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<title>ProFTPD mini-HOWTO - FTP and SSL/TLS</title>
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<hr>
<center><h2><b>FTP and SSL/TLS</b></h2></center>
<hr>
<p>
RFC 4217 defines FTP over SSL/TLS:
<pre>
<a href="http://www.faqs.org/rfcs/rfc4217.html">http://www.faqs.org/rfcs/rfc4217.html</a>
</pre>
The <code>mod_tls</code> module for <code>proftpd</code> is an implementation
of RFC 4217.
<p>
<a href="http://www.faqs.org/rfcs/rfc2228.html">RFC 2228</a> defines FTP Security Extensions, of which <code>mod_tls</code> is one implementation. Another
such RFC 2228 implementation is the <code>mod_gss</code> module, available
from SourceForge.
<p>
Example <a href="../contrib/mod_tls.html"><code>mod_tls</code></a> configuration:
<pre>
<IfModule mod_dso.c>
<font color=green># If mod_tls was built as a shared/DSO module, load it
LoadModule mod_tls.c
</IfModule>
<IfModule mod_tls.c>
TLSEngine on
TLSLog /var/ftpd/tls.log
<font color=green># Support both SSLv3 and TLSv1</font>
TLSProtocol SSLv3 TLSv1
<font color=green># Are clients required to use FTP over TLS when talking to this server?</font>
TLSRequired off
<font color=green># Server's certificate</font>
TLSRSACertificateFile /etc/ftpd/server.cert.pem
TLSRSACertificateKeyFile /etc/ftpd/server.key.pem
<font color=green># CA the server trusts</font>
TLSCACertificateFile /etc/ftpd/root.cert.pem
<font color=green># Authenticate clients that want to use FTP over TLS?</font>
TLSVerifyClient off
<font color=green># Allow SSL/TLS renegotiations when the client requests them, but
# do not force the renegotations. Some clients do not support
# SSL/TLS renegotiations; when mod_tls forces a renegotiation, these
# clients will close the data connection, or there will be a timeout
# on an idle data connection.</font>
TLSRenegotiate none
</IfModule>
</pre>
<p><a name="TLSDebugging"></a>
<b>Debugging</b><br>
There are a couple of tools available for debugging and analysing FTPS
traffic. One of the easiest to use is the <a href="http://www.openssl.org/docs/apps/s_client.html"><code>s_client</code></a> application, part of OpenSSL.
<p>
The following examples assume that <code>proftpd+mod_tls</code> is listening
on 127.0.0.1, port 21:
<pre>
# openssl s_client -connect 127.0.0.1:21 -starttls ftp
CONNECTED(00000003)
depth=1 /CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
verify error:num=20:unable to get local issuer certificate
verify return:0
---
<b>Certificate chain</b>
0 s:/CN=castaglia3-server/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
i:/CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
1 s:/CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
i:/CN=castaglia3/C=US/ST=Washington/L=Seattle/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/emailAddress=tj@castaglia.org
---
Server certificate
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
subject=/CN=castaglia3-server/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
issuer=/CN=castaglia3-serverCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
---
<b>Acceptable client certificate CA names</b>
/CN=castaglia3-clientCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
/CN=castaglia3/C=US/ST=Washington/L=Seattle/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/emailAddress=tj@castaglia.org
/CN=castaglia3-clientCA/C=US/emailAddress=tj@castaglia.org/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/ST=Washington
/CN=castaglia3/C=US/ST=Washington/L=Seattle/O=Castaglia/OU=Castaglia Research and Development/OU=TJ Saunders/emailAddress=tj@castaglia.org
---
SSL handshake has read 3731 bytes and written 344 bytes
---
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA
Server public key is 1024 bit
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : TLSv1
Cipher : DHE-RSA-AES256-SHA
Session-ID: D1F2E7C001BCFE57D797F34BD1518BDCC6160106D56A238CC0F957337C093435
Session-ID-ctx:
Master-Key: F8EE2812270E8FCD87D1B26F20546EF9BABAE40F36BC6F8DF45B0E2F089571E731EAFAEA5E61BCA7D9D204BE06F28B21
Key-Arg : None
Start Time: 1232997620
Timeout : 300 (sec)
Verify return code: 20 (unable to get local issuer certificate)
---
220 ProFTPD 1.3.2rc4 Server (TJ's FTPS Server) [127.0.0.1]
quit
221 Goodbye.
read:errno=0
</pre>
Note that the "verify error" message is not of particular concern for us,
since we are not using <code>s_client</code> to verify the server's
certificate in this example.
<p>
The parts of the <code>s_client</code> output which are of particular interest
are the highlighted "Certificate chain" and "Acceptable client certificate CA
names" sections.
<p>
The "Certificate chain" section shows the certificate chain/trust path, from
the server's certificate up through the root CA for that certificate. Note
that this assumes the certificates in the trust path are available on the
server. By default, OpenSSL constructs this certificate chain using the
server's certificate (configured using <code>TLSRSACertificateFile</code> or
<code>TLSDSACertificateFile</code>) and the trusted CA certificates configured
using <code>TLSCACertificateFile</code> and/or
<code>TLSCACertificatePath</code>. See the <code>TLSCertificateChainFile</code>
<a href="#TLSCertificateChainFile">FAQ</a> for more details on how to influence
the constructed certificate chain.
<p>
The "Acceptable client certificate CA names" section contains the list of
CAs that can issue certificates that <code>mod_tls</code> is willing to trust.
These CAs <i>always</i> come from the configured
<code>TLSCACertificateFile</code> and/or <code>TLSCACertificatePath</code>.
This list of acceptable client CAs is presented to the client whenever the
server is requesting the client's certificate (which is what
<code>mod_tls</code> does by default). If you use:
<pre>
TLSOptions NoCertRequest
</pre>
then the server <i>will not</i> send this list of acceptable client CAs;
using <code>s_client</code> in that case, you would see:
<pre>
---
No client certificate CA names sent
---
</pre>
In case you're wondering, a list of CAs is sent to the client, rather than
just a single CA, because this allows clients the ability to determine which
certificate (as a client can have many) to use when talking to this particular
server.
