How to avoid Permission denied (publickey) SSH key (Windows)

Error Overview

The error message “Permission denied (publickey)” typically occurs when attempting to establish an SSH connection using a public key authentication method on Windows. This error indicates that the SSH client was unable to use the provided private key to authenticate with the server. This can happen due to various reasons including improper permissions on the SSH key file, incorrect key usage, or missing SSH configuration.

Common Causes

Several factors can contribute to encountering the “Permission denied (publickey)” error on Windows. Understanding these common causes can help you troubleshoot the issue effectively:

1. Incorrect File Permissions: SSH keys must have strict file permissions to ensure they are not accessible by unauthorized users.
2. Wrong Key Format: The private key must be in the correct format for the SSH client to recognize it.
3. Key Not Loaded: The SSH agent may not have the key loaded, resulting in failed authentication.
4. Server Configuration: The server might not have the public key added to the authorized keys list.
5. Incorrect Username: Using the wrong username to connect to the server can lead to authentication failures.
6. Firewall or Network Issues: Firewalls or network configurations may prevent the SSH connection from being established.

Solution Methods

Method 1: Adjusting Key File Permissions

One effective solution to address the “Permission denied (publickey)” error is to adjust the permissions of the SSH key file. Follow these steps carefully:

1. Locate your SSH key file (e.g., first1.pem) in Windows Explorer.
2. Right-click on the file and select Properties.
3. Navigate to the Security tab and click on Advanced.
4. Click on Disable Inheritance to manage permissions explicitly.
5. Choose Convert inherited permissions into explicit permissions on this object.
6. Delete all entries in the permissions list, including Administrator, User, and User Groups.
7. Click the Add button.
8. Select Select a principal, then click on Advanced and choose Find Now.
9. Locate your user object from the list, select it, and click OK.
10. Ensure that the Full Control checkbox is ticked, then press OK.

By restricting access to your SSH key file, you ensure that only you can use it, which can resolve the “Permission denied (publickey)” error.

Method 2: Verify Key Permissions

If the above method does not resolve the issue, it is crucial to verify the key permissions. Follow these steps:

1. Open a Command Prompt window.
2. Navigate to the directory where your SSH key is located using the cd command.
3. Run the command to display the permissions:
   bash
icacls first1.pem
4. Ensure the output shows that only your user account has access to the file. If it is more open, repeat Method 1 to restrict permissions.

Method 3: Load the SSH Key into the SSH Agent

Another common reason for the “Permission denied (publickey)” error is that the SSH key is not loaded into the SSH agent. To load your key:

1. Open a Command Prompt or PowerShell window.
2. Start the SSH agent:
   bash
eval $(ssh-agent -s)
3. Load your SSH key into the agent:
   bash
ssh-add path\to\your\first1.pem
4. Now, try connecting to your SSH server again.

Method 4: Check Server Configuration

Ensure that the public key is correctly configured on the server. Follow these steps:

1. Log in to your server via another method (e.g., console access).
2. Open the ~/.ssh/authorized_keys file and confirm that your public key is listed there.
3. If it is missing, add the public key from your local machine.

Method 5: Confirm Username

Sometimes, the error can be due to using the wrong username during the SSH connection attempt. Verify the username required by the server. Use the correct format:

ssh username@server_address

Prevention Tips

To prevent encountering the “Permission denied (publickey)” error in the future, consider the following tips:

• Always ensure your SSH key has the correct permissions.
• Regularly check that your public key is added to the server’s authorized keys.
• Keep your SSH client and related tools updated to the latest versions.
• Use a strong passphrase for your private key to enhance security.
• Regularly backup your SSH keys securely.

Summary

The “Permission denied (publickey)” SSH key error on Windows can be a common yet frustrating issue. By understanding the common causes and implementing the solutions provided in this article, you can effectively troubleshoot and resolve the error. Adjusting file permissions, verifying key formats, and ensuring proper configuration on both the client and server sides are key steps in avoiding this error in the future. Following best practices will ensure smooth and secure SSH connections moving forward.