diff --git a/src/network/ssl/qdtls.cpp b/src/network/ssl/qdtls.cpp
new file mode 100644
index 0000000000..d241c0bb60
--- /dev/null
+++ b/src/network/ssl/qdtls.cpp
@@ -0,0 +1,569 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtNetwork module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qsslconfiguration.h"
+#include "qudpsocket.h"
+#include "qdtls_p.h"
+#include "qssl_p.h"
+#include "qdtls.h"
+
+#include "qglobal.h"
+
+#if QT_CONFIG(openssl)
+#include "qdtls_openssl_p.h"
+#endif // QT_CONFIG
+
+QT_BEGIN_NAMESPACE
+
+namespace
+{
+
+bool isDtlsProtocol(QSsl::SslProtocol protocol)
+{
+    switch (protocol) {
+    case QSsl::DtlsV1_0:
+    case QSsl::DtlsV1_0OrLater:
+    case QSsl::DtlsV1_2:
+    case QSsl::DtlsV1_2OrLater:
+        return true;
+    default:
+        return false;
+    }
+}
+
+}
+
+QSslConfiguration QDtlsBasePrivate::configuration() const
+{
+    auto copyPrivate = new QSslConfigurationPrivate(dtlsConfiguration);
+    copyPrivate->ref.store(0); // the QSslConfiguration constructor refs up
+    QSslConfiguration copy(copyPrivate);
+    copyPrivate->sessionCipher = sessionCipher;
+    copyPrivate->sessionProtocol = sessionProtocol;
+
+    return copy;
+}
+
+void QDtlsBasePrivate::setConfiguration(const QSslConfiguration &configuration)
+{
+    dtlsConfiguration.localCertificateChain = configuration.localCertificateChain();
+    dtlsConfiguration.privateKey = configuration.privateKey();
+    dtlsConfiguration.ciphers = configuration.ciphers();
+    dtlsConfiguration.ellipticCurves = configuration.ellipticCurves();
+    dtlsConfiguration.preSharedKeyIdentityHint = configuration.preSharedKeyIdentityHint();
+    dtlsConfiguration.dhParams = configuration.diffieHellmanParameters();
+    dtlsConfiguration.caCertificates = configuration.caCertificates();
+    dtlsConfiguration.peerVerifyDepth = configuration.peerVerifyDepth();
+    dtlsConfiguration.peerVerifyMode = configuration.peerVerifyMode();
+    Q_ASSERT(isDtlsProtocol(configuration.protocol()));
+    dtlsConfiguration.protocol = configuration.protocol();
+    dtlsConfiguration.sslOptions = configuration.d->sslOptions;
+    dtlsConfiguration.sslSession = configuration.sessionTicket();
+    dtlsConfiguration.sslSessionTicketLifeTimeHint = configuration.sessionTicketLifeTimeHint();
+    dtlsConfiguration.nextAllowedProtocols = configuration.allowedNextProtocols();
+    dtlsConfiguration.nextNegotiatedProtocol = configuration.nextNegotiatedProtocol();
+    dtlsConfiguration.nextProtocolNegotiationStatus = configuration.nextProtocolNegotiationStatus();
+    dtlsConfiguration.dtlsCookieEnabled = configuration.dtlsCookieVerificationEnabled();
+
+    clearDtlsError();
+}
+
+bool QDtlsBasePrivate::setCookieGeneratorParameters(QCryptographicHash::Algorithm alg,
+                                                    const QByteArray &key)
+{
+    if (!key.size()) {
+        setDtlsError(QDtlsError::InvalidInputParameters,
+                     QDtls::tr("Invalid (empty) secret"));
+        return false;
+    }
+
+    clearDtlsError();
+
+    hashAlgorithm = alg;
+    secret = key;
+
+    return true;
+}
+
+QDtlsClientVerifier::QDtlsClientVerifier(QObject *parent)
+#if QT_CONFIG(openssl)
+    : QObject(*new QDtlsClientVerifierOpenSSL, parent)
+#endif // openssl
+{
+    Q_D(QDtlsClientVerifier);
+
+    d->mode = QSslSocket::SslServerMode;
+    // The default configuration suffices: verifier never does a full
+    // handshake and upon verifying a cookie in a client hello message,
+    // it reports success.
+    auto conf = QSslConfiguration::defaultDtlsConfiguration();
+    conf.setPeerVerifyMode(QSslSocket::VerifyNone);
+    d->setConfiguration(conf);
+}
+
+bool QDtlsClientVerifier::setCookieGeneratorParameters(const GeneratorParameters &params)
+{
+    Q_D(QDtlsClientVerifier);
+
+    return d->setCookieGeneratorParameters(params.hash, params.secret);
+}
+
+QDtlsClientVerifier::GeneratorParameters QDtlsClientVerifier::cookieGeneratorParameters() const
+{
+    Q_D(const QDtlsClientVerifier);
+
+    return {d->hashAlgorithm, d->secret};
+}
+
+bool QDtlsClientVerifier::verifyClient(QUdpSocket *socket, const QByteArray &dgram,
+                                       const QHostAddress &address, quint16 port)
+{
+    Q_D(QDtlsClientVerifier);
+
+    if (!socket || address.isNull() || !dgram.size()) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters,
+                        tr("A valid UDP socket, non-empty datagram, valid address/port were expected"));
+        return false;
+    }
+
+    if (address.isBroadcast() || address.isMulticast()) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters,
+                        tr("Multicast and broadcast addresses are not supported"));
+        return false;
+    }
+
+    return d->verifyClient(socket, dgram, address, port);
+}
+
+QByteArray QDtlsClientVerifier::verifiedHello() const
+{
+    Q_D(const QDtlsClientVerifier);
+
+    return d->verifiedClientHello;
+}
+
+QDtlsError QDtlsClientVerifier::dtlsError() const
+{
+    Q_D(const QDtlsClientVerifier);
+
+    return d->errorCode;
+}
+
+QString QDtlsClientVerifier::dtlsErrorString() const
+{
+    Q_D(const QDtlsBase);
+
+    return d->errorDescription;
+}
+
+QDtls::QDtls(QSslSocket::SslMode mode, QObject *parent)
+#if QT_CONFIG(openssl)
+    : QObject(*new QDtlsPrivateOpenSSL, parent)
+#endif
+{
+    Q_D(QDtls);
+
+    d->mode = mode;
+    setDtlsConfiguration(QSslConfiguration::defaultDtlsConfiguration());
+}
+
+bool QDtls::setRemote(const QHostAddress &address, quint16 port,
+                      const QString &verificationName)
+{
+    Q_D(QDtls);
+
+    if (d->handshakeState != HandshakeNotStarted) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot set remote after handshake started"));
+        return false;
+    }
+
+    if (address.isNull()) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters,
+                        tr("Invalid address"));
+        return false;
+    }
+
+    if (address.isBroadcast() || address.isMulticast()) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters,
+                        tr("Multicast and broadcast addresses are not supported"));
+        return false;
+    }
+
+    d->clearDtlsError();
+
+    d->remoteAddress = address;
+    d->remotePort = port;
+    d->peerVerificationName = verificationName;
+
+    return true;
+}
+
+bool QDtls::setPeerVerificationName(const QString &name)
+{
+    Q_D(QDtls);
+
+    if (d->handshakeState != HandshakeNotStarted) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot set verification name after handshake started"));
+        return false;
+    }
+
+    d->clearDtlsError();
+    d->peerVerificationName = name;
+
+    return true;
+}
+
+QHostAddress QDtls::remoteAddress() const
+{
+    Q_D(const QDtls);
+
+    return d->remoteAddress;
+}
+
+quint16 QDtls::remotePort() const
+{
+    Q_D(const QDtlsBase);
+
+    return d->remotePort;
+}
+
+QString QDtls::peerVerificationName() const
+{
+    Q_D(const QDtls);
+
+    return d->peerVerificationName;
+}
+
+QSslSocket::SslMode QDtls::sslMode() const
+{
+    Q_D(const QDtls);
+
+    return d->mode;
+}
+
+void QDtls::setMtuHint(quint16 mtuHint)
+{
+    Q_D(QDtls);
+
+    d->mtuHint = mtuHint;
+}
+
+quint16 QDtls::mtuHint() const
+{
+    Q_D(const QDtls);
+
+    return d->mtuHint;
+}
+
+bool QDtls::setCookieGeneratorParameters(const GeneratorParameters &params)
+{
+    Q_D(QDtls);
+
+    return d->setCookieGeneratorParameters(params.hash, params.secret);
+}
+
+QDtls::GeneratorParameters QDtls::cookieGeneratorParameters() const
+{
+    Q_D(const QDtls);
+
+    return {d->hashAlgorithm, d->secret};
+}
+
+bool QDtls::setDtlsConfiguration(const QSslConfiguration &configuration)
+{
+    Q_D(QDtls);
+
+    if (d->handshakeState != HandshakeNotStarted) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot set configuration after handshake started"));
+        return false;
+    }
+
+    if (isDtlsProtocol(configuration.protocol())) {
+        d->setConfiguration(configuration);
+        return true;
+    }
+
+    d->setDtlsError(QDtlsError::InvalidInputParameters, tr("Unsupported protocol"));
+    return false;
+}
+
+QSslConfiguration QDtls::dtlsConfiguration() const
+{
+    Q_D(const QDtls);
+
+    return d->configuration();
+}
+
+QDtls::HandshakeState QDtls::handshakeState()const
+{
+    Q_D(const QDtls);
+
+    return d->handshakeState;
+}
+
+bool QDtls::doHandshake(QUdpSocket *socket, const QByteArray &dgram)
+{
+    Q_D(QDtls);
+
+    if (d->handshakeState == HandshakeNotStarted)
+        return startHandshake(socket, dgram);
+    else if (d->handshakeState == HandshakeInProgress)
+        return continueHandshake(socket, dgram);
+
+    d->setDtlsError(QDtlsError::InvalidOperation,
+                    tr("Cannot start/continue handshake, invalid handshake state"));
+    return false;
+}
+
+bool QDtls::startHandshake(QUdpSocket *socket, const QByteArray &datagram)
+{
+    Q_D(QDtls);
+
+    if (!socket) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters, tr("Invalid (nullptr) socket"));
+        return false;
+    }
+
+    if (d->remoteAddress.isNull()) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("To start a handshake you must set remote address and port first"));
+        return false;
+    }
+
+    if (sslMode() == QSslSocket::SslServerMode && !datagram.size()) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters,
+                        tr("To start a handshake, DTLS server requires non-empty datagram (client hello)"));
+        return false;
+    }
+
+    if (d->handshakeState != HandshakeNotStarted) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot start handshake, already done/in progress"));
+        return false;
+    }
+
+    return d->startHandshake(socket, datagram);
+}
+
+bool QDtls::handleTimeout(QUdpSocket *socket)
+{
+    Q_D(QDtls);
+
+    if (!socket) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters, tr("Invalid (nullptr) socket"));
+        return false;
+    }
+
+    if (sslMode() == QSslSocket::SslServerMode) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("DTLS server connection does not have/handle timeouts"));
+        return false;
+    }
+
+    return d->handleTimeout(socket);
+}
+
+bool QDtls::continueHandshake(QUdpSocket *socket, const QByteArray &datagram)
+{
+    Q_D(QDtls);
+
+    if (!socket || !datagram.size()) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters,
+                        tr("A valid QUdpSocket and non-empty datagram are needed to continue the handshake"));
+        return false;
+    }
+
+    if (d->handshakeState != HandshakeInProgress) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot continue handshake, not in InProgress state"));
+        return false;
+    }
+
+    return d->continueHandshake(socket, datagram);
+}
+
+bool QDtls::resumeHandshakeAfterError(QUdpSocket *socket)
+{
+    Q_D(QDtls);
+
+    if (!socket) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters, tr("Invalid (nullptr) socket"));
+        return false;
+    }
+
+    if (d->handshakeState != PeerVerificationFailed) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot resume, not in VerificationError state"));
+        return false;
+    }
+
+    return d->resumeHandshake(socket);
+}
+
+bool QDtls::abortHandshakeAfterError(QUdpSocket *socket)
+{
+    Q_D(QDtls);
+
+    if (!socket) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters, tr("Invalid (nullptr) socket"));
+        return false;
+    }
+
+    if (d->handshakeState != PeerVerificationFailed) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Not in VerificationError state, nothing to abort"));
+        return false;
+    }
+
+    d->abortHandshake(socket);
+    return true;
+}
+
+bool QDtls::sendShutdownAlert(QUdpSocket *socket)
+{
+    Q_D(QDtls);
+
+    if (!socket) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters,
+                        tr("Invalid (nullptr) socket"));
+        return false;
+    }
+
+    if (!d->connectionEncrypted) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot send shutdown alert, not encrypted"));
+        return false;
+    }
+
+    d->sendShutdownAlert(socket);
+    return true;
+}
+
+bool QDtls::connectionEncrypted() const
+{
+    Q_D(const QDtls);
+
+    return d->connectionEncrypted;
+}
+
+QSslCipher QDtls::sessionCipher() const
+{
+    Q_D(const QDtls);
+
+    return d->sessionCipher;
+}
+
+QSsl::SslProtocol QDtls::sessionProtocol() const
+{
+    Q_D(const QDtls);
+
+    return d->sessionProtocol;
+}
+
+qint64 QDtls::writeDatagramEncrypted(QUdpSocket *socket, const QByteArray &dgram)
+{
+    Q_D(QDtls);
+
+    if (!socket) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters, tr("Invalid (nullptr) socket"));
+        return -1;
+    }
+
+    if (!connectionEncrypted()) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot write a datagram, not in encrypted state"));
+        return -1;
+    }
+
+    return d->writeDatagramEncrypted(socket, dgram);
+}
+
+QByteArray QDtls::decryptDatagram(QUdpSocket *socket, const QByteArray &dgram)
+{
+    Q_D(QDtls);
+
+    if (!socket) {
+        d->setDtlsError(QDtlsError::InvalidInputParameters, tr("Invalid (nullptr) socket"));
+        return {};
+    }
+
+    if (!connectionEncrypted()) {
+        d->setDtlsError(QDtlsError::InvalidOperation,
+                        tr("Cannot read a datagram, not in encrypted state"));
+        return {};
+    }
+
+    if (!dgram.size())
+        return {};
+
+    return d->decryptDatagram(socket, dgram);
+}
+
+QDtlsError QDtls::dtlsError() const
+{
+    Q_D(const QDtls);
+
+    return d->errorCode;
+}
+
+QString QDtls::dtlsErrorString() const
+{
+    Q_D(const QDtls);
+
+    return d->errorDescription;
+}
+
+QVector<QSslError> QDtls::peerVerificationErrors() const
+{
+    Q_D(const QDtls);
+
+    return d->tlsErrors;
+}
+
+void QDtls::ignoreVerificationErrors(const QVector<QSslError> &errorsToIgnore)
+{
+    Q_D(QDtls);
+
+    d->tlsErrorsToIgnore = errorsToIgnore;
+}
+
+QT_END_NAMESPACE
diff --git a/src/network/ssl/qdtls.h b/src/network/ssl/qdtls.h
new file mode 100644
index 0000000000..859b8c2baa
--- /dev/null
+++ b/src/network/ssl/qdtls.h
@@ -0,0 +1,185 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtNetwork module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QDTLS_H
+#define QDTLS_H
+
+#include <QtNetwork/qtnetworkglobal.h>
+
+#include <QtNetwork/qsslsocket.h>
+#include <QtNetwork/qssl.h>
+
+#include <QtCore/qcryptographichash.h>
+#include <QtCore/qobject.h>
+
+QT_BEGIN_NAMESPACE
+
+enum class QDtlsError : unsigned char
+{
+    NoError,
+    InvalidInputParameters,
+    InvalidOperation,
+    UnderlyingSocketError,
+    RemoteClosedConnectionError,
+    PeerVerificationError,
+    TlsInitializationError,
+    TlsFatalError,
+    TlsNonFatalError
+};
+
+class QHostAddress;
+class QUdpSocket;
+class QByteArray;
+class QString;
+
+class QDtlsClientVerifierPrivate;
+class Q_NETWORK_EXPORT QDtlsClientVerifier : public QObject
+{
+    Q_OBJECT
+
+public:
+
+    explicit QDtlsClientVerifier(QObject *parent = nullptr);
+
+    struct GeneratorParameters
+    {
+        GeneratorParameters() = default;
+        GeneratorParameters(QCryptographicHash::Algorithm a, const QByteArray &s)
+            : hash(a), secret(s)
+        {
+        }
+        QCryptographicHash::Algorithm hash = QCryptographicHash::Sha1;
+        QByteArray secret;
+    };
+
+    bool setCookieGeneratorParameters(const GeneratorParameters &params);
+    GeneratorParameters cookieGeneratorParameters() const;
+
+    bool verifyClient(QUdpSocket *socket, const QByteArray &dgram,
+                      const QHostAddress &address, quint16 port);
+    QByteArray verifiedHello() const;
+
+    QDtlsError dtlsError() const;
+    QString dtlsErrorString() const;
+
+private:
+
+    Q_DECLARE_PRIVATE(QDtlsClientVerifier)
+    Q_DISABLE_COPY(QDtlsClientVerifier)
+};
+
+class QSslPreSharedKeyAuthenticator;
+template<class> class QVector;
+class QSslConfiguration;
+class QSslCipher;
+class QSslError;
+
+class QDtlsPrivate;
+class Q_NETWORK_EXPORT QDtls : public QObject
+{
+    Q_OBJECT
+
+public:
+
+    enum HandshakeState
+    {
+        HandshakeNotStarted,
+        HandshakeInProgress,
+        PeerVerificationFailed,
+        HandshakeComplete
+    };
+
+    explicit QDtls(QSslSocket::SslMode mode, QObject *parent = nullptr);
+
+    bool setRemote(const QHostAddress &address, quint16 port,
+                   const QString &verificationName = {});
+    bool setPeerVerificationName(const QString &name);
+    QHostAddress remoteAddress() const;
+    quint16 remotePort() const;
+    QString peerVerificationName() const;
+    QSslSocket::SslMode sslMode() const;
+
+    void setMtuHint(quint16 mtuHint);
+    quint16 mtuHint() const;
+
+    using GeneratorParameters = QDtlsClientVerifier::GeneratorParameters;
+    bool setCookieGeneratorParameters(const GeneratorParameters &params);
+    GeneratorParameters cookieGeneratorParameters() const;
+
+    bool setDtlsConfiguration(const QSslConfiguration &configuration);
+    QSslConfiguration dtlsConfiguration() const;
+
+    HandshakeState handshakeState() const;
+
+    bool doHandshake(QUdpSocket *socket, const QByteArray &dgram = {});
+    bool handleTimeout(QUdpSocket *socket);
+    bool resumeHandshakeAfterError(QUdpSocket *socket);
+    bool abortHandshakeAfterError(QUdpSocket *socket);
+    bool sendShutdownAlert(QUdpSocket *socket);
+
+    bool connectionEncrypted() const;
+    QSslCipher sessionCipher() const;
+    QSsl::SslProtocol sessionProtocol() const;
+
+    qint64 writeDatagramEncrypted(QUdpSocket *socket, const QByteArray &dgram);
+    QByteArray decryptDatagram(QUdpSocket *socket, const QByteArray &dgram);
+
+    QDtlsError dtlsError() const;
+    QString dtlsErrorString() const;
+
+    QVector<QSslError> peerVerificationErrors() const;
+    void ignoreVerificationErrors(const QVector<QSslError> &errorsToIgnore);
+
+Q_SIGNALS:
+
+    void pskRequired(QSslPreSharedKeyAuthenticator *authenticator);
+    void handshakeTimeout();
+
+private:
+
+    bool startHandshake(QUdpSocket *socket, const QByteArray &dgram);
+    bool continueHandshake(QUdpSocket *socket, const QByteArray &dgram);
+
+    Q_DECLARE_PRIVATE(QDtls)
+    Q_DISABLE_COPY(QDtls)
+};
+
+QT_END_NAMESPACE
+
+#endif // QDTLS_H
diff --git a/src/network/ssl/qdtls_openssl.cpp b/src/network/ssl/qdtls_openssl.cpp
new file mode 100644
index 0000000000..c3222bbd86
--- /dev/null
+++ b/src/network/ssl/qdtls_openssl.cpp
@@ -0,0 +1,1438 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtNetwork module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif // NOMINMAX
+#include "private/qnativesocketengine_p.h"
+
+#include "qsslpresharedkeyauthenticator_p.h"
+#include "qsslsocket_openssl_symbols_p.h"
+#include "qsslsocket_openssl_p.h"
+#include "qsslcertificate_p.h"
+#include "qdtls_openssl_p.h"
