crypt/md5-crypt.c

   1 /* One way encryption based on MD5 sum.
   2    Copyright (C) 1996, 1997, 1999 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <errno.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <sys/param.h>
  25
  26 #include "md5.h"
  27
  28
  29 /* Define our magic string to mark salt for MD5 "encryption"
  30    replacement.  This is meant to be the same as for other MD5 based
  31    encryption implementations.  */
  32 static const char md5_salt_prefix[] = "$1$";
  33
  34 /* Table with characters for base64 transformation.  */
  35 static const char b64t[64] =
  36 "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
  37
  38
  39 /* Prototypes for local functions.  */
  40 extern char *__md5_crypt_r __P ((const char *key, const char *salt,
  41                                  char *buffer, int buflen));
  42 extern char *__md5_crypt __P ((const char *key, const char *salt));
  43
  44
  45 /* This entry point is equivalent to the `crypt' function in Unix
  46    libcs.  */
  47 char *
  48 __md5_crypt_r (key, salt, buffer, buflen)
  49      const char *key;
  50      const char *salt;
  51      char *buffer;
  52      int buflen;
  53 {
  54   unsigned char alt_result[16];
  55   struct md5_ctx ctx;
  56   struct md5_ctx alt_ctx;
  57   size_t salt_len;
  58   size_t key_len;
  59   size_t cnt;
  60   char *cp;
  61
  62   /* Find beginning of salt string.  The prefix should normally always
  63      be present.  Just in case it is not.  */
  64   if (strncmp (md5_salt_prefix, salt, sizeof (md5_salt_prefix) - 1) == 0)
  65     /* Skip salt prefix.  */
  66     salt += sizeof (md5_salt_prefix) - 1;
  67
  68   salt_len = MIN (strcspn (salt, "$"), 8);
  69   key_len = strlen (key);
  70
  71   /* Prepare for the real work.  */
  72   __md5_init_ctx (&ctx);
  73
  74   /* Add the key string.  */
  75   __md5_process_bytes (key, key_len, &ctx);
  76
  77   /* Because the SALT argument need not always have the salt prefix we
  78      add it separately.  */
  79   __md5_process_bytes (md5_salt_prefix, sizeof (md5_salt_prefix) - 1, &ctx);
  80
  81   /* The last part is the salt string.  This must be at most 8
  82      characters and it ends at the first `$' character (for
  83      compatibility which existing solutions).  */
  84   __md5_process_bytes (salt, salt_len, &ctx);
  85
  86
  87   /* Compute alternate MD5 sum with input KEY, SALT, and KEY.  The
  88      final result will be added to the first context.  */
  89   __md5_init_ctx (&alt_ctx);
  90
  91   /* Add key.  */
  92   __md5_process_bytes (key, key_len, &alt_ctx);
  93
  94   /* Add salt.  */
  95   __md5_process_bytes (salt, salt_len, &alt_ctx);
  96
  97   /* Add key again.  */
  98   __md5_process_bytes (key, key_len, &alt_ctx);
  99
 100   /* Now get result of this (16 bytes) and add it to the other
 101      context.  */
 102   __md5_finish_ctx (&alt_ctx, alt_result);
 103
 104   /* Add for any character in the key one byte of the alternate sum.  */
 105   for (cnt = key_len; cnt > 16; cnt -= 16)
 106     __md5_process_bytes (alt_result, 16, &ctx);
 107   __md5_process_bytes (alt_result, cnt, &ctx);
 108
 109   /* For the following code we need a NUL byte.  */
 110   *alt_result = '\0';
 111
 112   /* The original implementation now does something weird: for every 1
 113      bit in the key the first 0 is added to the buffer, for every 0
 114      bit the first character of the key.  This does not seem to be
 115      what was intended but we have to follow this to be compatible.  */
 116   for (cnt = key_len; cnt > 0; cnt >>= 1)
 117     __md5_process_bytes ((cnt & 1) != 0 ? (const char *) alt_result : key, 1,
 118                          &ctx);
 119
 120   /* Create intermediate result.  */
 121   __md5_finish_ctx (&ctx, alt_result);
 122
 123   /* Now comes another weirdness.  In fear of password crackers here
