crypt/sha256-crypt.c

   1 /* One way encryption based on SHA256 sum.
   2    Copyright (C) 2007 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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <assert.h>
  22 #include <errno.h>
  23 #include <stdbool.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <sys/param.h>
  27
  28 #include "sha256.h"
  29
  30
  31 /* Define our magic string to mark salt for SHA256 "encryption"
  32    replacement.  */
  33 static const char sha256_salt_prefix[] = "$5$";
  34
  35 /* Prefix for optional rounds specification.  */
  36 static const char sha256_rounds_prefix[] = "rounds=";
  37
  38 /* Maximum salt string length.  */
  39 #define SALT_LEN_MAX 16
  40 /* Default number of rounds if not explicitly specified.  */
  41 #define ROUNDS_DEFAULT 5000
  42 /* Minimum number of rounds.  */
  43 #define ROUNDS_MIN 1000
  44 /* Maximum number of rounds.  */
  45 #define ROUNDS_MAX 999999999
  46
  47 /* Table with characters for base64 transformation.  */
  48 static const char b64t[64] =
  49 "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
  50
  51
  52 /* Prototypes for local functions.  */
  53 extern char *__sha256_crypt_r (const char *key, const char *salt,
  54                                char *buffer, int buflen);
  55 extern char *__sha256_crypt (const char *key, const char *salt);
  56
  57
  58 char *
  59 __sha256_crypt_r (key, salt, buffer, buflen)
  60      const char *key;
  61      const char *salt;
  62      char *buffer;
  63      int buflen;
  64 {
  65   unsigned char alt_result[32]
  66     __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
  67   unsigned char temp_result[32]
  68     __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
  69   struct sha256_ctx ctx;
  70   struct sha256_ctx alt_ctx;
  71   size_t salt_len;
  72   size_t key_len;
  73   size_t cnt;
  74   char *cp;
  75   char *copied_key = NULL;
  76   char *copied_salt = NULL;
  77   char *p_bytes;
  78   char *s_bytes;
  79   /* Default number of rounds.  */
  80   size_t rounds = ROUNDS_DEFAULT;
  81   bool rounds_custom = false;
  82
  83   /* Find beginning of salt string.  The prefix should normally always
  84      be present.  Just in case it is not.  */
  85   if (strncmp (sha256_salt_prefix, salt, sizeof (sha256_salt_prefix) - 1) == 0)
  86     /* Skip salt prefix.  */
  87     salt += sizeof (sha256_salt_prefix) - 1;
  88
  89   if (strncmp (salt, sha256_rounds_prefix, sizeof (sha256_rounds_prefix) - 1)
  90       == 0)
  91     {
  92       const char *num = salt + sizeof (sha256_rounds_prefix) - 1;
  93       char *endp;
  94       unsigned long int srounds = strtoul (num, &endp, 10);
  95       if (*endp == '$')
  96         {
  97           salt = endp + 1;
  98           rounds = MAX (ROUNDS_MIN, MIN (srounds, ROUNDS_MAX));
  99           rounds_custom = true;
 100         }
 101     }
 102
 103   salt_len = MIN (strcspn (salt, "$"), SALT_LEN_MAX);
 104   key_len = strlen (key);
 105
 106   if ((key - (char *) 0) % __alignof__ (uint32_t) != 0)
 107     {
 108       char *tmp = (char *) alloca (key_len + __alignof__ (uint32_t));
 109       key = copied_key =
 110         memcpy (tmp + __alignof__ (uint32_t)
 111                 - (tmp - (char *) 0) % __alignof__ (uint32_t),
 112                 key, key_len);
 113       assert ((key - (char *) 0) % __alignof__ (uint32_t) == 0);
 114     }
 115
 116   if ((salt - (char *) 0) % __alignof__ (uint32_t) != 0)
 117     {
 118       char *tmp = (char *) alloca (salt_len + __alignof__ (uint32_t));
 119       salt = copied_salt =
 120         memcpy (tmp + __alignof__ (uint32_t)
 121                 - (tmp - (char *) 0) % __alignof__ (uint32_t),
 122                 salt, salt_len);
 123       assert ((salt - (char *) 0) % __alignof__ (uint32_t) == 0);
 124     }
 125
 126   /* Prepare for the real work.  */
 127   __sha256_init_ctx (&ctx);
 128
 129   /* Add the key string.  */
 130   __sha256_process_bytes (key, key_len, &ctx);
 131
 132   /* The last part is the salt string.  This must be at most 8