+#include "qudpsocket.h"
+#include "qssl_p.h"
+
+#include "qmessageauthenticationcode.h"
+#include "qcryptographichash.h"
+
+#include "qdebug.h"
+
+#include <cstring>
+#include <cstddef>
+
+QT_BEGIN_NAMESPACE
+
+#define QT_DTLS_VERBOSE 0
+
+#if QT_DTLS_VERBOSE
+
+#define qDtlsWarning(arg) qWarning(arg)
+#define qDtlsDebug(arg) qDebug(arg)
+
+#else
+
+#define qDtlsWarning(arg)
+#define qDtlsDebug(arg)
+
+#endif // QT_DTLS_VERBOSE
+
+namespace dtlsutil
+{
+
+QByteArray cookie_for_peer(SSL *ssl)
+{
+    Q_ASSERT(ssl);
+
+    // SSL_get_rbio does not increment the reference count
+    BIO *readBIO = q_SSL_get_rbio(ssl);
+    if (!readBIO) {
+        qCWarning(lcSsl, "No BIO (dgram) found in SSL object");
+        return {};
+    }
+
+    auto listener = static_cast<dtlsopenssl::DtlsState *>(q_BIO_get_app_data(readBIO));
+    if (!listener) {
+        qCWarning(lcSsl, "BIO_get_app_data returned invalid (nullptr) value");
+        return {};
+    }
+
+    const QHostAddress peerAddress(listener->remoteAddress);
+    const quint16 peerPort(listener->remotePort);
+    QByteArray peerData;
+    if (peerAddress.protocol() == QAbstractSocket::IPv6Protocol) {
+        const Q_IPV6ADDR sin6_addr(peerAddress.toIPv6Address());
+        peerData.resize(int(sizeof sin6_addr + sizeof peerPort));
+        char *dst = peerData.data();
+        std::memcpy(dst, &peerPort, sizeof peerPort);
+        dst += sizeof peerPort;
+        std::memcpy(dst, &sin6_addr, sizeof sin6_addr);
+    } else if (peerAddress.protocol() == QAbstractSocket::IPv4Protocol) {
+        const quint32 sin_addr(peerAddress.toIPv4Address());
+        peerData.resize(int(sizeof sin_addr + sizeof peerPort));
+        char *dst = peerData.data();
+        std::memcpy(dst, &peerPort, sizeof peerPort);
+        dst += sizeof peerPort;
+        std::memcpy(dst, &sin_addr, sizeof sin_addr);
+    } else {
+        Q_UNREACHABLE();
+    }
+
+    return peerData;
+}
+
+struct FallbackCookieSecret
+{
+    FallbackCookieSecret()
+    {
+        key.resize(32);
+        const int status = q_RAND_bytes(reinterpret_cast<unsigned char *>(key.data()),
+                                        key.size());
+        if (status <= 0)
+            key.clear();
+    }
+
+    QByteArray key;
+
+    Q_DISABLE_COPY(FallbackCookieSecret)
+};
+
+QByteArray fallbackSecret()
+{
+    static const FallbackCookieSecret generator;
+    return generator.key;
+}
+
+int next_timeoutMs(SSL *tlsConnection)
+{
+    Q_ASSERT(tlsConnection);
+    timeval timeLeft = {};
+    q_DTLSv1_get_timeout(tlsConnection, &timeLeft);
+    return timeLeft.tv_sec * 1000;
+}
+
+
+void delete_connection(SSL *ssl)
+{
+    // The 'deleter' for QSharedPointer<SSL>.
+    if (ssl)
+        q_SSL_free(ssl);
+}
+
+#if QT_CONFIG(opensslv11)
+
+void delete_BIO_ADDR(BIO_ADDR *bio)
+{
+    // A deleter for QSharedPointer<BIO_ADDR>
+    if (bio)
+        q_BIO_ADDR_free(bio);
+}
+
+void delete_bio_method(BIO_METHOD *method)
+{
+    // The 'deleter' for QSharedPointer<BIO_METHOD>.
+    if (method)
+        q_BIO_meth_free(method);
+}
+
+#endif // openssl 1.1
+
+// The 'deleter' for QScopedPointer<BIO>.
+struct bio_deleter
+{
+    static void cleanup(BIO *bio)
+    {
+        if (bio)
+            q_BIO_free(bio);
+    }
+};
+
+// The path MTU discovery is non-trivial: it's a mix of getsockopt/setsockopt
+// (IP_MTU/IP6_MTU/IP_MTU_DISCOVER) and fallback MTU values. It's not
+// supported on all platforms, worse so - imposes specific requirements on
+// underlying UDP socket etc. So for now, we either try a user-proposed MTU
+// hint  or rely on our own fallback value. As a fallback mtu OpenSSL uses 576
+// for IPv4 and 1280 for IPv6 (RFC 791, RFC 2460). To KIS we use 576. This
+// rather small MTU value does not affect the size that can be read/written
+// by QDtls, only a handshake (which is allowed to fragment).
+enum class MtuGuess : long
+{
+    defaultMtu = 576
+};
+
+} // namespace dtlsutil
+
+namespace dtlscallbacks
+{
+
+extern "C" int q_generate_cookie_callback(SSL *ssl, unsigned char *dst,
+                                          unsigned *cookieLength)
+{
+    if (!ssl || !dst || !cookieLength) {
+        qCWarning(lcSsl,
+                  "Failed to generate cookie - invalid (nullptr) parameter(s)");
+        return 0;
+    }
+
+    void *generic = q_SSL_get_ex_data(ssl, QSslSocketBackendPrivate::s_indexForSSLExtraData);
+    if (!generic) {
+        qCWarning(lcSsl, "SSL_get_ex_data returned nullptr, cannot generate cookie");
+        return 0;
+    }
+
+    *cookieLength = 0;
+
+    auto dtls = static_cast<dtlsopenssl::DtlsState *>(generic);
+    if (!dtls->secret.size())
+        return 0;
+
+    const QByteArray peerData(dtlsutil::cookie_for_peer(ssl));
+    if (!peerData.size())
+        return 0;
+
+    QMessageAuthenticationCode hmac(dtls->hashAlgorithm, dtls->secret);
+    hmac.addData(peerData);
+    const QByteArray cookie = hmac.result();
+    Q_ASSERT(cookie.size() >= 0);
+    // DTLS1_COOKIE_LENGTH is erroneously 256 bytes long, must be 255 - RFC 6347, 4.2.1.
+    *cookieLength = qMin(DTLS1_COOKIE_LENGTH - 1, cookie.size());
+    std::memcpy(dst, cookie.constData(), *cookieLength);
+
+    return 1;
+}
+
+extern "C" int q_verify_cookie_callback(SSL *ssl, const unsigned char *cookie,
+                                        unsigned cookieLength)
+{
+    if (!ssl || !cookie || !cookieLength) {
+        qCWarning(lcSsl, "Could not verify cookie, invalid (nullptr or zero) parameters");
+        return 0;
+    }
+
+    unsigned char newCookie[DTLS1_COOKIE_LENGTH] = {};
+    unsigned newCookieLength = 0;
+    if (q_generate_cookie_callback(ssl, newCookie, &newCookieLength) != 1)
+        return 0;
+
+    return newCookieLength == cookieLength
+           && !std::memcmp(cookie, newCookie, cookieLength);
+}
+
+extern "C" int q_X509DtlsCallback(int ok, X509_STORE_CTX *ctx)
+{
+    if (!ok) {
+        // Store the error and at which depth the error was detected.
+        SSL *ssl = static_cast<SSL *>(q_X509_STORE_CTX_get_ex_data(ctx, q_SSL_get_ex_data_X509_STORE_CTX_idx()));
+        if (!ssl) {
+            qCWarning(lcSsl, "X509_STORE_CTX_get_ex_data returned nullptr, handshake failure");
+            return 0;
+        }
+
+        void *generic = q_SSL_get_ex_data(ssl, QSslSocketBackendPrivate::s_indexForSSLExtraData);
+        if (!generic) {
+            qCWarning(lcSsl, "SSL_get_ex_data returned nullptr, handshake failure");
+            return 0;
+        }
+
+        auto dtls = static_cast<dtlsopenssl::DtlsState *>(generic);
+        dtls->x509Errors.append(QSslErrorEntry::fromStoreContext(ctx));
+    }
+
+    // Always return 1 (OK) to allow verification to continue. We handle the
+    // errors gracefully after collecting all errors, after verification has
+    // completed.
+    return 1;
+}
+
+extern "C" unsigned q_PSK_client_callback(SSL *ssl, const char *hint, char *identity,
+                                          unsigned max_identity_len, unsigned char *psk,
+                                          unsigned max_psk_len)
+{
+    auto *dtls = static_cast<dtlsopenssl::DtlsState *>(q_SSL_get_ex_data(ssl,
+                            QSslSocketBackendPrivate::s_indexForSSLExtraData));
+    if (!dtls)
+        return 0;
+
+    Q_ASSERT(dtls->dtlsPrivate);
+    return dtls->dtlsPrivate->pskClientCallback(hint, identity, max_identity_len, psk, max_psk_len);
+}
+
+extern "C" unsigned q_PSK_server_callback(SSL *ssl, const char *identity, unsigned char *psk,
+                                          unsigned max_psk_len)
+{
+    auto *dtls = static_cast<dtlsopenssl::DtlsState *>(q_SSL_get_ex_data(ssl,
+                            QSslSocketBackendPrivate::s_indexForSSLExtraData));
+    if (!dtls)
+        return 0;
+
+    Q_ASSERT(dtls->dtlsPrivate);
+    return dtls->dtlsPrivate->pskServerCallback(identity, psk, max_psk_len);
+}
+
+} // namespace dtlscallbacks
+
+namespace dtlsbio
+{
+
+extern "C" int q_dgram_read(BIO *bio, char *dst, int bytesToRead)
+{
+    if (!bio || !dst || bytesToRead <= 0) {
+        qCWarning(lcSsl, "invalid input parameter(s)");
+        return 0;
+    }
+
+    q_BIO_clear_retry_flags(bio);
+
+    auto dtls = static_cast<dtlsopenssl::DtlsState *>(q_BIO_get_app_data(bio));
+    // It's us who set data, if OpenSSL does too, the logic here is wrong
+    // then and we have to use BIO_set_app_data then!
+    Q_ASSERT(dtls);
+    int bytesRead = 0;
+    if (dtls->dgram.size()) {
+        bytesRead = qMin(dtls->dgram.size(), bytesToRead);
+        std::memcpy(dst, dtls->dgram.constData(), bytesRead);
+
+        if (!dtls->peeking)
+            dtls->dgram = dtls->dgram.mid(bytesRead);
+    } else {
+        bytesRead = -1;
+    }
+
+    if (bytesRead <= 0)
+        q_BIO_set_retry_read(bio);
+
+    return bytesRead;
+}
+
+extern "C" int q_dgram_write(BIO *bio, const char *src, int bytesToWrite)
+{
+    if (!bio || !src || bytesToWrite <= 0) {
+        qCWarning(lcSsl, "invalid input parameter(s)");
+        return 0;
+    }
+
+    q_BIO_clear_retry_flags(bio);
+
+    auto dtls = static_cast<dtlsopenssl::DtlsState *>(q_BIO_get_app_data(bio));
+    Q_ASSERT(dtls);
+    if (dtls->writeSuppressed) {
+        // See the comment in QDtls::startHandshake.
+        return bytesToWrite;
+    }
+
+    QUdpSocket *udpSocket = dtls->udpSocket;
+    Q_ASSERT(udpSocket);
+
+    const QByteArray dgram(QByteArray::fromRawData(src, bytesToWrite));
+    qint64 bytesWritten = -1;
+    if (udpSocket->state() == QAbstractSocket::ConnectedState) {
+        bytesWritten = udpSocket->write(dgram);
+    } else {
+        bytesWritten = udpSocket->writeDatagram(dgram, dtls->remoteAddress,
+                                                dtls->remotePort);
+    }
+
+    if (bytesWritten <= 0)
+        q_BIO_set_retry_write(bio);
+
+    Q_ASSERT(bytesWritten <= std::numeric_limits<int>::max());
+    return int(bytesWritten);
+}
+
+extern "C" int q_dgram_puts(BIO *bio, const char *src)
+{
+    if (!bio || !src) {
+        qCWarning(lcSsl, "invalid input parameter(s)");
+        return 0;
+    }
+
+    return q_dgram_write(bio, src, int(std::strlen(src)));
+}
+
+extern "C" long q_dgram_ctrl(BIO *bio, int cmd, long num, void *ptr)
+{
+    // This is our custom BIO_ctrl. bio.h defines a lot of BIO_CTRL_*
+    // and BIO_* constants and BIO_somename macros that expands to BIO_ctrl
+    // call with one of those constants as argument. What exactly BIO_ctrl
+    // does - depends on the 'cmd' and the type of BIO (so BIO_ctrl does
+    // not even have a single well-defined value meaning success or failure).
+    // We handle only the most generic commands - the ones documented for
+    // BIO_ctrl - and also DGRAM specific ones. And even for them - in most
+    // cases we do nothing but report a success or some non-error value.
+    // Documents also state: "Source/sink BIOs return an 0 if they do not
+    // recognize the BIO_ctrl() operation." - these are covered by 'default'
+    // label in the switch-statement below. Debug messages in the switch mean:
+    // 1) we got a command that is unexpected for dgram BIO, or:
+    // 2) we do not call any function that would lead to OpenSSL using this
+    //    command.
+
+    if (!bio) {
+        qDebug(lcSsl, "invalid 'bio' parameter (nullptr)");
+        return -1;
+    }
+
+    auto dtls = static_cast<dtlsopenssl::DtlsState *>(q_BIO_get_app_data(bio));
+    Q_ASSERT(dtls);
+
+#if !QT_CONFIG(opensslv11)
+    Q_UNUSED(num)
+#endif
+
+    switch (cmd) {
+    // Let's start from the most generic ones, in the order in which they are
+    // documented (as BIO_ctrl):
+    case BIO_CTRL_RESET:
+        // BIO_reset macro.
+        // From documentation:
+        // "BIO_reset() normally returns 1 for success and 0 or -1 for failure.
+        // File BIOs are an exception, they return 0 for success and -1 for
+        // failure."
+        // We have nothing to reset and we are not file BIO.
+        return 1;
+    case BIO_C_FILE_SEEK:
+    case BIO_C_FILE_TELL:
+        qDtlsWarning("Unexpected cmd (BIO_C_FILE_SEEK/BIO_C_FILE_TELL)");
+        // These are for BIO_seek, BIO_tell. We are not a file BIO.
+        // Non-negative return value means success.
+        return 0;
+    case BIO_CTRL_FLUSH:
+        // BIO_flush, nothing to do, we do not buffer any data.
+        // 0 or -1 means error, 1 - success.
+        return 1;
+    case BIO_CTRL_EOF:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_EOF)");
+        // BIO_eof, 1 means EOF read. Makes no sense for us.
+        return 0;
+    case BIO_CTRL_SET_CLOSE:
+        // BIO_set_close with BIO_CLOSE/BIO_NOCLOSE flags. Documented as
+        // always returning 1.
+        // From the documentation:
+        // "Typically BIO_CLOSE is used in a source/sink BIO to indicate that
+        // the underlying I/O stream should be closed when the BIO is freed."
+        //
+        // QUdpSocket we work with is not BIO's business, ignoring.
+        return 1;
+    case BIO_CTRL_GET_CLOSE:
+        // BIO_get_close. No, never, see the comment above.
+        return 0;
+    case BIO_CTRL_PENDING:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_PENDING)");
+        // BIO_pending. Not used by DTLS/OpenSSL (we are not buffering).
+        return 0;
+    case BIO_CTRL_WPENDING:
+        // No, we have nothing buffered.
+        return 0;
+    // The constants below are not documented as a part BIO_ctrl documentation,
+    // but they are also not type-specific.
+    case BIO_CTRL_DUP:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DUP)");
+        // BIO_dup_state, not used by DTLS (and socket-related BIOs in general).
+        // For some very specific BIO type this 'cmd' would copy some state
+        // from 'bio' to (BIO*)'ptr'. 1 means success.
+        return 0;
+    case BIO_CTRL_SET_CALLBACK:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_SET_CALLBACK)");
+        // BIO_set_info_callback. We never call this, OpenSSL does not do this
+        // on its own (normally it's used if client code wants to have some
+        // debug information, for example, dumping handshake state via
+        // BIO_printf from SSL info_callback).
+        return 0;
+    case BIO_CTRL_GET_CALLBACK:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_GET_CALLBACK)");
+        // BIO_get_info_callback. We never call this.
+        if (ptr)
+            *static_cast<bio_info_cb **>(ptr) = nullptr;
+        return 0;
+    case BIO_CTRL_SET:
+    case BIO_CTRL_GET:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_SET/BIO_CTRL_GET)");
+        // Somewhat 'documented' as setting/getting IO type. Not used anywhere
+        // except BIO_buffer_get_num_lines (which contradics 'get IO type').
+        // Ignoring.
+        return 0;
+    // DGRAM-specific operation, we have to return some reasonable value
+    // (so far, I've encountered only peek mode switching, connect).
+    case BIO_CTRL_DGRAM_CONNECT:
+        // BIO_ctrl_dgram_connect. Not needed. Our 'dtls' already knows
+        // the peer's address/port. Report success though.
+        return 1;
+    case BIO_CTRL_DGRAM_SET_CONNECTED:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_SET_CONNECTED)");
+        // BIO_ctrl_dgram_set_connected. We never call it, OpenSSL does
+        // not call it on its own (so normally it's done by client code).
+        // Similar to BIO_CTRL_DGRAM_CONNECT, but it also informs the BIO
+        // that its UDP socket is connected. We never need it though.
+        return -1;
+    case BIO_CTRL_DGRAM_SET_RECV_TIMEOUT:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_SET_RECV_TIMEOUT)");
+        // Essentially setsockopt with SO_RCVTIMEO, not needed, our sockets
+        // are non-blocking.
+        return -1;
+    case BIO_CTRL_DGRAM_GET_RECV_TIMEOUT:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_GET_RECV_TIMEOUT)");
+        // getsockopt with SO_RCVTIMEO, not needed, our sockets are
+        // non-blocking. ptr is timeval *.
+        return -1;
+    case BIO_CTRL_DGRAM_SET_SEND_TIMEOUT:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_SET_SEND_TIMEOUT)");
+        // setsockopt, SO_SNDTIMEO, cannot happen.
+        return -1;
+    case BIO_CTRL_DGRAM_GET_SEND_TIMEOUT:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_GET_SEND_TIMEOUT)");
+        // getsockopt, SO_SNDTIMEO, cannot happen.
+        return -1;
+    case BIO_CTRL_DGRAM_GET_RECV_TIMER_EXP:
+        // BIO_dgram_recv_timedout. No, we are non-blocking.
+        return 0;
+    case BIO_CTRL_DGRAM_GET_SEND_TIMER_EXP:
+        // BIO_dgram_send_timedout. No, we are non-blocking.
+        return 0;
+    case BIO_CTRL_DGRAM_MTU_DISCOVER:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_MTU_DISCOVER)");
+        // setsockopt, IP_MTU_DISCOVER/IP6_MTU_DISCOVER, to be done
+        // in QUdpSocket instead. OpenSSL never calls it, only client
+        // code.
+        return 1;
+    case BIO_CTRL_DGRAM_QUERY_MTU:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_QUERY_MTU)");
+        // To be done in QUdpSocket instead.
+        return 1;
+    case BIO_CTRL_DGRAM_GET_FALLBACK_MTU:
+        qDtlsWarning("Unexpected command *BIO_CTRL_DGRAM_GET_FALLBACK_MTU)");
+        // Without SSL_OP_NO_QUERY_MTU set on SSL, OpenSSL can request for
+        // fallback MTU after several re-transmissions.
+        // Should never happen in our case.
+        return long(dtlsutil::MtuGuess::defaultMtu);
+    case BIO_CTRL_DGRAM_GET_MTU:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_GET_MTU)");
+        return -1;
+    case BIO_CTRL_DGRAM_SET_MTU:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_SET_MTU)");
+        // Should not happen (we don't call BIO_ctrl with this parameter)
+        // and set MTU on SSL instead.
+        return -1; // num is mtu and it's a return value meaning success.
+    case BIO_CTRL_DGRAM_MTU_EXCEEDED:
+        qDtlsWarning("Unexpected cmd (BIO_CTRL_DGRAM_MTU_EXCEEDED)");
+        return 0;
+    case BIO_CTRL_DGRAM_GET_PEER:
+        qDtlsDebug("BIO_CTRL_DGRAM_GET_PEER");
+        // BIO_dgram_get_peer. We do not return a real address (DTLS is not
+        // using this address), but let's pretend a success.
+        switch (dtls->remoteAddress.protocol()) {
+        case QAbstractSocket::IPv6Protocol:
+            return sizeof(sockaddr_in6);
+        case QAbstractSocket::IPv4Protocol:
+            return sizeof(sockaddr_in);
+        default:
+            return -1;
+        }
+    case BIO_CTRL_DGRAM_SET_PEER:
+        // Similar to BIO_CTRL_DGRAM_CONNECTED.
+        return 1;
+    case BIO_CTRL_DGRAM_SET_NEXT_TIMEOUT:
+        // DTLSTODO: I'm not sure yet, how it's used by OpenSSL.
+        return 1;
+    case BIO_CTRL_DGRAM_SET_DONT_FRAG:
+        qDtlsDebug("BIO_CTRL_DGRAM_SET_DONT_FRAG");
+        // To be done in QUdpSocket, it's about IP_DONTFRAG etc.