<p>
Another tool, slightly older, is <a href="http://www.rtfm.com/ssldump/"><code>ssldump</code></a>. This tool is more like <code>ethereal</code> or
<code>tcpdump</code> for any SSL/TLS traffic; it is deliberately modeled after
<code>tcpdump</code>.
<p>
To use <code>ssldump</code> for watching your FTPS traffic, you will need
the server key file (for decrypting), and possibly root privileges (for
listening on the network interface). Here is an example where
<code>ssldump</code> is used to listen on the loopback interface
(<code>lo0</code>), port 21:
<pre>
# sudo ssldump -d -k <i>server</i>.pem -i lo0 port 21
New TCP connection #1: localhost(64148) <-> localhost(21)
0.0423 (0.0423) S>C
---------------------------------------------------------------
220 ProFTPD 1.3.2rc4 Server (TJ's FTPS Server) [127.0.0.1]
---------------------------------------------------------------
0.0427 (0.0004) C>S
---------------------------------------------------------------
AUTH TLS
---------------------------------------------------------------
0.0430 (0.0002) S>C
---------------------------------------------------------------
234 AUTH TLS successful
---------------------------------------------------------------
1 1 0.0433 (0.0003) C>S SSLv2 compatible client hello
Version 3.1
cipher suites
Unknown value 0x39
Unknown value 0x38
Unknown value 0x35
TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA
SSL2_CK_3DES
Unknown value 0x33
Unknown value 0x32
Unknown value 0x2f
TLS_RSA_WITH_IDEA_CBC_SHA
SSL2_CK_IDEA
SSL2_CK_RC2
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_RC4_128_MD5
SSL2_CK_RC4
TLS_DHE_RSA_WITH_DES_CBC_SHA
TLS_DHE_DSS_WITH_DES_CBC_SHA
TLS_RSA_WITH_DES_CBC_SHA
SSL2_CK_DES
TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
SSL2_CK_RC2_EXPORT40
TLS_RSA_EXPORT_WITH_RC4_40_MD5
SSL2_CK_RC4_EXPORT40
1 2 0.0658 (0.0225) S>C Handshake
ServerHello
Version 3.1
session_id[32]=
09 25 df 7a a8 e8 71 a2 9f 56 a6 7b dd 95 ac 67
7d 2e 81 b2 1c ca b4 5f 1e 95 13 47 01 28 20 19
cipherSuite Unknown value 0x39
compressionMethod NULL
1 3 0.0658 (0.0000) S>C Handshake
Certificate
1 4 0.0658 (0.0000) S>C Handshake
ServerKeyExchange
1 5 0.0658 (0.0000) S>C Handshake
CertificateRequest
certificate_types rsa_fixed_dh
certificate_types dss_fixed_dh
certificate_types rsa_sign
certificate_types dss_sign
certificate_authority
30 81 b8 31 1c 30 1a 06 03 55 04 03 13 13 63 61
73 74 61 67 6c 69 61 33 2d 63 6c 69 65 6e 74 43
41 31 0b 30 09 06 03 55 04 06 13 02 55 53 31 1f
30 1d 06 09 2a 86 48 86 f7 0d 01 09 01 16 10 74
6a 40 63 61 73 74 61 67 6c 69 61 2e 6f 72 67 31
12 30 10 06 03 55 04 0a 13 09 43 61 73 74 61 67
6c 69 61 31 2b 30 29 06 03 55 04 0b 13 22 43 61
73 74 61 67 6c 69 61 20 52 65 73 65 61 72 63 68
20 61 6e 64 20 44 65 76 65 6c 6f 70 6d 65 6e 74
31 14 30 12 06 03 55 04 0b 13 0b 54 4a 20 53 61
75 6e 64 65 72 73 31 13 30 11 06 03 55 04 08 13
0a 57 61 73 68 69 6e 67 74 6f 6e
certificate_authority
30 81 c1 31 13 30 11 06 03 55 04 03 13 0a 63 61
73 74 61 67 6c 69 61 33 31 0b 30 09 06 03 55 04
06 13 02 55 53 31 13 30 11 06 03 55 04 08 13 0a
57 61 73 68 69 6e 67 74 6f 6e 31 10 30 0e 06 03
55 04 07 13 07 53 65 61 74 74 6c 65 31 12 30 10
06 03 55 04 0a 13 09 43 61 73 74 61 67 6c 69 61
31 2b 30 29 06 03 55 04 0b 13 22 43 61 73 74 61
67 6c 69 61 20 52 65 73 65 61 72 63 68 20 61 6e
64 20 44 65 76 65 6c 6f 70 6d 65 6e 74 31 14 30
12 06 03 55 04 0b 13 0b 54 4a 20 53 61 75 6e 64
65 72 73 31 1f 30 1d 06 09 2a 86 48 86 f7 0d 01
09 01 16 10 74 6a 40 63 61 73 74 61 67 6c 69 61
2e 6f 72 67
certificate_authority
30 81 b8 31 1c 30 1a 06 03 55 04 03 13 13 63 61
73 74 61 67 6c 69 61 33 2d 63 6c 69 65 6e 74 43
41 31 0b 30 09 06 03 55 04 06 13 02 55 53 31 1f
30 1d 06 09 2a 86 48 86 f7 0d 01 09 01 16 10 74
6a 40 63 61 73 74 61 67 6c 69 61 2e 6f 72 67 31
12 30 10 06 03 55 04 0a 13 09 43 61 73 74 61 67
6c 69 61 31 2b 30 29 06 03 55 04 0b 13 22 43 61
73 74 61 67 6c 69 61 20 52 65 73 65 61 72 63 68
20 61 6e 64 20 44 65 76 65 6c 6f 70 6d 65 6e 74
31 14 30 12 06 03 55 04 0b 13 0b 54 4a 20 53 61
75 6e 64 65 72 73 31 13 30 11 06 03 55 04 08 13
0a 57 61 73 68 69 6e 67 74 6f 6e
certificate_authority
30 81 c1 31 13 30 11 06 03 55 04 03 13 0a 63 61
73 74 61 67 6c 69 61 33 31 0b 30 09 06 03 55 04
06 13 02 55 53 31 13 30 11 06 03 55 04 08 13 0a
57 61 73 68 69 6e 67 74 6f 6e 31 10 30 0e 06 03
55 04 07 13 07 53 65 61 74 74 6c 65 31 12 30 10
06 03 55 04 0a 13 09 43 61 73 74 61 67 6c 69 61
31 2b 30 29 06 03 55 04 0b 13 22 43 61 73 74 61
67 6c 69 61 20 52 65 73 65 61 72 63 68 20 61 6e
64 20 44 65 76 65 6c 6f 70 6d 65 6e 74 31 14 30
12 06 03 55 04 0b 13 0b 54 4a 20 53 61 75 6e 64
65 72 73 31 1f 30 1d 06 09 2a 86 48 86 f7 0d 01
09 01 16 10 74 6a 40 63 61 73 74 61 67 6c 69 61
2e 6f 72 67
ServerHelloDone
1 6 0.1005 (0.0346) C>S Handshake
