SSH key authentication is far more secure than password-based login. A cryptographic key pair — private key on your machine, public key on the server — lets you connect without a password and protects against brute-force attacks. This guide covers generating a key pair and deploying it on Ubuntu 26.04 LTS.

Tested and valid on:

Ubuntu 26.04 LTS

Prerequisites

Ubuntu 26.04 LTS server with SSH running
A user account on the server
An SSH client on your local machine (Linux/macOS/Windows)

Step 1 – Generate an SSH Key Pair (on your local machine)

Ed25519 keys are recommended for their speed and security:

ssh-keygen -t ed25519 -C "[email protected]"

Accept the default path (~/.ssh/id_ed25519) and set an optional passphrase.

Step 2 – Copy the Public Key to the Server

The ssh-copy-id command handles this automatically:

ssh-copy-id username@your_server_ip

Or manually append it:

cat ~/.ssh/id_ed25519.pub | ssh username@your_server_ip "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

Step 3 – Set Correct Permissions on the Server

SSH requires strict permissions on the .ssh directory:

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

Step 4 – Test Key Authentication

ssh username@your_server_ip

If a passphrase is set, you will be prompted for it rather than the account password.

Step 5 – Disable Password Authentication

Once key login works, open the SSH config:

sudo nano /etc/ssh/sshd_config

Set or confirm:

PasswordAuthentication no
PubkeyAuthentication yes

Reload SSH:

sudo systemctl reload ssh

Step 6 – Add the Key to ssh-agent (optional)

To avoid entering the passphrase every session:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

Conclusion

Your Ubuntu 26.04 LTS server now requires SSH key authentication, eliminating password brute-force risk. Store your private key securely and never share it. Back up your key pair to a safe location.

How to Set Up SSH Keys on Ubuntu 26.04