+        return 1;
+    case BIO_CTRL_DGRAM_GET_MTU_OVERHEAD:
+        // AFAIK it's 28 for IPv4 and 48 for IPv6, but let's pretend it's 0
+        // so that OpenSSL does not start suddenly fragmenting the first
+        // client hello (which will result in DTLSv1_listen rejecting it).
+        return 0;
+#if QT_CONFIG(opensslv11)
+    case BIO_CTRL_DGRAM_SET_PEEK_MODE:
+        dtls->peeking = num;
+        return 1;
+#endif
+    default:;
+#if QT_DTLS_VERBOSE
+        qWarning() << "Unexpected cmd (" << cmd << ")";
+#endif
+    }
+
+    return 0;
+}
+
+extern "C" int q_dgram_create(BIO *bio)
+{
+#if QT_CONFIG(opensslv11)
+    q_BIO_set_init(bio, 1);
+#else
+    bio->init = 1;
+#endif
+    // With a custom BIO you'd normally allocate some implementation-specific
+    // data and append it to this new BIO: bio->ptr = ... (pre 1.0.2) or
+    // BIO_set_data (1.1). We don't need it and thus q_dgram_destroy below
+    // is a noop.
+    return 1;
+}
+
+extern "C" int q_dgram_destroy(BIO *bio)
+{
+    Q_UNUSED(bio)
+    return 1;
+}
+
+const char * const qdtlsMethodName = "qdtlsbio";
+
+#if !QT_CONFIG(opensslv11)
+
+/*
+typedef struct bio_method_st {
+    int type;
+    const char *name;
+    int (*bwrite) (BIO *, const char *, int);
+    int (*bread) (BIO *, char *, int);
+    int (*bputs) (BIO *, const char *);
+    int (*bgets) (BIO *, char *, int);
+    long (*ctrl) (BIO *, int, long, void *);
+    int (*create) (BIO *);
+    int (*destroy) (BIO *);
+    long (*callback_ctrl) (BIO *, int, bio_info_cb *);
+} BIO_METHOD;
+*/
+
+bio_method_st qdtlsCustomBioMethod =
+{
+    BIO_TYPE_DGRAM,
+    qdtlsMethodName,
+    q_dgram_write,
+    q_dgram_read,
+    q_dgram_puts,
+    nullptr,
+    q_dgram_ctrl,
+    q_dgram_create,
+    q_dgram_destroy,
+    nullptr
+};
+
+#endif // openssl < 1.1
+
+} // namespace dtlsbio
+
+namespace dtlsopenssl
+{
+
+bool DtlsState::init(QDtlsBasePrivate *dtlsBase, QUdpSocket *socket,
+                     const QHostAddress &remote, quint16 port,
+                     const QByteArray &receivedMessage)
+{
+    Q_ASSERT(dtlsBase);
+    Q_ASSERT(socket);
+
+    if (!tlsContext.data() && !initTls(dtlsBase))
+        return false;
+
+    udpSocket = socket;
+
+    setLinkMtu(dtlsBase);
+
+    dgram = receivedMessage;
+    remoteAddress = remote;
+    remotePort = port;
+
+    // SSL_get_rbio does not increment a reference count.
+    BIO *bio = q_SSL_get_rbio(tlsConnection.data());
+    Q_ASSERT(bio);
+    q_BIO_set_app_data(bio, this);
+
+    return true;
+}
+
+void DtlsState::reset()
+{
+    tlsConnection.reset();
+    tlsContext.reset();
+}
+
+bool DtlsState::initTls(QDtlsBasePrivate *dtlsBase)
+{
+    if (tlsContext.data())
+        return true;
+
+    if (!QSslSocket::supportsSsl())
+        return false;
+
+    if (!initCtxAndConnection(dtlsBase))
+        return false;
+
+    if (!initBIO(dtlsBase)) {
+        tlsConnection.reset();
+        tlsContext.reset();
+        return false;
+    }
+
+    return true;
+}
+
+bool DtlsState::initCtxAndConnection(QDtlsBasePrivate *dtlsBase)
+{
+    Q_ASSERT(dtlsBase);
+    Q_ASSERT(QSslSocket::supportsSsl());
+
+    // create a deep copy of our configuration
+    auto configurationCopy = new QSslConfigurationPrivate(dtlsBase->dtlsConfiguration);
+    configurationCopy->ref.store(0); // the QSslConfiguration constructor refs up
+
+    // DTLSTODO: check we do not set something DTLS-incompatible there ...
+    // 'true' - means load root certs on-demand loading - double check how this
+    // expected to be done (QSslSocket).
+    TlsContext newContext(QSslContext::sharedFromConfiguration(dtlsBase->mode,
+                                                               configurationCopy,
+                                                               true));
+
+    if (newContext->error() != QSslError::NoError) {
+        dtlsBase->setDtlsError(QDtlsError::TlsInitializationError, newContext->errorString());
+        return false;
+    }
+
+    TlsConnection newConnection(newContext->createSsl(), dtlsutil::delete_connection);
+    if (!newConnection.data()) {
+        dtlsBase->setDtlsError(QDtlsError::TlsInitializationError, QDtls::tr("SSL_new failed"));
+        return false;
+    }
+
+    const int set = q_SSL_set_ex_data(newConnection.data(),
+                                      QSslSocketBackendPrivate::s_indexForSSLExtraData,
+                                      this);
+
+    if (set != 1 && configurationCopy->peerVerifyMode != QSslSocket::VerifyNone) {
+        dtlsBase->setDtlsError(QDtlsError::TlsInitializationError, QDtls::tr("SSL_set_ex_data failed"));
+        return false;
+    }
+
+    if (dtlsBase->mode == QSslSocket::SslServerMode) {
+        if (dtlsBase->dtlsConfiguration.dtlsCookieEnabled)
+            q_SSL_set_options(newConnection.data(), SSL_OP_COOKIE_EXCHANGE);
+        q_SSL_set_psk_server_callback(newConnection.data(), dtlscallbacks::q_PSK_server_callback);
+    } else {
+        q_SSL_set_psk_client_callback(newConnection.data(), dtlscallbacks::q_PSK_client_callback);
+    }
+
+    tlsContext.swap(newContext);
+    tlsConnection.swap(newConnection);
+
+    return true;
+}
+
+bool DtlsState::initBIO(QDtlsBasePrivate *dtlsBase)
+{
+    Q_ASSERT(dtlsBase);
+    Q_ASSERT(tlsContext.data() && tlsConnection.data());
+
+#if QT_CONFIG(opensslv11)
+    BioMethod customMethod(q_BIO_meth_new(BIO_TYPE_DGRAM, dtlsbio::qdtlsMethodName),
+                           dtlsutil::delete_bio_method);
+    if (!customMethod.data()) {
+        dtlsBase->setDtlsError(QDtlsError::TlsInitializationError,
+                               QDtls::tr("BIO_meth_new failed"));
+        return false;
+    }
+
+    BIO_METHOD *biom = customMethod.data();
+    q_BIO_meth_set_create(biom, dtlsbio::q_dgram_create);
+    q_BIO_meth_set_destroy(biom, dtlsbio::q_dgram_destroy);
+    q_BIO_meth_set_read(biom, dtlsbio::q_dgram_read);
+    q_BIO_meth_set_write(biom, dtlsbio::q_dgram_write);
+    q_BIO_meth_set_puts(biom, dtlsbio::q_dgram_puts);
+    q_BIO_meth_set_ctrl(biom, dtlsbio::q_dgram_ctrl);
+#else
+    BIO_METHOD *biom = &dtlsbio::qdtlsCustomBioMethod;
+#endif // openssl 1.1
+
+    QScopedPointer<BIO, dtlsutil::bio_deleter> newBio(q_BIO_new(biom));
+    BIO *bio = newBio.data();
+    if (!bio) {
+        dtlsBase->setDtlsError(QDtlsError::TlsInitializationError, QDtls::tr("BIO_new failed"));
+        return false;
+    }
+
+    q_SSL_set_bio(tlsConnection.data(), bio, bio);
+    newBio.take();
+
+#if QT_CONFIG(opensslv11)
+    bioMethod.swap(customMethod);
+#endif // openssl 1.1
+
+    return true;
+}
+
+void DtlsState::setLinkMtu(QDtlsBasePrivate *dtlsBase)
+{
+    Q_ASSERT(dtlsBase);
+    Q_ASSERT(udpSocket);
+    Q_ASSERT(tlsConnection.data());
+
+    long mtu = dtlsBase->mtuHint;
+    if (!mtu) {
+        // If the underlying QUdpSocket was connected, getsockopt with
+        // IP_MTU/IP6_MTU can give us some hint:
+        bool optionFound = false;
+        if (udpSocket->state() == QAbstractSocket::ConnectedState) {
+            const QVariant val(udpSocket->socketOption(QAbstractSocket::PathMtuSocketOption));
+            if (val.isValid() && val.canConvert<int>())
+                mtu = val.toInt(&optionFound);
+        }
+
+        if (!optionFound || mtu <= 0) {
+            // OK, our own initial guess.
+            mtu = long(dtlsutil::MtuGuess::defaultMtu);
+        }
+    }
+
+    // For now, we disable this option.
+    q_SSL_set_options(tlsConnection.data(), SSL_OP_NO_QUERY_MTU);
+
+    q_DTLS_set_link_mtu(tlsConnection.data(), mtu);
+}
+
+} // namespace dtlsopenssl
+
+QDtlsClientVerifierOpenSSL::QDtlsClientVerifierOpenSSL()
+{
+    secret = dtlsutil::fallbackSecret();
+}
+
+bool QDtlsClientVerifierOpenSSL::verifyClient(QUdpSocket *socket, const QByteArray &dgram,
+                                              const QHostAddress &address, quint16 port)
+{
+    Q_ASSERT(socket);
+    Q_ASSERT(dgram.size());
+    Q_ASSERT(!address.isNull());
+    Q_ASSERT(port);
+
+    clearDtlsError();
+    verifiedClientHello.clear();
+
+    if (!dtls.init(this, socket, address, port, dgram))
+        return false;
+
+    dtls.secret = secret;
+    dtls.hashAlgorithm = hashAlgorithm;
+
+    Q_ASSERT(dtls.tlsConnection.data());
+#if QT_CONFIG(opensslv11)
+    QSharedPointer<BIO_ADDR> peer(q_BIO_ADDR_new(), dtlsutil::delete_BIO_ADDR);
+    if (!peer.data()) {
+        setDtlsError(QDtlsError::TlsInitializationError,
+                     QDtlsClientVerifier::tr("BIO_ADDR_new failed, ignoring client hello"));
+        return false;
+    }
+
+    const int ret = q_DTLSv1_listen(dtls.tlsConnection.data(), peer.data());
+    if (ret < 0) {
+        // Since 1.1 - it's a fatal error (not so in 1.0.2 for non-blocking socket)
+        setDtlsError(QDtlsError::TlsFatalError, QSslSocketBackendPrivate::getErrorsFromOpenSsl());
+        return false;
+    }
+#else
+    qt_sockaddr peer;
+    const int ret = q_DTLSv1_listen(dtls.tlsConnection.data(), &peer);
+#endif
+    if (ret > 0) {
+        verifiedClientHello = dgram;
+        return true;
+    }
+
+    return false;
+}
+
+void QDtlsPrivateOpenSSL::TimeoutHandler::start(int hintMs)
+{
+    Q_ASSERT(timerId == -1);
+    timerId = startTimer(hintMs > 0 ? hintMs : timeoutMs, Qt::PreciseTimer);
+}
+
+void QDtlsPrivateOpenSSL::TimeoutHandler::doubleTimeout()
+{
+    if (timeoutMs * 2 < 60000)
+        timeoutMs *= 2;
+    else
+        timeoutMs = 60000;
+}
+
+void QDtlsPrivateOpenSSL::TimeoutHandler::stop()
+{
+    if (timerId != -1) {
+        killTimer(timerId);
+        timerId = -1;
+    }
+}
+
+void QDtlsPrivateOpenSSL::TimeoutHandler::timerEvent(QTimerEvent *event)
+{
+    Q_UNUSED(event)
+    Q_ASSERT(timerId != -1);
+
+    killTimer(timerId);
+    timerId = -1;
+
+    Q_ASSERT(dtlsConnection);
+    dtlsConnection->reportTimeout();
+}
+
+QDtlsPrivateOpenSSL::QDtlsPrivateOpenSSL()
+{
+    secret = dtlsutil::fallbackSecret();
+    dtls.dtlsPrivate = this;
+}
+
+bool QDtlsPrivateOpenSSL::startHandshake(QUdpSocket *socket, const QByteArray &dgram)
+{
+    Q_ASSERT(socket);
+    Q_ASSERT(handshakeState == QDtls::HandshakeNotStarted);
+
+    clearDtlsError();
+    connectionEncrypted = false;
+
+    if (!dtls.init(this, socket, remoteAddress, remotePort, dgram))
+        return false;
+
+    if (mode == QSslSocket::SslServerMode && dtlsConfiguration.dtlsCookieEnabled) {
+        dtls.secret = secret;
+        dtls.hashAlgorithm = hashAlgorithm;
+        // Let's prepare the state machine so that message sequence 1 does not
+        // surprise DTLS/OpenSSL (such a message would be disregarded as
+        // 'stale or future' in SSL_accept otherwise):
+        int result = 0;
+#if QT_CONFIG(opensslv11)
+        QSharedPointer<BIO_ADDR> peer(q_BIO_ADDR_new(), dtlsutil::delete_BIO_ADDR);
+        if (!peer.data()) {
+            setDtlsError(QDtlsError::TlsInitializationError,
+                         QDtls::tr("BIO_ADD_new failed, cannot start handshake"));
+            return false;
+        }
+
+        // If it's an invalid/unexpected ClientHello, we don't want to send
+        // VerifyClientRequest - it's a job of QDtlsClientVerifier - so we
+        // suppress any attempts to write into socket:
+        dtls.writeSuppressed = true;
+        result = q_DTLSv1_listen(dtls.tlsConnection.data(), peer.data());
+        dtls.writeSuppressed = false;
+#else
+        qt_sockaddr peer;
+        result = q_DTLSv1_listen(dtls.tlsConnection.data(), &peer);
+#endif
+        if (result <= 0) {
+            setDtlsError(QDtlsError::TlsFatalError,
+                         QDtls::tr("Cannot start the handshake, verified client hello expected"));
+            dtls.reset();
+            return false;
+        }
+    }
+
+    handshakeState = QDtls::HandshakeInProgress;
+    opensslErrors.clear();
+    tlsErrors.clear();
+
+    return continueHandshake(socket, dgram);
+}
+
+bool QDtlsPrivateOpenSSL::continueHandshake(QUdpSocket *socket, const QByteArray &dgram)
+{
+    Q_ASSERT(socket);
+
+    Q_ASSERT(handshakeState == QDtls::HandshakeInProgress);
+
+    clearDtlsError();
+
+    if (timeoutHandler.data())
+        timeoutHandler->stop();
+
+    if (!dtls.init(this, socket, remoteAddress, remotePort, dgram))
+        return false;
+
+    dtls.x509Errors.clear();
+
+    int result = 0;
+    if (mode == QSslSocket::SslServerMode)
+        result = q_SSL_accept(dtls.tlsConnection.data());
+    else
+        result = q_SSL_connect(dtls.tlsConnection.data());
+
+    // DTLSTODO: Investigate/test if it makes sense - QSslSocket can emit
+    // peerVerifyError at this point (and thus potentially client code
+    // will close the underlying TCP connection immediately), but we are using
+    // QUdpSocket, no connection to close, our verification callback returns 1
+    // (verified OK) and this probably means OpenSSL has already sent a reply
+    // to the server's hello/certificate.
+
+    opensslErrors << dtls.x509Errors;
+
+    if (result <= 0) {
+        const auto code = q_SSL_get_error(dtls.tlsConnection.data(), result);
+        switch (code) {
+        case SSL_ERROR_WANT_READ:
+        case SSL_ERROR_WANT_WRITE:
+            // DTLSTODO: to be tested - in principle, if it was the first call to
+            // continueHandshake and server for some reason discards the client
+            // hello message (even the verified one) - our 'this' will probably
+            // forever stay in this strange InProgress state? (the client
+            // will dully re-transmit the same hello and we discard it again?)
+            // SSL_get_state can provide more information about state
+            // machine and we can switch to NotStarted (since we have not
+            // replied with our hello ...)
+            if (mode == QSslSocket::SslClientMode) {
+                if (!timeoutHandler.data()) {
+                    timeoutHandler.reset(new TimeoutHandler);
+                    timeoutHandler->dtlsConnection = this;
+                } else {
+                    // Back to 1s.
+                    timeoutHandler->resetTimeout();
+                }
+
+                timeoutHandler->start();
+            }
+            return true; // The handshake is not yet complete.
+        default:
+            storePeerCertificates();
+            setDtlsError(QDtlsError::TlsFatalError, QDtls::tr("Error during SSL handshake: ")
+                                                    + QSslSocketBackendPrivate::getErrorsFromOpenSsl());
+            dtls.reset();
+            handshakeState = QDtls::HandshakeNotStarted;
+            return false;
+        }
+    }
+
+    storePeerCertificates();
+    fetchNegotiatedParameters();
+
+    const bool doVerifyPeer = dtlsConfiguration.peerVerifyMode == QSslSocket::VerifyPeer
+                              || (dtlsConfiguration.peerVerifyMode == QSslSocket::AutoVerifyPeer
+                                  && mode == QSslSocket::SslClientMode);
+
+    if (!doVerifyPeer || verifyPeer()) {
+        connectionEncrypted = true;
+        handshakeState = QDtls::HandshakeComplete;
+        return true;
+    }
+
+    setDtlsError(QDtlsError::PeerVerificationError, QDtls::tr("Peer verification failed"));
+    handshakeState = QDtls::PeerVerificationFailed;
+    return false;
+}
+
+
+bool QDtlsPrivateOpenSSL::handleTimeout(QUdpSocket *socket)
+{
+    Q_ASSERT(socket);
+
+    Q_ASSERT(timeoutHandler.data());
+    Q_ASSERT(dtls.tlsConnection.data());
+
+    clearDtlsError();
+
+    dtls.udpSocket = socket;
+
+    if (q_DTLSv1_handle_timeout(dtls.tlsConnection.data()) > 0) {
+        timeoutHandler->doubleTimeout();
+        timeoutHandler->start();
+    } else {
+        timeoutHandler->start(dtlsutil::next_timeoutMs(dtls.tlsConnection.data()));
+    }
+
+    return true;
+}
+
+bool QDtlsPrivateOpenSSL::resumeHandshake(QUdpSocket *socket)
+{
+    Q_UNUSED(socket);
+    Q_ASSERT(socket);
+    Q_ASSERT(handshakeState == QDtls::PeerVerificationFailed);
+
+    clearDtlsError();
+
+    if (tlsErrorsWereIgnored()) {
+        handshakeState = QDtls::HandshakeComplete;
+        connectionEncrypted = true;
+        tlsErrors.clear();
+        tlsErrorsToIgnore.clear();
+        return true;
+    }
+
+    return false;
+}
+
+void QDtlsPrivateOpenSSL::abortHandshake(QUdpSocket *socket)
+{
+    Q_ASSERT(socket);
+    Q_ASSERT(handshakeState == QDtls::PeerVerificationFailed);
+
+    clearDtlsError();
+
+    // Yes, while peer verification failed, we were actually encrypted.
+    // Let's play it nice - inform our peer about connection shut down.
+    sendShutdownAlert(socket);
+}
+
+void QDtlsPrivateOpenSSL::sendShutdownAlert(QUdpSocket *socket)
+{
+    Q_ASSERT(socket);
+
+    clearDtlsError();
+
+    if (connectionEncrypted && !connectionWasShutdown) {
+        dtls.udpSocket = socket;
+        Q_ASSERT(dtls.tlsConnection.data());
+        q_SSL_shutdown(dtls.tlsConnection.data());
+    }
+
+    resetDtls();
+}
+
+qint64 QDtlsPrivateOpenSSL::writeDatagramEncrypted(QUdpSocket *socket,
+                                                   const QByteArray &dgram)
+{
+    Q_ASSERT(socket);
+    Q_ASSERT(dtls.tlsConnection.data());
+    Q_ASSERT(connectionEncrypted);
+
+    clearDtlsError();
+
+    dtls.udpSocket = socket;
+    const int written = q_SSL_write(dtls.tlsConnection.data(),
+                                    dgram.constData(), dgram.size());
+    if (written > 0)
+        return written;
+
+    const unsigned long errorCode = q_ERR_get_error();
+    if (!dgram.size() && errorCode == SSL_ERROR_NONE) {
+        // With OpenSSL <= 1.1 this can happen. For example, DTLS client
+        // tries to reconnect (while re-using the same address/port) -
+        // DTLS server drops a message with unexpected epoch but says - no
+        // error. We leave to client code to resolve such problems until
+        // OpenSSL provides something better.
+        return 0;
+    }
+
+    switch (errorCode) {
+    case SSL_ERROR_WANT_WRITE:
+    case SSL_ERROR_WANT_READ:
+        // We do not set any error/description ... a user can probably re-try
+        // sending a datagram.
+        break;
+    case SSL_ERROR_ZERO_RETURN:
+        connectionWasShutdown = true;
+        setDtlsError(QDtlsError::TlsFatalError, QDtls::tr("The DTLS connection has been closed"));
+        handshakeState = QDtls::HandshakeNotStarted;
+        dtls.reset();
+        break;
+    case SSL_ERROR_SYSCALL:
+    case SSL_ERROR_SSL:
+    default:
+        // DTLSTODO: we don't know yet what to do. Tests needed - probably,
+        // some errors can be just ignored (it's UDP, not TCP after all).
+        // Unlike QSslSocket we do not abort though.
+        QString description(QSslSocketBackendPrivate::getErrorsFromOpenSsl());
+        if (socket->error() != QAbstractSocket::UnknownSocketError && description.isEmpty()) {
