ubuntu 20.04 ssh keygen

admin3 April 2024Last Update :

Mastering SSH Key Generation in Ubuntu 20.04: A Comprehensive Guide

ubuntu 20.04 ssh keygen

Welcome to the world of secure shell (SSH) on Ubuntu 20.04, where the art of key generation enhances the security of your server connections. In this extensive guide, we will delve into the intricacies of creating and managing SSH keys, ensuring that your communication with remote servers is not just secure but virtually impenetrable. Whether you’re a system administrator, a developer, or simply an enthusiast looking to fortify your network communications, this article will equip you with the knowledge and tools necessary to master SSH keygen on Ubuntu 20.04.

Understanding SSH and Its Importance

Before we dive into the technicalities of generating SSH keys, let’s first understand what SSH is and why it’s crucial for secure communications. Secure Shell (SSH) is a cryptographic network protocol used for operating network services securely over an unsecured network. It provides a secure channel over an insecure network in a client-server architecture, connecting an SSH client with an SSH server.

The Need for SSH Keys

SSH keys are a pair of cryptographic keys that can be used to authenticate to an SSH server as an alternative to password-based logins. A private key, which is secret, and a public key, which is shared, make up this pair. The use of SSH keys over passwords has several advantages:

  • Enhanced Security: SSH keys are nearly impossible to decipher through brute force attacks, making them much more secure than traditional passwords.
  • Convenience: Once set up, SSH keys allow for passwordless sign-ins, streamlining the login process without compromising security.
  • Automation: Scripts and automated processes can utilize SSH keys to perform secure tasks across systems without human intervention.

Generating SSH Keys on Ubuntu 20.04

Now, let’s get to the core of this guide—generating SSH keys on Ubuntu 20.04. The process is straightforward, but it requires careful attention to detail to ensure maximum security.

Step-by-Step SSH Key Generation

To generate an SSH key pair, follow these steps:

  1. Open the terminal on your Ubuntu 20.04 system.
  2. Type the following command:
    ssh-keygen -t rsa -b 4096
  3. When prompted, specify the file in which to save the key (by default, this is ~/.ssh/id_rsa).
  4. Enter a secure passphrase when prompted. This adds an extra layer of security.

After completing these steps, you will have generated an RSA key pair with a length of 4096 bits. The private key will be stored in the file you specified, and the public key will be in a file with the same name but with .pub appended to it.

Choosing the Right Algorithm and Key Size

While RSA is widely used, there are other algorithms available such as ECDSA and Ed25519. Each comes with its own strengths and considerations:

  • RSA: A time-tested algorithm with widespread support. Recommended key size is at least 2048 bits, though 4096 bits is preferred for enhanced security.
  • ECDSA: Uses elliptic curve cryptography to offer equivalent security to RSA but with smaller key sizes, resulting in faster performance.
  • Ed25519: An algorithm known for its high performance and resistance to certain cryptographic attacks. It uses fixed-size keys for simplicity and efficiency.

Securing Your Private Key

Your private key is the gateway to your server, and thus, it must be kept secure. Here are some best practices:

  • Set a strong passphrase for your private key.
  • Store the key in a secure location with minimal access.
  • Regularly update your keys and rotate them if any potential breach is suspected.

Deploying SSH Public Keys

Once you’ve generated your SSH key pair, the next step is to deploy the public key to the server(s) you wish to connect to securely.

Copying the Public Key to the Server

You can copy your public key to the server using the ssh-copy-id utility:

ssh-copy-id user@hostname

This command will add your public key to the server’s authorized_keys file, allowing you to log in without a password.

Manually Installing Public Keys

If ssh-copy-id is not available, you can manually install the public key by appending it to the ~/.ssh/authorized_keys file on the server:

cat ~/.ssh/id_rsa.pub | ssh user@hostname 'mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys'

Ensure correct permissions are set on the server:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

Managing SSH Keys

Key management is critical for maintaining a secure environment. Regularly review and update your keys, remove old keys, and audit usage to ensure that only authorized users have access.

Best Practices for Key Management

Here are some tips for effective SSH key management:

  • Use a passphrase for all private keys.
  • Implement a key rotation policy to replace keys at regular intervals or upon personnel changes.
  • Audit your authorized_keys files periodically to ensure they contain only valid keys.

Troubleshooting Common SSH Key Issues

Even with proper setup, issues can arise. Let’s address some common problems and their solutions:

Permission Errors

If you encounter permission errors, verify that your home directory, ~/.ssh directory, and authorized_keys file have the correct permissions set.

Passphrase Prompts

If you’re being prompted for a passphrase repeatedly, consider using an SSH agent like ssh-agent or gnome-keyring to securely store your decrypted keys in memory during your session.

Frequently Asked Questions

Can I use the same SSH key pair on multiple servers?

Yes, you can use the same public key on multiple servers. However, for increased security, it’s recommended to use different key pairs for different servers or environments.

What should I do if my private key is compromised?

If you suspect your private key is compromised, immediately revoke access by removing the corresponding public key from all servers and generate a new key pair.

Is it safe to share my public key?

Yes, public keys are designed to be shared and do not compromise your security when distributed.


In conclusion, mastering SSH key generation and management on Ubuntu 20.04 is essential for anyone looking to secure their server communications. By following the guidelines outlined in this article, you’ll be well-equipped to create, deploy, and manage your SSH keys effectively. Remember to stay vigilant, regularly update your keys, and always follow best practices to maintain a robust security posture.


For further reading and advanced topics related to SSH and security, please refer to:

By adhering to the principles and practices presented in this comprehensive guide, you’ll be able to navigate the complexities of SSH key generation with confidence and precision, ensuring a fortified layer of protection for your Ubuntu 20.04 systems.

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