I have an open-ended project for a class and I picked to make a tool/use existing tools and applications to exploit the Diffie-Hellman key exchange to be able to inject, modify and delete messages that are transferred over an SSH connection. I have very limited knowledge about existing tools and I don't know where I should be looking for ways to actually implement it. I know that the general idea would be to use an arpspoof to put yourself in between the client and server to get the traffic to start the man-in-the-middle attack, but beyond that, I really don't know how to actually manage the packets that pass through to be able to edit/replace/forward them in order to be able to send the public key of the MITM instead of the public key of the actual client/server. I understand the way it works in theory, but I don't know how to actually implement it. I would appreciate any help.
Perhaps using ettercap to do a MITM attack also? But how to use it do be able to take over the SSH connection?