+            setDtlsError(QDtlsError::UnderlyingSocketError, socket->errorString());
+        } else {
+            setDtlsError(QDtlsError::TlsFatalError, QDtls::tr("Error while writing: ")
+                                                    + description);
+        }
+    }
+
+    return -1;
+}
+
+QByteArray QDtlsPrivateOpenSSL::decryptDatagram(QUdpSocket *socket, const QByteArray &tlsdgram)
+{
+    Q_ASSERT(socket);
+    Q_ASSERT(tlsdgram.size());
+
+    Q_ASSERT(dtls.tlsConnection.data());
+    Q_ASSERT(connectionEncrypted);
+
+    dtls.dgram = tlsdgram;
+    dtls.udpSocket = socket;
+
+    clearDtlsError();
+
+    QByteArray dgram;
+    dgram.resize(tlsdgram.size());
+    const int read = q_SSL_read(dtls.tlsConnection.data(), dgram.data(),
+                                dgram.size());
+
+    if (read > 0) {
+        dgram.resize(read);
+        return dgram;
+    }
+
+    dgram.clear();
+    unsigned long errorCode = q_ERR_get_error();
+    if (errorCode == SSL_ERROR_NONE) {
+        const int shutdown = q_SSL_get_shutdown(dtls.tlsConnection.data());
+        if (shutdown & SSL_RECEIVED_SHUTDOWN)
+            errorCode = SSL_ERROR_ZERO_RETURN;
+        else
+            return dgram;
+    }
+
+    switch (errorCode) {
+    case SSL_ERROR_WANT_READ:
+    case SSL_ERROR_WANT_WRITE:
+        return dgram;
+    case SSL_ERROR_ZERO_RETURN:
+        // "The connection was shut down cleanly" ... hmm, whatever,
+        // needs testing (DTLSTODO).
+        connectionWasShutdown = true;
+        setDtlsError(QDtlsError::RemoteClosedConnectionError,
+                     QDtls::tr("The DTLS connection has been shutdown"));
+        dtls.reset();
+        connectionEncrypted = false;
+        handshakeState = QDtls::HandshakeNotStarted;
+        return dgram;
+    case SSL_ERROR_SYSCALL: // some IO error
+    case SSL_ERROR_SSL:     // error in the SSL library
+        // DTLSTODO: Apparently, some errors can be ignored, for example,
+        // ECONNRESET etc. This all needs a lot of testing!!!
+    default:
+        setDtlsError(QDtlsError::TlsNonFatalError, QDtls::tr("Error while reading: ")
+                                                   + QSslSocketBackendPrivate::getErrorsFromOpenSsl());
+        return dgram;
+    }
+}
+
+unsigned QDtlsPrivateOpenSSL::pskClientCallback(const char *hint, char *identity,
+                                                unsigned max_identity_len,
+                                                unsigned char *psk,
+                                                unsigned max_psk_len)
+{
+    // The code below is taken (with some modifications) from qsslsocket_openssl
+    // - alas, we cannot simply re-use it, it's in QSslSocketPrivate.
+
+    Q_Q(QDtls);
+
+    {
+        QSslPreSharedKeyAuthenticator authenticator;
+        // Fill in some read-only fields (for client code)
+        if (hint) {
+            identityHint.clear();
+            identityHint.append(hint);
+            // From the original code in QSslSocket:
+            // "it's NULL terminated, but do not include the NULL" == this fromRawData(ptr/size).
+            authenticator.d->identityHint = QByteArray::fromRawData(identityHint.constData(),
+                                                                    int(std::strlen(hint)));
+        }
+
+        authenticator.d->maximumIdentityLength = int(max_identity_len) - 1; // needs to be NULL terminated
+        authenticator.d->maximumPreSharedKeyLength = int(max_psk_len);
+
+        pskAuthenticator.swap(authenticator);
+    }
+
+    // Let the client provide the remaining bits...
+    emit q->pskRequired(&pskAuthenticator);
+
+    // No PSK set? Return now to make the handshake fail
+    if (pskAuthenticator.preSharedKey().isEmpty())
+        return 0;
+
+    // Copy data back into OpenSSL
+    const int identityLength = qMin(pskAuthenticator.identity().length(),
+                                    pskAuthenticator.maximumIdentityLength());
+    std::memcpy(identity, pskAuthenticator.identity().constData(), identityLength);
+    identity[identityLength] = 0;
+
+    const int pskLength = qMin(pskAuthenticator.preSharedKey().length(),
+                               pskAuthenticator.maximumPreSharedKeyLength());
+    std::memcpy(psk, pskAuthenticator.preSharedKey().constData(), pskLength);
+
+    return pskLength;
+}
+
+unsigned QDtlsPrivateOpenSSL::pskServerCallback(const char *identity, unsigned char *psk,
+                                                unsigned max_psk_len)
+{
+    Q_Q(QDtls);
+
+    {
+        QSslPreSharedKeyAuthenticator authenticator;
+        // Fill in some read-only fields (for the user)
+        authenticator.d->identityHint = dtlsConfiguration.preSharedKeyIdentityHint;
+        authenticator.d->identity = identity;
+        authenticator.d->maximumIdentityLength = 0; // user cannot set an identity
+        authenticator.d->maximumPreSharedKeyLength = int(max_psk_len);
+
+        pskAuthenticator.swap(authenticator);
+    }
+
+    // Let the client provide the remaining bits...
+    emit q->pskRequired(&pskAuthenticator);
+
+    // No PSK set? Return now to make the handshake fail
+    if (pskAuthenticator.preSharedKey().isEmpty())
+        return 0;
+
+    // Copy data back into OpenSSL
+    const int pskLength = qMin(pskAuthenticator.preSharedKey().length(),
+                               pskAuthenticator.maximumPreSharedKeyLength());
+
+    std::memcpy(psk, pskAuthenticator.preSharedKey().constData(), pskLength);
+
+    return pskLength;
+}
+
+// The definition is located in qsslsocket_openssl.cpp.
+QSslError _q_OpenSSL_to_QSslError(int errorCode, const QSslCertificate &cert);
+
+bool QDtlsPrivateOpenSSL::verifyPeer()
+{
+    // DTLSTODO: Windows-specific code for CA fetcher is not here yet.
+    QVector<QSslError> errors;
+
+    // Check the whole chain for blacklisting (including root, as we check for
+    // subjectInfo and issuer)
+    for (const QSslCertificate &cert : qAsConst(dtlsConfiguration.peerCertificateChain)) {
+        if (QSslCertificatePrivate::isBlacklisted(cert))
+            errors << QSslError(QSslError::CertificateBlacklisted, cert);
+    }
+
+    if (dtlsConfiguration.peerCertificate.isNull()) {
+        errors << QSslError(QSslError::NoPeerCertificate);
+    } else if (mode == QSslSocket::SslClientMode) {
+        // Check the peer certificate itself. First try the subject's common name
+        // (CN) as a wildcard, then try all alternate subject name DNS entries the
+        // same way.
+
+        // QSslSocket has a rather twisted logic: if verificationPeerName
+        // is empty, we call QAbstractSocket::peerName(), which returns
+        // either peerName (can be set by setPeerName) or host name
+        // (can be set as a result of connectToHost).
+        QString name = peerVerificationName;
+        if (name.isEmpty()) {
+            Q_ASSERT(dtls.udpSocket);
+            name = dtls.udpSocket->peerName();
+        }
+
+        if (!QSslSocketPrivate::isMatchingHostname(dtlsConfiguration.peerCertificate, name))
+            errors << QSslError(QSslError::HostNameMismatch, dtlsConfiguration.peerCertificate);
+    }
+
+    // Translate errors from the error list into QSslErrors
+    errors.reserve(errors.size() + opensslErrors.size());
+    for (const auto &error : qAsConst(opensslErrors)) {
+        errors << _q_OpenSSL_to_QSslError(error.code,
+                                          dtlsConfiguration.peerCertificateChain.value(error.depth));
+    }
+
+    tlsErrors = errors;
+    return tlsErrors.isEmpty();
+}
+
+void QDtlsPrivateOpenSSL::storePeerCertificates()
+{
+    Q_ASSERT(dtls.tlsConnection.data());
+    // Store the peer certificate and chain. For clients, the peer certificate
+    // chain includes the peer certificate; for servers, it doesn't. Both the
+    // peer certificate and the chain may be empty if the peer didn't present
+    // any certificate.
+    X509 *x509 = q_SSL_get_peer_certificate(dtls.tlsConnection.data());
+    dtlsConfiguration.peerCertificate = QSslCertificatePrivate::QSslCertificate_from_X509(x509);
+    q_X509_free(x509);
+    if (dtlsConfiguration.peerCertificateChain.isEmpty()) {
+        auto stack = q_SSL_get_peer_cert_chain(dtls.tlsConnection.data());
+        dtlsConfiguration.peerCertificateChain = QSslSocketBackendPrivate::STACKOFX509_to_QSslCertificates(stack);
+        if (!dtlsConfiguration.peerCertificate.isNull() && mode == QSslSocket::SslServerMode)
+            dtlsConfiguration.peerCertificateChain.prepend(dtlsConfiguration.peerCertificate);
+    }
+}
+
+bool QDtlsPrivateOpenSSL::tlsErrorsWereIgnored() const
+{
+    // check whether the errors we got are all in the list of expected errors
+    // (applies only if the method QDtlsConnection::ignoreTlsErrors(const
+    // QVector<QSslError> &errors) was called)
+    for (const QSslError &error : tlsErrors) {
+        if (!tlsErrorsToIgnore.contains(error))
+            return false;
+    }
+
+    return !tlsErrorsToIgnore.empty();
+}
+
+void QDtlsPrivateOpenSSL::fetchNegotiatedParameters()
+{
+    Q_ASSERT(dtls.tlsConnection.data());
+
+    const SSL_CIPHER *cipher = q_SSL_get_current_cipher(dtls.tlsConnection.data());
+    sessionCipher = cipher ? QSslSocketBackendPrivate::QSslCipher_from_SSL_CIPHER(cipher)
+                           : QSslCipher();
+
+    // Note: cipher's protocol version will be reported as either TLS 1.0 or
+    // TLS 1.2, that's how it's set by OpenSSL (and that's what they are?).
+
+    switch (q_SSL_version(dtls.tlsConnection.data())) {
+    case DTLS1_VERSION:
+        sessionProtocol = QSsl::DtlsV1_0;
+        break;
+    case DTLS1_2_VERSION:
+        sessionProtocol = QSsl::DtlsV1_2;
+        break;
+    default:
+        qCWarning(lcSsl, "unknown protocol version");
+        sessionProtocol = QSsl::UnknownProtocol;
+    }
+}
+
+void QDtlsPrivateOpenSSL::reportTimeout()
+{
+    Q_Q(QDtls);
+
+    emit q->handshakeTimeout();
+}
+
+void QDtlsPrivateOpenSSL::resetDtls()
+{
+    dtls.reset();
+    connectionEncrypted = false;
+    tlsErrors.clear();
+    tlsErrorsToIgnore.clear();
+    dtlsConfiguration.peerCertificate.clear();
+    dtlsConfiguration.peerCertificateChain.clear();
+    connectionWasShutdown = false;
+    handshakeState = QDtls::HandshakeNotStarted;
+    sessionCipher = {};
+    sessionProtocol = QSsl::UnknownProtocol;
+}
+
+QT_END_NAMESPACE
diff --git a/src/network/ssl/qdtls_openssl_p.h b/src/network/ssl/qdtls_openssl_p.h
new file mode 100644
index 0000000000..6d8967d418
--- /dev/null
+++ b/src/network/ssl/qdtls_openssl_p.h
@@ -0,0 +1,212 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtNetwork module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QDTLS_OPENSSL_P_H
+#define QDTLS_OPENSSL_P_H
+
+#include <private/qtnetworkglobal_p.h>
+
+#include <QtCore/qglobal.h>
+
+QT_REQUIRE_CONFIG(openssl);
+
+#include <openssl/ossl_typ.h>
+
+#include "qdtls_p.h"
+
+#include <private/qsslcontext_openssl_p.h>
+#include <private/qsslsocket_openssl_p.h>
+
+#include <QtNetwork/qsslpresharedkeyauthenticator.h>
+#include <QtNetwork/qhostaddress.h>
+
+#include <QtCore/qcryptographichash.h>
+#include <QtCore/qsharedpointer.h>
+#include <QtCore/qbytearray.h>
+#include <QtCore/qvector.h>
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+QT_BEGIN_NAMESPACE
+
+class QDtlsPrivateOpenSSL;
+class QUdpSocket;
+
+namespace dtlsopenssl
+{
+
+class DtlsState
+{
+public:
+    // Note, bioMethod, if allocated (i.e. OpenSSL version >= 1.1) _must_
+    // outlive BIOs it was used to create. Thus the order of declarations
+    // here matters.
+    using BioMethod = QSharedPointer<BIO_METHOD>;
+    BioMethod bioMethod;
+
+    using TlsContext = QSharedPointer<QSslContext>;
+    TlsContext tlsContext;
+
+    using TlsConnection = QSharedPointer<SSL>;
+    TlsConnection tlsConnection;
+
+    QByteArray dgram;
+
+    QHostAddress remoteAddress;
+    quint16 remotePort = 0;
+
+    QVector<QSslErrorEntry> x509Errors;
+
+    long peeking = false;
+    QUdpSocket *udpSocket = nullptr;
+    bool writeSuppressed = false;
+
+    bool init(QDtlsBasePrivate *dtlsBase, QUdpSocket *socket,
+              const QHostAddress &remote, quint16 port,
+              const QByteArray &receivedMessage);
+
+    void reset();
+
+    QDtlsPrivateOpenSSL *dtlsPrivate = nullptr;
+    QByteArray secret;
+
+#ifdef QT_CRYPTOGRAPHICHASH_ONLY_SHA1
+    QCryptographicHash::Algorithm hashAlgorithm = QCryptographicHash::Sha1;
+#else
+    QCryptographicHash::Algorithm hashAlgorithm = QCryptographicHash::Sha256;
+#endif
+
+private:
+
+    bool initTls(QDtlsBasePrivate *dtlsBase);
+    bool initCtxAndConnection(QDtlsBasePrivate *dtlsBase);
+    bool initBIO(QDtlsBasePrivate *dtlsBase);
+    void setLinkMtu(QDtlsBasePrivate *dtlsBase);
+};
+
+} // namespace dtlsopenssl
+
+class QDtlsClientVerifierOpenSSL : public QDtlsClientVerifierPrivate
+{
+public:
+
+    QDtlsClientVerifierOpenSSL();
+
+    bool verifyClient(QUdpSocket *socket, const QByteArray &dgram,
+                      const QHostAddress &address, quint16 port) override;
+
+private:
+    dtlsopenssl::DtlsState dtls;
+};
+
+class QDtlsPrivateOpenSSL : public QDtlsPrivate
+{
+public:
+    QDtlsPrivateOpenSSL();
+
+    bool startHandshake(QUdpSocket *socket, const QByteArray &datagram) override;
+    bool continueHandshake(QUdpSocket *socket, const QByteArray &datagram) override;
+    bool resumeHandshake(QUdpSocket *socket) override;
+    void abortHandshake(QUdpSocket *socket) override;
+    bool handleTimeout(QUdpSocket *socket) override;
+    void sendShutdownAlert(QUdpSocket *socket) override;
+
+    qint64 writeDatagramEncrypted(QUdpSocket *socket, const QByteArray &datagram) override;
+    QByteArray decryptDatagram(QUdpSocket *socket, const QByteArray &tlsdgram) override;
+
+    unsigned pskClientCallback(const char *hint, char *identity, unsigned max_identity_len,
+                               unsigned char *psk, unsigned max_psk_len);
+    unsigned pskServerCallback(const char *identity, unsigned char *psk,
+                               unsigned max_psk_len);
+
+private:
+
+    bool verifyPeer();
+    void storePeerCertificates();
+    bool tlsErrorsWereIgnored() const;
+    void fetchNegotiatedParameters();
+    void reportTimeout();
+    void resetDtls();
+
+    QVector<QSslErrorEntry> opensslErrors;
+    dtlsopenssl::DtlsState dtls;
+
+    // We have to externally handle timeouts since we have non-blocking
+    // sockets and OpenSSL(DTLS) with non-blocking UDP sockets does not
+    // know if a timeout has occurred.
+    struct TimeoutHandler : QObject
+    {
+        TimeoutHandler() = default;
+
+        void start(int hintMs = 0);
+        void doubleTimeout();
+        void resetTimeout() {timeoutMs = 1000;}
+        void stop();
+        void timerEvent(QTimerEvent *event);
+
+        int timerId = -1;
+        int timeoutMs = 1000;
+
+        QDtlsPrivateOpenSSL *dtlsConnection = nullptr;
+    };
+
+    // We will initialize it 'lazily', just in case somebody wants to move
+    // QDtls to another thread.
+    QScopedPointer<TimeoutHandler> timeoutHandler;
+    bool connectionWasShutdown = false;
+    QSslPreSharedKeyAuthenticator pskAuthenticator;
+    QByteArray identityHint;
+
+    Q_DECLARE_PUBLIC(QDtls)
+};
+
+
+
+QT_END_NAMESPACE
+
+#endif // QDTLS_OPENSSL_P_H
diff --git a/src/network/ssl/qdtls_p.h b/src/network/ssl/qdtls_p.h
new file mode 100644
index 0000000000..1170eabe74
--- /dev/null
+++ b/src/network/ssl/qdtls_p.h
@@ -0,0 +1,151 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtNetwork module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QDTLS_P_H
+#define QDTLS_P_H
+
+#include <private/qtnetworkglobal_p.h>
+
+#include "qdtls.h"
+
+#include <private/qsslconfiguration_p.h>
+#include <private/qobject_p.h>
+
+#include <QtNetwork/qabstractsocket.h>
+#include <QtNetwork/qhostaddress.h>
+#include <QtNetwork/qsslsocket.h>
+#include <QtNetwork/qsslcipher.h>
+#include <QtNetwork/qssl.h>
+
+#include <QtCore/qcryptographichash.h>
+#include <QtCore/qbytearray.h>
+#include <QtCore/qstring.h>
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+QT_BEGIN_NAMESPACE
+
+class QHostAddress;
+
+class QDtlsBasePrivate : public QObjectPrivate
+{
+public:
+
+    void setDtlsError(QDtlsError code, const QString &description)
+    {
+        errorCode = code;
+        errorDescription = description;
+    }
+
+    void clearDtlsError()
+    {
+        errorCode = QDtlsError::NoError;
+        errorDescription.clear();
+    }
+
+    void setConfiguration(const QSslConfiguration &configuration);
+    QSslConfiguration configuration() const;
+
+    bool setCookieGeneratorParameters(QCryptographicHash::Algorithm alg,
+                                      const QByteArray &secret);
+
+    QHostAddress remoteAddress;
+    quint16 remotePort = 0;
+    quint16 mtuHint = 0;
+
+    QDtlsError errorCode = QDtlsError::NoError;
+    QString errorDescription;
+    QSslConfigurationPrivate dtlsConfiguration;
+    QSslSocket::SslMode mode = QSslSocket::SslClientMode;
+    QSslCipher sessionCipher;
+    QSsl::SslProtocol sessionProtocol = QSsl::UnknownProtocol;
+    QString peerVerificationName;
+    QByteArray secret;
+
+#ifdef QT_CRYPTOGRAPHICHASH_ONLY_SHA1
+    QCryptographicHash::Algorithm hashAlgorithm = QCryptographicHash::Sha1;
+#else
+    QCryptographicHash::Algorithm hashAlgorithm = QCryptographicHash::Sha256;
+#endif
+};
+
+class QDtlsClientVerifierPrivate : public QDtlsBasePrivate
+{
+public:
+
+    QByteArray verifiedClientHello;
+
+    virtual bool verifyClient(QUdpSocket *socket, const QByteArray &dgram,
+                              const QHostAddress &address, quint16 port) = 0;
+};
+
+class QDtlsPrivate : public QDtlsBasePrivate
+{
+public:
+
+    virtual bool startHandshake(QUdpSocket *socket, const QByteArray &dgram) = 0;
+    virtual bool handleTimeout(QUdpSocket *socket) = 0;
+    virtual bool continueHandshake(QUdpSocket *socket, const QByteArray &dgram) = 0;
+    virtual bool resumeHandshake(QUdpSocket *socket) = 0;
+    virtual void abortHandshake(QUdpSocket *socket) = 0;
+    virtual void sendShutdownAlert(QUdpSocket *socket) = 0;
+
+    virtual qint64 writeDatagramEncrypted(QUdpSocket *socket, const QByteArray &dgram) = 0;
+    virtual QByteArray decryptDatagram(QUdpSocket *socket, const QByteArray &dgram) = 0;
+
+    QDtls::HandshakeState handshakeState = QDtls::HandshakeNotStarted;
+
+    QVector<QSslError> tlsErrors;
+    QVector<QSslError> tlsErrorsToIgnore;
+
+    bool connectionEncrypted = false;
+};
+
+QT_END_NAMESPACE
+
+#endif // QDTLS_P_H
diff --git a/src/network/ssl/qsslconfiguration.h b/src/network/ssl/qsslconfiguration.h
index a872b1f37f..5435720b01 100644
--- a/src/network/ssl/qsslconfiguration.h
+++ b/src/network/ssl/qsslconfiguration.h
@@ -73,6 +73,11 @@ class QSslKey;
 class QSslEllipticCurve;
 class QSslDiffieHellmanParameters;
 
