Help: How to get client_hello length before executing workflowExecutor

[ayushbindlish]

When I try to print clientHelloMessage.getLength() before execution, I get null as output. How can I get length before execution?

WorkflowTrace trace = new WorkflowTrace();
        ClientHelloMessage clientHelloMessage = new ClientHelloMessage(tls12Init.getConf().getConfig());

        System.out.println(clientHelloMessage.getLength());

        System.out.println(clientHelloMessage.getProtocolVersion());

        tls12Init.setClientCipherSuite(CipherSuite.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256);

        clientHelloMessage.setLength(Modifiable.explicit(1));

        SendAction clienthello = new SendAction(clientHelloMessage);
        trace.addTlsAction(clienthello);
        trace.addTlsAction(new ReceiveAction(new AlertMessage()));
        State state = TLS12Execute.execute(tls12Init.getConf(), trace);  // executing workflowExecutor here

[ic0ns]

You cant. All originalValues are computed dynamically. The contents of messages depend on the context when the message will be sent so it is not possible to determine that beforehand.

For example, if your client hello contains the RenegotiationInfo extension, the length of the client hello will depend on whether you are sending the clienthello in the beginning of the connection or as a renegotiation request (in which case it might contain the verifyData which changes its size). If YOU already know in which context the message is sent, you can ask TLS-Attacker to fill the message contents to see how long the message will get. This requires some manual fiddling with the ClientHelloPreparator class.

[ic0ns]

Basically, you can create the TlsContext in which you want to send the message yourself (if you are in the beginning of the connection you can leave it as it is), and then create a Chooser with the ChooserFactory and you Config file. Then you can create a new ClientHelloPreparator with the chooser and the message in the constructor. If you then call preparator.prepare() the value will not be null anymore.

[ayushbindlish]

Oh okay got it. Also, will it be possible to get, in place of trace.addTlsAction(new ReceiveAction(new AlertMessage())); , check if server has closed the connection without sending back anything?

[ic0ns]

Usually the WorkflowExecutor closes the (TCP) connection for you after the execution of the WorkflowTrace. If you want to keep the connection open (for example to check if the server left the connection open itself), you can config.workflowExecutorShouldClose(false). If you do this, the workflowExecutor leaves the connection open and you can access the TransportHandler in the TlsContext yourself to check the state of connection. Eg. ((ClientTcpTransportHandler)state.getTlsContext().getTransportHandler()).getSocketState();

[ic0ns]

Don't forget to close the connection afterwards yourself.

[ayushbindlish]

I am doing this: But the openssl S_server keeps on waiting for data. And tlsattacker says socket state timeout

2021-04-16 18:41:07,641 main WARN No Root logger was configured, creating default ERROR-level Root logger with Console appender
20000
18:41:10.020 [main] INFO  de.rub.nds.tlsattacker.core.workflow.DefaultWorkflowExecutor - Connecting to 127.0.0.1:4433
18:41:10.035 [main] INFO  de.rub.nds.tlsattacker.core.workflow.action.SendAction - Sending messages (client): CLIENT_HELLO, 
18:41:11.114 [main] INFO  de.rub.nds.tlsattacker.core.workflow.action.ReceiveAction - Received Messages (client): 
TIMEOUT

WorkflowTrace trace = new WorkflowTrace();
        ClientHelloMessage clientHelloMessage = new ClientHelloMessage(tls12Init.getConf().getConfig());

        tls12Init.setClientCipherSuite(CipherSuite.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256);
        tls12Init.setWorkflowExecutorShouldClose(false);

        int x = 20000;
        int length = 1;
        while (x > length) {
            System.out.println(x);
            clientHelloMessage.setLength(Modifiable.explicit(x));
            SendAction clienthello = new SendAction(clientHelloMessage);
            trace.addTlsAction(clienthello);
            trace.addTlsAction(new ReceiveAction(new AlertMessage()));
            State state = TLS12Execute.execute(tls12Init.getConf(), trace);
            SocketState socket = ((ClientTcpTransportHandler)state.getTlsContext().getTransportHandler()).getSocketState();
            System.out.println(socket);
            AssertionCheck.checkAbsenceHandshakeMessages(state);
            String len = String.valueOf(clientHelloMessage.getLength());
            len = (len.substring(len.indexOf("=") + 1, len.indexOf("}")));
            length = Integer.parseInt(len);
            x--;
            break;
        }

[ic0ns]

Timeout is tls-attacker speak for the socket is still open. It's a little confusing, we have renamed it for the next version to just say "UP".

[ayushbindlish]

Thanks for clarifying that. @ic0ns