Enable SSL/TLS on Proftpd.
[1]
Create certificates first. See here.
[2] Configure for SSL/TLS
root@www:~# vi /etc/proftpd/proftpd.conf
# line 138: uncomment
Include /etc/proftpd/tls.conf
root@www:~# vi /etc/proftpd/tls.conf
# line 10,11,12: uncomment
TLSEngine on
TLSLog /var/log/proftpd/tls.log
TLSProtocol SSLv23
# line 27,28: uncomment and specify certificates
TLSRSACertificateFile /etc/ssl/private/server.crt
TLSRSACertificateKeyFile /etc/ssl/private/server.key
root@www:~# /etc/init.d/proftpd restart