Certificate
1 7 0.1005 (0.0000) C>S Handshake
ClientKeyExchange
1 8 0.1005 (0.0000) C>S ChangeCipherSpec
1 9 0.1005 (0.0000) C>S Handshake
1 10 0.1164 (0.0159) S>C ChangeCipherSpec
1 11 0.1164 (0.0000) S>C Handshake
1 12 1.7856 (1.6692) C>S application_data
1 13 1.7856 (0.0000) C>S application_data
1 14 1.7861 (0.0004) S>C application_data
1 1.7866 (0.0004) S>C TCP FIN
1 15 1.7868 (0.0002) C>S Alert
</pre>
<p>
As you can see, the level of granularity used by <code>ssldump</code> is on
the level of each SSL/TLS packet; while useful in some cases, I suspect that
using <code>openssl s_client</code> will provide most of the information you
will want in figuring out your certificate and verification issues.
<p><a name="FAQ"></a>
<b>Frequently Asked Questions</b><br>
<p><a name="TLSCertificates">
<font color=red>Question</font>: How do I generate the certificate files used
by <code>mod_tls</code>?<br>
<font color=blue>Answer</font>: The <code>mod_tls</code> module uses the
same certificate files as Apache's <code>mod_ssl</code>. The
<code>mod_ssl</code> documentation explains what the files are, how they
are used, and how to generate your own:
<pre>
<a href="http://www.modssl.org/docs/2.7/ssl_faq.html#ToC24">http://www.modssl.org/docs/2.7/ssl_faq.html</a>
</pre>
<p><a name="TLSProtection">
<font color=red>Question</font>: Does FTPS protect both the control connection
<b>and</b> the data connections?<br>
<font color=blue>Question</font>: Short answer: yes.
<p>
The long answer is, of course, that it depends. In the case of
<code>mod_tls</code>, it depends on your <code>TLSRequired</code> setting.
If you use:
<pre>
TLSRequired on
</pre>
then you are configuring <code>mod_tls</code> to <b>require</b> SSL/TLS
protection for both control connections (<i>e.g.</i> protecting the username
and password used to log in) <i>and</i> data connections. If you have:
<pre>
TLSRequired off
</pre>
then it is up to the FTPS client whether both control and data connections
will be protected via SSL/TLS. Other <code>TLSRequired</code> settings
can be used to specify specific combinations: data connections only,
control connections only, authentication plus data data connections only,
<i>etc</i>. The <code>TLSRequired</code>
<a href="../../contrib/mod_tls.html#TLSRequired">documentation</a> has the
details.
<p><a name="TLSClients">
<font color=red>Question</font>: Where can I find a list of clients that
support FTPS?<br>
<font color=blue>Answer</font>: This page is a good FTPS resource:
<pre>
<a href="http://www.ford-hutchinson.com/~fh-1-pfh/ftps-ext.html">http://www.ford-hutchinson.com/~fh-1-pfh/ftps-ext.html</a>
</pre>
including the list of FTPS <a href="http://www.ford-hutchinson.com/~fh-1-pfh/ftps-ext.html#client">clients</a>. On a related note, there have been some
reports that Debian's <code>ftp-ssl</code> client has a few bugs; using Peter
Runestig's <code>ftp-tls</code> is known to work.
<p>
Note, though, that there are known issues with some FTPS clients:
<pre>
<a href="http://www.runestig.com/osp.html#NOTE1">http://www.runestig.com/osp.html#NOTE1</a>
</pre>
<p><a name="TLSImplicit">
<font color=red>Question</font>: How come <code>mod_tls</code> does not support
"implicit" FTPS (<i>i.e.</i> automatically encrypting sessions on
port 990)?<br>
<font color=blue>Answer</font>: The short answer is because the Draft no longer
specifies support for such a mode. Here is a <a href="http://www.ford-hutchinson.com/~fh-1-pfh/ftps-ext.html#bad">description</a> of why the alternatives
to the current mode (client-requested encryption using standard control
channel) are "bad".
<p>
The long answer is covered in Eric Rescorla's excellent book, <a href="http://www.rtfm.com/sslbook/">"SSL and TLS"</a>. There tend to be two
different strategies used when adding new features to a protocol: separate
ports for protocol variants, or upward negotiation. Port 443 for HTTPS is an
example of the separate ports strategy. The drawback to the separate ports
approach is that there is a finite number of ports available, and so this
approach does not scale well. The benefit is that use of separate ports tends
to require smaller changes to client and server code. Upward negotiation
is more flexible, but requires that the protocol support some sort of feature
negotiation or extension discovery, allowing clients and servers to easily
agree to negotiate "upward" into a secure channel. The authors
of the FTPS Draft felt that upward negotiation was the more appropriate of
these two approaches for encrypting FTP channels.
<p>
All that said, in ProFTPD 1.3.3rc2, the <code>mod_tls</code> module was
enhanced to support implicit FTPS via the <code>UseImplicitSSL</code>
<a href="../contrib/mod_tls.html#TLSOption"><code>TLSOption</code></a>.
