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Fix “No Matching Host Key Type Found” SSH Error Fast

Posted on by William Zheng

Ever tried connecting to a server and been stumped by a “no matching host key type found” error? You’re not alone. As more servers update their security settings, this frustrating message is popping up for users everywhere, blocking access at the worst possible moment.

Understanding why this error appears and how to solve it is crucial for anyone who relies on remote connections. In this article, you’ll find clear explanations and step-by-step solutions to get connected smoothly.

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Understanding the “No Matching Host Key Type Found” SSH Error

When using SSH (Secure Shell) to connect to a server, you might sometimes face the dreaded error message:
No matching host key type found. Their offer: ssh-rsa
or a similar variation. This error can catch you off guard, especially if your SSH connections previously worked fine. In this article, we’ll explore what this message really means, why it occurs, and—most importantly—how you can fix it quickly and securely.

What Does the Error Mean?

This error tells you that the SSH client and the target server don’t have a shared way (or “key type”) to authenticate the server. SSH relies on certain types of cryptographic keys—such as ssh-rsa, ecdsa-sha2-nistp256, or ssh-ed25519—to verify you’re connecting to the correct machine. If your client and server can’t agree on any supported key type, the connection fails.

Why Is This Happening Now?


Fixing SSH

This problem usually pops up after one of two things happens:

  1. Your SSH Client Is Upgraded or Hardened
    Recent versions of OpenSSH (and similar clients) have disabled or deprecated older, less secure host key algorithms—like ssh-dss or older forms of ssh-rsa—as a security measure.
  2. Servers Are Old or Not Updated
    Some servers still use only the outdated authentication options, so your modern SSH client and a legacy server can’t find a mutually accepted key type.

How Authentication Works in SSH

To better understand the error, let’s break down the authentication dance between an SSH client and server:

  1. Client Proposes Supported Key Types:
    When you connect, your SSH client says, “Hey, I support these key types:…”.
  2. Server Responds with Its Offer:
    The server replies with what it can do, like “I can offer ssh-dss (DSA)” or “ssh-rsa.”
  3. Negotiation Phase:
    The client tries to pick a type from the list. If there’s no overlap, you’ll see the “No matching host key type found” error.

Common Scenarios Where This Error Occurs

  • You’re trying to SSH into an old router, network device, or legacy server.
  • You’re connecting to an SFTP server or using Git via SSH, and the error arises.
  • A recent update on your system’s SSH client tightens default security policies.
  • A server offers only “ssh-dss” or “ssh-rsa” (without newer algorithms).


SSH Error: No Matching Host Key Type Found (SOLVED!) - no matching host key type found

How to Fix “No Matching Host Key Type Found”

Here’s how you can get past this roadblock. The solutions range from quick fixes (for one-time access) to longer-term, more secure changes.

1. Use SSH’s -o HostKeyAlgorithms Option (Quick Fix)

If you just need to connect once, you can specify the accepted key types explicitly.

ssh -o HostKeyAlgorithms=+ssh-rsa username@host
  • Replace username and host as needed.
  • If the server only offers ssh-dss (rare these days), you can use ssh-dss instead of ssh-rsa.
  • The + sign adds the option to the list of accepted key types.

Example with SFTP

For SFTP:

sftp -o HostKeyAlgorithms=+ssh-rsa username@host

2. Update Your SSH Client Configuration

To avoid typing the long option each time, add a section to your ~/.ssh/config file:

Host legacy-server
    HostName 192.168.1.10
    User myuser
    HostKeyAlgorithms +ssh-rsa
    PubkeyAcceptedKeyTypes +ssh-rsa
  • This will always allow ssh-rsa for connections to “legacy-server”.
  • Replace the parameters for your environment.

3. Enable the Algorithm System-Wide (Not Recommended for Most)

You can adjust your system-wide SSH client configuration in /etc/ssh/ssh_config to re-enable older key types.
Caution: This can weaken security. Only consider this on isolated systems, and never for production or internet-facing machines.

HostKeyAlgorithms +ssh-rsa
PubkeyAcceptedKeyTypes +ssh-rsa

4. Update or Replace Host Keys on the Server (Recommended if Possible)

The best way to solve this issue is to update the server itself:

  • Generate Newer Host Keys:
    On the server, administrators can generate newer, secure keys like ecdsa or ed25519.
  • Update SSH Configuration:
    Edit /etc/ssh/sshd_config to include HostKey lines for the new algorithms.
  • Restart SSH Daemon:
    After changes, restart the SSH service:
    bash
    sudo systemctl restart sshd
  • Remove Legacy Keys:
    If possible, delete or comment out entries for outdated keys.

