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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*/
#include "tomcrypt.h"
#ifdef LTC_MDH
/**
Create a DH shared secret.
@param private_key The private DH key in the pair
@param public_key The public DH key in the pair
@param out [out] The destination of the shared data
@param outlen [in/out] The max size and resulting size of the shared data.
@return CRYPT_OK if successful
*/
int dh_shared_secret(dh_key *private_key, dh_key *public_key,
unsigned char *out, unsigned long *outlen)
{
void *tmp;
unsigned long x;
int err;
LTC_ARGCHK(private_key != NULL);
LTC_ARGCHK(public_key != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
/* types valid? */
if (private_key->type != PK_PRIVATE) {
return CRYPT_PK_NOT_PRIVATE;
}
/* same DH group? */
if (mp_cmp(private_key->prime, public_key->prime) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
if (mp_cmp(private_key->base, public_key->base) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
/* init big numbers */
if ((err = mp_init(&tmp)) != CRYPT_OK) {
return err;
}
/* check public key */
if ((err = dh_check_pubkey(public_key)) != CRYPT_OK) {
goto error;
}
/* compute tmp = y^x mod p */
if ((err = mp_exptmod(public_key->y, private_key->x, private_key->prime, tmp)) != CRYPT_OK) {
goto error;
}
/* enough space for output? */
x = (unsigned long)mp_unsigned_bin_size(tmp);
if (*outlen < x) {
*outlen = x;
err = CRYPT_BUFFER_OVERFLOW;
goto error;
}
if ((err = mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) {
goto error;
}
*outlen = x;
err = CRYPT_OK;
error:
mp_clear(tmp);
return err;
}
#endif /* LTC_MDH */
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
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