// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \page ssl.html
    \title Secure Sockets Layer (SSL) Classes
    \brief Classes for secure communication over network sockets.

    \keyword SSL

    The classes below provide support for secure network communication using
    the Secure Sockets Layer (SSL) protocol, using a native TLS backend,
    the \l{OpenSSL Toolkit}, or any appropriate TLS plugin to perform encryption
    and protocol handling.

    \annotatedlist ssl

    For Android applications see \l{Adding OpenSSL Support for Android}.

    \section1 Using Encryption in Networked Applications

    Use encryption when transporting data on any network whenever possible.
    \e Plaintext, which is unencrypted data that is easily readable, exposes
    sensitive data such as user information and information about network
    systems.

    Use QSslSocket::connectToHostEncrypted() to connect using encryption and
    check for SSL issues using QSslSocket::sslHandshakeErrors(). Use
    QSslSocket::ignoreSslErrors() with caution as it will create security risks
    in your application.

    Use QSslConfiguration to enforce strong security settings. The supported
    protocols depend on the SSL backend and the risk level of a protocol could
    change in the future. You can use a newer and more secure protocol using
    QSslConfiguration::setProtocol(). For more information, refer to
    QSsl::SslProtocol for the available protocols.


    \section1 Enabling and Disabling SSL Support when Building Qt from Source

    When building Qt from source, Qt builds plugins for native TLS libraries
    that are supported for the operating system you are building for. For
    Windows this means
    \l{https://docs.microsoft.com/en-us/windows/win32/com/schannel}{Schannel},
    while for macOS this is
    \l{https://developer.apple.com/documentation/security/secure_transport}{Secure Transport}.

    On all platforms, the configuration system checks for the presence of the
    \c{openssl/opensslv.h} header provided by source or developer packages
    of OpenSSL. If found, it will enable and build the OpenSSL backend for Qt.

    \note While Qt can still support the older OpenSSL 1.1.1 version when built
    from sources, the builds of Qt in the \l{Get and Install Qt with \QOI}{\QOI} require
    OpenSSL 3 at runtime.

    By default, an OpenSSL-enabled Qt library dynamically loads any installed
    OpenSSL library at run-time. However, it is possible to link against the
    library at compile-time by configuring Qt with the \c{-openssl-linked}
    option.

    When building a version of Qt linked against OpenSSL, Qt's build system will
    use CMake's \c{FindOpenSSL} command to find OpenSSL in several standard
    locations. You can set the CMake variable OPENSSL_ROOT_DIR to force a
    specific location.

    For example:
    \code
        configure -openssl-linked -- -D OPENSSL_ROOT_DIR=<openssl_dir>
    \endcode

    To disable SSL support in a Qt build, configure Qt with the \c{-no-openssl}
    option.

    \section1 Considerations While Packaging Your Application

    When you package your application, you may run a tool like \l{windeployqt}. This
    copies all the plugins for the libraries you use to the \c{plugins/} folder.
    However, for TLS you only need one backend, and you may delete the other
    plugins before packaging your application. For example, if you're on Windows
    and don't require any of the extra features the OpenSSL backend provides,
    you can choose to forego shipping the \c{qopensslbackend} plugin as well as
    the OpenSSL library, and simply ship the \c{qschannelbackend} plugin.

    However, shipping multiple backends is not a problem. Qt will
    attempt to load the backends in order (with OpenSSL attempted first) until
    one is successfully loaded. The other backends are then unused.

    \section1 Datagram Transport Layer Security

    Datagram Transport Layer Security (DTLS) is a protocol that enables security
    for datagram-based applications, providing them with protection against
    eavesdropping, tampering, or message forgery. The DTLS protocol is based on the
    stream-oriented Transport Layer Security (TLS) protocol. QtNetwork enables
    the use of DTLS with User Datagram Protocol (UDP), as defined by
    \l {RFC 6347}.

    \section1 Import and Export Restrictions

    Import and export restrictions apply for some types of software, and for
    some parts of the world. Developers wishing to use SSL communication in
    their deployed applications should either ensure that their users have the
    appropriate libraries installed, or they should consult a suitably
    qualified legal professional to ensure that applications using code from
    the OpenSSL project are correctly certified for import and export in
    relevant regions of the world.

    Refer to \l{Export Control of Qt Framework and Tools} for more information.
*/
