When you’re troubleshooting connectivity issues between Secure Shell (SSH)/Secure File Transfer Protocol (SFTP) clients and servers, it pays to inspect the error messages generated on both sides of a connection. Those messages often provide vital clues about the problem. If your error messages involve the Diffie-Hellman-Group1-SHA1 key exchange algorithm, you’ll want to stick around. In the succeeding sections, we’ll be discussing the underlying cause of this particular issue and how to fix it.