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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/s2n_key_update.h"
#include "crypto/s2n_sequence.h"
#include "error/s2n_errno.h"
#include "tls/s2n_connection.h"
#include "tls/s2n_record.h"
#include "tls/s2n_tls.h"
#include "tls/s2n_tls13_handshake.h"
#include "utils/s2n_safety.h"
int s2n_key_update_write(struct s2n_blob *out);
int s2n_check_record_limit(struct s2n_connection *conn, struct s2n_blob *sequence_number);
int s2n_key_update_recv(struct s2n_connection *conn, struct s2n_stuffer *request)
{
POSIX_ENSURE_REF(conn);
POSIX_ENSURE(conn->actual_protocol_version >= S2N_TLS13, S2N_ERR_BAD_MESSAGE);
POSIX_ENSURE(!s2n_connection_is_quic_enabled(conn), S2N_ERR_BAD_MESSAGE);
uint8_t key_update_request;
POSIX_GUARD(s2n_stuffer_read_uint8(request, &key_update_request));
S2N_ERROR_IF(key_update_request != S2N_KEY_UPDATE_NOT_REQUESTED && key_update_request != S2N_KEY_UPDATE_REQUESTED,
S2N_ERR_BAD_MESSAGE);
conn->key_update_pending = key_update_request;
/* Update peer's key since a key_update was received */
if (conn->mode == S2N_CLIENT) {
POSIX_GUARD(s2n_update_application_traffic_keys(conn, S2N_SERVER, RECEIVING));
} else {
POSIX_GUARD(s2n_update_application_traffic_keys(conn, S2N_CLIENT, RECEIVING));
}
return S2N_SUCCESS;
}
int s2n_key_update_send(struct s2n_connection *conn, s2n_blocked_status *blocked)
{
POSIX_ENSURE_REF(conn);
POSIX_ENSURE_REF(conn->secure);
struct s2n_blob sequence_number = { 0 };
if (conn->mode == S2N_CLIENT) {
POSIX_GUARD(s2n_blob_init(&sequence_number, conn->secure->client_sequence_number, S2N_TLS_SEQUENCE_NUM_LEN));
} else {
POSIX_GUARD(s2n_blob_init(&sequence_number, conn->secure->server_sequence_number, S2N_TLS_SEQUENCE_NUM_LEN));
}
POSIX_GUARD(s2n_check_record_limit(conn, &sequence_number));
if (conn->key_update_pending) {
/* Flush any buffered records to ensure an empty output buffer.
*
* This is important when buffering multiple records because we don't:
* 1) Respect max fragment length for handshake messages
* 2) Check if there is sufficient space in the output buffer for
* post-handshake messages.
*/
POSIX_GUARD(s2n_flush(conn, blocked));
uint8_t key_update_data[S2N_KEY_UPDATE_MESSAGE_SIZE];
struct s2n_blob key_update_blob = { 0 };
POSIX_GUARD(s2n_blob_init(&key_update_blob, key_update_data, sizeof(key_update_data)));
/* Write key update message */
POSIX_GUARD(s2n_key_update_write(&key_update_blob));
/* Encrypt the message */
POSIX_GUARD_RESULT(s2n_record_write(conn, TLS_HANDSHAKE, &key_update_blob));
/* Update encryption key */
POSIX_GUARD(s2n_update_application_traffic_keys(conn, conn->mode, SENDING));
conn->key_update_pending = false;
POSIX_GUARD(s2n_flush(conn, blocked));
}
return S2N_SUCCESS;
}
int s2n_key_update_write(struct s2n_blob *out)
{
POSIX_ENSURE_REF(out);
struct s2n_stuffer key_update_stuffer = { 0 };
POSIX_GUARD(s2n_stuffer_init(&key_update_stuffer, out));
POSIX_GUARD(s2n_stuffer_write_uint8(&key_update_stuffer, TLS_KEY_UPDATE));
POSIX_GUARD(s2n_stuffer_write_uint24(&key_update_stuffer, S2N_KEY_UPDATE_LENGTH));
/* s2n currently does not require peers to update their encryption keys. */
POSIX_GUARD(s2n_stuffer_write_uint8(&key_update_stuffer, S2N_KEY_UPDATE_NOT_REQUESTED));
return S2N_SUCCESS;
}
int s2n_check_record_limit(struct s2n_connection *conn, struct s2n_blob *sequence_number)
{
POSIX_ENSURE_REF(conn);
POSIX_ENSURE_REF(sequence_number);
POSIX_ENSURE_REF(conn->secure);
POSIX_ENSURE_REF(conn->secure->cipher_suite);
POSIX_ENSURE_REF(conn->secure->cipher_suite->record_alg);
/*
* This is the sequence number that will be used for the next record,
* because we incremented the sequence number after sending the last record.
*/
uint64_t next_seq_num = 0;
POSIX_GUARD(s2n_sequence_number_to_uint64(sequence_number, &next_seq_num));
/*
* If the next record is the last record we can send, then the next record needs
* to contain a KeyUpdate message.
*
* This should always trigger on "==", but we use ">=" just in case.
*/
if (next_seq_num >= conn->secure->cipher_suite->record_alg->encryption_limit) {
conn->key_update_pending = true;
}
return S2N_SUCCESS;
}
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