The Secure Shell (SSH) protocol is widely used to provide secure and encrypted communication between two remote systems. One of the key aspects of SSH is to establish a secure connection between the client and the server. This connection relies on cryptographic keys to provide secure communication, which involves key exchange and authentication. However, some older SSH implementations may have vulnerabilities that can be exploited by attackers. This is why it’s essential to keep the SSH protocol and its components up to date.

At IIT Kanpur webhome server, there is an issue with the key exchange (KEX) algorithm and host key algorithm, which can result in connection errors when trying to establish an SSH connection from a newer machine. The server uses an older version of SSH, which may not support newer key exchange and host key algorithms.

When you try to connect to the IITK webhome server from a newer machine, you may receive an error message that says “no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1”. This error occurs because your machine offers newer key exchange algorithms, but the server only supports older, less secure algorithms.

To resolve this issue, you can modify your SSH configuration file to specify the key exchange and host key algorithms that your machine should offer during the SSH handshake. You can do this by adding the following lines to your SSH configuration file (usually located at ~/.ssh/config):

Host webhome.cc.iitk.ac.in
  KexAlgorithms +diffie-hellman-group1-sha1
  HostKeyAlgorithms +ssh-dss

In the above configuration, KexAlgorithms specifies the key exchange algorithms that your machine can use, and HostKeyAlgorithms specifies the host key algorithms that your machine can accept. By adding these lines to your SSH configuration file, you are telling your machine to offer only the specified algorithms when connecting to the IITK webhome server. This ensures that your SSH connection is established using the most secure algorithms available to both your machine and the server.

In conclusion, keeping your SSH protocol and components up to date is crucial for maintaining secure communication between remote systems. If you encounter connection errors when trying to establish an SSH connection to an older server, such as the IITK webhome server, you can modify your SSH configuration file to specify the key exchange and host key algorithms that your machine should offer during the SSH handshake.