+namespace dtlsopenssl
+{
+class DtlsState;
+}
+
 class QSslConfigurationPrivate;
 class Q_NETWORK_EXPORT QSslConfiguration
 {
@@ -188,6 +193,8 @@ private:
     friend class QSslConfigurationPrivate;
     friend class QSslSocketBackendPrivate;
     friend class QSslContext;
+    friend class QDtlsBasePrivate;
+    friend class dtlsopenssl::DtlsState;
     QSslConfiguration(QSslConfigurationPrivate *dd);
     QSharedDataPointer<QSslConfigurationPrivate> d;
 };
diff --git a/src/network/ssl/qsslcontext_openssl11.cpp b/src/network/ssl/qsslcontext_openssl11.cpp
index 0f4878c98d..bf0c1aedbf 100644
--- a/src/network/ssl/qsslcontext_openssl11.cpp
+++ b/src/network/ssl/qsslcontext_openssl11.cpp
@@ -59,11 +59,24 @@ QT_BEGIN_NAMESPACE
 extern int q_X509Callback(int ok, X509_STORE_CTX *ctx);
 extern QString getErrorsFromOpenSsl();
 
+// defined in qdtls_openssl.cpp:
+namespace dtlscallbacks
+{
+extern "C" int q_X509DtlsCallback(int ok, X509_STORE_CTX *ctx);
+extern "C" int q_generate_cookie_callback(SSL *ssl, unsigned char *dst,
+                                          unsigned *cookieLength);
+extern "C" int q_verify_cookie_callback(SSL *ssl, const unsigned char *cookie,
+                                        unsigned cookieLength);
+}
+
 static inline QString msgErrorSettingEllipticCurves(const QString &why)
 {
     return QSslSocket::tr("Error when setting the elliptic curves (%1)").arg(why);
 }
 
