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/* 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;
}
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