Let’s get started with Let’s Encrypt

Finally it’s here: the chance for people to encrypt their websites free of charge. This can be done with Let’s Encrypt.

Clone the Let’s Encrypt tools

git clone https://github.com/letsencrypt/letsencrypt

Go in the directory

cd letsencrypt/

First time certificate generation

./letsencrypt-auto  certonly –server https://acme-v01.api.letsencrypt.org/directory -a webroot –webroot-path=/var/www/www.sysstem.at –agree-dev-preview -d www.sysstem.at

/var/www/www.sysstem.at is my webroot and -www.sysstem.at is my domain.

Make sure your Webserver ist running on port 80, because Let’s Encrypt places a verification file in your webroot and tries to download it.

Set up your Apache VirtualHost like this

#010-www.sysstem.at.conf
<VirtualHost *:443>
 ServerAdmin admin@sysstem.at
 ServerName www.sysstem.at
 DocumentRoot /var/www/www.sysstem.at


 ErrorLog ${APACHE_LOG_DIR}/www.sysstem.at_error.log
 CustomLog ${APACHE_LOG_DIR}/www.sysstem.at_access.log combined

 SSLEngine on

 SSLCertificateFile /etc/letsencrypt/live/www.sysstem.at/fullchain.pem
 SSLCertificateKeyFile /etc/letsencrypt/live/www.sysstem.at/privkey.pem
 SSLProtocol all -SSLv2 -SSLv3
 SSLHonorCipherOrder on
 SSLCipherSuite "ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA"

 BrowserMatch "MSIE [2-6]" \
 nokeepalive ssl-unclean-shutdown \
 downgrade-1.0 force-response-1.0
 BrowserMatch "MSIE [17-9]" ssl-unclean-shutdown

</VirtualHost>

enable the site with

a2ensite 010-www.sysstem.at.conf

You may wonder where I got this huge load of cypher suites in the Apache config. Depending on which kind of site you are hosting you can decide for weaker or stronger suites. I chose the Intermediate from the Mozilla Site.

And make sure, that you forward all http traffic to https. This is important, because the Let’s Encrypt client tries to get the verification file from http. With the redirect the client will be able to get the file with https enabled.

#000-catchall.conf 
<VirtualHost *:80>
 ServerAdmin admin@sysstem.at
 ServerName catchall
 ErrorLog ${APACHE_LOG_DIR}/catchall.log
 LogLevel warn
 CustomLog ${APACHE_LOG_DIR}/catchall_access.log combined
 RewriteEngine On
 # This will enable the Rewrite capabilities
 RewriteCond %{HTTPS} !=on
 # This checks to make sure the connection is not already HTTPS
 RewriteRule ^/?(.*) https://%{SERVER_NAME}/$1 [R,L]
</VirtualHost>

enable the site with

a2ensite 000-catchall.conf

We need to make sure to load every Apache module so that everything in our configuration will work.

Enable the SSL Module and the Rewrite Module with

a2enmod ssl
a2enmod rewrite

Restart the Apache Server

service apache2 restart

Let’s do a SSL-test on our site. SSL-Labs is my tool of choice for this job.

My site has a great score for now:

Now we have a certificate which is not valid for a very long time. This is by intention by Let’s encrypt. The goal is that certificate renewals should be automated. For this I wrote a little script.

Place this script in /opt/letsencrypt as letsencrypt-renew.sh

This script makes sure that you get a new certificate for your website. It also has a check enabled for people with a dynamic IP. In case this script runs and your provider switches the IP before your dynamic DNS service (like dynDNS and noip) gets the information about it, it will end.

#!/bin/bash
export DOMAIN=www.sysstem.at
export DIR=/var/www/www.sysstem.at
export LETSENCRYPT=/opt/letsencrypt

#if Cert older than 30 days and if IP in DNS is current IP
find -L /etc/letsencrypt/live/$DOMAIN/fullchain.pem -mtime +30 | egrep '.*' \
&& if [ `dig +short $DOMAIN | head -1` == `curl canihazip.com/s` ];then
#then renew cert
 mkdir -p $DIR && cd $LETSENCRYPT && ./letsencrypt-auto --renew-by-default certonly --server https://acme-v01.api.letsencrypt.org/directory -a webroot --webroot-path=$DIR -d $DOMAIN
#reload apache with new Cert
 service apache2 reload
fi

Make changes to comply with your website and make the file executable with

chmod +x letsencrypt-renew.sh

Now we check every day if our certificate is up to date. For this open crontab with

crontab -e

and append the following line

0 1 * * * /opt/letsencrypt/letsencrypt-renew.sh

Now you are ready to host your own websites with HTTPS enabled, a valid certificate and good security.