<p><a name="TLSPerUser">
<font color=red>Question</font>: Can I require TLS on a per-user basis?<br>
<font color=blue>Answer</font>: Prior to ProFTPD 1.2.10rc2, no. The IETF
Draft specifying FTP over TLS requires that the TLS handshake occur
<i>before</i> the client sends the <code>USER</code> command. This means that
the server does not know the name of the user that the client will be using
when the TLS session is established. It is possible that the client's
certificate, if one is even presented, may contain information the server may
use to map that certificate to a user, but such mapping is not currently
supported by <code>mod_tls</code>. Note that this is also the reason the
<code>TLSRequired</code> directive cannot appear in the
<code><Anonymous></code> context: anonymous logins are based on the
<code>USER</code> command.
<p>
However, in 1.2.10rc2, the <code>mod_tls</code> module was modified to allow
such per-user TLS requirements. To do this, the <code>AllowPerUser</code>
parameter of the <code>TLSOptions</code> directive is used. For example,
the following example <code>mod_tls</code> configuration allows non-SSL
anonymous sessions, but requires SSL/TLS for all other sessions:
<pre>
<IfModule mod_tls.c>
TLSEngine on
TLSRSACertificateFile ...
TLSCACertificateFile ...
TLSOptions AllowPerUser
TLSRequired on
<Anonymous ~ftp>
User ftp
Group ftp
UserAlias anonymous ftp
RequireValidShell off
# Note how TLSRequired is set to off here in the <Anonymous> context
TLSRequired off
</Anonymous>
</IfModule>
</pre>
The modification also allows <code>mod_ifsession</code>-based conditions, so
that one can have settings like:
<pre>
<IfGroup trusted>
TLSRequired off
</IfGroup>
</pre>
However, there is a risk involved in using the <code>AllowPerUser</code>
option: it causes <code>mod_tls</code> not to enforce <code>TLSRequired</code>
until <i>after</i> the potentially sensitive USER and PASS commands have
been sent by the client. This allows clients, even when
<code>TLSRequired on</code> or <code>TLSRequired ctrl</code> are in effect,
to send the USER and PASS commands <i>unencrypted</i>. Depending on your
site's security needs, the ability to require SSL/TLS on a per-user basis
may or may not be worth the ability to require SSL/TLS for the USER and PASS
commands.
<p><a name="TLSRequiredPlusPerUser">
<font color=red>Question</font>: When I use the following in my
<code>proftpd.conf</code>:
<pre>
TLSRequired on <font color=green># or "TLSRequired auth", or "TLSRequired auth+data"</font>
TLSOptions AllowPerUser
</pre>
I get the following error when I try to start <code>proftpd</code>:
<pre>
cannot enforce both 'TLSRequired auth' and 'TLSOptions AllowPerUser' at the same time
</pre>
<font color=blue>Answer</font>: The reason this error occurs is because
you have a configuration which is impossible to support. The
<code>TLSRequired</code> setting (<i>e.g.</i> "on", "auth", or "auth+data")
requires that SSL/TLS be in use during authentication. But in order to
support the <code>TLSOption AllowPerUser</code> setting, the
<code>mod_tls</code> <b>cannot</b> require that SSL/TLS be in use during
authentication, since it does not know the user until <i>after</i>
authentication has completed. The requested configuration cannot be supported,
and thus the server will refuse to start.
<p><a name="TLSFXP">
<font color=red>Question</font>: Why does <code>mod_tls</code> break FXP
transfers?<br>
<font color=blue>Answer</font>: The Draft specifying FTP over SSL explicitly
omits site-to-site transfers. A TLS session is established between the client
and the server on the control channel and, to save on the expensive overhead of
TLS handshake, that session is reused for encrypting traffic on the data
channel. In a site-to-site transfer, the client opens <i>two</i> control
channels, one with each server, and then arranges for those servers to open a
data channel between themselves. However, since the servers have not
established a TLS session between themselves, that opening of the data channel
fails.
<p>
Note that the above happens only if the server requires that TLS be used on data
connections (<i>e.g.</i> <code>TLSRequired</code> is either <em>on</em> or
<em>data</em>), of if the client tells the server that the client will be
using TLS on the data connections (<i>e.g.</i> when it sends the
<code>AUTH</code> command with an argument of <code>TLS-P</code>). Without
these conditions, site-to-site transfers can occur normally, albeit unencrypted.
Encrypted site-to-site transfers are not supported.
<p><a name="TLSv2">
<font color=red>Question</font>: How come <code>mod_tls</code> does not support
SSLv2?<br>
<font color=blue>Answer</font>: Various defects have been found in the SSLv2
protocol. Some legacy sites need to support SSLv2 for their HTTP traffic, in
spite of its flaws. Use of FTP over TLS is fairly new, however, and there is
not much "legacy" in that regard; it was felt that, as
<code>mod_tls</code> aims to provide strong cryptographic security, supporting
a known bad protocol is a Bad Idea.
<p><a name="TLSFirewall">
<font color=red>Question</font>: Using <code>mod_tls</code>, FTP sessions
through my firewall now no longer work. What's going on?<br>
<font color=blue>Answer</font>: The short answer is that FTPS and firewalls
(and devices performing NAT) do not interact well. The control connection
happens on a well-known port, and has no issues; it is the data connection
that poses problems for FTP-aware firewalls. In a non-FTPS session, the
firewall can inspect the FTP server's responses on the control connection to a
client's <code>PASV</code> or <code>PORT</code> command, and thus know which
on which ports/addresses the data connection will be established. In an FTPS
session, though, those control connection messages are encrypted (that is the
point of using FTPS, right?), and so the FTP-aware firewall cannot peek.
Hence, it cannot know which on which ports the data connection will be
established. For firewalls that are configured to always allow a certain
range of ports (such as might be configured using the <code>PassivePorts</code>
directive), FTPS should function without issue.
