This class implements server-side DTLS cookie generation and verification. More...
#include <qdtls.h>
Classes | |
| class | GeneratorParameters |
| This class defines parameters for DTLS cookie generator. More... | |
Public Member Functions inherited from 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:
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():
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()
Constructor & Destructor Documentation
◆ QDtlsClientVerifier()
Constructs a QDtlsClientVerifier object, parent is passed to QObject's constructor.
◆ ~QDtlsClientVerifier()
| QDtlsClientVerifier::~QDtlsClientVerifier | ( | ) |
Destroys the QDtlsClientVerifier object.
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.
◆ dtlsError()
| QDtlsError QDtlsClientVerifier::dtlsError | ( | ) | const |
Returns the last error that occurred or QDtlsError::NoError.
- See also
- QDtlsError, dtlsErrorString()
Definition at line 512 of file qdtls.cpp.
◆ dtlsErrorString()
| QString QDtlsClientVerifier::dtlsErrorString | ( | ) | const |
Returns a textual description of the last error, or an empty string.
- See also
- dtlsError()
◆ 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.
◆ 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()
◆ 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:
- See also
- QHostAddress::isNull(), QHostAddress::isBroadcast(), QHostAddress::isMulticast(), setCookieGeneratorParameters(), cookieGeneratorParameters()
Definition at line 467 of file qdtls.cpp.
The documentation for this class was generated from the following files:
