Dealing with the “Signature from server’s host key is invalid Putty” error

Hello Dev, have you ever encountered the “Signature from server’s host key is invalid Putty” error while connecting to a remote server using Putty? This error message can be quite frustrating, especially if you are on a deadline. But don’t worry, in this article, we will guide you through the various causes of this error and how to fix it.

Understanding the “Signature from server’s host key is invalid Putty” error

Before we dive into how to solve the error, let’s first understand what it means. This error usually occurs when you try to connect to a remote server through SSH using Putty. It suggests that the host key of the server you are trying to connect to has changed or does not match the key stored in your cached keys.

The host key is a security feature that ensures the authenticity of the remote server. It prevents man-in-the-middle attacks by verifying that the server you are connecting to is the same server you intended to connect to. Therefore, when the host key changes, Putty alerts you of this change and asks for your confirmation before proceeding with the connection.

Causes of the “Signature from server’s host key is invalid Putty” error

Several factors can cause this error message. Some of the causes include:

Solutions to the “Signature from server’s host key is invalid Putty” error

Method 1: Clear your cached keys

The first solution to the “Signature from server’s host key is invalid Putty” error is to clear your cached keys. Follow these steps:

1. Open Putty and connect to the remote server.
2. Click on the “SSH” category from the navigation menu on the left-hand side.
3. Select “Auth” from the SSH category.
4. Click on the “Clear” button to clear your cached keys.
5. Attempt to reconnect to the remote server.

Method 2: Update your host keys

If clearing your cached keys does not solve the error, you may need to update your host keys. Follow these steps:

1. Open Putty and connect to the remote server.
2. Click on the “SSH” category from the navigation menu on the left-hand side.
3. Select “Auth” from the SSH category.
4. Click on the “Browse” button next to “Private key file for authentication.”
5. Select the private key file for the server you are trying to connect to.
6. Click on the “Open” button to connect to the remote server.

Method 3: Check your permissions

If you are still experiencing the error message, you may want to check your permissions. Make sure that the .ssh directory and authorized_keys file on the remote server have the correct permissions. You can change the permissions by running the following commands:

chmod 700 ~/.ssh

chmod 600 ~/.ssh/authorized_keys

Method 4: Check for third-party software interference

If the error persists, you may want to check if third-party security software is interfering with the connection. You can try disabling this software temporarily to see if it resolves the issue. If it does, you will need to add Putty to your software’s whitelist or configure it to allow SSH connections.

FAQ:

Q1. Can I ignore the “Signature from server’s host key is invalid Putty” error?

A1. It is not recommended to ignore this error as it may indicate a security breach. Always verify with the server administrator to ensure that the host key change is valid before accepting the new key.

Q2. I am still experiencing the error after trying all the methods. What should I do?

A2. If you have tried all the methods and are still experiencing the error message, you may want to contact the server administrator for further assistance.

Q3. Will clearing my cached keys affect other connections?

A3. No, clearing your cached keys only affects the server you are trying to connect to. Your other connections are not affected.

Q4. Why does the host key change?

A4. The host key may change due to various reasons, such as a server upgrade or reinstallation, a hostname change, or a security breach.

Q5. What are the best practices for managing host keys?

A5. It is recommended to periodically check your host keys for any changes and update them accordingly. You can also store your host keys in a centralized location, such as Active Directory, to ensure that they are consistent across all servers.

Conclusion

We hope that this article has helped you understand the “Signature from server’s host key is invalid Putty” error and how to fix it. Remember, always verify with the server administrator to ensure that the host key change is valid before accepting the new key.