<p>
Unfortunately, this is a rather intractable--and known--issue. Earlier
versions of the Draft defining FTPS used to allow something known as
"implicit" FTPS, by which a client could contact a well-known port
(akin to port 443 for HTTPS; FTPS used port 990) and the server, simply
because the client contacted that certain port, would automatically encrypt
the session. This approach has several drawbacks (the reason why it was
removed from later versions of the Draft), but it <i>did</i> allow for simple
TCP proxying.
<p><a name="TLSCCC">
To attempt to deal with the above issue, the RFC for FTP over SSL/TLS
suggests using the <code>CCC</code> FTP command (<b>C</b>lear <b>C</b>ommand <b>C</b>hannel). The <code>CCC</code> command makes an encrypted control channel
revert back to an unencrypted channel. This helps to solve data connection
problems in situations where network equipment (such as firewalls, routers,
NAT) peek at the control channel in order to open ports. By sending the
<code>CCC</code> command and unecrypting the control channel, the network
equipment can once again peek at the commands (<i>i.e.</i> <code>PORT</code>
and <code>EPRT</code>) in the control channel. Since the CCC command must
come <em>after</em> the client has logged in, the <code>USER</code> and
<code>PASS</code> commands on the control channel will still be protected by
SSL/TLS.
<p>
Note that in order to configure the <code>mod_tls</code> module to allow use of
the <code>CCC</code> command by clients, the following must appear in your
<code>proftpd.conf</code>:
<pre>
TLSRequired auth+data
</pre>
See the <a href="../contrib/mod_tls.html#TLSRequired"><code>TLSRequired</code></a> description for more details.
<p><a name="TLSSlow">
<font color=red>Question</font>: Sometimes my encrypted transfers are slow.
Is there a way to speed them up?<br>
<font color=blue>Answer</font>: There have been reports that increasing the
tunable buffer size (using the <code>--enable-buffer-size</code> option
of the <code>configure</code> script) to 8192 increases transfer speeds, most
notably on very high speed networks. Increasing the buffer size does not
appear to affect normal FTP transfers (in fact, it may benefit them as well,
depending on the client).
<p><a name="TLSDataProtection">
<font color=red>Question</font>: I can login using FTPS, but I cannot see
any directories. Why not?<br>
<font color=blue>Answer</font>: You have most likely configured
<code>mod_tls</code> to require SSL/TLS protection for data transfers as
well as control commands, by using:
<pre>
TLSRequired on
</pre>
However, if your FTPS client does not expect to handle encrypted data
transfers (and directory listings count as data transfers, as they are
sent over a data channel), you may see your client appear to hang, waiting
for data it can read. Make sure your client is prepared to handle the
security requirements you have configured on the server.
<p>
The following may also appear in the <code>TLS</code> for any data
transfers (which include directory listings):
<pre>
client did not reuse SSL session, rejecting data connection (see the NoSessionReuseRequired TLSOptions parameter
</pre>
This message appears because an additional security restriction that was
added in ProFTPD 1.3.3rc1. The <a href="../contrib/mod_tls.html#TLSOptions"><code>TLSOptions</code></a> documentation for this "NoSessionReuseRequired" option
describes the situation in more detail.
<p>
You may also see the following appear in the <code>TLSLog</code> on occasion:
<pre>
PROT: unwilling to accept security parameter (C), declining
</pre>
The <code>PROT</code> FTP command is used to set the protection level to
be used for data transfers. Some clients send a <code>PROT</code> command
with a security parameter of <code>C</code>, meaning "Clear",
which effectively tells the server not to protect data transfers. The
<code>mod_tls</code> module will refuse the <code>C</code> security parameter
if, like above, there is "TLSRequired on" in your
<code>proftpd.conf</code>. This case also indicates a disagreement between
the client's security expectations and the security policy you have configured
on the server.
<p><a name="TLSErrorAfterLargeUpload">
<font color=red>Question</font>: Using FTPS, after uploading a very large file,
my next directory listing fails:
<pre>
425 Unable to build data connection: Operation not permitted
</pre>
The <code>TLSLog</code> contains:
<pre>
client did not reuse SSL session, rejecting data connection (see the NoSessionReuseRequired TLSOptions parameter
</pre>
but I do <i>not</i> want to use that option, and would like to rely on the
additional security protection provided by requring SSL session reuse.
And my FTPS client is correctly reusing SSL session IDs (as earlier data
transfers were working properly). So why is my data transfer failing after
the upload of a very large file?<br>
<font color=blue>Answer</font>: The answer involves SSL session caching
on the server side (<i>i.e.</i> <code>mod_tls</code>), cache timeouts, and
session renegotiations.
<p>
By default, <code>mod_tls</code> uses OpenSSL's "internal" session cache,
which is an in-memory caching of SSL session IDs. And by default, OpenSSL's
internal session cache has a cache timeout of 5 minutes; after that amount
of time in the internal session cache, a cached SSL session ID is considered
stale and is available for reuse.
<p>
This means that 5 minutes or more into an FTPS session, even if your FTPS
client reused an SSL session ID, the OpenSSL internal session cache will
time out that SSL session ID. The next time your FTPS client goes to reuse
that session ID for a data transfer, <code>mod_tls</code> won't find it in
the OpenSSL internal session cache, and will think that your FTPS client is
not reusing the SSL session ID as is required, and fail the transfer.
<p>
Fixing this situation requires two parts: <i>a)</i> the ability to change
the cache timeout used for the OpenSSL internal session cache, and <i>b)</i>
renegotiating the SSL session ID with the FTPS client periodically, to keep
the SSL session ID up-to-date in the session cache.
<p>
The first part, configuring the session cache timeout for the OpenSSL internal
session cache, is only possible in ProFTPD 1.3.4rc2 and later (see
<a href="http://bugs.proftpd.org/show_bug.cgi?id=3580">Bug#3580</a>). The
<a href="../contrib/mod_tls.html#TLSSessionCache"><code>TLSSessionCache</code></a> directive was modified to allow a configuration such as:
<pre>
TLSSessionCache internal: 1800
</pre>
(Unfortunately, the ':' after "internal" <i>is</i> necessary.) This configures
<code>mod_tls</code> such that the OpenSSL internal session cache uses
a cache timeout of 1800 seconds (30 minutes), rather than the default of 300
seconds (5 minutes).
