lib/x509/pbkdf2-sha1.c

   1 /* gc-pbkdf2-sha1.c --- Password-Based Key Derivation Function a'la PKCS#5
   2    Copyright (C) 2002-2012 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as published by
   6    the Free Software Foundation; either version 3, or (at your option)
   7    any later version.
   8
   9    This program 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
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>
  16
  17 */
  18
  19 /* Written by Simon Josefsson.  The comments in this file are taken
  20    from RFC 2898.  */
  21
  22 #include <gnutls_int.h>
  23 #include <gnutls_datum.h>
  24 #include <gnutls_errors.h>
  25 #include <gnutls_hash_int.h>
  26 #include <pbkdf2-sha1.h>
  27
  28 /*
  29  * 5.2 PBKDF2
  30  *
  31  *  PBKDF2 applies a pseudorandom function (see Appendix B.1 for an
  32  *  example) to derive keys. The length of the derived key is essentially
  33  *  unbounded. (However, the maximum effective search space for the
  34  *  derived key may be limited by the structure of the underlying
  35  *  pseudorandom function. See Appendix B.1 for further discussion.)
  36  *  PBKDF2 is recommended for new applications.
  37  *
  38  *  PBKDF2 (P, S, c, dkLen)
  39  *
  40  *  Options:        PRF        underlying pseudorandom function (hLen
  41  *                             denotes the length in octets of the
  42  *                             pseudorandom function output)
  43  *
  44  *  Input:          P          password, an octet string (ASCII or UTF-8)
  45  *                  S          salt, an octet string
  46  *                  c          iteration count, a positive integer
  47  *                  dkLen      intended length in octets of the derived
  48  *                             key, a positive integer, at most
  49  *                             (2^32 - 1) * hLen
  50  *
  51  *  Output:         DK         derived key, a dkLen-octet string
  52  */
  53
  54 int
  55 _gnutls_pbkdf2_sha1 (const char *P, size_t Plen,
  56                      const unsigned char *S, size_t Slen,
  57                      unsigned int c, unsigned char *DK, size_t dkLen)
  58 {
  59   unsigned int hLen = 20;
  60   char U[20];
  61   char T[20];
  62   unsigned int u;
  63   unsigned int l;
  64   unsigned int r;
  65   unsigned int i;
  66   unsigned int k;
  67   int rc;
  68   char *tmp;
  69   size_t tmplen = Slen + 4;
  70
  71   if (c == 0)
  72     {
  73       gnutls_assert ();
  74       return GNUTLS_E_INVALID_REQUEST;
  75     }
  76
  77   if (dkLen == 0)
  78     {
  79       gnutls_assert ();
  80       return GNUTLS_E_INVALID_REQUEST;
  81     }
  82   /*
  83    *
  84    *  Steps:
  85    *
  86    *     1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
  87    *        stop.
  88    */
  89
  90   if (dkLen > 4294967295U)
  91     {
  92       gnutls_assert ();
  93       return GNUTLS_E_INVALID_REQUEST;
  94     }
  95
  96   /*
  97    *     2. Let l be the number of hLen-octet blocks in the derived key,
  98    *        rounding up, and let r be the number of octets in the last
  99    *        block:
 100    *
 101    *                  l = CEIL (dkLen / hLen) ,
 102    *                  r = dkLen - (l - 1) * hLen .
 103    *
 104    *        Here, CEIL (x) is the "ceiling" function, i.e. the smallest
 105    *        integer greater than, or equal to, x.
 106    */
 107
 108   l = ((dkLen - 1) / hLen) + 1;
 109   r = dkLen - (l - 1) * hLen;
 110
 111   /*
 112    *     3. For each block of the derived key apply the function F defined
 113    *        below to the password P, the salt S, the iteration count c, and
 114    *        the block index to compute the block:
 115    *
 116    *                  T_1 = F (P, S, c, 1) ,
 117    *                  T_2 = F (P, S, c, 2) ,
 118    *                  ...
 119    *                  T_l = F (P, S, c, l) ,
 120    *
 121    *        where the function F is defined as the exclusive-or sum of the
 122    *        first c iterates of the underlying pseudorandom function PRF
 123    *        applied to the password P and the concatenation of the salt S
 124    *        and the block index i:
 125    *
 126    *                  F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
 127    *
 128    *        where
 129    *
 130    *                  U_1 = PRF (P, S || INT (i)) ,
 131    *                  U_2 = PRF (P, U_1) ,
 132    *                  ...
 133    *                  U_c = PRF (P, U_{c-1}) .
 134    *
 135    *        Here, INT (i) is a four-octet encoding of the integer i, most
 136    *        significant octet first.
 137    *
 138    *     4. Concatenate the blocks and extract the first dkLen octets to
 139    *        produce a derived key DK:
 140    *
 141    *                  DK = T_1 || T_2 ||  ...  || T_l<0..r-1>
 142    *
 143    *     5. Output the derived key DK.
 144    *
 145    *  Note. The construction of the function F follows a "belt-and-
 146    *  suspenders" approach. The iterates U_i are computed recursively to
 147    *  remove a degree of parallelism from an opponent; they are exclusive-
 148    *  ored together to reduce concerns about the recursion degenerating
 149    *  into a small set of values.
 150    *
 151    */
 152
 153   tmp = gnutls_malloc (tmplen);
 154   if (tmp == NULL)
 155     {
 156       gnutls_assert ();
 157       return GNUTLS_E_MEMORY_ERROR;
 158     }
 159
 160   memcpy (tmp, S, Slen);
 161
 162   for (i = 1; i <= l; i++)
 163     {
 164       memset (T, 0, hLen);
 165
 166       for (u = 1; u <= c; u++)
 167         {
 168           if (u == 1)
 169             {
 170               tmp[Slen + 0] = (i & 0xff000000) >> 24;
 171               tmp[Slen + 1] = (i & 0x00ff0000) >> 16;
 172               tmp[Slen + 2] = (i & 0x0000ff00) >> 8;
 173               tmp[Slen + 3] = (i & 0x000000ff) >> 0;
 174
 175               rc =
 176                 _gnutls_hmac_fast (GNUTLS_MAC_SHA1, P, Plen, tmp, tmplen, U);
 177             }
 178           else
 179             rc = _gnutls_hmac_fast (GNUTLS_MAC_SHA1, P, Plen, U, hLen, U);
 180
 181           if (rc < 0)
 182             {
 183               gnutls_free (tmp);
 184               return rc;
 185             }
 186
 187           for (k = 0; k < hLen; k++)
 188             T[k] ^= U[k];
 189         }
 190
 191       memcpy (DK + (i - 1) * hLen, T, i == l ? r : hLen);
 192     }
 193
 194   gnutls_free (tmp);
 195
 196   return 0;
 197 }