+// Defined in qsslsocket.cpp
+QList<QSslCipher> q_getDefaultDtlsCiphers();
+
 // static
 void QSslContext::initSslContext(QSslContext *sslContext, QSslSocket::SslMode mode, const QSslConfiguration &configuration, bool allowRootCertOnDemandLoading)
 {
@@ -74,14 +87,25 @@ void QSslContext::initSslContext(QSslContext *sslContext, QSslSocket::SslMode mo
 
     bool reinitialized = false;
     bool unsupportedProtocol = false;
+    bool isDtls = false;
 init_context:
     if (sslContext->sslConfiguration.protocol() == QSsl::SslV2) {
         // SSL 2 is no longer supported, but chosen deliberately -> error
         sslContext->ctx = nullptr;
         unsupportedProtocol = true;
     } else {
-        // The ssl options will actually control the supported methods
-        sslContext->ctx = q_SSL_CTX_new(client ? q_TLS_client_method() : q_TLS_server_method());
+        switch (sslContext->sslConfiguration.protocol()) {
+        case QSsl::DtlsV1_0:
+        case QSsl::DtlsV1_0OrLater:
+        case QSsl::DtlsV1_2:
+        case QSsl::DtlsV1_2OrLater:
+            isDtls = true;
+            sslContext->ctx = q_SSL_CTX_new(client ? q_DTLS_client_method() : q_DTLS_server_method());
+            break;
+        default:
+            // The ssl options will actually control the supported methods
+            sslContext->ctx = q_SSL_CTX_new(client ? q_TLS_client_method() : q_TLS_server_method());
+        }
     }
 
