Device level security setup

Configure remote access via SSH keypair

Generating an SSH key pair

On your client machine (e.g. working laptop), open up your terminal (Mac) or Windows Powershell (Windows) and run:

ssh-keygen -t ed25519 -C ethnode

Press Enter and set a password to encrypt your SSH private key.

Expected output:

Add SSH pubkey to your Node

While the private key portion of the SSH keypair stays in your working laptop, we will need to add the public key portion to your Node.

Transfer remotely

On your working laptop, run:

ssh-copy-id -i ~/.ssh/id_ed25519.pub <username>@<node_IP_address>

Enter the password of your NUC device when prompted.

Transfer physically

Print out the SSH pubkey string and copy it. On your working laptop, run:

cat ~/.ssh/id_ed25519.pub

You will see a similar output below:

ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBKRXS4XpZoBcuqvXVN2sRNNolKL+ZHy2Xnzx27Op3uY ethnode

SSH into your NUC and enter your password when prompted:

ssh <username>@<node_IP_address> -v

Create the authorized SSH key file manually.

sudo mkdir -p ~/.ssh
sudo nano ~/.ssh/authorized_keys

Paste your copied SSH pubkey string into the authorized_keys file and press CTRL + O, enter, CTRL + X to save the file and exit.

Change the SSH port and disable remote password login

You can make it harder for attackers to access your node by changing your SSH port away from the default port 22.

Pick a port number between 1024–49151 and check that it is not already in use by running

sudo ss -tulpn | grep <Chosen_SSH_Port_Number>

Expected output: None. i.e. If there is no output, it means that your chosen port is free to use.

Next, we will change your SSH port number and disable remote password login concurrently

Run the following command to open up the SSH server configuration file.

sudo nano /etc/ssh/sshd_config

1. Find the line Port 22 in the file. Change it to your chosen port number and then uncomment the line by removing the # prefix (if it exists)

2. Uncomment #AuthorizedKeysFile if it is commented (by removing the # in front of it)

3. Change KbdInteractiveAuthentication yes to KbdInteractiveAuthentication no and uncomment (by removing the # in front of it)

4. Change PasswordAuthentication yes to PasswordAuthentication no and uncomment (by removing the # in front of it)

5. Change #PermitRootLogin prohibit-password to PermitRootLogin no , removing the # prefix

Once you're done, save with Ctrl+O and Enter, then exit with Ctrl+X.

Now we restart the SSH server so it registers the new settings:

sudo systemctl restart sshd

Now you will only be able to access your node remotely using your SSH private key. The command for your SSH connection will be amended slightly from before to:

ssh <username>@<node_IP_address> -p <new_port_no.> -i .ssh/id_ed25519 -v

Configure the firewall rules

The basic rules we will implement are as follows:

1. Deny all incoming traffic by default

2. Allow all outgoing traffic by default

3. Allow incoming traffic via port <your_chosen_SSH_port> for SSH access

4. Allow incoming traffic via port 30303 and 30304 for the execution clients to connect with other nodes

5. Allow incoming traffic via port 9000 and 9001 for the consensus clients to connect with other nodes

6. Allow incoming traffic via port 3000 and 3001 for Grafana to display monitoring dashboards for your node

sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw allow <your_chosen_SSH_port>/tcp
sudo ufw allow 30303 # for the EL via Diva
sudo ufw allow 30304 # for the native EL 
sudo ufw allow 9000 # for the CL via Diva
sudo ufw allow 9001 # for the native CL
sudo ufw allow 3000 # for the native Grafana
sudo ufw allow 3001 # for Grafana via Diva

With these configurations set up, you will have blocked off all but 4 possible openings for potential attackers to enter from.

• Ports 30303 and 9000 will be used by Nethermind and Teku. We will create dedicated user accounts with root access disabled for these services

• Port 3000 is only accessible within your local area network (i.e. not exposed to the public internet

• Your chosen SSH port is secured by your SSH private key so its virtually impossible to brute force the access.

Turn on the firewall

Now lets turn the firewall on and check our configurations before moving on.

sudo ufw enable
sudo ufw status numbered

You should see something similar to the screenshot below:

Set up brute force protection

Even though having our SSH key access implemented means an attacker will need 25 million years to try all combinations, lets go ahead and make it even harder for them - by limiting the number of attempts per IP address to 5 tries and blocking them after.

Install the software:

sudo apt install -y fail2ban

Open the configuration file:

sudo nano /etc/fail2ban/jail.d/ssh.local

Add the following contents to the configuration file:

[sshd]
enabled = true
banaction = ufw
port = <your_chosen_SSH_port>
filter = sshd
logpath = %(sshd_log)s
maxretry = 5

Once you're done, save and exit with Ctrl+Oand Enter, then Ctrl+X.

Finally, restart the service:

sudo systemctl restart fail2ban

Enable automatic security updates

sudo apt update
sudo apt install -y unattended-upgrades update-notifier-common
sudo nano /etc/apt/apt.conf.d/20auto-upgrades

Add the following contents to the configuration file:

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";
APT::Periodic::AutocleanInterval "7";
Unattended-Upgrade::Remove-Unused-Dependencies "true";
Unattended-Upgrade::Remove-New-Unused-Dependencies "true";
Unattended-Upgrade::Automatic-Reboot "true";
Unattended-Upgrade::Automatic-Reboot-Time "02:00";

Once you're done, save and exit with Ctrl+Oand Enter, then Ctrl+X.

Finally, restart the service:

sudo systemctl restart unattended-upgrades

Check the logs for any warnings:

sudo cat /var/log/unattended-upgrades/unattended-upgrades.log

If you see following warnings, proceed to the next step.

2024-02-01 04:48:24,012 WARNING System is on battery power, stopping
2024-02-01 06:19:01,972 WARNING System is on battery power, stopping
2024-02-01 17:53:48,650 WARNING System is on battery power, stopping

If your device is definitely connected to a power source, amend the 50unattended-upgrades file directly.

sudo nano /etc/apt/apt.conf.d/50unattended-upgrades

Look for the following line and uncomment it by removing the // prefix.

// Unattended-Upgrade::OnlyOnACPower "false";