 133      characters and it ends at the first `$' character (for
 134      compatibility with existing implementations).  */
 135   __sha256_process_bytes (salt, salt_len, &ctx);
 136
 137
 138   /* Compute alternate SHA256 sum with input KEY, SALT, and KEY.  The
 139      final result will be added to the first context.  */
 140   __sha256_init_ctx (&alt_ctx);
 141
 142   /* Add key.  */
 143   __sha256_process_bytes (key, key_len, &alt_ctx);
 144
 145   /* Add salt.  */
 146   __sha256_process_bytes (salt, salt_len, &alt_ctx);
 147
 148   /* Add key again.  */
 149   __sha256_process_bytes (key, key_len, &alt_ctx);
 150
 151   /* Now get result of this (32 bytes) and add it to the other
 152      context.  */
 153   __sha256_finish_ctx (&alt_ctx, alt_result);
 154
 155   /* Add for any character in the key one byte of the alternate sum.  */
 156   for (cnt = key_len; cnt > 32; cnt -= 32)
 157     __sha256_process_bytes (alt_result, 32, &ctx);
 158   __sha256_process_bytes (alt_result, cnt, &ctx);
 159
 160   /* Take the binary representation of the length of the key and for every
 161      1 add the alternate sum, for every 0 the key.  */
 162   for (cnt = key_len; cnt > 0; cnt >>= 1)
 163     if ((cnt & 1) != 0)
 164       __sha256_process_bytes (alt_result, 32, &ctx);
 165     else
 166       __sha256_process_bytes (key, key_len, &ctx);
 167
 168   /* Create intermediate result.  */
 169   __sha256_finish_ctx (&ctx, alt_result);
 170
 171   /* Start computation of P byte sequence.  */
 172   __sha256_init_ctx (&alt_ctx);
 173
 174   /* For every character in the password add the entire password.  */
 175   for (cnt = 0; cnt < key_len; ++cnt)
 176     __sha256_process_bytes (key, key_len, &alt_ctx);
 177
 178   /* Finish the digest.  */
 179   __sha256_finish_ctx (&alt_ctx, temp_result);
 180
 181   /* Create byte sequence P.  */
 182   cp = p_bytes = alloca (key_len);
 183   for (cnt = key_len; cnt >= 32; cnt -= 32)
 184     cp = mempcpy (cp, temp_result, 32);
 185   memcpy (cp, temp_result, cnt);
 186
 187   /* Start computation of S byte sequence.  */
 188   __sha256_init_ctx (&alt_ctx);
 189
 190   /* For every character in the password add the entire password.  */
 191   for (cnt = 0; cnt < 16 + alt_result[0]; ++cnt)
 192     __sha256_process_bytes (salt, salt_len, &alt_ctx);
 193
 194   /* Finish the digest.  */
 195   __sha256_finish_ctx (&alt_ctx, temp_result);
 196
 197   /* Create byte sequence S.  */
 198   cp = s_bytes = alloca (salt_len);
 199   for (cnt = salt_len; cnt >= 32; cnt -= 32)
 200     cp = mempcpy (cp, temp_result, 32);
 201   memcpy (cp, temp_result, cnt);
 202
 203   /* Repeatedly run the collected hash value through SHA256 to burn
 204      CPU cycles.  */
 205   for (cnt = 0; cnt < rounds; ++cnt)
 206     {
 207       /* New context.  */
 208       __sha256_init_ctx (&ctx);
 209
 210       /* Add key or last result.  */
 211       if ((cnt & 1) != 0)
 212         __sha256_process_bytes (p_bytes, key_len, &ctx);
 213       else
 214         __sha256_process_bytes (alt_result, 32, &ctx);
 215
 216       /* Add salt for numbers not divisible by 3.  */
 217       if (cnt % 3 != 0)
 218         __sha256_process_bytes (s_bytes, salt_len, &ctx);
 219
 220       /* Add key for numbers not divisible by 7.  */
 221       if (cnt % 7 != 0)
 222         __sha256_process_bytes (p_bytes, key_len, &ctx);
 223
 224       /* Add key or last result.  */
 225       if ((cnt & 1) != 0)
 226         __sha256_process_bytes (alt_result, 32, &ctx);
 227       else
 228         __sha256_process_bytes (p_bytes, key_len, &ctx);
 229
 230       /* Create intermediate result.  */
 231       __sha256_finish_ctx (&ctx, alt_result);
 232     }
 233
 234   /* Now we can construct the result string.  It consists of three
 235      parts.  */
 236   cp = __stpncpy (buffer, sha256_salt_prefix, MAX (0, buflen));
 237   buflen -= sizeof (sha256_salt_prefix) - 1;
 238
 239   if (rounds_custom)
 240     {
 241       int n = snprintf (cp, MAX (0, buflen), "%s%zu$",
 242                         sha256_rounds_prefix, rounds);
 243       cp += n;
