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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
*/
/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
*
* All curves taken from NIST recommendation paper of July 1999
* Available at http://csrc.nist.gov/cryptval/dss.htm
*/
#include "tomcrypt.h"
/**
@file ecc_shared_secret.c
ECC Crypto, Tom St Denis
*/
#ifdef LTC_MECC
/**
Create an ECC shared secret between two keys
@param private_key The private ECC key
@param public_key The public key
@param out [out] Destination of the shared secret (Conforms to EC-DH from ANSI X9.63)
@param outlen [in/out] The max size and resulting size of the shared secret
@return CRYPT_OK if successful
*/
int ecc_shared_secret(ecc_key *private_key, ecc_key *public_key,
unsigned char *out, unsigned long *outlen)
{
unsigned long x;
ecc_point *result;
void *prime;
int err;
LTC_ARGCHK(private_key != NULL);
LTC_ARGCHK(public_key != NULL);
LTC_ARGCHK(out != NULL);
LTC_ARGCHK(outlen != NULL);
/* type valid? */
if (private_key->type != PK_PRIVATE) {
return CRYPT_PK_NOT_PRIVATE;
}
if (ltc_ecc_is_valid_idx(private_key->idx) == 0 || ltc_ecc_is_valid_idx(public_key->idx) == 0) {
return CRYPT_INVALID_ARG;
}
if (XSTRCMP(private_key->dp->name, public_key->dp->name) != 0) {
return CRYPT_PK_TYPE_MISMATCH;
}
/* make new point */
result = ltc_ecc_new_point();
if (result == NULL) {
return CRYPT_MEM;
}
if ((err = mp_init(&prime)) != CRYPT_OK) {
ltc_ecc_del_point(result);
return err;
}
if ((err = mp_read_radix(prime, (char *)private_key->dp->prime, 16)) != CRYPT_OK) { goto done; }
if ((err = ltc_mp.ecc_ptmul(private_key->k, &public_key->pubkey, result, prime, 1)) != CRYPT_OK) { goto done; }
x = (unsigned long)mp_unsigned_bin_size(prime);
if (*outlen < x) {
*outlen = x;
err = CRYPT_BUFFER_OVERFLOW;
goto done;
}
zeromem(out, x);
if ((err = mp_to_unsigned_bin(result->x, out + (x - mp_unsigned_bin_size(result->x)))) != CRYPT_OK) { goto done; }
err = CRYPT_OK;
*outlen = x;
done:
mp_clear(prime);
ltc_ecc_del_point(result);
return err;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */
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