Understanding and Resolving the SCP “No Matching Host Key Type Found” Error

Hello fellow server administrators and enthusiasts!

If you’ve been managing Linux servers for a while, you might have come across the intriguing error: “no matching host key type found” when trying to establish an SCP connection. Today, I’m diving deep into this error, explaining its roots, and providing a solution for those who encounter it.

The Culprit:

Imagine this scenario: You’re trying to copy some files from a remote server using the scp command, and you’re greeted with this error:

Unable to negotiate with port 22: no matching host key type found. Their offer: ssh-rsa,ssh-dss
scp: Connection closed

This error can be a bit perplexing, especially if you’ve been connecting to servers without any issues until now. So, what’s happening here?

Decoding the Error:

  1. Unable to negotiate with port 22: This indicates that there’s a negotiation problem between your SCP client and the remote server on the default SSH port, 22.
  2. no matching host key type found. Their offer: ssh-rsa,ssh-dss: This is where the real issue lies. The remote server is offering two types of host key algorithms for authentication: ssh-rsa and ssh-dss. Both of these are older algorithms. Due to potential vulnerabilities, many modern SCP clients have deprecated or disabled them by default. Hence, the “no matching host key type” error.

The Fix:

To address this, we can tweak our SCP client’s configuration to accept the ssh-rsa algorithm. Here’s how:

– Edit (or create) the SSH configuration file in your home directory:bash

nano ~/.ssh/config

– Add the following lines:

    HostkeyAlgorithms +ssh-rsa
    PubkeyAcceptedAlgorithms +ssh-rsa

Replace with the IP address or hostname of your remote server.

– Save and close the file.

– For security reasons, ensure that the configuration file is only accessible by you:

chmod 600 ~/.ssh/config

Now, when you try to connect or copy files using scp, the connection should be established without any errors.

A Word of Caution:

While this solution works, it’s essential to understand the implications. By enabling older algorithms, you might be exposing your connection to potential vulnerabilities. It’s always a good practice to ensure both your client and server are updated and configured to use the latest and most secure algorithms.

If you have control over the remote server, consider updating its SSH configuration to support more modern and secure key algorithms. This way, you can maintain the highest security standards while ensuring compatibility.

Wrapping Up:

SCP errors can be daunting, but with a bit of understanding and the right configuration tweaks, they can be easily resolved. Always prioritize security and keep your server configurations updated. Happy server managing!

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