Secure Sockets Layer (SSL) Classes

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

From Qt version 5.15 onwards, the officially supported version for OpenSSL is 1.1.1 or later.


This class provides encryption for UDP sockets


This class implements server-side DTLS cookie generation and verification


This class defines parameters for DTLS cookie generator


This class represents Online Certificate Status Protocol response


Declares enums common to all SSL classes in Qt Network


Convenient API for an X509 certificate


API for accessing the extensions of an X509 certificate


Represents an SSL cryptographic cipher


Holds the configuration and state of an SSL connection


Interface for Diffie-Hellman parameters for servers


Represents an elliptic curve for use by elliptic-curve cipher algorithms


SSL error


Interface for private and public keys


Authentication data for pre shared keys (PSK) ciphersuites


SSL encrypted socket for both clients and servers


Describes the level of an alert message


Enumerates possible codes that an alert message can have


Describes the current state of DTLS handshake


Enumerates classes that a TLS backend implements


Describes errors that can be found by QDtls and QDtlsClientVerifier


Describes the Online Certificate Status


Describes the reason for revocation


Enumerates possible features that a TLS backend supports

Enabling and Disabling SSL Support

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, while for macOS this is

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

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 -openssl-linked option.

When building a version of Qt linked against OpenSSL, Qt's build system will use CMake's 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:

configure -openssl-linked -- -D OPENSSL_ROOT_DIR=<openssl_dir>

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

Considerations While Packaging Your Application

When you package your application, you may run a tool like windeployqt. This copies all the plugins for the libraries you use to the 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 qopensslbackend plugin as well as the OpenSSL library, and simply ship the 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.

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 RFC 6347.

Import and Export Restrictions

Qt binary installers include the OpenSSL libraries used by QtNetwork. However, those are not automatically deployed with applications that are built with Qt. 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.

© 2024 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.