Using Let’s Encrypt with ProFTPd on Ubuntu
Let’s Encrypt is a new Certificate Authority which provides free SSL certificates. There’s quite a few guides online on using LE to secure a web server such as Nginx or Apache but you can also secure an FTP server using ProFTPd.
Step 1: Generate Certificate
This step is the same as for a web server, so just follow Step 2 of this Digital Ocean guide. You may need to open port 443 on your firewall.
If you’re not using Ubuntu just follow any other guide for generating LE certificates.
Step 2: Configure ProFTPd
After generating the certificate you should have all the files you need to configure ProFTPd. Simply copy the below options into your ProFTPd config file (usually located in /etc/proftpd/conf.d), replacing [your domain] with the domain name from Step 1.
Restart the server (sudo service proftpd restart). You should now be able to connect to your server using FTPS.
Note: A Let’s Encrypt certificate only lasts for 3 months so you’ll need to manually renew it by running Step 1 again, or set up a cron job.