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      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 
     75 static int dev_random_fdes = RAND_SOURCE_NOT_READY;
     76 
     77 
     78 err_status_t
     79 rand_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 
     99 err_status_t
    100 rand_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   if (read(dev_random_fdes, dest, len) != len)
    109     return err_status_fail;
    110 #elif defined(HAVE_RAND_S)
    111   uint8_t *dst = (uint8_t *)dest;
    112   while (len)
    113   {
    114     unsigned int val;
    115     errno_t err = rand_s(&val);
    116 
    117     if (err != 0)
    118       return err_status_fail;
    119 
    120     *dst++ = val & 0xff;
    121     len--;
    122   }
    123 #else
    124   /* Generic C-library (rand()) version */
    125   /* This is a random source of last resort */
    126   uint8_t *dst = (uint8_t *)dest;
    127   while (len)
    128   {
    129 	  int val = rand();
    130 	  /* rand() returns 0-32767 (ugh) */
    131 	  /* Is this a good enough way to get random bytes?
    132 	     It is if it passes FIPS-140... */
    133 	  *dst++ = val & 0xff;
    134 	  len--;
    135   }
    136 #endif
    137   return err_status_ok;
    138 }
    139 
    140 err_status_t
    141 rand_source_deinit(void) {
    142   if (dev_random_fdes < 0)
    143     return err_status_dealloc_fail;  /* well, we haven't really failed, *
    144 				      * but there is something wrong    */
    145 #ifdef DEV_URANDOM
    146   close(dev_random_fdes);
    147 #endif
    148   dev_random_fdes = RAND_SOURCE_NOT_READY;
    149 
    150   return err_status_ok;
    151 }
    152