     if (!sslContext->ctx) {
@@ -100,8 +124,10 @@ init_context:
         return;
     }
 
-    long minVersion = TLS_ANY_VERSION;
-    long maxVersion = TLS_ANY_VERSION;
+    const long anyVersion = isDtls ? DTLS_ANY_VERSION : TLS_ANY_VERSION;
+    long minVersion = anyVersion;
+    long maxVersion = anyVersion;
+
     switch (sslContext->sslConfiguration.protocol()) {
     // The single-protocol versions first:
     case QSsl::SslV3:
@@ -140,12 +166,21 @@ init_context:
         maxVersion = TLS_MAX_VERSION;
         break;
     case QSsl::DtlsV1_0:
+        minVersion = DTLS1_VERSION;
+        maxVersion = DTLS1_VERSION;
+        break;
     case QSsl::DtlsV1_0OrLater:
+        minVersion = DTLS1_VERSION;
+        maxVersion = DTLS_MAX_VERSION;
+        break;
     case QSsl::DtlsV1_2:
+        minVersion = DTLS1_2_VERSION;
+        maxVersion = DTLS1_2_VERSION;
+        break;
     case QSsl::DtlsV1_2OrLater:
-        sslContext->errorStr = QSslSocket::tr("unsupported protocol");
-        sslContext->errorCode = QSslError::UnspecifiedError;
-        return;
+        minVersion = DTLS1_2_VERSION;
+        maxVersion = DTLS_MAX_VERSION;
+        break;
     case QSsl::SslV2:
         // This protocol is not supported by OpenSSL 1.1 and we handle
         // it as an error (see the code above).
@@ -155,14 +190,14 @@ init_context:
         break;
     }
 
-    if (minVersion != TLS_ANY_VERSION
+    if (minVersion != anyVersion
         && !q_SSL_CTX_set_min_proto_version(sslContext->ctx, minVersion)) {
         sslContext->errorStr = QSslSocket::tr("Error while setting the minimal protocol version");
         sslContext->errorCode = QSslError::UnspecifiedError;
         return;
     }
 
-    if (maxVersion != TLS_ANY_VERSION
+    if (maxVersion != anyVersion
         && !q_SSL_CTX_set_max_proto_version(sslContext->ctx, maxVersion)) {
         sslContext->errorStr = QSslSocket::tr("Error while setting the maximum protocol version");
         sslContext->errorCode = QSslError::UnspecifiedError;
@@ -182,7 +217,8 @@ init_context:
     bool first = true;
     QList<QSslCipher> ciphers = sslContext->sslConfiguration.ciphers();
     if (ciphers.isEmpty())
-        ciphers = QSslSocketPrivate::defaultCiphers();
+        ciphers = isDtls ? q_getDefaultDtlsCiphers() : QSslSocketPrivate::defaultCiphers();
+
     for (const QSslCipher &cipher : qAsConst(ciphers)) {
         if (first)
             first = false;
@@ -289,7 +325,13 @@ init_context:
     if (sslContext->sslConfiguration.peerVerifyMode() == QSslSocket::VerifyNone) {
         q_SSL_CTX_set_verify(sslContext->ctx, SSL_VERIFY_NONE, nullptr);
     } else {
-        q_SSL_CTX_set_verify(sslContext->ctx, SSL_VERIFY_PEER, q_X509Callback);
+        q_SSL_CTX_set_verify(sslContext->ctx, SSL_VERIFY_PEER,
+                             isDtls ? dtlscallbacks::q_X509DtlsCallback : q_X509Callback);
+    }
+
+    if (mode == QSslSocket::SslServerMode && isDtls && configuration.dtlsCookieVerificationEnabled()) {
+        q_SSL_CTX_set_cookie_generate_cb(sslContext->ctx, dtlscallbacks::q_generate_cookie_callback);
+        q_SSL_CTX_set_cookie_verify_cb(sslContext->ctx, dtlscallbacks::q_verify_cookie_callback);
     }
 
     // Set verification depth.
diff --git a/src/network/ssl/qsslcontext_opensslpre11.cpp b/src/network/ssl/qsslcontext_opensslpre11.cpp
index 7994892cfc..a54b0ac5f0 100644
--- a/src/network/ssl/qsslcontext_opensslpre11.cpp
+++ b/src/network/ssl/qsslcontext_opensslpre11.cpp
@@ -56,11 +56,24 @@ QT_BEGIN_NAMESPACE
 extern int q_X509Callback(int ok, X509_STORE_CTX *ctx);
 extern QString getErrorsFromOpenSsl();
 
+// defined in qdtls_openssl.cpp:
+namespace dtlscallbacks
+{
+extern "C" int q_X509DtlsCallback(int ok, X509_STORE_CTX *ctx);
+extern "C" int q_generate_cookie_callback(SSL *ssl, unsigned char *dst,
+                                          unsigned *cookieLength);
+extern "C" int q_verify_cookie_callback(SSL *ssl, const unsigned char *cookie,
+                                        unsigned cookieLength);
+}
+
 static inline QString msgErrorSettingEllipticCurves(const QString &why)
 {
     return QSslSocket::tr("Error when setting the elliptic curves (%1)").arg(why);
 }
 
