pkcs5.c

   1 /* pkcs5.c     Partial Password-Based Cryptography (PKCS#5) implementation
   2  * Copyright (C) 2002 Free Software Foundation, Inc.
   3  *
   4  * This file is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2.1 of the License, or (at your option) any later version.
   8  *
   9  * This file is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this file; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17  *
  18  */
  19
  20 #include <gcrypt.h>
  21
  22 /*
  23  * 5.2 PBKDF2
  24  *
  25  *  PBKDF2 applies a pseudorandom function (see Appendix B.1 for an
  26  *  example) to derive keys. The length of the derived key is essentially
  27  *  unbounded. (However, the maximum effective search space for the
  28  *  derived key may be limited by the structure of the underlying
  29  *  pseudorandom function. See Appendix B.1 for further discussion.)
  30  *  PBKDF2 is recommended for new applications.
  31  *
  32  *  PBKDF2 (P, S, c, dkLen)
  33  *
  34  *  Options:        PRF        underlying pseudorandom function (hLen
  35  *                             denotes the length in octets of the
  36  *                             pseudorandom function output)
  37  *
  38  *  Input:          P          password, an octet string
  39  *                  S          salt, an octet string
  40  *                  c          iteration count, a positive integer
  41  *                  dkLen      intended length in octets of the derived
  42  *                             key, a positive integer, at most
  43  *                             (2^32 - 1) * hLen
  44  *
  45  *  Output:         DK         derived key, a dkLen-octet string
  46  */
  47
  48 gpg_err_code_t
  49 gcry_pbkdf2 (int PRF, const char *P, size_t Plen, const char *S,
  50              size_t Slen, unsigned int c, unsigned int dkLen, char *DK)
  51 {
  52   gcry_md_hd_t prf;
  53   gcry_error_t maybeError;
  54   char *U;
  55   unsigned int u;
  56   unsigned int hLen;
  57   unsigned int l;
  58   unsigned int r;
  59   int rc;
  60   unsigned char *p;
  61   unsigned int i;
  62   unsigned int k;
  63
  64   hLen = gcry_md_get_algo_dlen (PRF);
  65   if (hLen == 0)
  66     return GPG_ERR_UNSUPPORTED_ALGORITHM;
  67
  68   if (c == 0)
  69     return GPG_ERR_INV_ARG;
  70
  71   if (dkLen == 0)
  72     return GPG_ERR_TOO_SHORT;
  73
  74   /*
  75    *
  76    *  Steps:
  77    *
  78    *     1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
  79    *        stop.
  80    */
  81
  82   if (dkLen > 4294967295U)
  83     return GPG_ERR_TOO_LARGE;
  84
  85   /*
  86    *     2. Let l be the number of hLen-octet blocks in the derived key,
  87    *        rounding up, and let r be the number of octets in the last
  88    *        block:
  89    *
  90    *                  l = CEIL (dkLen / hLen) ,
  91    *                  r = dkLen - (l - 1) * hLen .
  92    *
  93    *        Here, CEIL (x) is the "ceiling" function, i.e. the smallest
  94    *        integer greater than, or equal to, x.
  95    */
  96
  97   l = dkLen / hLen;
  98   if (dkLen % hLen)
  99     l++;
 100   r = dkLen - (l - 1) * hLen;
 101
 102   /*
 103    *     3. For each block of the derived key apply the function F defined
 104    *        below to the password P, the salt S, the iteration count c, and
 105    *        the block index to compute the block:
 106    *
 107    *                  T_1 = F (P, S, c, 1) ,
 108    *                  T_2 = F (P, S, c, 2) ,
 109    *                  ...
 110    *                  T_l = F (P, S, c, l) ,
 111    *
 112    *        where the function F is defined as the exclusive-or sum of the
 113    *        first c iterates of the underlying pseudorandom function PRF
 114    *        applied to the password P and the concatenation of the salt S
 115    *        and the block index i:
 116    *
 117    *                  F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
 118    *
 119    *        where
 120    *
 121    *                  U_1 = PRF (P, S || INT (i)) ,
 122    *                  U_2 = PRF (P, U_1) ,
 123    *                  ...
 124    *                  U_c = PRF (P, U_{c-1}) .
 125    *
 126    *        Here, INT (i) is a four-octet encoding of the integer i, most
 127    *        significant octet first.
 128    *
 129    *     4. Concatenate the blocks and extract the first dkLen octets to
 130    *        produce a derived key DK:
 131    *
 132    *                  DK = T_1 || T_2 ||  ...  || T_l<0..r-1>
 133    *
 134    *     5. Output the derived key DK.
 135    *
 136    *  Note. The construction of the function F follows a "belt-and-
 137    *  suspenders" approach. The iterates U_i are computed recursively to
 138    *  remove a degree of parallelism from an opponent; they are exclusive-
 139    *  ored together to reduce concerns about the recursion degenerating
 140    *  into a small set of values.
 141    *
 142    */
 143   maybeError = gcry_md_open (&prf, PRF, GCRY_MD_FLAG_HMAC | GCRY_MD_FLAG_SECURE);
 144   if (maybeError != GPG_ERR_NO_ERROR)
 145     return (-1 *maybeError);
 146
 147   U = (char*)gcry_malloc(hLen);
 148   if (!U)
 149     {
 150       rc = GPG_ERR_ENOMEM;
 151       goto done_nofree;
 152     }
 153
 154   for (i = 1; i <= l; i++)
 155     {
 156       memset(DK + (i - 1) * hLen, 0, i == l ? r : hLen);
 157
 158       for (u = 1; u <= c; u++)
 159        {
 160          gcry_md_reset (prf);
 161
 162          rc = gcry_md_setkey (prf, P, Plen);
 163          if (rc != GPG_ERR_NO_ERROR) {
 164            goto done;
 165          }
 166          if (u == 1)
 167            {
 168              char tmp[4];
 169              gcry_md_write (prf, S, Slen);
 170              tmp[0] = (i & 0xff000000) >> 24;
 171              tmp[1] = (i & 0x00ff0000) >> 16;
 172              tmp[2] = (i & 0x0000ff00) >> 8;
 173              tmp[3] = (i & 0x000000ff) >> 0;
 174              gcry_md_write (prf, tmp, 4);
 175            }
 176          else
 177            gcry_md_write (prf, U, hLen);
 178
 179          p = gcry_md_read (prf, PRF);
 180          if (p == NULL)
 181            {
 182              rc = GPG_ERR_CONFIGURATION;
 183              goto done;
 184           }
 185
 186          memcpy (U, p, hLen);
 187         for (k = 0; k < (i == l ? r : hLen); k++)
 188            DK[(i - 1) * hLen + k] ^= U[k];
 189        }
 190     }
 191
 192   rc = GPG_ERR_NO_ERROR;
 193  done_nofree:
 194   gcry_free(U);
 195  done:
 196   gcry_md_close (prf);
 197   return rc;
 198 }
 199