Troubleshooting SSHD Connection Issues with Public Key in Cygwin

Thu, 24 Dec 2015 23:19:58 +0700

Cygwin provides a Unix-like environment for Windows, including an implementation of OpenSSH, which allows you to establish secure remote connections using the SSH (Secure Shell) protocol. However, connecting to Cygwin’s SSH server (sshd) using public key authentication can sometimes present challenges. This blog post will guide you through a troubleshooting process to resolve issues related to connecting to Cygwin sshd with public key authentication.

Step 1: Update /etc/sshd_config

Open the Cygwin terminal and navigate to the Cygwin installation directory (typically C:\cygwin64 or C:\cygwin).
Locate the “sshd_config” file in the etc directory. The full path should be something like C:\cygwin64\etc\sshd_config.
Open the “sshd_config” file using a text editor (e.g., Notepad++).
Look for the “StrictModes” option and set it to “no.” This allows more relaxed permission checking for the authorized_keys file.
Save the changes and close the text editor.

Step 2: Generate SSH Key Pair

If you haven’t already done so, generate an SSH key pair on the client machine using the “ssh-keygen” command. Make sure to choose a strong passphrase to protect your private key.
By default, the key pair will be saved in the “.ssh” directory in the user’s home directory (e.g., C:\Users\YourUsername.ssh).

Step 3: Copy Public Key to Cygwin Server

In the Cygwin terminal, navigate to the user’s home directory (e.g., cd ~).
Create the “.ssh” directory if it doesn’t exist: mkdir .ssh
Use the “scp” command to copy the public key to the Cygwin server: scp <public_key_file> user@server:/home/user/.ssh/authorized_keys Replace “<public_key_file>” with the path to your public key file. Replace “user” with your username on the Cygwin server. Replace “server” with the hostname or IP address of the Cygwin server.

Step 4: Restart SSHD Service

In the Cygwin terminal, run the following command to restart the sshd service: net stop sshd && net start sshd

Step 5: Test SSH Connection

On the client machine, open a new terminal or command prompt.
Run the following command to connect to the Cygwin server using SSH: ssh user@server Replace “user” with your username on the Cygwin server. Replace “server” with the hostname or IP address of the Cygwin server.
If the connection is successful and prompts for the passphrase, enter the passphrase associated with your private key.

Conclusion

By following the troubleshooting steps outlined in this blog post, you should be able to connect to the Cygwin sshd server using public key authentication. Remember to ensure that the “StrictModes” option in the sshd_config file is set to “no” to allow more flexible permission checking for the authorized_keys file. Generating an SSH key pair, copying the public key to the Cygwin server, and restarting the sshd service are critical steps in establishing a successful SSH connection.