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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 "tls/extensions/s2n_cookie.h"
#include "tls/s2n_tls.h"
#include "utils/s2n_random.h"
/*
*= https://tools.ietf.org/rfc/rfc8446#section-4.2.2
*# When sending the new ClientHello, the client MUST copy
*# the contents of the extension received in the HelloRetryRequest into
*# a "cookie" extension in the new ClientHello.
*
* If the server sent a cookie, send it back.
*/
static bool s2n_client_cookie_should_send(struct s2n_connection *conn)
{
return conn && conn->cookie.size > 0;
}
/*
*= https://tools.ietf.org/rfc/rfc8446#section-4.2.2
*# struct {
*# opaque cookie<1..2^16-1>;
*# } Cookie;
*/
int s2n_cookie_send(struct s2n_connection *conn, struct s2n_stuffer *out)
{
POSIX_ENSURE_REF(conn);
POSIX_GUARD(s2n_stuffer_write_uint16(out, conn->cookie.size));
POSIX_GUARD(s2n_stuffer_write(out, &conn->cookie));
return S2N_SUCCESS;
}
/*
* Our server does not send cookies in production, so
* should never receive a cookie back from the client.
*
* However, we may enable cookies for testing.
* In that case, verify the proper client behavior by
* checking that the cookie sent matches the cookie received.
* This is also why the "if_missing" behavior is an error.
*/
static int s2n_client_cookie_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
POSIX_ENSURE_REF(conn);
POSIX_ENSURE(s2n_in_unit_test(), S2N_ERR_UNSUPPORTED_EXTENSION);
uint16_t size = 0;
POSIX_GUARD(s2n_stuffer_read_uint16(extension, &size));
POSIX_ENSURE(size == conn->cookie.size, S2N_ERR_BAD_MESSAGE);
POSIX_ENSURE(size >= s2n_stuffer_data_available(extension), S2N_ERR_BAD_MESSAGE);
uint8_t *cookie = s2n_stuffer_raw_read(extension, size);
POSIX_ENSURE_REF(cookie);
POSIX_ENSURE(s2n_constant_time_equals(cookie, conn->cookie.data, size), S2N_ERR_BAD_MESSAGE);
return S2N_SUCCESS;
}
const s2n_extension_type s2n_client_cookie_extension = {
.iana_value = TLS_EXTENSION_COOKIE,
.minimum_version = S2N_TLS13,
.is_response = true,
.send = s2n_cookie_send,
.recv = s2n_client_cookie_recv,
.should_send = s2n_client_cookie_should_send,
.if_missing = s2n_extension_error_if_missing,
};
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