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/* dh.c
*
* Copyright (C) 2006-2011 Sawtooth Consulting Ltd.
*
* This file is part of CyaSSL.
*
* CyaSSL is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* CyaSSL 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#ifndef NO_DH
#include "ctc_dh.h"
#include "error.h"
#ifndef USER_MATH_LIB
#include <math.h>
#define XPOW(x,y) pow((x),(y))
#define XLOG(x) log((x))
#else
/* user's own math lib */
#endif
#ifndef min
static INLINE word32 min(word32 a, word32 b)
{
return a > b ? b : a;
}
#endif /* min */
void InitDhKey(DhKey* key)
{
/* TomsFastMath doesn't use memory allocation */
#ifndef USE_FAST_MATH
key->p.dp = 0;
key->g.dp = 0;
#endif
}
void FreeDhKey(DhKey* key)
{
/* TomsFastMath doesn't use memory allocation */
#ifndef USE_FAST_MATH
mp_clear(&key->p);
mp_clear(&key->g);
#endif
}
static word32 DiscreteLogWorkFactor(word32 n)
{
/* assuming discrete log takes about the same time as factoring */
if (n<5)
return 0;
else
return (word32)(2.4 * XPOW((double)n, 1.0/3.0) *
XPOW(XLOG((double)n), 2.0/3.0) - 5);
}
static void GeneratePrivate(DhKey* key, RNG* rng, byte* priv, word32* privSz)
{
word32 sz = mp_unsigned_bin_size(&key->p);
sz = min(sz, 2 * DiscreteLogWorkFactor(sz * BIT_SIZE) / BIT_SIZE + 1);
RNG_GenerateBlock(rng, priv, sz);
priv[0] |= 0x0C;
*privSz = sz;
}
static int GeneratePublic(DhKey* key, const byte* priv, word32 privSz,
byte* pub, word32* pubSz)
{
int ret = 0;
mp_int x;
mp_int y;
if (mp_init_multi(&x, &y, 0, 0, 0, 0) != MP_OKAY)
return MP_INIT_E;
if (mp_read_unsigned_bin(&x, priv, privSz) != MP_OKAY)
ret = MP_READ_E;
if (ret == 0 && mp_exptmod(&key->g, &x, &key->p, &y) != MP_OKAY)
ret = MP_EXPTMOD_E;
if (ret == 0 && mp_to_unsigned_bin(&y, pub) != MP_OKAY)
ret = MP_TO_E;
if (ret == 0)
*pubSz = mp_unsigned_bin_size(&y);
mp_clear(&y);
mp_clear(&x);
return ret;
}
int DhGenerateKeyPair(DhKey* key, RNG* rng, byte* priv, word32* privSz,
byte* pub, word32* pubSz)
{
GeneratePrivate(key, rng, priv, privSz);
return GeneratePublic(key, priv, *privSz, pub, pubSz);
}
int DhAgree(DhKey* key, byte* agree, word32* agreeSz, const byte* priv,
word32 privSz, const byte* otherPub, word32 pubSz)
{
int ret = 0;
mp_int x;
mp_int y;
mp_int z;
if (mp_init_multi(&x, &y, &z, 0, 0, 0) != MP_OKAY)
return MP_INIT_E;
if (mp_read_unsigned_bin(&x, priv, privSz) != MP_OKAY)
ret = MP_READ_E;
if (ret == 0 && mp_read_unsigned_bin(&y, otherPub, pubSz) != MP_OKAY)
ret = MP_READ_E;
if (ret == 0 && mp_exptmod(&y, &x, &key->p, &z) != MP_OKAY)
ret = MP_EXPTMOD_E;
if (ret == 0 && mp_to_unsigned_bin(&z, agree) != MP_OKAY)
ret = MP_TO_E;
if (ret == 0)
*agreeSz = mp_unsigned_bin_size(&z);
mp_clear(&z);
mp_clear(&y);
mp_clear(&x);
return ret;
}
#endif /* NO_DH */
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