1.5 Security

We make sure that your MiniBolt is secured against unauthorized remote access.

The MiniBolt needs to be secured against online attacks using various methods.

Uncomplicated Firewall

A firewall controls what kind of outside traffic your machine accepts and which applications can send data out. By default, many network ports are open and listening for incoming connections. Closing unnecessary ports can mitigate many potential system vulnerabilities.

For now, only SSH should be reachable from the outside. Bitcoin Core and LND are using Tor and don't need incoming ports. We'll open the port for Electrs and web applications later if needed.

Check IPv6 availability

• With user admin, check your IPv6 availability

ping6 -c2 2001:858:2:2:aabb:0:563b:1526 && ping6 -c2 2620:13:4000:6000::1000:118 && ping6 -c2 2001:67c:289c::9 && ping6 -c2 2001:678:558:1000::244 && ping6 -c2 2001:638:a000:4140::ffff:189 && echo OK.

-> 2 output options:

First (more common)

If you obtain ping6: connect: Network is unreachable, you don't have IPv6 availability, don't worry, the IPv6 adoption is new, you will use your internet connection using the common IPv4. Additionally, you can obtain your public IPv4 with: curl -s ipv4.icanhazip.com

Second

If you obtain the "OK." output, you have IPv6 availability, additionally, you can obtain your IPv6 with: curl -s ipv6.icanhazip.com you are OK, continue the guide without modifications

Configuration

If you don't have IPv6 availability, you can disable IPv6 on UFW to avoid the creation of rules related to it:

• Edit the UFW configuration

sudo nano /etc/default/ufw

• Change IPV6=yes to IPV6=no. Save and exit

IPV6=no

• Disable logging

sudo ufw logging off

• Allow SSH incoming connection

Attention! Don't forget the next step!

sudo ufw allow 22/tcp comment 'allow SSH from anywhere'

Enable

• Enable the UFW, when the prompt shows you "Command may disrupt existing ssh connections. Proceed with operation (y|n)?", press "y" and enter

sudo ufw enable

Expected output:

> Firewall is active and enabled on system startup

• Check if the UFW is properly configured and active

sudo ufw status verbose

Expected output ⬇️

> Status: active
> Logging: off
> Default: deny (incoming), allow (outgoing), disabled (routed)
> New profiles: skip

>
> To                    Action      From
> --                    ------      ----
> 22                    ALLOW       Anywhere       # allow SSH from anywhere

If you find it locked out by mistake, you can connect a keyboard and screen to your PC to log in locally and fix these settings (especially for the SSH port 22)

More: UFW Essentials

Monitoring SSH authentication logs (optional)

• You can monitor authentication general logs in your system in real-time

sudo tail -f /var/log/auth.log

• Or filtering only by SSH authentication logs in the last 500 lines

sudo tail --lines 500 /var/log/auth.log | grep sshd

• With this command, you can show a listing of the last satisfactory logged-in users in your MiniBolt since 7 days ago. Change -7days option to do whatever you want

last -s -7days -t today

In this way, you can detect a possible brute-force attack and take appropriate mitigation measures

Do this regularly to get security-related incidents

Install Nginx

Several components of this guide will expose a communication port, for example, the Block Explorer, or the ThunderHub web interface for your Lightning node. Even if you use these services only within your own home network, communication should always be encrypted. Otherwise, any device in the same network can listen to the exchanged data, including passwords.

We use Ngnix to encrypt the communication with SSL/TLS (Transport Layer Security). This setup is called a "reverse proxy": Nginx provides secure communication to the outside and routes the traffic back to the internal service without encryption.

• With user admin, update and upgradeth OS

sudo apt update && sudo apt full-upgrade

• Install Ngnix

sudo apt install nginx

• Check the correct installation

nginx -v

Example of expected output:

> nginx version: nginx/1.18.0 (Ubuntu)

• Create a self-signed SSL/TLS certificate (valid for 10 years)

sudo openssl req -x509 -nodes -newkey rsa:4096 -keyout /etc/ssl/private/nginx-selfsigned.key -out /etc/ssl/certs/nginx-selfsigned.crt -subj "/CN=localhost" -days 3650

Example of expected output:

> .......+......+...+..+....+.....+......++++++........

• NGINX is also a full web server. To use it only as a reverse proxy, backup the default configuration

sudo mv /etc/nginx/nginx.conf /etc/nginx/nginx.conf.bak

• Create a new blank configuration file

sudo nano /etc/nginx/nginx.conf

• Paste the following configuration into the nginx.conf file. Save and exit

user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;

events {
  worker_connections 768;
}

http {
  ssl_certificate /etc/ssl/certs/nginx-selfsigned.crt;
  ssl_certificate_key /etc/ssl/private/nginx-selfsigned.key;
  ssl_session_cache shared:HTTP-TLS:1m;
  ssl_session_timeout 4h;
  ssl_protocols TLSv1.2 TLSv1.3;
  ssl_prefer_server_ciphers on;
  include /etc/nginx/sites-enabled/*.conf;
}

stream {
  ssl_certificate /etc/ssl/certs/nginx-selfsigned.crt;
  ssl_certificate_key /etc/ssl/private/nginx-selfsigned.key;
  ssl_session_cache shared:STREAM-TLS:1m;
  ssl_session_timeout 4h;
  ssl_protocols TLSv1.2 TLSv1.3;
  ssl_prefer_server_ciphers on;
  include /etc/nginx/streams-enabled/*.conf;
}

• Create the streams-available and streams-enabled directories for future configuration files

sudo mkdir /etc/nginx/streams-available

sudo mkdir /etc/nginx/streams-enabled

• Remove the Nginx site available and site enabled default configuration files

sudo rm /etc/nginx/sites-available/default

sudo rm /etc/nginx/sites-enabled/default

• Test this barebone Nginx configuration

sudo nginx -t

Expected output:

> nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
> nginx: configuration file /etc/nginx/nginx.conf test is successful

• Reload Nginx to apply the configuration

sudo systemctl reload nginx

You can monitor the Nginx logs by entering this command. Exit with Ctrl + C

journalctl -fu nginx

Expected output:

> Jun 04 18:21:09 minibolt systemd[1]: Starting A high performance web server and a reverse proxy server...
> Jun 04 18:21:09 minibolt systemd[1]: Started A high performance web server and a reverse proxy server.
> Jun 04 18:25:18 minibolt systemd[1]: Reloading A high performance web server and a reverse proxy server...
> Jun 04 18:25:18 minibol systemd[1]: Reloaded A high performance web server and a reverse proxy server.

You can monitor Nginx error logs by entering this command. Exit with Ctrl + C

sudo tail -f /var/log/nginx/error.log