libcrypt/sha256-crypt.c

   1 /* One way encryption based on SHA256 sum.
   2    Copyright (C) 2007, 2009 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@redhat.com>, 2007.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the 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    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <stdbool.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/param.h>
  26
  27 #include "sha256.h"
  28 #include "libcrypt.h"
  29
  30 /* Define our magic string to mark salt for SHA256 "encryption"
  31    replacement.  */
  32 static const char sha256_salt_prefix[] = "$5$";
  33
  34 /* Prefix for optional rounds specification.  */
  35 static const char sha256_rounds_prefix[] = "rounds=";
  36
  37 /* Maximum salt string length.  */
  38 #define SALT_LEN_MAX 16
  39 /* Default number of rounds if not explicitly specified.  */
  40 #define ROUNDS_DEFAULT 5000
  41 /* Minimum number of rounds.  */
  42 #define ROUNDS_MIN 1000
  43 /* Maximum number of rounds.  */
  44 #define ROUNDS_MAX 999999999
  45
  46 /* Table with characters for base64 transformation.  */
  47 static const char b64t[64] =
  48 "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
  49
  50 #define B64_FROM_24BIT(b2, b1, b0, steps) \
  51         { \
  52                 int n = (steps); \
  53                 unsigned int w = ((b2) << 16) | ((b1) << 8) | (b0); \
  54                 while (n-- > 0 && buflen > 0) \
  55                 { \
  56                         *cp++ = b64t[w & 0x3f]; \
  57                         --buflen; \
  58                         w >>= 6; \
  59                 } \
  60         }
  61
  62 char *
  63 __sha256_crypt_r (const char *key,
  64      const char *salt,
  65      char *buffer,
  66      int buflen)
  67 {
  68   unsigned char alt_result[32]
  69     __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
  70   unsigned char temp_result[32]
  71     __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
  72   size_t salt_len;
  73   size_t key_len;
  74   size_t cnt;
  75   char *cp;
  76   char *copied_key = NULL;
  77   char *copied_salt = NULL;
  78   char *p_bytes;
  79   char *s_bytes;
  80   /* Default number of rounds.  */
  81   size_t rounds = ROUNDS_DEFAULT;
  82   bool rounds_custom = false;
  83
  84   /* Find beginning of salt string.  The prefix should normally always
  85      be present.  Just in case it is not.  */
  86   if (strncmp (sha256_salt_prefix, salt, sizeof (sha256_salt_prefix) - 1) == 0)
  87     /* Skip salt prefix.  */
  88     salt += sizeof (sha256_salt_prefix) - 1;
  89
  90   if (strncmp (salt, sha256_rounds_prefix, sizeof (sha256_rounds_prefix) - 1)
  91       == 0)
  92     {
  93       const char *num = salt + sizeof (sha256_rounds_prefix) - 1;
  94       char *endp;
  95       unsigned long int srounds = strtoul (num, &endp, 10);
  96       if (*endp == '$')
  97         {
  98           salt = endp + 1;
  99           rounds = MAX (ROUNDS_MIN, MIN (srounds, ROUNDS_MAX));
 100           rounds_custom = true;
 101         }
 102     }
 103
 104   salt_len = MIN (strcspn (salt, "$"), SALT_LEN_MAX);
 105   key_len = strlen (key);
 106
 107   if ((key - (char *) 0) % __alignof__ (uint32_t) != 0)
 108     {
 109       char *tmp = (char *) alloca (key_len + __alignof__ (uint32_t));
 110       key = copied_key =
 111         memcpy (tmp + __alignof__ (uint32_t)
 112                 - (tmp - (char *) 0) % __alignof__ (uint32_t),
 113                 key, key_len);
 114       assert ((key - (char *) 0) % __alignof__ (uint32_t) == 0);
 115     }
 116
 117   if ((salt - (char *) 0) % __alignof__ (uint32_t) != 0)
 118     {
 119       char *tmp = (char *) alloca (salt_len + __alignof__ (uint32_t));
 120       salt = copied_salt =
