buf, md4_buf, sizeof(md4_buf));
 239                 memcpy(p, tmp_buf, copy_len);
 240                 p += copy_len;
 241                 len -= copy_len;
 242         }
 243 }
 244
 245 /*
 246   generate a single random uint32_t
 247 */
 248 uint32_t generate_random(void)
 249 {
 250         uint8_t v[4];
 251         generate_random_buffer(v, 4);
 252         return IVAL(v, 0);
 253 }
 254
 255
 256 /*
 257   very basic password quality checker
 258 */
 259 BOOL check_password_quality(const char *s)
 260 {
 261         int has_digit=0, has_capital=0, has_lower=0;
 262         while (*s) {
 263                 if (isdigit((unsigned char)*s)) {
 264                         has_digit++;
 265                 } else if (isupper((unsigned char)*s)) {
 266                         has_capital++;
 267                 } else if (islower((unsigned char)*s)) {
 268                         has_lower++;
 269                 }
 270                 s++;
 271         }
 272
 273         return has_digit && has_lower && has_capital;
 274 }
 275
 276 /*******************************************************************
 277  Use the random number generator to generate a random string.
 278 ********************************************************************/
 279
 280 char *generate_random_str_list(TALLOC_CTX *mem_ctx, size_t len, const char *list)
 281 {
 282         size_t i;
 283         size_t list_len = strlen(list);
 284
 285         char *retstr = talloc_array(mem_ctx, char, len + 1);
 286         if (!retstr) return NULL;
 287
 288         generate_random_buffer((uint8_t *)retstr, len);
 289         for (i = 0; i < len; i++) {
 290                 retstr[i] = list[retstr[i] % list_len];
 291         }
 292         retstr[i] = '\0';
 293
 294         return retstr;
 295 }
 296
 297 char *generate_random_str(TALLOC_CTX *mem_ctx, size_t len)
 298 {
 299         char *retstr;
 300         const char *c_list = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,";
 301
 302 again:
 303         retstr = generate_random_str_list(mem_ctx, len, c_list);
 304         if (!retstr) return NULL;
 305
 306         /* we need to make sure the random string passes basic quality tests
 307            or it might be rejected by windows as a password */
 308         if (len >= 7 && !check_password_quality(retstr)) {
 309                 talloc_free(retstr);
 310                 goto again;
 311         }
 312
 313         return retstr;
 314 }