In part 1, we showed you the basic configuration of our Turris Omnia. In this article, we configure the Omnia to use HTTPS-only and harden its TLS configuration. Using HTTPS-only is a good practice even in your home network.
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By default, our Turris Omnia is reachable via port 80 (HTTP) and 22 (SSH). HTTP is an unencrypted network protocol. This means that other devices in our local network could monitor and read the network traffic between a computer and the Omnia. Furthermore, we can't be sure that we are really connected with our Omnia when connecting to 192.168.1.1. There is no cryptographic proof.
The solution: Get a certificate, enable HTTPS (port 443) and disable HTTP. Turris OS already shows a warning message that you should enable HTTPS. You can enable this configuration which uses a Turris certificate and not so strict TLS cipher suites. Use this configuration provided by CZ.NIC if you are not a tech-savvy person. For more tech-savvy people, we provide the following guide.
We want to use our own certificate and only strong/modern cipher suites. If you don't own a Turris Omnia, you can still try to find according guides for your home router. The idea is to encrypt and authenticate all HTTP traffic between local devices and your router's web server.
This time, we need:
- our Turris Omnia which is connected with our computer and the internet
- an SSH client on our computer
- tools like nmap, sslyze or sslscan to verify our setup
Step by step from HTTP to hardened HTTPS
Our plan is really straightforward: Our Omnia runs Lighttpd, an open-source web server optimized for speed-critical environments. So we have to generate a private key, a public certificate, change the configuration of Lighttpd, and restart our router.
Step 1: Connect via SSH
The first step is to establish an SSH connection between your computer and your Omnia. This requires that you installed an SSH client on your device (if you use Linux, it is very likely that you have it installed). Windows users can use KiTTY. The password is the “advanced password” which you can configure separately in Turris OS.
The simple command here is
ssh root@[turris-router-ip]. It is most likely
Usability tip: Instead of using a password for SSH, you can use keys. Look at step 3 of part 1 of our web server security series. The steps are identical for your Omnia or other routers that run OpenSSH.
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Step 2: Generate your private key and certificate
The second step is to create a new folder for certificates and keys:
mkdir -p /etc/lighttpd/certs. After that, go to the new folder:
Now, we generate two things:
- A private key, using the EC parameter “secp384r1”.
- An ECDSA certificate.
To create the private key, enter
openssl ecparam -name secp384r1 -genkey -noout -out eckey.pem.
The command in detail:
openssl ecparamis OpenSSL's EC parameter manipulation and generation tool.
-name secp384r1uses the EC parameter “secp384r1”.
-genkeycreate an EC private key using the specified parameters.
-nooutinhibits the output of the encoded version of the parameters.
-out eckey.pemwrites the new key to “eckey.pem”.
Afterwards, we create a public certificate using the key we just created. Enter
openssl req -key eckey.pem -x509 -out ecdsa-cert.pem -subj '/CN=192.168.1.1' -days 365.
The command in detail:
openssl reqis OpenSSL's PKCS#10 certificate request and certificate generating utility.
-key eckey.pemreads the private key from “eckey.pem”.
-x509outputs a self-signed certificate instead of a certificate request.
-out ecdsa-cert.pemwrites the public certificate to “ecdsa-cert.pem”.
-subj '/CN=192.168.1.1'sets the Common Name of the certificate to “192.168.1.1”.
-days 365means that the self-signed certificate will be valid for the next 365 days (1 year).
Now, there are two different ways to proceed. Enter
lighttpd -v to see the version of Lighttpd on your router.
- If your Omnia still runs Lighttpd 1.4.50, you do not have the possibility to load the private key from its own file. This option is available in Lighttpd 1.4.53 or newer. Due to this, you must append your private key to your certificate file. Enter
cat eckey.pem >> ecdsa-cert.pem. Then, delete the private key (since it is appended now) by entering
- If your Omnia runs Lighttpd 1.4.53 or newer, leave your private key in its separate file. You don't have to enter an additional command for this.
Finally, we set the permission of our pem file(s) to read-only for the root user:
chmod 400 *.pem. You can use the
ls -l command to see if all pem files are set to
-r-------- 1 root root.
Step 3: Harden your TLS configuration
We generated our ECDSA certificate. Now we configure TLS parameters. Simply using the defaults here results in a warning when we test our connection:
The screenshot of an nmap scan shows that weak DH parameters and a weak elliptic curve are in use. There are also several cipher suites without ECDHE. Frankly speaking, it is unlikely that an attacker easily bypasses this protection. In spite of that, we can change the defaults to modern configuration.
In case of any errors, you may want to revert your changes. So back up the TLS configuration of Lighttpd before changing anything:
cp /etc/lighttpd/conf.d/ssl-enable.conf /etc/lighttpd/conf.d/ssl-enable.conf.backup.
Open the TLS configuration of Lighttpd using the vi editor:
vi /etc/lighttpd/conf.d/ssl-enable.conf. We are using Vim here. If you never used it before, read some beginner's guides or use your favorite command line editor.
After opening “ssl-enable.conf”, we change the configuration to:
Please note that CHACHA20-POLY1305-based cipher suites require OpenSSL 1.1.0 or higher. Enter
openssl version to check your version. In our case, the Omnia runs “OpenSSL 1.0.2s 28 May 2019”, so we can't make use of ChaCha20-Poly1305 at the moment.
In case of any critical errors, use your backup to revert your changes:
cp /etc/lighttpd/conf.d/ssl-enable.conf.backup /etc/lighttpd/conf.d/ssl-enable.conf.
Step 4: Restart and test your connection
After saving, we restart lighttpd:
/etc/init.d/lighttpd restart. Try to connect to your Omnia using your web browser. Your web browser should be redirected to HTTPS.
You can validate your TLS configuration using nmap, sslyze and/or sslscan:
nmap --script +ssl-enum-ciphers -n -p 443 [turris-omnia-ip]
sslyze --regular [turris-omnia-ip]
The following screenshot shows the final configuration using modern cipher suites and TLS 1.2 only:
This article is part of the Home network security series.
Read other articles of this series.
The above-mentioned configuration enables HTTPS-only and enforces strong TLS cipher suites. One weak point remains: We are using our own, untrusted ECDSA certificate. However, this is sufficient for our purposes since the certificate is only used for internal purposes.
To harden your SSH configuration, you can check our Web server security series part 1.
In part 3a, you can read about using a Turris Omnia as network-attached storage which is a big plus for privacy.
- Turris Omniaexternal link
- Let's Encrypt: Certificates for localhostexternal link
- lighttpdexternal link
- KiTTYexternal link
- Sep 18, 2019: Add information about keeping the private key in its separate file (requires Lighttpd 1.4.53 or newer).
- Jul 28, 2019: Changed from RSA certificate to ECDSA certificate.
- Jul 13, 2019: Changed TLS configuration according to current good practices.
- Dec 8, 2018: Updated code for better understanding, added information about filenames in use, added modern TLS configuration.