kadmin/random_password.c

   1 /*
   2  * Copyright (c) 1998, 1999 Kungliga Tekniska Högskolan
   3  * (Royal Institute of Technology, Stockholm, Sweden).
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  *
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * 3. Neither the name of the Institute nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 #include "kadmin_locl.h"
  35
  36 /* This file defines some a function that generates a random password,
  37    that can be used when creating a large amount of principals (such
  38    as for a batch of students). Since this is a political matter, you
  39    should think about how secure generated passwords has to be.
  40
  41    Both methods defined here will give you at least 55 bits of
  42    entropy.
  43    */
  44
  45 /* If you want OTP-style passwords, define OTP_STYLE */
  46
  47 #ifdef OTP_STYLE
  48 #include <otp.h>
  49 #else
  50 static void generate_password(char **pw, int num_classes, ...);
  51 #endif
  52
  53 void
  54 random_password(char *pw, size_t len)
  55 {
  56 #ifdef OTP_STYLE
  57     {
  58         OtpKey newkey;
  59
  60         krb5_generate_random_block(&newkey, sizeof(newkey));
  61         otp_print_stddict (newkey, pw, len);
  62         strlwr(pw);
  63     }
  64 #else
  65     char *pass;
  66     generate_password(&pass, 3,
  67                       "abcdefghijklmnopqrstuvwxyz", 7,
  68                       "ABCDEFGHIJKLMNOPQRSTUVWXYZ", 2,
  69                       "@$%&*()-+=:,/<>1234567890", 1);
  70     strlcpy(pw, pass, len);
  71     len = strlen(pass);
  72     memset_s(pass, len, 0, len);
  73     free(pass);
  74 #endif
  75 }
  76
  77 /* some helper functions */
  78
  79 #ifndef OTP_STYLE
  80 /* return a random value in range 0-127 */
  81 static int
  82 RND(unsigned char *key, int keylen, int *left)
  83 {
  84     if(*left == 0){
  85         krb5_generate_random_block(key, keylen);
  86         *left = keylen;
  87     }
  88     (*left)--;
  89     return ((unsigned char*)key)[*left];
  90 }
  91
  92 /* This a helper function that generates a random password with a
  93    number of characters from a set of character classes.
  94
  95    If there are n classes, and the size of each class is Pi, and the
  96    number of characters from each class is Ni, the number of possible
  97    passwords are (given that the character classes are disjoint):
  98
  99      n             n
 100    -----        /  ----  \
 101    |   |  Ni    |  \     |
 102    |   | Pi     |   \  Ni| !
 103    |   | ---- * |   /    |
 104    |   | Ni!    |  /___  |
 105     i=1          \  i=1  /
 106
 107     Since it uses the RND function above, neither the size of each
 108     class, nor the total length of the generated password should be
 109     larger than 127 (without fixing RND).
 110
 111    */
 112 static void
 113 generate_password(char **pw, int num_classes, ...)
 114 {
 115     struct {
 116         const char *str;
 117         int len;
 118         int freq;
 119     } *classes;
 120     va_list ap;
 121     int len, i;
 122     unsigned char rbuf[8]; /* random buffer */
 123     int rleft = 0;
 124
 125     *pw = NULL;
 126
 127     classes = malloc(num_classes * sizeof(*classes));
 128     if(classes == NULL)
 129         return;
 130     va_start(ap, num_classes);
 131     len = 0;
 132     for(i = 0; i < num_classes; i++){
 133         classes[i].str = va_arg(ap, const char*);
 134         classes[i].len = strlen(classes[i].str);
 135         classes[i].freq = va_arg(ap, int);
 136         len += classes[i].freq;
 137     }
 138     va_end(ap);
 139     *pw = malloc(len + 1);
 140     if(*pw == NULL) {
 141         free(classes);
 142         return;
 143     }
 144     for(i = 0; i < len; i++) {
 145         int j;
 146         int x = RND(rbuf, sizeof(rbuf), &rleft) % (len - i);
 147         int t = 0;
 148         for(j = 0; j < num_classes; j++) {
 149             if(x < t + classes[j].freq) {
 150                 (*pw)[i] = classes[j].str[RND(rbuf, sizeof(rbuf), &rleft)
 151                                          % classes[j].len];
 152                 classes[j].freq--;
 153                 break;
 154             }
 155             t += classes[j].freq;
 156         }
 157     }
 158     (*pw)[len] = '\0';
 159     memset_s(rbuf, sizeof(rbuf), 0, sizeof(rbuf));
 160     free(classes);
 161 }
 162 #endif