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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.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
#include "tomcrypt.h"
/**
@file dsa_shared_secret.c
DSA Crypto, Tom St Denis
*/
#ifdef LTC_MDSA
/**
Create a DSA shared secret between two keys
@param private_key The private DSA key (the exponent)
@param base The base of the exponentiation (allows this to be used for both encrypt and decrypt)
@param public_key The public key
@param out [out] Destination of the shared secret
@param outlen [in/out] The max size and resulting size of the shared secret
@return CRYPT_OK if successful
*/
int dsa_shared_secret(void *private_key, void *base,
dsa_key *public_key,
unsigned char *out, unsigned long *outlen)
{
unsigned long x;
void *res;
int err;
LTC_ARGCHK(private_key != NULL);
LTC_ARGCHK(public_key != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
/* make new point */
if ((err = mp_init(&res)) != CRYPT_OK) {
return err;
}
if ((err = mp_exptmod(base, private_key, public_key->p, res)) != CRYPT_OK) {
mp_clear(res);
return err;
}
x = (unsigned long)mp_unsigned_bin_size(res);
if (*outlen < x) {
*outlen = x;
err = CRYPT_BUFFER_OVERFLOW;
goto done;
}
zeromem(out, x);
if ((err = mp_to_unsigned_bin(res, out + (x - mp_unsigned_bin_size(res)))) != CRYPT_OK) { goto done; }
err = CRYPT_OK;
*outlen = x;
done:
mp_clear(res);
return err;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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