Sameh Attia: How To Configure PureFTPd To Accept TLS Sessions On CentOS 6.2

FTP is a very insecure protocol because all passwords and all data are transferred in clear text. By using TLS, the whole communication can be encrypted, thus making FTP much more secure. This article explains how to configure PureFTPd to accept TLS sessions on a CentOS 6.2 server.
I do not issue any guarantee that this will work for you!

1 Preliminary Note

You should have a working PureFTPd setup on your CentOS 6.2 server, e.g. as shown in this tutorial: Virtual Hosting With PureFTPd And MySQL (Incl. Quota And Bandwidth Management) On CentOS 6.2.

2 Installing OpenSSL

OpenSSL is needed by TLS; to install OpenSSL, we simply run:

yum install openssl

3 Configuring PureFTPd

Open /etc/pure-ftpd/pure-ftpd.conf...

vi /etc/pure-ftpd/pure-ftpd.conf

If you want to allow FTP and TLS sessions, set TLS to 1:

[...]
# This option can accept three values :
# 0 : disable SSL/TLS encryption layer (default).
# 1 : accept both traditional and encrypted sessions.
# 2 : refuse connections that don't use SSL/TLS security mechanisms,
#     including anonymous sessions.
# Do _not_ uncomment this blindly. Be sure that :
# 1) Your server has been compiled with SSL/TLS support (--with-tls),
# 2) A valid certificate is in place,
# 3) Only compatible clients will log in.

TLS                      1
[...]

If you want to accept TLS sessions only (no FTP), set TLS to 2:

[...]
# This option can accept three values :
# 0 : disable SSL/TLS encryption layer (default).
# 1 : accept both traditional and encrypted sessions.
# 2 : refuse connections that don't use SSL/TLS security mechanisms,
#     including anonymous sessions.
# Do _not_ uncomment this blindly. Be sure that :
# 1) Your server has been compiled with SSL/TLS support (--with-tls),
# 2) A valid certificate is in place,
# 3) Only compatible clients will log in.

TLS                      2
[...]

To not allow TLS at all (only FTP), set TLS to 0:

[...]
# This option can accept three values :
# 0 : disable SSL/TLS encryption layer (default).
# 1 : accept both traditional and encrypted sessions.
# 2 : refuse connections that don't use SSL/TLS security mechanisms,
#     including anonymous sessions.
# Do _not_ uncomment this blindly. Be sure that :
# 1) Your server has been compiled with SSL/TLS support (--with-tls),
# 2) A valid certificate is in place,
# 3) Only compatible clients will log in.

TLS                      0
[...]

4 Creating The SSL Certificate For TLS

In order to use TLS, we must create an SSL certificate. I create it in /etc/ssl/private/, therefore I create that directory first:

mkdir -p /etc/ssl/private/

Afterwards, we can generate the SSL certificate as follows:

openssl req -x509 -nodes -days 7300 -newkey rsa:2048 -keyout /etc/ssl/private/pure-ftpd.pem -out /etc/ssl/private/pure-ftpd.pem

Country Name (2 letter code) [XX]: <-- Enter your Country Name (e.g., "DE").
State or Province Name (full name) []: <-- Enter your State or Province Name.
Locality Name (eg, city) [Default City]: <-- Enter your City.
Organization Name (eg, company) [Default Company Ltd]: <-- Enter your Organization Name (e.g., the name of your company).
Organizational Unit Name (eg, section) []: <-- Enter your Organizational Unit Name (e.g. "IT Department").
Common Name (eg, your name or your server's hostname) []: <-- Enter the Fully Qualified Domain Name of the system (e.g. "server1.example.com").
Email Address []: <-- Enter your Email Address.

Change the permissions of the SSL certificate:

chmod 600 /etc/ssl/private/pure-ftpd.pem

Finally restart PureFTPd:

/etc/init.d/pure-ftpd restart

That's it. You can now try to connect using your FTP client; however, you should configure your FTP client to use TLS - see the next chapter how to do this with FileZilla.