Covert Channel:

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The basic idea is that the server will listen/close ports to transmit data to a client.

The client will attempt to connect to the ports:
if the connection is successful then 1 has been transmitted,
else ECONNREFUSED, then 0 has been transmitted.

The Server and the Client have been implemented in two modules each.

Server:

First compile keyconv.cpp using: g++ -std=c++11 keyconv.cpp -o key.
This module will find SSH keys and print them to stdout.

Then, compile blink.cpp using: g++ -pthread -std=c++11 blink.cpp -o blink.
This module will transmit the SSH key.

Client:

First, compile bin2key.cpp using: g++ -std=c++11 bin2key.cpp -o bin2key.
This module will convert key from binary and print it out.

The client, will also need client.py.
This module is responsible for connecting to ports and interpreting the result.
Please, change the IP global variable to match that of the server.

Run:

After compiling, run the following commands:

Server:
./key | ./blink

Client:
python client.py && cat bin_file.txt | ./bin2key