This class implements server-side DTLS cookie generation and verification. More...

#include <qdtls.h>

Inheritance diagram for QDtlsClientVerifier:

Collaboration diagram for QDtlsClientVerifier:

Classes
class	GeneratorParameters
	This class defines parameters for DTLS cookie generator. More...

Public Member Functions
	QDtlsClientVerifier (QObject *parent=nullptr)
	Constructs a QDtlsClientVerifier object, parent is passed to QObject's constructor.

	~QDtlsClientVerifier ()
	Destroys the QDtlsClientVerifier object.

bool	setCookieGeneratorParameters (const GeneratorParameters &params)
	Sets the secret and the cryptographic hash algorithm from params.

GeneratorParameters	cookieGeneratorParameters () const
	Returns the current secret and hash algorithm used to generate cookies.

bool	verifyClient (QUdpSocket *socket, const QByteArray &dgram, const QHostAddress &address, quint16 port)
	socket must be a valid pointer, dgram must be a non-empty datagram, address cannot be null, broadcast, or multicast.

QByteArray	verifiedHello () const
	Convenience function.

QDtlsError	dtlsError () const
	Returns the last error that occurred or QDtlsError::NoError.

QString	dtlsErrorString () const
	Returns a textual description of the last error, or an empty string.

Public Member Functions inherited from QObject
Q_INVOKABLE	QObject (QObject *parent=nullptr)
	Constructs an object with parent object parent.

virtual	~QObject ()
	Destroys the object, deleting all its child objects.

virtual bool	event (QEvent *event)
	This virtual function receives events to an object and should return true if the event e was recognized and processed.

virtual bool	eventFilter (QObject watched, QEvent event)
	Filters events if this object has been installed as an event filter for the watched object.

QString	objectName () const

Q_WEAK_OVERLOAD void	setObjectName (const QString &name)
	Sets the object's name to name.

void	setObjectName (QAnyStringView name)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

QBindable< QString >	bindableObjectName ()

bool	isWidgetType () const
	Returns `true` if the object is a widget; otherwise returns `false`.

bool	isWindowType () const
	Returns `true` if the object is a window; otherwise returns `false`.

bool	isQuickItemType () const
	Returns `true` if the object is a QQuickItem; otherwise returns `false`.

bool	signalsBlocked () const noexcept
	Returns `true` if signals are blocked; otherwise returns `false`.

bool	blockSignals (bool b) noexcept
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it).

QThread *	thread () const
	Returns the thread in which the object lives.

bool	moveToThread (QThread *thread QT6_DECL_NEW_OVERLOAD_TAIL)
	Changes the thread affinity for this object and its children and returns `true` on success.

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)
	This is an overloaded function that will start a timer of type timerType and a timeout of interval milliseconds.

int	startTimer (std::chrono::nanoseconds time, Qt::TimerType timerType=Qt::CoarseTimer)

void	killTimer (int id)
	Kills the timer with timer identifier, id.

void	killTimer (Qt::TimerId id)

template<typename T >
T	findChild (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns the child of this object that can be cast into type T and that is called name, or \nullptr if there is no such object.

template<typename T >
QList< T >	findChildren (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects.

template<typename T >
T	findChild (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

template<typename T >
QList< T >	findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

const QObjectList &	children () const
	Returns a list of child objects.

void	setParent (QObject *parent)
	Makes the object a child of parent.

void	installEventFilter (QObject *filterObj)
	Installs an event filter filterObj on this object.

void	removeEventFilter (QObject *obj)
	Removes an event filter object obj from this object.

QMetaObject::Connection	connect (const QObject sender, const char signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const

bool	disconnect (const char signal=nullptr, const QObject receiver=nullptr, const char *member=nullptr) const

bool	disconnect (const QObject receiver, const char member=nullptr) const

void	dumpObjectTree () const
	Dumps a tree of children to the debug output.

void	dumpObjectInfo () const
	Dumps information about signal connections, etc.

bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value.

bool	setProperty (const char *name, QVariant &&value)

QVariant	property (const char *name) const
	Returns the value of the object's name property.

QList< QByteArray >	dynamicPropertyNames () const

QBindingStorage *	bindingStorage ()

const QBindingStorage *	bindingStorage () const

QObject *	parent () const
	Returns a pointer to the parent object.

bool	inherits (const char *classname) const
	Returns `true` if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns `false`.

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	\threadsafe

Signals inherited from QObject
void	destroyed (QObject *=nullptr)
	This signal is emitted immediately before the object obj is destroyed, after any instances of QPointer have been notified, and cannot be blocked.

void	objectNameChanged (const QString &objectName, QPrivateSignal)
	This signal is emitted after the object's name has been changed.