+// Defined in qsslsocket.cpp
+QList<QSslCipher> q_getDefaultDtlsCiphers();
+
 // static
 void QSslContext::initSslContext(QSslContext *sslContext, QSslSocket::SslMode mode, const QSslConfiguration &configuration, bool allowRootCertOnDemandLoading)
 {
@@ -68,17 +81,25 @@ void QSslContext::initSslContext(QSslContext *sslContext, QSslSocket::SslMode mo
     sslContext->errorCode = QSslError::NoError;
 
     bool client = (mode == QSslSocket::SslClientMode);
-
     bool reinitialized = false;
     bool unsupportedProtocol = false;
+    bool isDtls = false;
 init_context:
     switch (sslContext->sslConfiguration.protocol()) {
     case QSsl::DtlsV1_0:
-    case QSsl::DtlsV1_0OrLater:
+        isDtls = true;
+        sslContext->ctx = q_SSL_CTX_new(client ? q_DTLSv1_client_method() : q_DTLSv1_server_method());
+        break;
     case QSsl::DtlsV1_2:
     case QSsl::DtlsV1_2OrLater:
-        sslContext->ctx = 0;
-        unsupportedProtocol = true;
+        // OpenSSL 1.0.2 and below will probably never receive TLS 1.3, so
+        // technically 1.2 or later is 1.2 and will stay so.
+        isDtls = true;
+        sslContext->ctx = q_SSL_CTX_new(client ? q_DTLSv1_2_client_method() : q_DTLSv1_2_server_method());
+        break;
+    case QSsl::DtlsV1_0OrLater:
+        isDtls = true;
+        sslContext->ctx = q_SSL_CTX_new(client ? q_DTLS_client_method() : q_DTLS_server_method());
         break;
     case QSsl::SslV2:
 #ifndef OPENSSL_NO_SSL2
@@ -145,6 +166,12 @@ init_context:
         break;
     }
 
+    if (!client && isDtls && configuration.peerVerifyMode() != QSslSocket::VerifyNone) {
+        sslContext->errorStr = QSslSocket::tr("DTLS server requires a 'VerifyNone' mode with your version of OpenSSL");
+        sslContext->errorCode = QSslError::UnspecifiedError;
+        return;
+    }
+
     if (!sslContext->ctx) {
         // After stopping Flash 10 the SSL library loses its ciphers. Try re-adding them
         // by re-initializing the library.
@@ -162,6 +189,7 @@ init_context:
     }
 
     // Enable bug workarounds.
+    // DTLSTODO: check this setupOpenSslOptions ...
     long options = QSslSocketBackendPrivate::setupOpenSslOptions(configuration.protocol(), configuration.d->sslOptions);
     q_SSL_CTX_set_options(sslContext->ctx, options);
 
@@ -177,7 +205,7 @@ init_context:
     bool first = true;
     QList<QSslCipher> ciphers = sslContext->sslConfiguration.ciphers();
     if (ciphers.isEmpty())
-        ciphers = QSslSocketPrivate::defaultCiphers();
+        ciphers = isDtls ? q_getDefaultDtlsCiphers() : QSslSocketPrivate::defaultCiphers();
     for (const QSslCipher &cipher : qAsConst(ciphers)) {
         if (first)
             first = false;
@@ -284,7 +312,13 @@ init_context:
     if (sslContext->sslConfiguration.peerVerifyMode() == QSslSocket::VerifyNone) {
         q_SSL_CTX_set_verify(sslContext->ctx, SSL_VERIFY_NONE, 0);
     } else {
-        q_SSL_CTX_set_verify(sslContext->ctx, SSL_VERIFY_PEER, q_X509Callback);
+        q_SSL_CTX_set_verify(sslContext->ctx, SSL_VERIFY_PEER,
+                             isDtls ? dtlscallbacks::q_X509DtlsCallback : q_X509Callback);
+    }
+
+    if (mode == QSslSocket::SslServerMode && isDtls && configuration.dtlsCookieVerificationEnabled()) {
+        q_SSL_CTX_set_cookie_generate_cb(sslContext->ctx, dtlscallbacks::q_generate_cookie_callback);
+        q_SSL_CTX_set_cookie_verify_cb(sslContext->ctx, CookieVerifyCallback(dtlscallbacks::q_verify_cookie_callback));
     }
 
     // Set verification depth.
diff --git a/src/network/ssl/qsslpresharedkeyauthenticator.h b/src/network/ssl/qsslpresharedkeyauthenticator.h
index a012ff489a..d0e2eda973 100644
--- a/src/network/ssl/qsslpresharedkeyauthenticator.h
+++ b/src/network/ssl/qsslpresharedkeyauthenticator.h
@@ -76,6 +76,7 @@ public:
 private:
     friend Q_NETWORK_EXPORT bool operator==(const QSslPreSharedKeyAuthenticator &lhs, const QSslPreSharedKeyAuthenticator &rhs);
     friend class QSslSocketBackendPrivate;
+    friend class QDtlsPrivateOpenSSL;
 
     QSharedDataPointer<QSslPreSharedKeyAuthenticatorPrivate> d;
 };
diff --git a/src/network/ssl/qsslsocket_openssl.cpp b/src/network/ssl/qsslsocket_openssl.cpp
index 9a9b5be302..9a5997253c 100644
--- a/src/network/ssl/qsslsocket_openssl.cpp
+++ b/src/network/ssl/qsslsocket_openssl.cpp
@@ -842,7 +842,7 @@ void QSslSocketBackendPrivate::transmit()
     } while (ssl && transmitting);
 }
 
-static QSslError _q_OpenSSL_to_QSslError(int errorCode, const QSslCertificate &cert)
+QSslError _q_OpenSSL_to_QSslError(int errorCode, const QSslCertificate &cert)
 {
     QSslError error;
     switch (errorCode) {
diff --git a/src/network/ssl/qsslsocket_openssl_symbols.cpp b/src/network/ssl/qsslsocket_openssl_symbols.cpp
index a978dfc5f4..05b7d91315 100644
--- a/src/network/ssl/qsslsocket_openssl_symbols.cpp
+++ b/src/network/ssl/qsslsocket_openssl_symbols.cpp
@@ -307,6 +307,12 @@ DEFINEFUNC3(DSA *, d2i_DSAPrivateKey, DSA **a, a, unsigned char **b, b, long c,
 DEFINEFUNC3(EC_KEY *, d2i_ECPrivateKey, EC_KEY **a, a, unsigned char **b, b, long c, c, return 0, return)
 #endif
 #endif
+
+DEFINEFUNC(const SSL_METHOD *, DTLSv1_server_method, void, DUMMYARG, return nullptr, return)
+DEFINEFUNC(const SSL_METHOD *, DTLSv1_client_method, void, DUMMYARG, return nullptr, return)
+DEFINEFUNC(const SSL_METHOD *, DTLSv1_2_server_method, void, DUMMYARG, return nullptr, return)
+DEFINEFUNC(const SSL_METHOD *, DTLSv1_2_client_method, void, DUMMYARG, return nullptr, return)
+
 DEFINEFUNC(char *, CONF_get1_default_config_file, DUMMYARG, DUMMYARG, return 0, return)
 DEFINEFUNC(void, OPENSSL_add_all_algorithms_noconf, void, DUMMYARG, return, DUMMYARG)
 DEFINEFUNC(void, OPENSSL_add_all_algorithms_conf, void, DUMMYARG, return, DUMMYARG)
@@ -555,7 +561,6 @@ DEFINEFUNC3(void, SSL_get0_alpn_selected, const SSL *s, s, const unsigned char *
 // DTLS:
 DEFINEFUNC2(void, SSL_CTX_set_cookie_generate_cb, SSL_CTX *ctx, ctx, CookieGenerateCallback cb, cb, return, DUMMYARG)
 DEFINEFUNC2(void, SSL_CTX_set_cookie_verify_cb, SSL_CTX *ctx, ctx, CookieVerifyCallback cb, cb, return, DUMMYARG)
-DEFINEFUNC2(BIO *, BIO_new_dgram, int fd, fd, int flag, flag, return nullptr, return)
 DEFINEFUNC(const SSL_METHOD *, DTLS_server_method, DUMMYARG, DUMMYARG, return nullptr, return)
 DEFINEFUNC(const SSL_METHOD *, DTLS_client_method, DUMMYARG, DUMMYARG, return nullptr, return)
 DEFINEFUNC2(void, BIO_set_flags, BIO *b, b, int flags, flags, return, DUMMYARG)
@@ -1046,6 +1051,12 @@ bool q_resolveOpenSslSymbols()
     RESOLVEFUNC(d2i_DSAPrivateKey)
     RESOLVEFUNC(d2i_RSAPrivateKey)
 #endif
+
+    RESOLVEFUNC(DTLSv1_server_method)
+    RESOLVEFUNC(DTLSv1_client_method)
+    RESOLVEFUNC(DTLSv1_2_server_method)
+    RESOLVEFUNC(DTLSv1_2_client_method)
+
     RESOLVEFUNC(CONF_get1_default_config_file)
     RESOLVEFUNC(OPENSSL_add_all_algorithms_noconf)
     RESOLVEFUNC(OPENSSL_add_all_algorithms_conf)
@@ -1081,7 +1092,6 @@ bool q_resolveOpenSslSymbols()
     RESOLVEFUNC(BIO_free)
     RESOLVEFUNC(BIO_new)
     RESOLVEFUNC(BIO_new_mem_buf)
-    RESOLVEFUNC(BIO_new_dgram)
     RESOLVEFUNC(BIO_read)
     RESOLVEFUNC(BIO_s_mem)
     RESOLVEFUNC(BIO_write)
diff --git a/src/network/ssl/qsslsocket_openssl_symbols_p.h b/src/network/ssl/qsslsocket_openssl_symbols_p.h
index 386ca746cf..056ab1c12f 100644
--- a/src/network/ssl/qsslsocket_openssl_symbols_p.h
+++ b/src/network/ssl/qsslsocket_openssl_symbols_p.h
@@ -541,7 +541,6 @@ typedef int (*CookieGenerateCallback)(SSL *, unsigned char *, unsigned *);
 
 void q_SSL_CTX_set_cookie_generate_cb(SSL_CTX *ctx, CookieGenerateCallback cb);
 void q_SSL_CTX_set_cookie_verify_cb(SSL_CTX *ctx, CookieVerifyCallback cb);
-BIO *q_BIO_new_dgram(int fd, int close_flag);
 const SSL_METHOD *q_DTLS_server_method();
 const SSL_METHOD *q_DTLS_client_method();
 
diff --git a/src/network/ssl/qsslsocket_opensslpre11_symbols_p.h b/src/network/ssl/qsslsocket_opensslpre11_symbols_p.h
index 6676f768a7..f499af228d 100644
--- a/src/network/ssl/qsslsocket_opensslpre11_symbols_p.h
+++ b/src/network/ssl/qsslsocket_opensslpre11_symbols_p.h
@@ -234,4 +234,9 @@ typedef int (*CookieVerifyCallback)(SSL *, unsigned char *, unsigned);
 }
 #define q_DTLSv1_listen(ssl, peer) q_SSL_ctrl(ssl, DTLS_CTRL_LISTEN, 0, (void *)peer)
 
+const SSL_METHOD *q_DTLSv1_server_method();
+const SSL_METHOD *q_DTLSv1_client_method();
+const SSL_METHOD *q_DTLSv1_2_server_method();
+const SSL_METHOD *q_DTLSv1_2_client_method();
+
 #endif // QSSLSOCKET_OPENSSL_PRE11_SYMBOLS_P_H
diff --git a/src/network/ssl/ssl.pri b/src/network/ssl/ssl.pri
index 3529c8828b..397005e14b 100644
--- a/src/network/ssl/ssl.pri
+++ b/src/network/ssl/ssl.pri
@@ -6,7 +6,7 @@ qtConfig(ssl) {
                ssl/qsslcertificate.h \
                ssl/qsslcertificate_p.h \
                ssl/qsslconfiguration.h \
-	       ssl/qsslconfiguration_p.h \
+               ssl/qsslconfiguration_p.h \
                ssl/qsslcipher.h \
                ssl/qsslcipher_p.h \
                ssl/qssldiffiehellmanparameters.h \
@@ -59,14 +59,19 @@ qtConfig(ssl) {
     qtConfig(openssl) {
         HEADERS += ssl/qsslcontext_openssl_p.h \
                    ssl/qsslsocket_openssl_p.h \
-                   ssl/qsslsocket_openssl_symbols_p.h
+                   ssl/qsslsocket_openssl_symbols_p.h \
+                   ssl/qdtls.h \
+                   ssl/qdtls_p.h \
+                   ssl/qdtls_openssl_p.h
         SOURCES += ssl/qsslsocket_openssl_symbols.cpp \
                    ssl/qssldiffiehellmanparameters_openssl.cpp \
                    ssl/qsslcertificate_openssl.cpp \
                    ssl/qsslellipticcurve_openssl.cpp \
                    ssl/qsslkey_openssl.cpp \
                    ssl/qsslsocket_openssl.cpp \
-                   ssl/qsslcontext_openssl.cpp
+                   ssl/qsslcontext_openssl.cpp \
+                   ssl/qdtls.cpp \
+                   ssl/qdtls_openssl.cpp
 
         qtConfig(opensslv11) {
             HEADERS += ssl/qsslsocket_openssl11_symbols_p.h