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/* gc-pbkdf2-sha1.c --- Password-Based Key Derivation Function a'la PKCS#5
Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
This program 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, or (at your option)
any later version.
This program 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 program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
/* Written by Simon Josefsson. The comments in this file are taken
from RFC 2898. */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include "gc.h"
#include <stdlib.h>
#include <string.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 (ASCII or UTF-8)
* 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
*/
Gc_rc
gc_pbkdf2_sha1 (const char *P, size_t Plen,
const char *S, size_t Slen,
unsigned int c,
char *DK, size_t dkLen)
{
unsigned int hLen = 20;
char U[20];
char T[20];
unsigned int u;
unsigned int l;
unsigned int r;
unsigned int i;
unsigned int k;
int rc;
char *tmp;
size_t tmplen = Slen + 4;
if (c == 0)
return GC_PKCS5_INVALID_ITERATION_COUNT;
if (dkLen == 0)
return GC_PKCS5_INVALID_DERIVED_KEY_LENGTH;
/*
*
* Steps:
*
* 1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
* stop.
*/
if (dkLen > 4294967295U)
return GC_PKCS5_DERIVED_KEY_TOO_LONG;
/*
* 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 - 1) / hLen) + 1;
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.
*
*/
tmp = malloc (tmplen);
if (tmp == NULL)
return GC_MALLOC_ERROR;
memcpy (tmp, S, Slen);
for (i = 1; i <= l; i++)
{
memset (T, 0, hLen);
for (u = 1; u <= c; u++)
{
if (u == 1)
{
tmp[Slen + 0] = (i & 0xff000000) >> 24;
tmp[Slen + 1] = (i & 0x00ff0000) >> 16;
tmp[Slen + 2] = (i & 0x0000ff00) >> 8;
tmp[Slen + 3] = (i & 0x000000ff) >> 0;
rc = gc_hmac_sha1 (P, Plen, tmp, tmplen, U);
}
else
rc = gc_hmac_sha1 (P, Plen, U, hLen, U);
if (rc != GC_OK)
{
free (tmp);
return rc;
}
for (k = 0; k < hLen; k++)
T[k] ^= U[k];
}
memcpy (DK + (i - 1) * hLen, T, i == l ? r : hLen);
}
free (tmp);
return GC_OK;
}
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