Static Public Member Functions inherited from QObject
static QMetaObject::Connection	connect (const QObject sender, const char signal, const QObject receiver, const char member, Qt::ConnectionType=Qt::AutoConnection)
	\threadsafe

static QMetaObject::Connection	connect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::ContextTypeForFunctor< Func2 >::ContextType context, Func2 &&slot, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 &&slot)

static bool	disconnect (const QObject sender, const char signal, const QObject receiver, const char member)
	\threadsafe

static bool	disconnect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &member)

static bool	disconnect (const QMetaObject::Connection &)
	Disconnect a connection.

template<typename Func1 , typename Func2 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object receiver, Func2 slot)

template<typename Func1 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject receiver, void **zero)

Protected Member Functions inherited from QObject
QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns \nullptr.

int	senderSignalIndex () const

int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal.

bool	isSignalConnected (const QMetaMethod &signal) const

virtual void	timerEvent (QTimerEvent *event)
	This event handler can be reimplemented in a subclass to receive timer events for the object.

virtual void	childEvent (QChildEvent *event)
	This event handler can be reimplemented in a subclass to receive child events.

virtual void	customEvent (QEvent *event)
	This event handler can be reimplemented in a subclass to receive custom events.

virtual void	connectNotify (const QMetaMethod &signal)

virtual void	disconnectNotify (const QMetaMethod &signal)

	QObject (QObjectPrivate &dd, QObject *parent=nullptr)

Protected Attributes inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Properties inherited from QObject
QString	objectName
	the name of this object

Related Symbols inherited from QObject
template< class T > T	qobject_cast (const QObject *object)
	Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns \nullptr.

template< typename T > T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

template< typename T > QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

	QObjectList
	\macro Q_CLASSINFO(Name, Value)

Detailed Description

This class implements server-side DTLS cookie generation and verification.

Since: 5.12

\inmodule QtNetwork

The QDtlsClientVerifier class implements server-side DTLS cookie generation and verification. Datagram security protocols are highly susceptible to a variety of Denial-of-Service attacks. According to \l {RFC 6347, section 4.2.1}, these are two of the more common types of attack:

\list

An attacker transmits a series of handshake initiation requests, causing a server to allocate excessive resources and potentially perform expensive cryptographic operations.
An attacker transmits a series of handshake initiation requests with a forged source of the victim, making the server act as an amplifier. Normally, the server would reply to the victim machine with a Certificate message, which can be quite large, thus flooding the victim machine with datagrams. \endlist

As a countermeasure to these attacks, \l {RFC 6347, section 4.2.1} proposes a stateless cookie technique that a server may deploy:

\list

In response to the initial ClientHello message, the server sends a HelloVerifyRequest, which contains a cookie. This cookie is a cryptographic hash and is generated using the client's address, port number, and the server's secret (which is a cryptographically strong pseudo-random sequence of bytes).
A reachable DTLS client is expected to reply with a new ClientHello message containing this cookie.
When the server receives the ClientHello message with a cookie, it generates a new cookie as described above. This new cookie is compared to the one found in the ClientHello message.
In the cookies are equal, the client is considered to be real, and the server can continue with a TLS handshake procedure. \endlist

Note: A DTLS server is not required to use DTLS cookies.

QDtlsClientVerifier is designed to work in pair with QUdpSocket, as shown in the following code-excerpt:

class DtlsServer : public QObject
{
public:
    bool listen(const QHostAddress &address, quint16 port);
    // ...
 
private:
    void readyRead();
    // ...
 
    QUdpSocket serverSocket;
    QDtlsClientVerifier verifier;
    // ...
};
 
bool DtlsServer::listen(const QHostAddress &serverAddress, quint16 serverPort)
{
    if (serverSocket.bind(serverAddress, serverPort))
        connect(&serverSocket, &QUdpSocket::readyRead, this, &DtlsServer::readyRead);
    return serverSocket.state() == QAbstractSocket::BoundState;
}
 
void DtlsServer::readyRead()
{
    QByteArray dgram(serverSocket.pendingDatagramSize(), Qt::Uninitialized);
    QHostAddress address;
    quint16 port = {};
    serverSocket.readDatagram(dgram.data(), dgram.size(), &address, &port);
    if (verifiedClients.contains({address, port}) {
        // This client was verified previously, we either continue the
        // handshake or decrypt the incoming message.
    } else if (verifier.verifyClient(&serverSocket, dgram, address, port)) {
        // Apparently we have a real DTLS client who wants to send us
        // encrypted datagrams. Remember this client as verified
        // and proceed with a handshake.
    } else {
        // No matching cookie was found in the incoming datagram,
        // verifyClient() has sent a ClientVerify message.
        // We'll hear from the client again soon, if they're real.
    }
}

QDtlsClientVerifier does not impose any restrictions on how the application uses QUdpSocket. For example, it is possible to have a server with a single QUdpSocket in state QAbstractSocket::BoundState, handling multiple DTLS clients simultaneously:

\list

Testing if new clients are real DTLS-capable clients.
Completing TLS handshakes with the verified clients (see QDtls).
Decrypting datagrams coming from the connected clients (see QDtls).
Sending encrypted datagrams to the connected clients (see QDtls). \endlist

This implies that QDtlsClientVerifier does not read directly from a socket, instead it expects the application to read an incoming datagram, extract the sender's address, and port, and then pass this data to verifyClient(). To send a HelloVerifyRequest message, verifyClient() can write to the QUdpSocket.

Note: QDtlsClientVerifier does not take ownership of the QUdpSocket object.