 244       buflen -= n;
 245     }
 246
 247   cp = __stpncpy (cp, salt, MIN ((size_t) MAX (0, buflen), salt_len));
 248   buflen -= MIN ((size_t) MAX (0, buflen), salt_len);
 249
 250   if (buflen > 0)
 251     {
 252       *cp++ = '$';
 253       --buflen;
 254     }
 255
 256 #define b64_from_24bit(B2, B1, B0, N)                                         \
 257   do {                                                                        \
 258     unsigned int w = ((B2) << 16) | ((B1) << 8) | (B0);                       \
 259     int n = (N);                                                              \
 260     while (n-- > 0 && buflen > 0)                                             \
 261       {                                                                       \
 262         *cp++ = b64t[w & 0x3f];                                               \
 263         --buflen;                                                             \
 264         w >>= 6;                                                              \
 265       }                                                                       \
 266   } while (0)
 267
 268   b64_from_24bit (alt_result[0], alt_result[10], alt_result[20], 4);
 269   b64_from_24bit (alt_result[21], alt_result[1], alt_result[11], 4);
 270   b64_from_24bit (alt_result[12], alt_result[22], alt_result[2], 4);
 271   b64_from_24bit (alt_result[3], alt_result[13], alt_result[23], 4);
 272   b64_from_24bit (alt_result[24], alt_result[4], alt_result[14], 4);
 273   b64_from_24bit (alt_result[15], alt_result[25], alt_result[5], 4);
 274   b64_from_24bit (alt_result[6], alt_result[16], alt_result[26], 4);
 275   b64_from_24bit (alt_result[27], alt_result[7], alt_result[17], 4);
 276   b64_from_24bit (alt_result[18], alt_result[28], alt_result[8], 4);
 277   b64_from_24bit (alt_result[9], alt_result[19], alt_result[29], 4);
 278   b64_from_24bit (0, alt_result[31], alt_result[30], 3);
 279   if (buflen <= 0)
 280     {
 281       __set_errno (ERANGE);
 282       buffer = NULL;
 283     }
 284   else
 285     *cp = '\0';         /* Terminate the string.  */
 286
 287   /* Clear the buffer for the intermediate result so that people
 288      attaching to processes or reading core dumps cannot get any
 289      information.  We do it in this way to clear correct_words[]
 290      inside the SHA256 implementation as well.  */
 291   __sha256_init_ctx (&ctx);
 292   __sha256_finish_ctx (&ctx, alt_result);
 293   memset (temp_result, '\0', sizeof (temp_result));
 294   memset (p_bytes, '\0', key_len);
 295   memset (s_bytes, '\0', salt_len);
 296   memset (&ctx, '\0', sizeof (ctx));
 297   memset (&alt_ctx, '\0', sizeof (alt_ctx));
 298   if (copied_key != NULL)
 299     memset (copied_key, '\0', key_len);
 300   if (copied_salt != NULL)
 301     memset (copied_salt, '\0', salt_len);
 302
 303   return buffer;
 304 }
 305
 306 #ifndef _LIBC
 307 # define libc_freeres_ptr(decl) decl
 308 #endif
 309 libc_freeres_ptr (static char *buffer);
 310
 311 /* This entry point is equivalent to the `crypt' function in Unix
 312    libcs.  */
 313 char *
 314 __sha256_crypt (const char *key, const char *salt)
 315 {
 316   /* We don't want to have an arbitrary limit in the size of the
 317      password.  We can compute an upper bound for the size of the
 318      result in advance and so we can prepare the buffer we pass to
 319      `sha256_crypt_r'.  */
 320   static int buflen;
 321   int needed = (sizeof (sha256_salt_prefix) - 1
 322                 + sizeof (sha256_rounds_prefix) + 9 + 1
 323                 + strlen (salt) + 1 + 43 + 1);
 324
 325   if (buflen < needed)
 326     {
 327       char *new_buffer = (char *) realloc (buffer, needed);
 328       if (new_buffer == NULL)
 329         return NULL;
 330
 331       buffer = new_buffer;
 332       buflen = needed;
 333     }
 334
 335   return __sha256_crypt_r (key, salt, buffer, buflen);
 336 }
 337
 338 #ifndef _LIBC
 339 static void
 340 __attribute__ ((__destructor__))
 341 free_mem (void)
 342 {
 343   free (buffer);
 344 }
 345 #endif