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dropbear/ecc.c  view on Meta::CPAN

	buf_setpos(buf, 0);
	first = buf_getbyte(buf);
	if (first == 2 || first == 3) {
		dropbear_log(LOG_WARNING, "Dropbear doesn't support ECC point compression");
		return NULL;
	}
	if (first != 4 || buf->len != 1+2*size) {
		TRACE(("leave, wrong size"))
		return NULL;
	}

	key = new_ecc_key();
	key->dp = curve->dp;

	if (mp_from_ubin(key->pubkey.x, buf_getptr(buf, size), size) != MP_OKAY) {
		TRACE(("failed to read x"))
		goto out;
	}
	buf_incrpos(buf, size);

	if (mp_from_ubin(key->pubkey.y, buf_getptr(buf, size), size) != MP_OKAY) {
		TRACE(("failed to read y"))
		goto out;
	}
	buf_incrpos(buf, size);

	mp_set(key->pubkey.z, 1);

	if (ecc_is_point(key) != CRYPT_OK) {
		TRACE(("failed, not a point"))
		goto out;
	}

   /* SEC1 3.2.3.1 Check that Q != 0 */
	if (mp_cmp_d(key->pubkey.x, 0) == LTC_MP_EQ) {
		TRACE(("failed, x == 0"))
		goto out;
	}
	if (mp_cmp_d(key->pubkey.y, 0) == LTC_MP_EQ) {
		TRACE(("failed, y == 0"))
		goto out;
	}

	ret = DROPBEAR_SUCCESS;

	out:
	if (ret == DROPBEAR_FAILURE) {
		if (key) {
			ecc_free(key);
			m_free(key);
			key = NULL;
		}
	}

	return key;

}

/* a modified version of libtomcrypt's "ecc_shared_secret" to output
   a mp_int instead. */
mp_int * dropbear_ecc_shared_secret(ecc_key *public_key, const ecc_key *private_key)
{
	ecc_point *result = NULL;
	mp_int *prime = NULL, *shared_secret = NULL;
	int err = DROPBEAR_FAILURE;

   /* type valid? */
	if (private_key->type != PK_PRIVATE) {
		goto out;
	}

	if (private_key->dp != public_key->dp) {
		goto out;
	}

   /* make new point */
	result = ltc_ecc_new_point();
	if (result == NULL) {
		goto out;
	}

	prime = m_malloc(sizeof(*prime));
	m_mp_init(prime);

	if (mp_read_radix(prime, (char *)private_key->dp->prime, 16) != CRYPT_OK) { 
		goto out;
	}
	if (ltc_mp.ecc_ptmul(private_key->k, &public_key->pubkey, result, prime, 1) != CRYPT_OK) { 
		goto out;
	}

	shared_secret = m_malloc(sizeof(*shared_secret));
	m_mp_init(shared_secret);
	if (mp_copy(result->x, shared_secret) != CRYPT_OK) {
		goto out;
	}

	mp_clear(prime);
	m_free(prime);
	ltc_ecc_del_point(result);

	err = DROPBEAR_SUCCESS;
	out:
	if (err == DROPBEAR_FAILURE) {
		dropbear_exit("ECC error");
	}
	return shared_secret;
}

#endif