File indexing completed on 2024-04-28 04:43:43

 /* pkcs5.c     Partial Password-Based Cryptography (PKCS#5) implementation
  * Copyright (C) 2002 Free Software Foundation, Inc.
  *
  * This file is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This file is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this file; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
  *
  */
 
 #include "gcrypt.h"
 
 /*
  * 5.2 PBKDF2
  *
  *  PBKDF2 applies a pseudorandom function (see Appendix B.1 for an
  *  example) to derive keys. The length of the derived key is essentially
  *  unbounded. (However, the maximum effective search space for the
  *  derived key may be limited by the structure of the underlying
  *  pseudorandom function. See Appendix B.1 for further discussion.)
  *  PBKDF2 is recommended for new applications.
  *
  *  PBKDF2 (P, S, c, dkLen)
  *
  *  Options:        PRF        underlying pseudorandom function (hLen
  *                             denotes the length in octets of the
  *                             pseudorandom function output)
  *
  *  Input:          P          password, an octet string
  *                  S          salt, an octet string
  *                  c          iteration count, a positive integer
  *                  dkLen      intended length in octets of the derived
  *                             key, a positive integer, at most
  *                             (2^32 - 1) * hLen
  *
  *  Output:         DK         derived key, a dkLen-octet string
  */
 
 static gcry_error_t gcry_pbkdf2(int          PRF,
                                 const char  *P,
                                 size_t       Plen,
                                 const char  *S,
                                 size_t       Slen,
                                 unsigned int c,
                                 unsigned int dkLen,
                                 char        *DK)
 {
     gcry_md_hd_t   prf;
     gcry_error_t   rc;
     char          *U;
     unsigned int   u;
     unsigned int   hLen;
     unsigned int   l;
     unsigned int   r;
     unsigned char *p;
     unsigned int   i;
     unsigned int   k;
 
     hLen = gcry_md_get_algo_dlen(PRF);
     if (hLen == 0)
         return GPG_ERR_UNSUPPORTED_ALGORITHM;
 
     if (c == 0)
         return GPG_ERR_INV_ARG;
 
     if (dkLen == 0)
         return GPG_ERR_TOO_SHORT;
 
     /*
      *
      *  Steps:
      *
      *     1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
      *        stop.
      */
 
     if (dkLen > 4294967295U)
         return GPG_ERR_TOO_LARGE;
 
     /*
      *     2. Let l be the number of hLen-octet blocks in the derived key,
      *        rounding up, and let r be the number of octets in the last
      *        block:
      *
      *                  l = CEIL (dkLen / hLen) ,
      *                  r = dkLen - (l - 1) * hLen .
      *
      *        Here, CEIL (x) is the "ceiling" function, i.e. the smallest
      *        integer greater than, or equal to, x.
      */
 
     l = dkLen / hLen;
     if (dkLen % hLen)
         l++;
     r = dkLen - (l - 1) * hLen;
 
     /*
      *     3. For each block of the derived key apply the function F defined
      *        below to the password P, the salt S, the iteration count c, and
      *        the block index to compute the block:
      *
      *                  T_1 = F (P, S, c, 1) ,
      *                  T_2 = F (P, S, c, 2) ,
      *                  ...
      *                  T_l = F (P, S, c, l) ,
      *
      *        where the function F is defined as the exclusive-or sum of the
      *        first c iterates of the underlying pseudorandom function PRF
      *        applied to the password P and the concatenation of the salt S
      *        and the block index i:
      *
      *                  F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
      *
      *        where
      *
      *                  U_1 = PRF (P, S || INT (i)) ,
      *                  U_2 = PRF (P, U_1) ,
      *                  ...
      *                  U_c = PRF (P, U_{c-1}) .
      *
      *        Here, INT (i) is a four-octet encoding of the integer i, most
      *        significant octet first.
      *
      *     4. Concatenate the blocks and extract the first dkLen octets to
      *        produce a derived key DK:
      *
      *                  DK = T_1 || T_2 ||  ...  || T_l<0..r-1>
      *
      *     5. Output the derived key DK.
      *
      *  Note. The construction of the function F follows a "belt-and-
      *  suspenders" approach. The iterates U_i are computed recursively to
      *  remove a degree of parallelism from an opponent; they are exclusive-
      *  ored together to reduce concerns about the recursion degenerating
      *  into a small set of values.
      *
      */
     rc = gcry_md_open(&prf, PRF, GCRY_MD_FLAG_HMAC | GCRY_MD_FLAG_SECURE);
     if (rc != GPG_ERR_NO_ERROR)
         return rc;
 
     U = (char *)gcry_malloc(hLen);
     if (!U) {
         rc = GPG_ERR_ENOMEM;
         goto done;
     }
 
     for (i = 1; i <= l; i++) {
         memset(DK + (i - 1) * hLen, 0, i == l ? r : hLen);
 
         for (u = 1; u <= c; u++) {
             gcry_md_reset(prf);
 
             rc = gcry_md_setkey(prf, P, Plen);
             if (rc != GPG_ERR_NO_ERROR) {
                 goto done;
             }
             if (u == 1) {
                 char tmp[4];
                 gcry_md_write(prf, S, Slen);
                 tmp[0] = (i & 0xff000000) >> 24;
                 tmp[1] = (i & 0x00ff0000) >> 16;
                 tmp[2] = (i & 0x0000ff00) >> 8;
                 tmp[3] = (i & 0x000000ff) >> 0;
                 gcry_md_write(prf, tmp, 4);
             } else
                 gcry_md_write(prf, U, hLen);
 
             p = gcry_md_read(prf, PRF);
             if (p == nullptr) {
                 rc = GPG_ERR_CONFIGURATION;
                 goto done;
             }
 
             memcpy(U, p, hLen);
             for (k = 0; k < (i == l ? r : hLen); k++)
                 DK[(i - 1) * hLen + k] ^= U[k];
         }
     }
 
     rc = GPG_ERR_NO_ERROR;
 done:
     gcry_md_close(prf);
     gcry_free(U);
     return rc;
 }