<p>
No matter how long you configure the cache timeout, eventually you will have
a session which lasts longer than that timeout. Which brings us to the second
part of the solution: renegotiating a new SSL session ID periodically, which
keeps it fresh in the session cache. The
<a href="../contrib/mod_tls.html#TLSRenegotiate"><code>TLSRenegotiate</code></a>
directive is needed for this. For example, the following configuration
should address the issue of failed data transfers after very large uploads:
<pre>
TLSRenegotiate ctrl 1500 timeout 300
TLSSessionCache internal: 1800
</pre>
This tells <code>mod_tls</code> to request a renegotiation of the SSL session
on the control channel every 1500 seconds (25 minutes), and to allow
300 seconds (5 minutes) for the client to perform the renegotiation. It also
tells <code>mod_tls</code> to cache the SSL session data for 1800 seconds
(30 minutes), <i>i.e.</i> longer than the renegotiation time of 1500 seconds.
<p>
This way, as long as your client supports renegotiations and is updating the
SSL session ID properly for data transfers, when a data transfer is requested,
the SSL session ID presented by the client should always be fresh and in the
session cache.
<p><a name="TLSBuildErrors">
<font color=red>Question</font>: Why would I see the following errors while attempting to build <code>proftpd</code> with <code>mod_tls</code>?
<pre>
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x35): In function `dlfcn_load': : undefined reference to `dlopen'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x95): In function `dlfcn_load': : undefined reference to `dlclose'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0xbc): In function `dlfcn_load': : undefined reference to `dlerror'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x147): In function `dlfcn_bind_var': : undefined reference to `dlsym'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x172): In function `dlfcn_bind_var': : undefined reference to `dlerror'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x237): In function `dlfcn_bind_func': : undefined reference to `dlsym'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x262): In function `dlfcn_bind_func': : undefined reference to `dlerror'
/usr/local/ssl/lib/libcrypto.a(dso_dlfcn.o)(.text+0x50b): In function `dlfcn_unload': : undefined reference to `dlclose'
collect2: ld returned 1 exit status
make: *** [proftpd] Error 1
</pre>
<font color=blue>Answer</font>:
Add <code>-ldl</code> to your configure command, for example:
<pre>
make clean
./configure LDFLAGS=-ldl ...
make
</pre>
This tells the <code>proftpd</code> build system to add <code>libdl</code>,
an OS-specific library for handling dynamically loaded code, to the list
of libraries used when linking <code>proftpd</code>. On some systems, the
functions in the <code>libdl</code> library are part of <code>libc</code>, and
are not in a separate library.
<p>
I suspect that the reason this build option may be necessary is that OpenSSL
0.9.8 contained changes regarding how OpenSSL loads "engines", software modules
that talk to hardware devices that can do specialized cryptographic operations.
These changes involve being able to dynamically load the "engine" software
modules.
<p><a name="TLSNoSharedCipher">
<font color=red>Question</font>: Why would I see a "no shared cipher" error in the TLSLog when attempting to connect with my FTPS client?<br>
<pre>
Jan 10 17:15:18 mod_tls/2.1.1[2212]: TLS/TLS-C requested, starting TLS handshake
Jan 10 17:15:18 mod_tls/2.1.1[2212]: unable to accept TLS connection:
(1) error:1408A0C1:SSL routines:SSL3_GET_CLIENT_HELLO:no shared cipher
Jan 10 17:15:18 mod_tls/2.1.1[2212]: TLS/TLS-C negotiation failed on control channel
</pre>
<font color=blue>Answer</font>:
There are two reasons this might happen.
<p>
The first is that there is indeed no ciphersuite in common between
<code>mod_tls</code> and your FTPS client. The SSL/TLS ciphersuites used by
<code>mod_tls</code> are configured using the <code>TLSCipherSuite</code>
directive. If you have a complex or restrictive <code>TLSCipherSuite</code>
configured, that could be the culprit. Try relaxing (or removing outright)
your <code>TLSCipherSuite</code>, or try to configure your FTPS client to use
the same SSL/TLS ciphersuites.
<p>
Another possibility is a misconfiguration. If your
<code>TLSCACertificateFile</code> and <code>TLSRSACertificateFile</code>
directives are in the "server config" context of the
<code>proftpd.conf</code> file, <i>and</i> you have
<code><VirtualHost></code> sections in your <code>proftpd.conf</code>,
then you might see the "no shared cipher" error. The easiest
thing is to move those <code>TLSCACertificateFile</code> and
<code>TLSRSACertificateFile</code> directives into a <code><Global></code>
section in your <code>proftpd.conf</code>, so that they apply to all
vhosts configured. The virtual hosting <a href="Vhost.html">howto</a>
describes this in more detail.
<p><a name="TLSRenegotiations">
<font color=red>Question</font>: My FTPS client sometimes times out after uploading/downloading more than 1 GB of data. When I turn off SSL/TLS, the upload/download works. Why?<br>
<font color=blue>Answer</font>:
The culprit behind this is most likely SSL/TLS renegotiations. By default,
<code>mod_tls</code> uses SSL/TLS renegotiations to periodically update the
session key which protects the data being transferred; see the
<a href="../contrib/mod_tls.html#TLSRenegotiate"><code>TLSRenegotiate</code></a> documentation for more details, particularly the time-based <i>and</i>
bytes-based limits at which renegotations are forced.
<p>
Some FTPS clients, however, do not support server-initiated SSL/TLS
renegotations. When the server does try to force a renegotiation, the client
fails that new handshake, cannot upload/download any more data over the
protected channel, and the transfer will eventually time out. Alternatively,
the transfer could terminate strangely in the middle of the upload/download.
<b>Note</b>, however, that not <i>all</i> transfer issues will be caused
by SSL/TLS renegotiations. Bugs in firewalls and routers can also cause
these symptoms.
