/* kdf.c - Key Derivation Functions
* Copyright (C) 1998, 2011 Free Software Foundation, Inc.
* Copyright (C) 2013 g10 Code GmbH
*
* This file is part of Libgcrypt.
*
* Libgcrypt 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.
*
* Libgcrypt 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, see <http://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "g10lib.h"
#include "cipher.h"
#include "kdf-internal.h"
/* Transform a passphrase into a suitable key of length KEYSIZE and
store this key in the caller provided buffer KEYBUFFER. The caller
must provide an HASHALGO, a valid ALGO and depending on that algo a
SALT of 8 bytes and the number of ITERATIONS. Code taken from
gnupg/agent/protect.c:hash_passphrase. */
static gpg_err_code_t
openpgp_s2k (const void *passphrase, size_t passphraselen,
int algo, int hashalgo,
const void *salt, size_t saltlen,
unsigned long iterations,
size_t keysize, void *keybuffer)
{
gpg_err_code_t ec;
gcry_md_hd_t md;
char *key = keybuffer;
int pass, i;
int used = 0;
int secmode;
if ((algo == GCRY_KDF_SALTED_S2K || algo == GCRY_KDF_ITERSALTED_S2K)
&& (!salt || saltlen != 8))
return GPG_ERR_INV_VALUE;
secmode = _gcry_is_secure (passphrase) || _gcry_is_secure (keybuffer);
ec = _gcry_md_open (&md, hashalgo, secmode? GCRY_MD_FLAG_SECURE : 0);
if (ec)
return ec;
for (pass=0; used < keysize; pass++)
{
if (pass)
{
_gcry_md_reset (md);
for (i=0; i < pass; i++) /* Preset the hash context. */
_gcry_md_putc (md, 0);
}
if (algo == GCRY_KDF_SALTED_S2K || algo == GCRY_KDF_ITERSALTED_S2K)
{
int len2 = passphraselen + 8;
unsigned long count = len2;
if (algo == GCRY_KDF_ITERSALTED_S2K)
{
count = iterations;
if (count < len2)
count = len2;
}
while (count > len2)
{
_gcry_md_write (md, salt, saltlen);
_gcry_md_write (md, passphrase, passphraselen);
count -= len2;
}
if (count < saltlen)
_gcry_md_write (md, salt, count);
else
{
_gcry_md_write (md, salt, saltlen);
count -= saltlen;
_gcry_md_write (md, passphrase, count);
}
}
else
_gcry_md_write (md, passphrase, passphraselen);
_gcry_md_final (md);
i = _gcry_md_get_algo_dlen (hashalgo);
if (i > keysize - used)
i = keysize - used;
memcpy (key+used, _gcry_md_read (md, hashalgo), i);
used += i;
}
_gcry_md_close (md);
return 0;
}
/* Transform a passphrase into a suitable key of length KEYSIZE and
store this key in the caller provided buffer KEYBUFFER. The caller
must provide PRFALGO which indicates the pseudorandom function to
use: This shall be the algorithms id of a hash algorithm; it is
used in HMAC mode. SALT is a salt of length SALTLEN and ITERATIONS
gives the number of iterations. */
gpg_err_code_t
_gcry_kdf_pkdf2 (const void *passphrase, size_t passphraselen,
int hashalgo,
const void *salt, size_t saltlen,
unsigned long iterations,
size_t keysize, void *keybuffer)
{
gpg_err_code_t ec;
gcry_md_hd_t md;
int secmode;
unsigned long dklen = keysize;
char *dk = keybuffer;
unsigned int hlen; /* Output length of the digest function. */
unsigned int l; /* Rounded up number of blocks. */
unsigned int r; /* Number of octets in the last block. */
char *sbuf; /* Malloced buffer to concatenate salt and iter
as well as space to hold TBUF and UBUF. */
char *tbuf; /* Buffer for T; ptr into SBUF, size is HLEN. */
char *ubuf; /* Buffer for U; ptr into SBUF, size is HLEN. */
unsigned int lidx; /* Current block number. */
unsigned long iter; /* Current iteration number. */
unsigned int i;
/* We allow for a saltlen of 0 here to support scrypt. It is not
clear whether rfc2898 allows for this this, thus we do a test on
saltlen > 0 only in gcry_kdf_derive. */
