How to Resolve “Putty Signature from Server’s Host Key is Invalid” Error

Hello Dev, have you ever encountered the error message “Putty Signature from Server’s Host Key is Invalid” while trying to connect to a server through Putty? This error can be frustrating, especially when you’re in the middle of an important task. In this article, we’ll walk you through the causes of this error and provide step-by-step instructions on how to resolve it. Let’s dive in!

Understanding the Error Message

Before we delve into the solutions, let’s first understand what this error message means. Putty is an SSH client used to connect to a server securely. When you try to connect to a server, Putty checks the server’s key to ensure that the server you’re connecting to is not a fake one. The error message “Putty Signature from Server’s Host Key is Invalid” occurs when the server’s host key has changed, and Putty doesn’t recognize the new key. This could happen due to various reasons, which we’ll explore in the next section.

Causes of “Putty Signature from Server’s Host Key is Invalid” Error

There could be several reasons why you’re experiencing this error message. Some of the common causes include:

Solutions for “Putty Signature from Server’s Host Key is Invalid” Error

Method 1: Updating the Host Key

The first solution is to update the server’s host key on Putty. Follow the steps below:

1. Open Putty and go to the “Session” category on the left-hand side
2. Enter the server’s IP address or DNS name in the “Host Name” field
3. Expand the “SSH” category and click on “Auth”
4. Click on the “Browse” button and select the new host key file
5. Click on “Open” to connect to the server

Method 2: Updating the IP Address

If the server’s IP address has changed, you’ll need to update it on Putty. Follow the steps below:

1. Open Putty and go to the “Session” category on the left-hand side
2. Enter the new IP address in the “Host Name” field
3. Click on “Open” to connect to the server

Method 3: Renewing the Server’s Certificate

If the server’s certificate has expired, you’ll need to renew it. Follow the steps below:

1. Contact the server administrator and request for a new certificate
2. Once you receive the new certificate, open Putty and go to the “Session” category on the left-hand side
3. Enter the server’s IP address or DNS name in the “Host Name” field
4. Expand the “SSH” category and click on “Auth”
5. Click on the “Browse” button and select the new certificate file
6. Click on “Open” to connect to the server

Method 4: Updating the DNS Name

If the server’s DNS name has changed, you’ll need to update it on Putty. Follow the steps below:

1. Open Putty and go to the “Session” category on the left-hand side
2. Enter the new DNS name in the “Host Name” field
3. Click on “Open” to connect to the server

Method 5: Checking for Third-Party Interception

If you suspect that the connection is being intercepted by a third-party, you’ll need to take necessary actions to secure the connection. Follow the steps below:

1. Check if the server’s host key has changed by contacting the server administrator
2. If the host key has changed, update it on Putty (Method 1)
3. If the host key hasn’t changed, try connecting to the server from a different network or using a VPN
4. If the problem persists, contact the server administrator for further assistance

FAQs

Q. What is a server’s host key?

A. A server’s host key is a cryptographic key that is used to identify the server when you connect to it through an SSH client like Putty.

Q. Why does the server’s host key change?

A. The server’s host key could change due to various reasons like a server rebuild, a security breach or a software upgrade.

Q. Is it safe to ignore the “Putty Signature from Server’s Host Key is Invalid” error?

A. No, it’s not safe to ignore this error as it could be an indication of a security breach or a man-in-the-middle attack.

Q. Can I automate the process of updating the host key on Putty?

A. Yes, you can use tools like Plink or WinSCP’s “PuTTYgen” tool to automate the process of updating the host key on Putty.

Conclusion

We hope this article has helped you resolve the “Putty Signature from Server’s Host Key is Invalid” error. Always ensure that you keep your SSH connections secure by regularly updating your host key and certificate, and checking for any third-party interception. If you have any further queries, feel free to leave a comment below.