By default QDtlsClientVerifier obtains its secret from a cryptographically strong pseudorandom number generator.

Note: The default secret is shared by all objects of the classes QDtlsClientVerifier and QDtls. Since this can impose security risks, RFC 6347 recommends to change the server's secret frequently. Please see \l {RFC 6347, section 4.2.1} for hints about possible server implementations. Cookie generator parameters can be set using the class QDtlsClientVerifier::GeneratorParameters and setCookieGeneratorParameters():

void DtlsServer::updateServerSecret()
{
    const QByteArray newSecret(generateCryptoStrongSecret());
    if (newSecret.size()) {
        usedCookies.append(newSecret);
        verifier.setCookieGeneratorParameters({QCryptographicHash::Sha1, newSecret});
    }
}

The \l{secureudpserver}{DTLS server} example illustrates how to use QDtlsClientVerifier in a server application.

See also: QUdpSocket, QAbstractSocket::BoundState, QDtls, verifyClient(), GeneratorParameters, setCookieGeneratorParameters(), cookieGeneratorParameters(), QDtls::setCookieGeneratorParameters(), QDtls::cookieGeneratorParameters(), QCryptographicHash::Algorithm, QDtlsError, dtlsError(), dtlsErrorString()

Definition at line 43 of file qdtls.h.

Constructor & Destructor Documentation

◆ QDtlsClientVerifier()

QDtlsClientVerifier::QDtlsClientVerifier ( QObject * parent = nullptr )

explicit

Constructs a QDtlsClientVerifier object, parent is passed to QObject's constructor.

Definition at line 354 of file qdtls.cpp.

References d, and QSslSocket::VerifyNone.

◆ ~QDtlsClientVerifier()

QDtlsClientVerifier::~QDtlsClientVerifier ( )

Destroys the QDtlsClientVerifier object.

Definition at line 372 of file qdtls.cpp.

Member Function Documentation

◆ cookieGeneratorParameters()

QDtlsClientVerifier::GeneratorParameters QDtlsClientVerifier::cookieGeneratorParameters ( ) const

Returns the current secret and hash algorithm used to generate cookies.

The default hash algorithm is QCryptographicHash::Sha256 if Qt was configured to support it, QCryptographicHash::Sha1 otherwise. The default secret is obtained from the backend-specific cryptographically strong pseudorandom number generator.

See also: QCryptographicHash::Algorithm, QDtlsClientVerifier::GeneratorParameters, setCookieGeneratorParameters()

Definition at line 406 of file qdtls.cpp.

References d.

◆ dtlsError()

QDtlsError QDtlsClientVerifier::dtlsError ( ) const

Returns the last error that occurred or QDtlsError::NoError.

See also: QDtlsError, dtlsErrorString()

Definition at line 476 of file qdtls.cpp.

References d, and TlsInitializationError.

◆ dtlsErrorString()

QString QDtlsClientVerifier::dtlsErrorString ( ) const

Returns a textual description of the last error, or an empty string.

See also: dtlsError()

Definition at line 491 of file qdtls.cpp.

References d, and QStringLiteral.

◆ setCookieGeneratorParameters()

bool QDtlsClientVerifier::setCookieGeneratorParameters ( const GeneratorParameters & params )

Sets the secret and the cryptographic hash algorithm from params.

This QDtlsClientVerifier will use these to generate cookies. If the new secret has size zero, this function returns false and does not change the cookie generator parameters.

Note: The secret is supposed to be a cryptographically secure sequence of bytes.

See also: QDtlsClientVerifier::GeneratorParameters, cookieGeneratorParameters(), QCryptographicHash::Algorithm

Definition at line 387 of file qdtls.cpp.

References d.

◆ verifiedHello()

QByteArray QDtlsClientVerifier::verifiedHello ( ) const

Convenience function.

Returns the last ClientHello message that was successfully verified, or an empty QByteArray if no verification has completed.

See also: verifyClient()

Definition at line 461 of file qdtls.cpp.

References d.

◆ verifyClient()

bool QDtlsClientVerifier::verifyClient	(	QUdpSocket *	socket,
		const QByteArray &	dgram,
		const QHostAddress &	address,
		quint16	port )

socket must be a valid pointer, dgram must be a non-empty datagram, address cannot be null, broadcast, or multicast.

port is the remote peer's port. This function returns true if dgram contains a ClientHello message with a valid cookie. If no matching cookie is found, verifyClient() will send a HelloVerifyRequest message using socket and return false.

The following snippet shows how a server application may check for errors:

if (!verifier.verifyClient(&socket, message, address, port)) {
    switch (verifyClient.dtlsError()) {
    case QDtlsError::NoError:
        // Not verified yet, but no errors found and we have to wait for the next
        // message from this client.
        return;
    case QDtlsError::TlsInitializationError:
        // This error is fatal, nothing we can do about it.
        // Probably, quit the server after reporting the error.
        return;
    case QDtlsError::UnderlyingSocketError:
        // There is some problem in QUdpSocket, handle it (see QUdpSocket::error())
        return;
    case QDtlsError::InvalidInputParameters:
    default:
        Q_UNREACHABLE();
    }
}