 121         memcpy (tmp + __alignof__ (uint32_t)
 122                 - (tmp - (char *) 0) % __alignof__ (uint32_t),
 123                 salt, salt_len);
 124       assert ((salt - (char *) 0) % __alignof__ (uint32_t) == 0);
 125     }
 126
 127   struct sha256_ctx ctx;
 128   struct sha256_ctx alt_ctx;
 129
 130   /* Prepare for the real work.  */
 131   __sha256_init_ctx (&ctx);
 132
 133   /* Add the key string.  */
 134   __sha256_process_bytes (key, key_len, &ctx);
 135
 136   /* The last part is the salt string.  This must be at most 16
 137      characters and it ends at the first `$' character.  */
 138   __sha256_process_bytes (salt, salt_len, &ctx);
 139
 140
 141   /* Compute alternate SHA256 sum with input KEY, SALT, and KEY.  The
 142      final result will be added to the first context.  */
 143   __sha256_init_ctx (&alt_ctx);
 144
 145   /* Add key.  */
 146   __sha256_process_bytes (key, key_len, &alt_ctx);
 147
 148   /* Add salt.  */
 149   __sha256_process_bytes (salt, salt_len, &alt_ctx);
 150
 151   /* Add key again.  */
 152   __sha256_process_bytes (key, key_len, &alt_ctx);
 153
 154   /* Now get result of this (32 bytes) and add it to the other
 155      context.  */
 156   __sha256_finish_ctx (&alt_ctx, alt_result);
 157
 158   /* Add for any character in the key one byte of the alternate sum.  */
 159   for (cnt = key_len; cnt > 32; cnt -= 32)
 160     __sha256_process_bytes (alt_result, 32, &ctx);
 161   __sha256_process_bytes (alt_result, cnt, &ctx);
 162
 163   /* Take the binary representation of the length of the key and for every
 164      1 add the alternate sum, for every 0 the key.  */
 165   for (cnt = key_len; cnt > 0; cnt >>= 1)
 166     if ((cnt & 1) != 0)
 167       __sha256_process_bytes (alt_result, 32, &ctx);
 168     else
 169       __sha256_process_bytes (key, key_len, &ctx);
 170
 171   /* Create intermediate result.  */
 172   __sha256_finish_ctx (&ctx, alt_result);
 173
 174   /* Start computation of P byte sequence.  */
 175   __sha256_init_ctx (&alt_ctx);
 176
 177   /* For every character in the password add the entire password.  */
 178   for (cnt = 0; cnt < key_len; ++cnt)
 179     __sha256_process_bytes (key, key_len, &alt_ctx);
 180
 181   /* Finish the digest.  */
 182   __sha256_finish_ctx (&alt_ctx, temp_result);
 183
 184   /* Create byte sequence P.  */
 185   cp = p_bytes = alloca (key_len);
 186   for (cnt = key_len; cnt >= 32; cnt -= 32)
 187     cp = mempcpy (cp, temp_result, 32);
 188   memcpy (cp, temp_result, cnt);
 189
 190   /* Start computation of S byte sequence.  */
 191   __sha256_init_ctx (&alt_ctx);
 192
 193   /* For every character in the password add the entire password.  */
 194   for (cnt = 0; cnt < 16 + alt_result[0]; ++cnt)
 195     __sha256_process_bytes (salt, salt_len, &alt_ctx);
 196
 197   /* Finish the digest.  */
 198   __sha256_finish_ctx (&alt_ctx, temp_result);
 199
 200   /* Create byte sequence S.  */
 201   cp = s_bytes = alloca (salt_len);
 202   for (cnt = salt_len; cnt >= 32; cnt -= 32)
 203     cp = mempcpy (cp, temp_result, 32);
 204   memcpy (cp, temp_result, cnt);
 205
 206   /* Repeatedly run the collected hash value through SHA256 to burn
 207      CPU cycles.  */
 208   for (cnt = 0; cnt < rounds; ++cnt)
 209     {
 210       /* New context.  */
 211       __sha256_init_ctx (&ctx);
 212
 213       /* Add key or last result.  */
 214       if ((cnt & 1) != 0)
 215         __sha256_process_bytes (p_bytes, key_len, &ctx);
 216       else
 217         __sha256_process_bytes (alt_result, 32, &ctx);
 218
 219       /* Add salt for numbers not divisible by 3.  */
 220       if (cnt % 3 != 0)
 221         __sha256_process_bytes (s_bytes, salt_len, &ctx);
 222
 223       /* Add key for numbers not divisible by 7.  */
 224       if (cnt % 7 != 0)