<p>
Should you suspect that you are having issues with your FTPS client because
of SSL/TLS renegotiations, you can configure <code>mod_tls</code> to
accept renegotiations if the client requests one, but not to otherwise force
them:
<pre>
TLSRenegotiate required off
</pre>
<p><a name="TLSNoCertRequest">
<font color=red>Question</font>: My FTPS client has trouble connecting to <code>proftpd</code> using SSL/TLS, with the following error appearing in the <code>TLSLog</code>:
<pre>
Sep 17 11:03:46 mod_tls/2.1.2[9628]: TLS/TLS-C requested, starting TLS handshake
Sep 17 11:03:46 mod_tls/2.1.2[9628]: unable to accept TLS connection: received EOF that violates protocol
Sep 17 11:03:46 mod_tls/2.1.2[9628]: TLS/TLS-C negotiation failed on control channel
</pre>
Is this a bug in <code>mod_tls</code>, in the client, or something else?<br><br>
<font color=blue>Answer</font>: There might be several different causes for
this error. It could be a bug in the OpenSSL library, in <code>mod_tls</code>,
in the FTPS client, or it could be a transient network issue.
<p>
Now, one possible thing to try is to use the following in your <code>proftpd.conf</code> file:
<pre>
TLSOptions NoCertRequest
</pre>
This option tells the OpenSSL library to <b>not</b> include a message requesting
the client's certificate in the SSL/TLS handshake messages. Some older
SSL implementations seem to have trouble with this certificate request message,
and react badly. This includes some Windows FTP clients, as well as some
FTP clients for the Mac.
<p>
One user tried using both the <a href="http://www.panic.com/transmit/">Transmit</a> and the <a href="http://www.fetchsoftworks.com/">Fetch</a> applications for
the Mac; both state that they can handle FTP over SSL/TLS. Using both of
these applications, the user saw the above error. The user, when using
Transmit, saw the following error message appear from the client:
<pre>
Server said:
AUTH TLS successful
error:00000000:lib(0):func(0):reason(0)
</pre>
And when using Fetch, the error message displayed by that client was:
<pre>
SSL Error -9844
Server responded: "AUTH TLS successful"
</pre>
In <b>both</b> causes, using "TLSOptions NoCertRequest" appeared to make
those clients happy.
<p><a name="TLSNoPassphrasePrompt">
<font color=red>Question</font>: When <code>proftpd</code> starts up, I am
prompted to enter the passphrases for my certificates. How can I get the
daemon to start without having to enter passphrases?<br>
<font color=blue>Answer</font>: You can either remove the passphrase from
the certificate key file (as mentioned in the Apache <code>mod_ssl</code>
<a href="http://www.modssl.org/docs/2.7/ssl_faq.html#remove-passphrase">FAQ</a>), or you can use the <code>TLSPassPhraseProvider</code> directive to configure
a program will which provide the passphrases to <code>proftpd</code>
automatically.
<p><a name="TLSFIPS">
<font color=red>Question</font>: How can I configure <code>mod_tls</code> to
use OpenSSL in FIPS mode?<br>
<font color=blue>Answer</font>: Using OpenSSL in FIPS mode requires quite
a few steps. First, you would configure <code>proftpd</code> to use the
<code>mod_tls</code> module as normal, assuming your OpenSSL installation
has been compiled with FIPS support:
<pre>
./configure --with-modules=mod_tls ...
</pre>
<p>
Compiling <code>proftpd</code> requires the following, for FIPS support
to work properly:
<pre>
make CC=<em>/path/to/openssl/bin/</em>fipsld FIPSLD_CC=<em>gcc</em>
</pre>
The <code>FIPSLD_CC</code> variable should point to your normal C compiler,
<i>e.g.</i> <code>gcc</code>. The use of this <code>fipsld</code> program
is <b>mandatory</b>. The FIPS standard requires that the linking process
happen a very specific way, involving verification of calculated and expected
checksums of compiled code, <i>etc</i>. The OpenSSL packages with FIPS
support supply this <code>fipsld</code> program which will link the compiled
code according to the FIPS specifications. <i>If you do not use
<code>fipsld</code>, then attempts to use OpenSSL in FIPS mode will fail.</i>
For example, you would see the following if starting a <code>proftpd</code>
daemon which has not been linked using <code>fipsld</code> while requesting
use of FIPS:
<pre>
- mod_tls/2.1.2: unable to use FIPS mode: (unknown)
- Fatal: unable to load module 'mod_tls.c': Operation not permitted
</pre>
<p>
Now, assuming you have compiled and installed your <code>proftpd</code>
properly, <i>e.g.</i>:
<pre>
make CC=<em>/path/to/openssl/bin/</em>fipsld FIPSLD_CC=<em>gcc</em>
make CC=<em>/path/to/openssl/bin/</em>fipsld FIPSLD_CC=<em>gcc</em> install
</pre>
you will now be ready to start <code>proftpd</code>.
<p>
In order for FIPS mode to be effective, OpenSSL must be told to run in FIPS
mode from the very beginning. The <code>mod_tls</code> module initializes the
OpenSSL library when the <code>mod_tls</code> module is loaded, <i>before the
<code>proftpd.conf</code> file is parsed</i>. Thus the requesting of FIPS mode
<b>cannot</b> be done via a setting in <code>proftpd.conf</code>. (Annoying,
I know.)
<p>
Instead, you must use the -D command-line parameter when starting
<code>proftpd</code> (see the docs for the <code><IfDefine></code> and
<code>Define</code> directives) to define a specific variable, which the
<code>mod_tls</code> module will look for. Specifically, you will need to
start <code>proftpd</code> like thus:
<pre>
/path/to/proftpd -DTLS_USE_FIPS ...
</pre>
This will define the <code>TLS_USE_FIPS</code> variable; this tells
<code>mod_tls</code> to initialize OpenSSL using FIPS mode. When this works,
you will see the following when <code>proftpd</code> starts up:
<pre>
- mod_tls/2.1.2: FIPS mode enabled
</pre>
<p>
For additional reading on OpenSSL and FIPS, see:
<pre>
<a href="http://www.openssl.org/docs/fips/SecurityPolicy-1.1.1.pdf">http://www.openssl.org/docs/fips/SecurityPolicy-1.1.1.pdf</a>
<a href="http://www.openssl.org/docs/fips/UserGuide-1.1.1.pdf">http://www.openssl.org/docs/fips/UserGuide-1.1.1.pdf</a>
</pre>
<p><a name="TLSVersionWarning">
<font color=red>Question</font>: Why do I see the following in my logs when
I start <code>proftpd</code> using <code>mod_tls</code>?
