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updated TLS documentation with HOWTO on certificate generation

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Rainer Gerhards 2008-05-23 11:28:31 +02:00
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@ -13,11 +13,12 @@ messages on the network.</b> Encryption
is vital to keep the confidiental content of syslog messages secure. I
describe the overall
approach and provide an HOWTO do it with <a href="http://www.rsyslog.com">rsyslog's</a> TLS
features.&nbsp;</i></p><p>Please
features.&nbsp;</i></p>
<p>Please
note that TLS is the more secure successor of SSL. While people often
talk about "SSL encryption" they actually mean "TLS encryption". So
don't look any further if you look for how to SSL-encrypt syslog. You
have found the right spot.<i></i></p>
have found the right spot.</p>
<h2>Background</h2>
<p><b>Traditional syslog is a clear-text protocol. That
means anyone with a sniffer can have a peek at your data.</b> In
@ -36,17 +37,20 @@ of TCP syslog</a>).
GSSAP</a>I since long to overcome these limitatinos. However,
syslog via GSSAPI is a rsyslog-exclusive transfer mode and it requires
a proper Kerberos environment. As such, it isn't a really universal
solution. The <a href="http://www.ietf.org/">IETF</a> has begun standardizing syslog over plain tcp over
solution. The <a href="http://www.ietf.org/">IETF</a>
has begun standardizing syslog over plain tcp over
TLS for a while now. While I am not fully satisfied with the results so
far, this obviously has the&nbsp; potential to become the long-term
solution. The Internet Draft in question, syslog-transport-tls has been
dormant for some time but is now (May of 2008) again being worked on. I
expect it to turn into a RFC within the next 12 month (but don't take
this for granted ;)). I didn't want to wait for it, because there
obviously is need for TLS syslog right now (and, honestly, I have waited long enough...). Consequently, I have
obviously is need for TLS syslog right now (and, honestly, I have
waited long enough...). Consequently, I have
implemented the current draft, with some interpretations I made (there
will be a compliance doc soon). So in essence, a TLS-protected syslog
transfer mode is available right now. As a side-note, Rsyslog is&nbsp;the world's first
transfer mode is available right now. As a side-note, Rsyslog
is&nbsp;the world's first
implementation of syslog-transport-tls.</p>
<p>Please note that in theory it should be compatible with other,
non IETF syslog-transport-tls implementations. If you would like to run
@ -129,8 +133,10 @@ following these steps, you should have a working secure
syslog forwarding system. To verify, you can type "logger test" or a
similar "smart" command on the client. It should show up in the
respective server log file. If you dig out your sniffer, you should see
that the traffic on the wire is actually protected.</p><h3>Limitations</h3>
<p>The current implementation has a number of limitations. These are
that the traffic on the wire is actually protected.</p>
<h3>Limitations</h3>
<p>The current implementation has a number of limitations. These
are
being worked on. Most importantly, neither the client nor the server
are authenticated. So while the message transfer is encrypted, you can
not be sure which peer you are talking to. Please note that this is a
@ -138,14 +144,109 @@ limitation found in most real-world SSL syslog systems. Of course, that
is not an excuse for not yet providing this feature - but it tells you
that it is acceptable and can be worked around by proper firewalling,
ACLs and other organizational measures. Mutual authentication will be
added shortly to rsyslog.</p><p>Secondly, the plain tcp syslog listener
added shortly to rsyslog.</p>
<p>Secondly, the plain tcp syslog listener
can currently listen to a single port, in a single mode. So if you use
a TLS-based listener, you can not run unencrypted syslog on the same
instance at the same time. A work-around is to run a second rsyslogd
instance. This limitation, too, is scheduled to be removed soon.</p><p>The
instance. This limitation, too, is scheduled to be removed soon.</p>
<p>The
RELP transport can currently not be protected by TLS. A work-around is
to use stunnel. TLS support for RELP will be added once plain TCP
syslog has sufficiently matured.</p><h2>Conclusion</h2>
syslog has sufficiently matured.</p>
<h2>Certificates</h2>
<p>In order to be really secure, certificates are needed. This is
a short summary on how to generate the necessary certificates with
GnuTLS' certtool. You can also generate certificates via other tools,
but as we currently support GnuTLS as the only TLS library, we thought
it is a good idea to use their tools.<br></p>
<p>Note that this section aims at people who are not involved
with PKI at all. The main goal is to get them going in a reasonable
secure way.&nbsp;</p>
<h3>CA Certificate</h3>
<p>This is used to sign all of your other certificates. The CA
cert must be trusted by all clients and servers. The private key must
be well-protected and not given to any third parties. The certificate
itself can (and must) be distributed. To generate it, do the following:</p>
<ol>
<li>generate the private key:
<pre>certtool --generate-privkey --outfile ca-key.pem</pre>
<br>
This takes a short while. Be sure to do some work on your workstation,
it waits for radom input. Switching between windows is sufficient
;)&nbsp;
</li>
<li>now create the (self-signed) CA certificate itself:<br>
<pre>certtool --generate-self-signed --load-privkey ca-key.pem --outfile ca.pem</pre>
This generates the CA certificate. This command queries you for a
number of things. Use appropriate responses. When it comes to
certificate validity, keep in mind that you need to recreate all
certificates when this one expires. So it may be a good idea to use a
long period, eg. 3650 days (roughly 10 years). You need to specify that
the certificates belongs to an authrity. The certificate is used to
sign other certificates.<br>
</li>
<li>You need to distribute this certificate
to all peers and you need to point to it via the
$DefaultNetstreamDriverCAFile config directive. All other certificates
will be issued by this CA.<br>
Important: do only distribute the ca.pem, NOT ca-key.pem (the private
key). Distributing the CA private key would totally breach security as
everybody could issue new certificates on the behalf of this CA.