Benefits and Challenges of Each Solution

Benefits

  • Explicitly Enabling Algorithms (Quick Fix):
  • Fast and minimally invasive.

  • Great for one-off connections or emergencies.

  • Updating Client Config:

  • Convenient for regular access to older devices.

  • Keeps changes localized to your user account.

  • Updating the Server:

  • Provides strong, future-proof security.
  • Ensures compatibility with new SSH clients.

Challenges

  • Security:
    Enabling older algorithms can expose you to known vulnerabilities (such as weak or broken cryptography). Only do this if absolutely necessary, and never on public-facing servers.
  • Server Access:
    Updating host keys on the server requires admin access. Sometimes you may be connecting to a service you don’t control.
  • Compatibility:
    Older devices or embedded systems may not support newer key types at all.

Practical Tips and Best Practices

  1. Avoid Global Changes:
    Don’t weaken your entire system’s security for one legacy device. Prefer per-host settings in ~/.ssh/config.

  2. Ask for Upgrades:
    If you don’t control the server, politely suggest the admin update their SSH host keys to support stronger algorithms.

  3. Plan for Upgrades:
    Devices that only support ssh-dss or legacy ssh-rsa may be end-of-life. Plan to upgrade or replace them.

  4. Retire Outdated Devices:
    If the device can’t be updated and regularly requires insecure keys, consider decommissioning it to avoid security risks.

  5. Audit Your Devices:
    Keep an inventory of servers and their SSH key support, so you’re not caught off guard during future upgrades.

Addressing SSH in Special Contexts (SFTP, Git, Windows)

  • SFTP:
    The same key negotiation applies when using SFTP (Secure File Transfer Protocol). Use the same -o HostKeyAlgorithms=+ssh-rsa flag with your SFTP client.

  • Git Over SSH:
    If you notice this error while running Git commands over SSH, configure your SSH client as above or update your repo’s remote host config to support newer keys.

  • Windows SSH Clients:
    The error and solutions are similar with Windows OpenSSH and popular clients like PuTTY. Make sure your client supports current encryption and key types, and if needed, adjust PuTTY’s HostKeyAlgorithms or regenerate server keys to include modern algorithms.

Cost Considerations and Shipping-Related Tips

While SSH host key negotiation doesn’t directly relate to costs or shipping, some real-world scenarios to consider include:

  • Device Replacement and Budget:
    If you have old network hardware or IoT devices that can’t be updated and require legacy SSH support, budgeting for replacement with modern, secure equipment makes sense. Factor in procurement and shipping lead times when planning such upgrades.

  • Downtime Planning:
    Updating keys on remote or internationally shipped servers may require coordination, as you could lose access if something goes wrong. Always plan changes to minimize disruptions, and ensure you have failover or backup access.

Concluding Summary

The “No matching host key type found” error is a security-centric roadblock put in place to keep your connections safe. While it feels like an obstacle, it signals that your software is looking out for you by refusing weaker, outdated cryptography. With a few targeted configuration changes or, ideally, server upgrades, you can resolve the issue and keep your workflow moving forward—without sacrificing security.

Frequently Asked Questions (FAQs)

1. What triggers the “no matching host key type found” error?
This error appears when your SSH client and the server cannot agree on a mutually supported host key type. It most often occurs when the client removes support for older, less secure key algorithms, or the server only offers outdated options.

2. Is it safe to re-enable old SSH algorithms like ssh-rsa?
Re-enabling old algorithms is not recommended unless absolutely necessary. These keys may have known security weaknesses. If possible, update the server to use newer key types like ecdsa or ed25519. Only use workarounds for non-critical, isolated systems.

3. Can I fix this error without updating the server?
Yes, you can use the -o HostKeyAlgorithms=+ssh-rsa option or update your SSH client configuration to explicitly allow older algorithms. However, this is a temporary and less secure solution. Always aim to update the server in the long term.

4. Why did this error start showing up after a software update?
SSH clients like OpenSSH are updated regularly to keep users safe. Recent updates have disabled or deprecated weaker algorithms. If you see this error after an update, your client is likely refusing old server keys for security reasons.

5. What should I do if I don’t have admin access to the SSH server?
If you can’t update the server, use the configuration workarounds on your client to enable the necessary algorithms for that specific host. Also, contact the server administrator to encourage upgrading to stronger key types to ensure future compatibility.

By understanding this error and handling it with care, you can maintain both your connectivity and your security. Remember, the best long-term approach is to ensure that both clients and servers use up-to-date, secure SSH key algorithms.

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