This is the setup we have - we have an application running on a Windows 10 machine that sends TCP traffic to another Windows 10 machine. The 2 machines are in the same subnet but are not in a domain. Neither are allowed access to the internet.
We need to encrypt the traffic between the 2 machines to prevent a 'man in the middle attack'. Can you please advise on the best method to achieve this? We can use third party software but cannot change our application. The current method we're exploring is an IPsec tunnel between the machines but have yet to get this to work.