</li>
</ol>
<h3>Individual Peer Certificate</h3>
<p>Each peer (be it client, server or both), needs a certificate
that conveys its identity. Access control is based on these
certificates. You can, for example, configure a server to accept
connections only from configured clients. The client ID is taken from
the client instances certificate. So as a general rule of thumb, you
need to create a certificate for each instance of rsyslogd that you
run. That instance also needs the private key, so that it can properly
decrypt the traffic. Safeguard the peer's private key file. If somebody
gets hold of it, it can malicously pretend to be the compromised host.
If such happens, regenerate the certificate and make sure you use a
different name instead of the compromised one (if you use name-based
authentication).&nbsp;</p>
<p>These are the steps to generate the indivudual certificates
(repeat: you need to do this for every instance, do NOT share the
certificates created in this step):</p>
<ol>
<li>generate a private key (do NOT mistake this with the CA's
private key - this one is different):<br>
<pre>certtool --generate-privkey --outfile key.pem</pre>
Again, this takes a short while.</li>
<li>generate a certificate request:<br>
<pre>certtool --generate-request --load-privkey key.pem --outfile request.pem</pre>
If you do not have the CA's private key (because you are not authorized
for this), you can send the certificate request to the responsible
person. If you do this, you can skip the remaining steps, as the CA
will provide you with the final certificate. If you submit the request
to the CA, you need to tell the CA the answers that you would normally
provide in step 3 below.
</li>
<li>Sign (validate, authorize) the certificate request and
generate the instances certificate. You need to have the CA's
certificate and private key for this:<br>
<pre>certtool --generate-certificate --load-request request.pem --outfile cert.pem \<br> --load-ca-certificate ca.pem --load-ca-privkey ca-key.pem</pre>
Answer questions as follows: Cert does not belogn to an authority; it
is a TLS web server and client certificate; the dnsName MUST be the
name of the peer in question (e.g. centralserver.example.net) - this is
the name used for authenticating the peers. Please note that you may
use an IP address in dnsName. This is a good idea if you would like to
use default server authentication and you use selector lines with IP
addresses (e.g. "*.* @@192.168.0.1") - in that case you need to select
a dnsName of 192.168.0.1. But, of course, changing the server IP then
requires generating a new certificate.</li>
</ol>After you have generated the certificate, you need to place it
onto the local machine running rsyslogd. Specify the certificate and
key via the $DefaultNetstreamDriverCertFile /path/to/cert.pem and
$DefaultNetstreamDriverKeyFile /path/to/key.pem configuration
directives. Make sure that nobody has access to key.pem, as that would
breach security. And, once again: do NOT use these files on more than
one instance. Doing so would prevent you from distinguising between the
instances and thus would disable useful authentication.
<h2>Conclusion</h2>
<p>With minumal effort, you can set up a secure logging
infrastructure employing TLS encrypted syslog message transmission.</p>
<h3>Feedback requested</h3>
@ -156,7 +257,8 @@ please
<h2>Revision History</h2>
<ul>
<li>2008-05-06 * <a href="http://www.gerhards.net/rainer">Rainer
Gerhards</a> * Initial Version created</li></ul>
Gerhards</a> * Initial Version created</li>
</ul>
<h2>Copyright</h2>
<p>Copyright (c) 2008 <a href="http://www.adiscon.com/en/people/rainer-gerhards.php">Rainer
Gerhards</a> and