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Let's Encrypt on Turris Omnia

Posted on May 18, 2019

This is a guide about how I use Let’s Encrypt certificates on my Turris Omnia router.

This guide assumes that you already have a domain pointing to your router and that it’s IP is updated when the IP of your router changes.

Connect to the router

For any of these steps, you need to ssh to your router:

ssh root@your.domain

Install acme.sh

The following command will install acme.sh (a Let’s Encrypt client) in /root/.acme.sh/. The install script automatically creates a cronjob for it. Adjust the email address to receive emails should a certificate expire.

EMAIL=email@your.domain
cd /root
curl https://get.acme.sh | sh
./.acme.sh/acme.sh --accountemail "$EMAIL" --register-account # First Time Only
./.acme.sh/acme.sh --accountemail "$EMAIL" --update-account

Configure Lighttpd

We’re going to use acme.sh in webroot mode. Therefore we must slightly extend lighttpd’s config.

echo 'alias.url += ( "/.well-known/acme-challenge/" => "/www/letsencrypt/.well-known/acme-challenge/")' \
     > /etc/lighttpd/conf.d/80-letsencrypt.conf
mkdir -p /www/letsencrypt/.well-known/acme-challenge/

Configure the Firewall

This adds a rule which is disabled by default. When enabled, the rule allows traffic to port 80 on your router. Every time a certificate is renewed, this rule will be temporarily enabled. It will automatically get disabled after the certificate was renewed.

uci set firewall.letsencrypt=rule
uci set firewall.letsencrypt.target=ACCEPT
uci set firewall.letsencrypt.src=wan
uci set firewall.letsencrypt.proto=tcp
uci set firewall.letsencrypt.dest_port=80
uci set firewall.letsencrypt.name='allow http on wan'
uci set firewall.letsencrypt.enabled=0
uci commit firewall
/etc/init.d/firewall reload

Note: Make sure, that traffic from wan zone to the input chain is allowed!

Issue the First Certificate

See below if you enabled Minipot on your Router

DOMAIN=your.domain
/root/.acme.sh/acme.sh \
    --issue \
    -d "$DOMAIN" \
    -w /www/letsencrypt/ \
    --pre-hook "uci set firewall.letsencrypt.enabled=1; uci commit firewall; /etc/init.d/firewall reload" \
    --post-hook "uci set firewall.letsencrypt.enabled=0; uci commit firewall; /etc/init.d/firewall reload" \
    --reloadcmd "cat /root/.acme.sh/$DOMAIN/$DOMAIN.cer /root/.acme.sh/$DOMAIN/$DOMAIN.key > /etc/lighttpd-self-signed.pem; /etc/init.d/lighttpd restart"

acme.sh will automatically renew the certificate after it’s issued for the first time.

If Minipot is Active

If you run a Minipot honeypot on your router, then you will see a conflict on port 80. The solution is to disable Minipot while updating the certificate. Use the following command to get your certificate instead:

DOMAIN=your.domain
/root/.acme.sh/acme.sh \
    --issue \
    -d "$DOMAIN" \
    -w /www/letsencrypt/ \
    --pre-hook "uci set sentinel.minipot.http_port=0; uci set firewall.letsencrypt.enabled=1; uci commit firewall; /etc/init.d/firewall reload" \
    --post-hook "uci delete sentinel.minipot.http_port; uci set firewall.letsencrypt.enabled=0; uci commit firewall; /etc/init.d/firewall reload" \
    --reloadcmd "cat /root/.acme.sh/$DOMAIN/$DOMAIN.cer /root/.acme.sh/$DOMAIN/$DOMAIN.key > /etc/lighttpd-self-signed.pem; /etc/init.d/lighttpd restart"

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