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------------------------ TLS SUPPORT ------------------------

Pure-FTPd supports encryption of the control and data channels using
TLS security mechanisms. Support for encrypted commands began with
version 1.0.16, and encryption of the data channel has been
implemented in version 1.0.22.

When this extra security layer is enabled, login and passwords are no more
sent as cleartext. Neither are other commands sent by your client nor replies
made by the server.

------------------------ COMPILATION ------------------------

To support TLS, the OpenSSL library must already be installed on your
system. This is a common requirement so your operating system probably
already ships with it.

Pure-FTPd also has to be configured with the --with-tls switch before
compilation :

./configure --with-tls ...
  make install-strip

If something goes wrong, try to bring your OpenSSL library up-to-date.

------------------------ CERTIFICATES ------------------------

To use TLS, you must provide a file called /etc/ssl/private/pure-ftpd.pem
with a private key for your host and the related certificate.

The location can be changed at compile-time with the --with-certfile option
passed to ./configure.

A certificate is similar to an identity card. You fill a form with a set of
personal info, then you have some trusted third-party bash an official stamp
onto it to confirm its validity.

If you already have a certificate for another service on the same host
(commonly for HTTPS/HTTP2), you can use it as well with Pure-FTPd and other
TLS-enabled services.

If you don't have any certificate, you have to get one. Make a Google search
for "SSL certificates" to find authorities that will provide certificates with
valid "official" signatures.

Once you have a valid and stamped certificate, clients will usually be able
to seamlessly connect to your host.

Both RSA and ECDSA signatures are supported, but not simultaneously.

For testing purposes, a self-signed certificate can be created as follows:

mkdir -p /etc/ssl/private

openssl dhparam -out /etc/ssl/private/pure-ftpd-dhparams.pem 2048

openssl req -x509 -nodes -newkey rsa:2048 -sha256 -keyout \
  /etc/ssl/private/pure-ftpd.pem \
  -out /etc/ssl/private/pure-ftpd.pem

chmod 600 /etc/ssl/private/*.pem

In this example, 2048 is the number of bits used for the RSA key.

Here's what the /etc/ssl/private/pure-ftpd.pem should look like :

If you need client certificate verification, prefix the list of
ciphers (-J/--tlsciphersuite) with -C:

pure-ftpd --tlsciphersuite=-C:HIGH -Y2 ...

In order to verify client certificates, the clients public keys must
be included in the pure-ftpd.pem file.

If you changed the installation prefix when pure-ftpd was compiled, the
certificate must be in the <prefix sysconf dir>/ssl/private/pure-ftpd.pem file.

------------------------ ACCEPTING TLS SESSIONS ------------------------

Once the certificate has been installed, you need to start a TLS-enabled
pure-ftpd daemon with the -Y (or --tls=) switch. Example :

/usr/local/sbin/pure-ftpd --tls=1 &

- With "--tls=0", support for TLS is disabled. This is the default.

- With "--tls=1", clients can connect either the traditional way or through an
TLS layer. This is probably the setting you need if you want to enable
TLS without having too many angry customers.

- With "--tls=2", cleartext sessions are refused and only TLS compatible
clients are accepted.

- With "--tls=3", cleartext sessions are refused and only TLS compatible
clients are accepted. Clear data connections are also refused, so private
data connections are enforced. This is an extreme setting.

When TLS has been successfully negociated for a connection, you'll see
something similar to this in log files :

<<
TLS: Enabled TLSv1.2 with AES256-SHA, 256 secret bits cipher
>>

------------------------ COMPATIBLE CLIENTS ------------------------

Pure-FTPd was reported to be fully compatible with the following clients with
the TLS encryption layer turned on :

* Transmit (OSX)
  URL: http://panic.com/transmit/

TLS works out of the box, both in implicit and explicit modes.
  CCC support has some issues, but Transmit quickly recovers and keeps
working.

* CoreFTP Lite (Windows)
  URL: http://www.coreftp.com/

TLS perfectly works when "AUTH TLS" is enabled. CoreFTP Lite has some
neat features like IPv6 support, remote file searching, .htaccess editing,
queueing, bandwidth control, etc.

CoreFTP Lite is free both for personal and business use.

* SmartFTP (Windows)
  URL: http://www.smartftp.com/

An excellent client with IPv6 support, port range limitation and other
useful features (!= bloat) . And it's free for personal, educational and non-
commercial use. And it detects Pure-FTPd :)

TLS perfectly works when the "FTP over SSL (explicit)" protocol is
selected and when the data connection mode (Tools->Settings->SSL) is set to
"clear data connection" while the AUTH mode (also in Tools->Settings->SSL) is
set to "TLS".

* IglooFTP Pro (Windows, Linux)
  URL: http://www.iglooftp.com/

TLS is automatically detected and works when Preferences->Security->
Encrypt is set to "Commands [if possible], Transfers [if possible]".

* FlashFXP (Windows)
  URL: http://www.flashfxp.com/

TLS works. In the "Quick connect" dialog box, pick the "SSL"
tab and :
 - enable Auth TLS
 - disable Secure File Listing
 - disable Secure File Transfers

* SDI FTP (Windows)
  URL: http://www.sdisw.com/

TLS works. In the "Connection" tab, just pick "SSL Support: TLSv1".

* LFTP (Unix, MacOS X)
  URL: http://lftp.yar.ru/

TLS is automatically detected and works out of the box.

* RBrowser (MacOS X)
  URL: http://www.rbrowser.com/

A cute graphical client for MacOS that was reported to work by Jason Rust
and Robert Vasvari.

* Glub Tech Secure FTP Client (at least Unix, MacOS X and Windows)
  URL: http://secureftp.glub.com/

TLS is automatically detected and works out of the box.

* Cyberduck (OSX)
  http://cyberduck.ch/

TLS works out of the box.

* WinSCP (Windows)
  WinSCP should be configured with "File protocol" set to "FTP" with
"TLS Explicit encryption".

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