if (!salt || !iterations || !dklen)
return GPG_ERR_INV_VALUE;
hlen = _gcry_md_get_algo_dlen (hashalgo);
if (!hlen)
return GPG_ERR_DIGEST_ALGO;
secmode = _gcry_is_secure (passphrase) || _gcry_is_secure (keybuffer);
/* Step 1 */
/* If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
* stop. We use a stronger inequality but only if our type can hold
* a larger value. */
#if SIZEOF_UNSIGNED_LONG > 4
if (dklen > 0xffffffffU)
return GPG_ERR_INV_VALUE;
#endif
/* Step 2 */
l = ((dklen - 1)/ hlen) + 1;
r = dklen - (l - 1) * hlen;
/* Setup buffers and prepare a hash context. */
sbuf = (secmode
? xtrymalloc_secure (saltlen + 4 + hlen + hlen)
: xtrymalloc (saltlen + 4 + hlen + hlen));
if (!sbuf)
return gpg_err_code_from_syserror ();
tbuf = sbuf + saltlen + 4;
ubuf = tbuf + hlen;
ec = _gcry_md_open (&md, hashalgo, (GCRY_MD_FLAG_HMAC
| (secmode?GCRY_MD_FLAG_SECURE:0)));
if (ec)
{
xfree (sbuf);
return ec;
}
ec = _gcry_md_setkey (md, passphrase, passphraselen);
if (ec)
{
_gcry_md_close (md);
xfree (sbuf);
return ec;
}
/* Step 3 and 4. */
memcpy (sbuf, salt, saltlen);
for (lidx = 1; lidx <= l; lidx++)
{
for (iter = 0; iter < iterations; iter++)
{
_gcry_md_reset (md);
if (!iter) /* Compute U_1: */
{
sbuf[saltlen] = (lidx >> 24);
sbuf[saltlen + 1] = (lidx >> 16);
sbuf[saltlen + 2] = (lidx >> 8);
sbuf[saltlen + 3] = lidx;
_gcry_md_write (md, sbuf, saltlen + 4);
memcpy (ubuf, _gcry_md_read (md, 0), hlen);
memcpy (tbuf, ubuf, hlen);
}
else /* Compute U_(2..c): */
{
_gcry_md_write (md, ubuf, hlen);
memcpy (ubuf, _gcry_md_read (md, 0), hlen);
for (i=0; i < hlen; i++)
tbuf[i] ^= ubuf[i];
}
}
if (lidx == l) /* Last block. */
memcpy (dk, tbuf, r);
else
{
memcpy (dk, tbuf, hlen);
dk += hlen;
}
}
_gcry_md_close (md);
xfree (sbuf);
return 0;
}
/* Derive a key from a passphrase. KEYSIZE gives the requested size
of the keys in octets. KEYBUFFER is a caller provided buffer
filled on success with the derived key. The input passphrase is
taken from (PASSPHRASE,PASSPHRASELEN) which is an arbitrary memory
buffer. ALGO specifies the KDF algorithm to use; these are the
constants GCRY_KDF_*. SUBALGO specifies an algorithm used
internally by the KDF algorithms; this is usually a hash algorithm
but certain KDF algorithm may use it differently. {SALT,SALTLEN}
is a salt as needed by most KDF algorithms. ITERATIONS is a
positive integer parameter to most KDFs. 0 is returned on success,
or an error code on failure. */
gpg_err_code_t
_gcry_kdf_derive (const void *passphrase, size_t passphraselen,
int algo, int subalgo,
const void *salt, size_t saltlen,
unsigned long iterations,
size_t keysize, void *keybuffer)
{
gpg_err_code_t ec;
if (!passphrase)
{
ec = GPG_ERR_INV_DATA;
goto leave;
}
if (!keybuffer || !keysize)
{
ec = GPG_ERR_INV_VALUE;
goto leave;
}
switch (algo)
{
case GCRY_KDF_SIMPLE_S2K:
case GCRY_KDF_SALTED_S2K:
case GCRY_KDF_ITERSALTED_S2K:
if (!passphraselen)
ec = GPG_ERR_INV_DATA;
else
ec = openpgp_s2k (passphrase, passphraselen, algo, subalgo,
salt, saltlen, iterations, keysize, keybuffer);
break;
case GCRY_KDF_PBKDF1:
ec = GPG_ERR_UNSUPPORTED_ALGORITHM;
break;
case GCRY_KDF_PBKDF2:
if (!saltlen)
ec = GPG_ERR_INV_VALUE;
else
ec = _gcry_kdf_pkdf2 (passphrase, passphraselen, subalgo,
salt, saltlen, iterations, keysize, keybuffer);
break;
case 41:
case GCRY_KDF_SCRYPT:
#if USE_SCRYPT
ec = _gcry_kdf_scrypt (passphrase, passphraselen, algo, subalgo,
salt, saltlen, iterations, keysize, keybuffer);
#else
ec = GPG_ERR_UNSUPPORTED_ALGORITHM;
#endif /*USE_SCRYPT*/
break;
default:
ec = GPG_ERR_UNKNOWN_ALGORITHM;
break;
}
leave:
return ec;
}
