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Asked: 2024-09-23T20:48:30+05:30 In:

I’m encountering an issue where my SSH connection fails with a message indicating that no compatible host key type was found. The server is offering DSS keys, but my client seems to reject this type. How can I resolve this issue and establish a successful SSH connection?

So, I’m having a pretty frustrating time trying to SSH into my server. I get this error message saying something like “no compatible host key type found.” It seems that my server is only offering DSS keys, but my SSH client doesn’t seem to support them or something? I’ve done some digging, and it appears that DSS keys are considered outdated and not very secure anymore, which is probably why my client is rejecting them.

I’ve tried a few things already. First, I checked the configuration files on both my client and server to see if there were any specific settings related to host key algorithms. I found some options in the `sshd_config` on the server side that mention supported key types, but I’m not entirely sure which algorithms I should be enabling.

To make matters worse, I’m not really familiar with key types and how they work. I’ve seen mentions of RSA and Ed25519 as more modern alternatives, but I’m a bit lost on how to switch my server over to use those instead. I think I need to generate new host keys, but could someone guide me on how to do that without messing everything up?

Also, do I need to make any changes on my SSH client side, or is it mainly a server-side fix? I’m using an Ubuntu machine for both the server and client, which adds another layer of complexity since any command I try to run could have different options based on my environment.

I’d love any step-by-step guidance or advice on how to get this resolved. I just want to be able to connect without all this hassle. I’m sure I’m not the only one facing this problem, so I appreciate any tips or tricks that worked for you. Thanks in advance for your help!

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    2 Answers



    1. SSH Host Key Issue

      SSH Host Key Error Help

      Sounds like you’re in a bit of a bind with the SSH into your server! That error about “no compatible host key type found” is definitely frustrating. It looks like your server is sticking to old DSS keys, which modern clients don’t really like, and you’re right—DSS is considered kinda outdated. Let’s try to sort this out step-by-step!

      1. Check Current Keys

      First, let’s see which host keys your server is currently using. You can check them with this command:

      ls /etc/ssh/

      Look for files like ssh_host_rsa_key, ssh_host_ed25519_key, etc. If you only see the ssh_host_dsa_key, that’s your problem!

      2. Generate New Keys

      To add some modern keys like RSA or Ed25519, you can run the following commands:

      
    sudo ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key
    sudo ssh-keygen -t ed25519 -f /etc/ssh/ssh_host_ed25519_key

      This will generate new RSA and Ed25519 host keys. You can just press Enter for all the prompts to use the defaults.

      3. Update SSH Configuration

      Now, you’ll want to edit your sshd_config file (located at /etc/ssh/sshd_config) to ensure it uses the new keys. Look for lines that start with HostKey and add these:

      
    HostKey /etc/ssh/ssh_host_rsa_key
    HostKey /etc/ssh/ssh_host_ed25519_key

      Then, comment out or remove any lines related to DSS keys.

      4. Restart SSH Service

      After that, restart the SSH service to apply your changes:

      sudo systemctl restart ssh

      5. Update Your SSH Client (If Needed)

      Usually, nothing extra is needed on the client side, especially if it’s also Ubuntu. Just make sure your SSH client is up to date. You can do that with:

      sudo apt update && sudo apt upgrade

      6. Test Your Connection

      Now, try connecting again to your server using SSH. You should be able to connect without that pesky error!

      Final Thoughts

      If you hit any snags along the way or things still don’t work, don’t hesitate to reach out with what errors you’re seeing. Good luck!


    2. To resolve the SSH connection issue due to outdated DSS keys, you will need to generate new host keys using more secure algorithms like RSA or Ed25519. Begin by logging into your Ubuntu server via the console (or any other method that allows you access). You can generate new keys by executing the following command: `sudo ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key` for RSA keys or `sudo ssh-keygen -t ed25519 -f /etc/ssh/ssh_host_ed25519_key` for Ed25519 keys. Make sure to replace existing files only if you are certain they won’t be used for other connections. After generating the keys, you should check your SSH daemon configuration file (`/etc/ssh/sshd_config`) to ensure it supports the newly generated keys by including lines like `HostKey /etc/ssh/ssh_host_rsa_key` and/or `HostKey /etc/ssh/ssh_host_ed25519_key` if not already present.

      After you’ve updated the configuration, restart the SSH service with `sudo systemctl restart sshd`. On the client side, you typically shouldn’t need any changes as long as your OpenSSH version supports the algorithms. However, ensure that your SSH client is up to date. You can check supported host key algorithms by running `ssh -Q key` on your client machine. This command will return a list of supported keys, which should include the ones you just generated. Once everything is configured correctly, attempt your SSH connection again. If you still encounter issues, check any firewall settings or access configurations. When troubleshooting, paying attention to the specific SSH error messages can offer valuable clues about other potential misconfigurations.

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