 124      comes a quite long loop which just processes the output of the
 125      previous round again.  We cannot ignore this here.  */
 126   for (cnt = 0; cnt < 1000; ++cnt)
 127     {
 128       /* New context.  */
 129       __md5_init_ctx (&ctx);
 130
 131       /* Add key or last result.  */
 132       if ((cnt & 1) != 0)
 133         __md5_process_bytes (key, key_len, &ctx);
 134       else
 135         __md5_process_bytes (alt_result, 16, &ctx);
 136
 137       /* Add salt for numbers not divisible by 3.  */
 138       if (cnt % 3 != 0)
 139         __md5_process_bytes (salt, salt_len, &ctx);
 140
 141       /* Add key for numbers not divisible by 7.  */
 142       if (cnt % 7 != 0)
 143         __md5_process_bytes (key, key_len, &ctx);
 144
 145       /* Add key or last result.  */
 146       if ((cnt & 1) != 0)
 147         __md5_process_bytes (alt_result, 16, &ctx);
 148       else
 149         __md5_process_bytes (key, key_len, &ctx);
 150
 151       /* Create intermediate result.  */
 152       __md5_finish_ctx (&ctx, alt_result);
 153     }
 154
 155   /* Now we can construct the result string.  It consists of three
 156      parts.  */
 157   cp = __stpncpy (buffer, md5_salt_prefix, MAX (0, buflen));
 158   buflen -= sizeof (md5_salt_prefix);
 159
 160   cp = __stpncpy (cp, salt, MIN ((size_t) buflen, salt_len));
 161   buflen -= MIN ((size_t) buflen, salt_len);
 162
 163   if (buflen > 0)
 164     {
 165       *cp++ = '$';
 166       --buflen;
 167     }
 168
 169 #define b64_from_24bit(B2, B1, B0, N)                                         \
 170   do {                                                                        \
 171     unsigned int w = ((B2) << 16) | ((B1) << 8) | (B0);                       \
 172     int n = (N);                                                              \
 173     while (n-- > 0 && buflen > 0)                                             \
 174       {                                                                       \
 175         *cp++ = b64t[w & 0x3f];                                               \
 176         --buflen;                                                             \
 177         w >>= 6;                                                              \
 178       }                                                                       \
 179   } while (0)
 180
 181
 182   b64_from_24bit (alt_result[0], alt_result[6], alt_result[12], 4);
 183   b64_from_24bit (alt_result[1], alt_result[7], alt_result[13], 4);
 184   b64_from_24bit (alt_result[2], alt_result[8], alt_result[14], 4);
 185   b64_from_24bit (alt_result[3], alt_result[9], alt_result[15], 4);
 186   b64_from_24bit (alt_result[4], alt_result[10], alt_result[5], 4);
 187   b64_from_24bit (0, 0, alt_result[11], 2);
 188   if (buflen <= 0)
 189     {
 190       __set_errno (ERANGE);
 191       buffer = NULL;
 192     }
 193   else
 194     *cp = '\0';         /* Terminate the string.  */
 195
 196   /* Clear the buffer for the intermediate result so that people
 197      attaching to processes or reading core dumps cannot get any
 198      information.  */
 199   memset (alt_result, '\0', sizeof (alt_result));
 200
 201   return buffer;
 202 }
 203
 204
 205 char *
 206 __md5_crypt (const char *key, const char *salt)
 207 {
 208   /* We don't want to have an arbitrary limit in the size of the
 209      password.  We can compute the size of the result in advance and
 210      so we can prepare the buffer we pass to `md5_crypt_r'.  */
 211   static char *buffer = NULL;
 212   static int buflen = 0;
 213   int needed = 3 + strlen (salt) + 1 + 26 + 1;
 214
 215   if (buflen < needed)
 216     {
 217       buflen = needed;
 218       if ((buffer = realloc (buffer, buflen)) == NULL)
 219         return NULL;
 220     }
 221
 222   return __md5_crypt_r (key, salt, buffer, buflen);
 223 }