 225         __sha256_process_bytes (p_bytes, key_len, &ctx);
 226
 227       /* Add key or last result.  */
 228       if ((cnt & 1) != 0)
 229         __sha256_process_bytes (alt_result, 32, &ctx);
 230       else
 231         __sha256_process_bytes (p_bytes, key_len, &ctx);
 232
 233       /* Create intermediate result.  */
 234       __sha256_finish_ctx (&ctx, alt_result);
 235     }
 236
 237   /* Now we can construct the result string.  It consists of three
 238      parts.  */
 239   cp = stpncpy (buffer, sha256_salt_prefix, MAX (0, buflen));
 240   buflen -= sizeof (sha256_salt_prefix) - 1;
 241
 242   if (rounds_custom)
 243     {
 244       int n = snprintf (cp, MAX (0, buflen), "%s%zu$",
 245                         sha256_rounds_prefix, rounds);
 246       cp += n;
 247       buflen -= n;
 248     }
 249
 250   cp = stpncpy (cp, salt, MIN ((size_t) MAX (0, buflen), salt_len));
 251   buflen -= MIN ((size_t) MAX (0, buflen), salt_len);
 252
 253   if (buflen > 0)
 254     {
 255       *cp++ = '$';
 256       --buflen;
 257     }
 258
 259   B64_FROM_24BIT (alt_result[0], alt_result[10], alt_result[20], 4);
 260   B64_FROM_24BIT (alt_result[21], alt_result[1], alt_result[11], 4);
 261   B64_FROM_24BIT (alt_result[12], alt_result[22], alt_result[2], 4);
 262   B64_FROM_24BIT (alt_result[3], alt_result[13], alt_result[23], 4);
 263   B64_FROM_24BIT (alt_result[24], alt_result[4], alt_result[14], 4);
 264   B64_FROM_24BIT (alt_result[15], alt_result[25], alt_result[5], 4);
 265   B64_FROM_24BIT (alt_result[6], alt_result[16], alt_result[26], 4);
 266   B64_FROM_24BIT (alt_result[27], alt_result[7], alt_result[17], 4);
 267   B64_FROM_24BIT (alt_result[18], alt_result[28], alt_result[8], 4);
 268   B64_FROM_24BIT (alt_result[9], alt_result[19], alt_result[29], 4);
 269   B64_FROM_24BIT (0, alt_result[31], alt_result[30], 3);
 270   if (buflen <= 0)
 271     {
 272       __set_errno (ERANGE);
 273       buffer = NULL;
 274     }
 275   else
 276     *cp = '\0';         /* Terminate the string.  */
 277
 278   /* Clear the buffer for the intermediate result so that people
 279      attaching to processes or reading core dumps cannot get any
 280      information.  We do it in this way to clear correct_words[]
 281      inside the SHA256 implementation as well.  */
 282   __sha256_init_ctx (&ctx);
 283   __sha256_finish_ctx (&ctx, alt_result);
 284   memset (&ctx, '\0', sizeof (ctx));
 285   memset (&alt_ctx, '\0', sizeof (alt_ctx));
 286
 287   memset (temp_result, '\0', sizeof (temp_result));
 288   memset (p_bytes, '\0', key_len);
 289   memset (s_bytes, '\0', salt_len);
 290   if (copied_key != NULL)
 291     memset (copied_key, '\0', key_len);
 292   if (copied_salt != NULL)
 293     memset (copied_salt, '\0', salt_len);
 294
 295   return buffer;
 296 }
 297
 298 static char *buffer;
 299
 300 /* This entry point is equivalent to the `crypt' function in Unix
 301    libcs.  */
 302 char *
 303 __sha256_crypt (const unsigned char *key, const unsigned char *salt)
 304 {
 305   /* We don't want to have an arbitrary limit in the size of the
 306      password.  We can compute an upper bound for the size of the
 307      result in advance and so we can prepare the buffer we pass to
 308      `sha256_crypt_r'.  */
 309   static int buflen;
 310   int needed = (sizeof (sha256_salt_prefix) - 1
 311                 + sizeof (sha256_rounds_prefix) + 9 + 1
 312                 + strlen (salt) + 1 + 43 + 1);
 313
 314   if (buflen < needed)
 315     {
 316       char *new_buffer = (char *) realloc (buffer, needed);
 317       if (new_buffer == NULL)
 318         return NULL;
 319
 320       buffer = new_buffer;
 321       buflen = needed;
 322     }
 323
 324   return __sha256_crypt_r ((const char *) key, (const char *) salt, buffer, buflen);
 325 }