tls/s2n_server_finished.c

/*
 * 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 "error/s2n_errno.h"
#include "stuffer/s2n_stuffer.h"
#include "tls/s2n_connection.h"
#include "tls/s2n_resume.h"
#include "tls/s2n_tls.h"
#include "tls/s2n_tls13_handshake.h"
#include "utils/s2n_safety.h"

S2N_RESULT s2n_finished_recv(struct s2n_connection *conn, uint8_t *local_verify_data)
{
    RESULT_ENSURE_REF(conn);

    uint8_t length = conn->handshake.finished_len;
    /* Recalculate length to ensure that we're validating the right number of bytes */
    if (conn->actual_protocol_version == S2N_SSLv3) {
        RESULT_ENSURE_EQ(length, S2N_SSL_FINISHED_LEN);
    } else {
        RESULT_ENSURE_EQ(length, S2N_TLS_FINISHED_LEN);
    }

    uint8_t *peer_verify_data = s2n_stuffer_raw_read(&conn->handshake.io, length);
    RESULT_ENSURE_REF(peer_verify_data);

    RESULT_ENSURE(s2n_constant_time_equals(local_verify_data, peer_verify_data, length), S2N_ERR_BAD_MESSAGE);
    return S2N_RESULT_OK;
}

S2N_RESULT s2n_finished_send(struct s2n_connection *conn, uint8_t *verify_data)
{
    RESULT_ENSURE_REF(conn);

    uint8_t length = conn->handshake.finished_len;
    RESULT_ENSURE_GT(length, 0);

    RESULT_GUARD_POSIX(s2n_stuffer_write_bytes(&conn->handshake.io, verify_data, length));
    return S2N_RESULT_OK;
}

int s2n_server_finished_recv(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);
    uint8_t *verify_data = conn->handshake.server_finished;
    POSIX_GUARD_RESULT(s2n_finished_recv(conn, verify_data));
    return S2N_SUCCESS;
}

int s2n_server_finished_send(struct s2n_connection *conn)
{
    POSIX_ENSURE_REF(conn);

    uint8_t *verify_data = conn->handshake.server_finished;
    POSIX_GUARD(s2n_prf_server_finished(conn));
    POSIX_GUARD_RESULT(s2n_finished_send(conn, verify_data));
    POSIX_GUARD_RESULT(s2n_crypto_parameters_switch(conn));

    if (s2n_connection_is_session_resumed(conn)) {
        POSIX_GUARD(s2n_prf_key_expansion(conn));
    }

    return S2N_SUCCESS;
}

int s2n_tls13_server_finished_recv(struct s2n_connection *conn)
{
    POSIX_ENSURE_EQ(conn->actual_protocol_version, S2N_TLS13);

    uint8_t length = s2n_stuffer_data_available(&conn->handshake.io);
    S2N_ERROR_IF(length == 0, S2N_ERR_BAD_MESSAGE);

    /* read finished mac from handshake */
    struct s2n_blob wire_finished_mac = { 0 };
    POSIX_GUARD(s2n_blob_init(&wire_finished_mac, s2n_stuffer_raw_read(&conn->handshake.io, length), length));

    /* get tls13 keys */
    s2n_tls13_connection_keys(keys, conn);

    /* get transcript hash */
    POSIX_ENSURE_REF(conn->handshake.hashes);
    struct s2n_hash_state *hash_state = &conn->handshake.hashes->hash_workspace;
    POSIX_GUARD_RESULT(s2n_handshake_copy_hash_state(conn, keys.hash_algorithm, hash_state));

    /* look up finished secret key */
    struct s2n_blob finished_key = { 0 };
    POSIX_GUARD(s2n_blob_init(&finished_key, conn->handshake.server_finished, keys.size));

    /* generate the hashed message authenticated code */
    s2n_tls13_key_blob(server_finished_mac, keys.size);
    POSIX_GUARD(s2n_tls13_calculate_finished_mac(&keys, &finished_key, hash_state, &server_finished_mac));

    /* compare mac with received message */
    POSIX_GUARD(s2n_tls13_mac_verify(&keys, &server_finished_mac, &wire_finished_mac));

    return 0;
}

int s2n_tls13_server_finished_send(struct s2n_connection *conn)
{
    POSIX_ENSURE_EQ(conn->actual_protocol_version, S2N_TLS13);

    /* get tls13 keys */
    s2n_tls13_connection_keys(keys, conn);

    /* get transcript hash */
    POSIX_ENSURE_REF(conn->handshake.hashes);
    struct s2n_hash_state *hash_state = &conn->handshake.hashes->hash_workspace;
    POSIX_GUARD_RESULT(s2n_handshake_copy_hash_state(conn, keys.hash_algorithm, hash_state));

    /* look up finished secret key */
    struct s2n_blob finished_key = { 0 };
    POSIX_GUARD(s2n_blob_init(&finished_key, conn->handshake.server_finished, keys.size));

    /* generate the hashed message authenticated code */
    s2n_tls13_key_blob(server_finished_mac, keys.size);
    POSIX_GUARD(s2n_tls13_calculate_finished_mac(&keys, &finished_key, hash_state, &server_finished_mac));

    /* write to handshake io */
    POSIX_GUARD(s2n_stuffer_write(&conn->handshake.io, &server_finished_mac));

    return 0;
}