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/*
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed
* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
#include <stdint.h>
#include <sys/param.h>
#include "tls/extensions/s2n_ems.h"
#include "tls/s2n_tls.h"
#include "utils/s2n_safety.h"
static int s2n_client_ems_recv(struct s2n_connection *conn, struct s2n_stuffer *extension);
static bool s2n_client_ems_should_send(struct s2n_connection *conn);
/**
*= https://tools.ietf.org/rfc/rfc7627#section-5.1
*#
*# This document defines a new TLS extension, "extended_master_secret"
*# (with extension type 0x0017), which is used to signal both client and
*# server to use the extended master secret computation. The
*# "extension_data" field of this extension is empty. Thus, the entire
*# encoding of the extension is 00 17 00 00 (in hexadecimal.)
**/
const s2n_extension_type s2n_client_ems_extension = {
.iana_value = TLS_EXTENSION_EMS,
.is_response = false,
.send = s2n_extension_send_noop,
.recv = s2n_client_ems_recv,
.should_send = s2n_client_ems_should_send,
.if_missing = s2n_extension_noop_if_missing,
};
static int s2n_client_ems_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
POSIX_ENSURE_REF(conn);
/* Read nothing. The extension just needs to exist without data. */
POSIX_ENSURE(s2n_stuffer_data_available(extension) == 0, S2N_ERR_UNSUPPORTED_EXTENSION);
conn->ems_negotiated = true;
return S2N_SUCCESS;
}
/**
*= https://www.rfc-editor.org/rfc/rfc7627#section-5.3
*= type=exception
*# When offering an abbreviated handshake, the client MUST send the
*# "extended_master_secret" extension in its ClientHello.
*
* We added an exception here in order to prevent a drop in
* session resumption rates during deployment. Eventually clients
* will be forced to do a full handshake as sessions expire and pick up EMS at that point.
**/
static bool s2n_client_ems_should_send(struct s2n_connection *conn)
{
/* Don't send this extension if the previous session did not negotiate EMS */
if (conn && conn->set_session && !conn->ems_negotiated) {
return false;
} else {
return true;
}
}
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