

       ------------------------ SSL/TLS SUPPORT ------------------------  

  Starting with version 1.0.16, Pure-FTPd has experimental support for
encryption of the control channel using SSL/TLS security mechanisms.

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

  However, the data channel is not affected by SSL/TLS. This combination
brings no significant decrease of performance and the FXP protocol keeps
working even when mixing SSL/TLS-enabled and non SSL/TLS-enabled servers.


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

  To support SSL/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.  
  Using at least version 0.9.6 is strongly advised, not only for full
compatibility with Pure-FTPd, but also because there are known vulnerabilities
in previous versions of the library.

  If your system does not have a working randomness device like /dev/srandom,
/dev/arandom or /dev/random, please have a look at the OpenSSL FAQ in order to
properly seed the PRNG for your operating system.


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

  To use SSL/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 an SSL certificate for another service on the same host
(commonly for HTTPS), you can use it as well with Pure-FTPd and other
SSL-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 sell you certificates with
valid "official" signatures.

  Once you have a valid and stamped certificate, clients will usually be able
to connect to your host with no further question.

  You can also avoid these third-party authorities and put your own stamp. You
will get a so called "self-signed certificate".

  With a self-signed certificate, only you can tell whether the certificate is
valid or not. If bad dudes are able to take on your server (ex: man-in-the
middle attacks), clients won't notice. Also some client software will ask the
user whether he's willing to accept your certificate.

  On the other hand, self-signed certificates are free and ready to serve.
  
  To summarize : if you are an ISP, buy a certificate or lousy customers will
call your support before clicking on "accept this certificate". If you are
paranoid, if a man-in-the-middle attack would be a disaster for your business
and if you don't trust the hops between clients and servers, buy a
certificate. Or better, use ssh. In all other cases, a self-certificate is
probably good enough.

  To create a self-signed certificate, you can use the following commands :

mkdir -p /etc/ssl/private

openssl req -x509 -nodes -newkey rsa:1024 -keyout \
  /etc/ssl/private/pure-ftpd.pem \
  -out /etc/ssl/private/pure-ftpd.pem

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

  In this example, 1024 is the number of bits used for authentication. In some
countries, using or exporting keys whoose size is more than 512 bits is
prohibited. Take care of this. There's no need to use huge keys either. A key
of 1024 bits is considered extremely secure. And to be fair, even a 512 bits
key is extremely long to brute-force with standard hardware.

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

SwWH5WI9d0CffE30Ab1VpDnzKRn1ncBfvh3GIdLBgtjy
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----

QZ2/xw==
-----END CERTIFICATE-----

  Note: theorically, a client should always connect using a valid, verifiable
certificate. In the real world this is rarely the case. Most clients just use
invalid certificates. It's why Pure-FTPd doesn't require client certificates
to be valid, but if you absolutely need this feature and you know what you are
doing, define the REQUIRE_VALID_CLIENT_CERTIFICATE macro before compiling the
server.

  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 SSL/TLS is disabled. This is the default.

- With "--tls=1", clients can connect either the traditional way or through an
SSL/TLS layer.

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

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

<<
SSL/TLS: Enabled TLSv1/SSLv3 with DES-CBC3-SHA, 168 secret bits cipher
>>

A cipher using traditional algorithms with a 40 bits key is weak but
exportable to almost any country. This is the minimum size accepted by the
server, else a "Cipher too weak" error message will be logged and reported to
the client.


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

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


* CoreFTP Lite (Windows)
  URL: http://www.coreftp.com/
  
  SSL/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 personnal and business use, but people who want
to register in order to get the enhanced (non-"lite") version and commercial
support can get a special discount for Pure-FTPd users, through this secret link :
  http://www.2checkout.com/cgi-bin/ccbuyers/purchase.2c?sid=62821&product_id=9&quantity=1


* 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 :)

  SSL/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/

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


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


* FTPTLS (OpenBSD, possibly other Unices as well)
  URL: http://www-user.tu-chemnitz.de/~grmo/ftptls/
  Port: http://www-user.tu-chemnitz.de/~grmo/ftptls/port/ftptls-port.tar.gz
  
  This is the OpenBSD's default FTP client with TLS support merged in.
  It perfectly works with Pure-FTPd with no special tuning.
  

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

  SSL/TLS is automatically detected and works out of the box.


* FileZilla (Windows)
  URL: http://filezilla.sourceforge.net
  
  SSL/TLS works. In the "Site details" dialog box, pick "FTP over TLS
(explicit encryption)" as the "Servertype".
  Reported by Philip Hallstrom.


The following clients are _not_ compatible with Pure-FTPd's TLS :

* WS_FTP Pro 8

  Only the old authentication scheme (AUTH SSL) seems to be implemented, the
recommended one (AUTH TLS) is missing.
  Workaround: none.
 
 
* FTP Voyager 9

  No support for AUTH TLS.
  
  
