generate ssh key ubuntu 16.04

SSH, or Secure Shell, is a protocol used to securely connect to remote systems. It’s widely used by system administrators and developers to manage servers and applications remotely. 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, is stored on the client machine; and a public key that is shared with the world. Using SSH keys not only increases security but also allows for more efficient management of multiple servers.

Types of SSH Key Algorithms

RSA (Rivest-Shamir-Adleman)
DSA (Digital Signature Algorithm)
ECDSA (Elliptic Curve Digital Signature Algorithm)
Ed25519 (Edwards-curve Digital Signature Algorithm)

Each algorithm has its own strengths, with RSA being the most commonly used. However, Ed25519 is gaining popularity due to its high level of security and performance.

Generating SSH Keys on Ubuntu 16.04

To generate SSH keys on Ubuntu 16.04, you’ll need access to the terminal and the ssh-keygen utility, which comes pre-installed with the OpenSSH package.

Step-by-Step Guide to Generating SSH Keys

Open your terminal.
Type the following command:
```
ssh-keygen -t rsa -b 4096
```
When prompted, specify the file in which to save the key.
Enter a secure passphrase when prompted.

This process creates a new SSH key, using the provided email as a label. The -t flag specifies the type of key to create, and -b stands for the key length.

Selecting a Strong Passphrase

A passphrase adds an additional layer of security to prevent unauthorized users from logging in. It should be complex enough to defend against brute force attacks yet memorable enough for you to recall.

Configuring SSH Key Authentication on Ubuntu 16.04

Once you have generated your SSH keys, the next step is to set up the public key on your server.

Copying the Public Key to Your Server

You can copy the public key to your server using the ssh-copy-id script or manually by appending it to the ~/.ssh/authorized_keys file on the server.

ssh-copy-id user@hostname

Replace “user” with your username and “hostname” with the server’s IP address or domain name.

Manual Copy Method

If you cannot use ssh-copy-id, you can manually copy the public key using the following steps:

Display your public key with:
```
cat ~/.ssh/id_rsa.pub
```
Log into your server and edit the authorized_keys file:
```
nano ~/.ssh/authorized_keys
```
Paste your public key into this file, save, and exit.

Enhancing SSH Security

With your SSH keys in place, you can further enhance security by making some changes to the SSH daemon configuration.

Disabling Password Authentication

To prevent password-based login attempts, disable password authentication on your server by editing the SSH config file.

sudo nano /etc/ssh/sshd_config

Find the line that reads PasswordAuthentication and change it to no. Then restart the SSH service.

sudo systemctl restart sshd

Changing the Default SSH Port

Changing the default SSH port from 22 to another number can help deter automated attacks.

Port 2222

Remember to update any firewall rules to allow traffic on the new port.

Troubleshooting Common SSH Key Issues

Sometimes, even after setting up everything correctly, you might face issues while connecting to the server.

Permission Errors

Ensure your private key file (~/.ssh/id_rsa) is only readable by you and that your ~/.ssh directory has appropriate permissions set.

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_rsa

Passphrase Problems

If you forget your passphrase, you’ll need to generate a new key pair and replace the public key on any servers you connect to.

Frequently Asked Questions

Can I use the same SSH key for multiple servers?

Yes, you can use the same SSH key to connect to multiple servers. You just need to copy your public key to each server’s authorized_keys file.

What if my Ubuntu 16.04 system doesn’t have ssh-keygen?

The ssh-keygen utility should come pre-installed with OpenSSH. If it’s missing, you can install it with:

sudo apt-get install openssh-client

How do I know if my SSH key is RSA, DSA, ECDSA, or Ed25519?

You can check the type of your SSH key by looking at the header inside the key file itself. For example, an RSA key will start with ‘—–BEGIN RSA PRIVATE KEY—–‘.

Yes, it’s perfectly safe to share your public SSH key. It’s designed to be distributed and cannot be used to derive the private key.

What should I do if my SSH key is compromised?

If you suspect your SSH key has been compromised, generate a new key pair immediately and replace the public key on all servers you access.