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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_server_psk.h"
#include <stdint.h>
#include <sys/param.h>
#include "tls/s2n_tls.h"
#include "utils/s2n_bitmap.h"
#include "utils/s2n_safety.h"
static bool s2n_server_psk_should_send(struct s2n_connection *conn);
static int s2n_server_psk_send(struct s2n_connection *conn, struct s2n_stuffer *out);
static int s2n_server_psk_recv(struct s2n_connection *conn, struct s2n_stuffer *extension);
const s2n_extension_type s2n_server_psk_extension = {
.iana_value = TLS_EXTENSION_PRE_SHARED_KEY,
.minimum_version = S2N_TLS13,
.is_response = true,
.send = s2n_server_psk_send,
.recv = s2n_server_psk_recv,
.should_send = s2n_server_psk_should_send,
.if_missing = s2n_extension_noop_if_missing,
};
static bool s2n_server_psk_should_send(struct s2n_connection *conn)
{
/* Only send a server pre_shared_key extension if a chosen PSK is set on the connection */
return conn && conn->psk_params.chosen_psk;
}
static int s2n_server_psk_send(struct s2n_connection *conn, struct s2n_stuffer *out)
{
POSIX_ENSURE_REF(conn);
/* Send the index of the chosen PSK that is stored on the connection. */
POSIX_GUARD(s2n_stuffer_write_uint16(out, conn->psk_params.chosen_psk_wire_index));
return S2N_SUCCESS;
}
static int s2n_server_psk_recv(struct s2n_connection *conn, struct s2n_stuffer *extension)
{
POSIX_ENSURE_REF(conn);
/* Currently in s2n, only (EC)DHE key exchange mode is supported.
* Any other mode selected by the server is invalid because it was not offered by the client.
* A key_share extension MUST have been received in order to use a pre-shared key in (EC)DHE key exchange mode.
*/
s2n_extension_type_id key_share_ext_id = s2n_unsupported_extension;
POSIX_GUARD(s2n_extension_supported_iana_value_to_id(TLS_EXTENSION_KEY_SHARE, &key_share_ext_id));
POSIX_ENSURE(S2N_CBIT_TEST(conn->extension_responses_received, key_share_ext_id), S2N_ERR_MISSING_EXTENSION);
/* From RFC section: https://tools.ietf.org/html/rfc8446#section-4.2.8.1
* Any future values that are allocated must ensure that the transmitted protocol messages
* unambiguously identify which mode was selected by the server; at present, this is
* indicated by the presence of the "key_share" in the ServerHello.
*/
conn->psk_params.psk_ke_mode = S2N_PSK_DHE_KE;
uint16_t chosen_psk_wire_index = 0;
POSIX_GUARD(s2n_stuffer_read_uint16(extension, &chosen_psk_wire_index));
/* From RFC section: https://tools.ietf.org/html/rfc8446#section-4.2.11
* Clients MUST verify that the server's selected_identity is within the
* range supplied by the client.
*/
POSIX_ENSURE(chosen_psk_wire_index < conn->psk_params.psk_list.len, S2N_ERR_INVALID_ARGUMENT);
conn->psk_params.chosen_psk_wire_index = chosen_psk_wire_index;
POSIX_GUARD_RESULT(s2n_array_get(&conn->psk_params.psk_list, conn->psk_params.chosen_psk_wire_index,
(void **) &conn->psk_params.chosen_psk));
return S2N_SUCCESS;
}
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