<pre>
- mod_tls/2.2: compiled using OpenSSL version 'OpenSSL 0.9.7i 14 Oct 2005'
headers, but linked to OpenSSL version 'OpenSSL 0.9.7l 28 Sep 2006' library
</pre>
What does this mean?<br>
<font color=blue>Answer</font>: That is an informational/warning message.
<p>
Some systems are badly maintained by their admins (and/or by the packages
installed on the systems), such that the OpenSSL headers can become quite badly
out of sync with the OpenSSL libraries. If this discrepancy becomes bad
enough, you can see strange behavior from OpenSSL, ranging from random behavior
to segfaults. So <code>mod_tls</code> tries to let the admin know about the
system's mismatched OpenSSL header/library versions.
<p>
Usually a minor OpenSSL version difference like the example above is OK,
but it really depends on exactly what changed in OpenSSL, and how.
<p>
If you see the above message, it is not a <i>requirement</i> that you recompile
<code>proftpd</code> against the OpenSSL headers of the same version as the
OpenSSL libraries. However, the version discrepancy <em>is</em> a possible
source of trouble.
<p>
This header/library version check was added recently, hence why older
<code>proftpd</code> releases do not log the warning.
<p><a name="TLSCertificateChainFile">
<font color=red>Question</font>: When should the <a href="../contrib/mod_tls.html#TLSCertificateChainFile"><code>TLSCertificateChainFile</code></a> directive be used?<br>
<font color=blue>Answer</font>: Short answer: only in very specific
arrangements of CA hierarchies. Most of the time, you probably do not need
it.
<p>
The long explanation requires an illustration. Let's say we have a CA hierarchy
that looks something like this:
<pre>
MyRootCA TheirRootCA
| |
MyServerCA TheirClientCA
| |
+------+------+ +------+------+
| | | | | |
certA certB certC cert1 cert2 cert3
</pre>
<p>
Another way of asking the question thus is: "How to I send MyServerCA and
MyRootCA to the client <i>without</i> having them in my trusted CA locations"?
<p>
We might configure <code>mod_tls</code> to have "certA" as the server's
certificate, via <code>TLSRSACertificateFile</code>. The "certA" certificate
is issued by MyServerCA. And let's assume that we do <b>not</b> want to verify
any client certificates issued by MyServerCA.
<p>
We <i>do</i> want to be able to verify client certs issued by a different CA,
say, TheirClientCA. We configure TheirClientCA in <code>mod_tls</code> using
<code>TLSCACertificateFile</code> or <code>TLSCACertificatePath</code>.
<p>
The client connects to <code>mod_tls</code>, and starts the SSL/TLS handshake.
<code>mod_tls</code> sends its "certA" certificate, along with any certs that
may be needed on the client for verifying the server's certificate. (This
is what appears in the "Certificate chain" output from <code>s_client</code>;
see <a href="#TLSDebugging">SSL/TLS debugging</a> above.) Perhaps the client
does not have MyServerCA present in the client certificate store. So we need
to tell <code>mod_tls</code> to send the MyServerCA and MyRootCA certs, along
with "certA". We <i>could</i> place the MyServerCA and MyRootCA certs in
<code>TLSCACertificatePath</code>, but then any client certs issued by
MyServerCA would be trusted as well (and that's not what we want for this
example).
<p>
The solution here is to use <code>TLSCertificateChainFile</code> to supply the
MyServerCA and MyRootCA certs, as part of the server cert chain. The
configured <code>TLSCertificateChainFile</code> would contain the PEM-formatted
MyServerCA and MyRootCA public certs. And although the
<code>TLSCertificateChainFile</code> states that the certs contained in the
file should be in certificate chain order, this is not strictly necessary; the
OpenSSL library will adjust the ordering as appropriate.
<p>
<font color=red>Question</font>: I am having trouble connecting to my
SSL/TLS-enabled <code>proftpd</code>; my FTPS client shows this error:
<pre>
error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure
</pre>
What is wrong?<br>
<font color=blue>Answer</font>: It depends; the first thing is to check
your <code>TLSLog</code> to see what errors, if any, are logged by the
<code>mod_tls</code> module. For example, you might see:
<pre>
Dec 14 10:47:58 mod_tls/2.4.1[13393]: unable to accept TLS connection: protocol error:
(1) error:1408A0C1:SSL routines:SSL3_GET_CLIENT_HELLO:no shared cipher
</pre>
The most common causes of these problems are: <i>a)</i> overly restrictive
<code>TLSCipherSuite</code> configuration, or <i>b)</i> missing server
certificate (<i>i.e.</i> <code>TLSRSACertificateFile</code>,
<code>TLSDSACertificateFile</code>, or <code>TLSPKCS12File</code>). The
file configured for the server certificate might also be badly formatted,
which would result in the same error.
<p>
<font color=red>Question</font>: Is there a way to require TLS (FTPS) for
remote clients <b>only</b>, and allow simple FTP (without TLS) for local
clients (<i>i.e.</i> for clients in networks which we will be able to define
as "local")?<br>
<font color=blue>Answer</font>: Yes.
<p>
To do this, you would use a combination of
<a href="Classes.html"><code><Class></code></a> sections and
<a href="../contrib/mod_ifsession.html">mod_ifsession</a>'s
<code><IfClass></code>, <i>e.g.</i>:
<pre>
<Class local>
From ...
</Class>
<IfModule mod_tls.c>
# Normal mod_tls configuration here
<IfClass local>
# Don't require FTPS from local clients
TLSRequired off
</IfClass>
<IfClass !local>
# Require FTPS from remote/non-local clients
TLSRequired on
</IfClass>
</IfModule>
</pre>
<p>
<hr>
Last Updated: <i>$Date: 2011/05/11 16:09:24 $</i><br>
<hr>
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