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<book id="tls" xmlns:xi="http://www.w3.org/2001/XInclude">
    <bookinfo>
	<title>TLS Module</title>
	<authorgroup>
		<author>
		<firstname>Andrei</firstname>
		<surname>Pelinescu-Onciul</surname>
		<affiliation><orgname>iptelorg GmbH</orgname></affiliation>
		<address>
			<email>andrei@iptel.org</email>
		</address>
		</author>
		<author>
		<firstname>Carsten</firstname>
		<surname>Bock</surname>
		<affiliation><orgname>ng-voice GmbH</orgname></affiliation>
		<address>
			<email>carsten@ng-voice.com</email>
		</address>
		</author>
	</authorgroup>
	<copyright>
		<year>2007</year>
		<holder>iptelorg GmbH</holder>
	</copyright>
	<copyright>
		<year>2014</year>
		<holder>ng-voice GmbH</holder>
	</copyright>
	</bookinfo>
	<toc></toc>

	<chapter>
	<title>Admin Guide</title>
	<section id="tls.overview">
		<title>Overview</title>
		<para>
			This module implements the TLS transport for &kamailio;
			using the <ulink url="http://www.openssl.org">OpenSSL library</ulink>
			(http://www.openssl.org). To enable the &kamailio; TLS support this
			module must be loaded and <emphasis>enable_tls=yes</emphasis> core setting
			must be added to the Kamailio config file.
		</para>
		<para>
			IMPORTANT: tls module must be loaded before any other &kamailio; module
			that uses libssl (OpenSSL library). A safe option is to have tls module
			loaded first (be in the first "loadmodule" inside &kamailio;.cfg).
		</para>
	</section>
	<section id="tls.quick_start">
		<title>Quick Start</title>
		<para>
			Make sure you have a proper certificate and private key and either
			use the <varname>certificate</varname> and <varname>private_key</varname>
			module parameters, or make sure the certificate and key are in the same PEM file,
			named <emphasis>cert.pem</emphasis> an placed in [your-cfg-install-prefix]/etc/kamailio/.
			Don't forget to load the tls module and to enable TLS
			(add <emphasis>enable_tls=yes</emphasis> to your config).
		</para>
		<example>
		<title>Quick start config</title>
		<programlisting>
#...
loadmodule "modules/tls/tls.so"

modparam("tls", "private_key", "./andrei-test.pem")
modparam("tls", "certificate", "./andrei-test.pem")
modparam("tls", "ca_list", "./calist.pem")

enable_tls=yes

route{
	# ....
}
		</programlisting>
		</example>
	</section>

	<section id="tls.notes">
		<title>Important Notes</title>
		<para>
			The TLS module needs some special options enabled when compiling
			Kamailio. These options are enabled by default, however in case
			you're using a modified Kamailio version or Makefile, make sure
			that you enable -DUSE_TLS and -DTLS_HOOKS (or compile with make
			TLS_HOOKS=1 which will take care of both options).
		</para>
		<para>
			To quickly check if your Kamailio version was compiled with these
			options, run kamailio -V and look for USE_TLS and TLS_HOOKS among the flags.
		</para>
		<para>
			This module includes several workarounds for various Openssl bugs
			(like compression and Kerberos using the wrong memory allocations
			functions, low memory problems a.s.o). On startup it will try to enable 
			the needed workarounds based on the OpenSSL library version. Each time
			a known problem is detected and a workaround is enabled, a message will
			be logged. In general it is recommended to compile this module on the
			same machine or a similar machine to where kamailio will be run or to
			link it statically with <emphasis>libssl</emphasis>. For example if on
			the compile machine OpenSSL does not have the Kerberos support enabled,
			but on the target machine a Kerberos enabled OpenSSL library is installed,
			Kamailio cannot apply the needed workarounds and will refuse to start.
			The same thing will happen if the OpenSSL versions are too different
			(to force Kamailio startup anyway, see the <varname>tls_force_run</varname>
			module parameter).
		</para>
		<para>
			Compression is fully supported if you have a new enough OpenSSL version
			(starting with 0.9.8). Although there are some problems with zlib compression
			in currently deployed OpenSSL versions (up to and including 0.9.8d, see
			openssl bug #1468), the TLS module will automatically switch to its own fixed version.
			Note however that starting with &kamailio; 3.1 compression is not enabled by
			default, due to the huge extra memory consumption that it causes (about 10x
			more memory). To enable it use
			<emphasis>modparam("tls", "tls_disable_compression", 0)</emphasis>
 			(see <varname>tls_disable_compression</varname>).
		</para>
		<para>
			The TLS module includes workarounds for the following known openssl bugs: 
			<itemizedlist>
                        <listitem><para>
			openssl #1204 (disable SS_OP_TLS_BLOCK_PADDING_BUG if compression is enabled,
			for versions between 0.9.8 and 0.9.8c),
                        </para></listitem>
                        <listitem><para>
			openssl #1468 (fix zlib compression memory allocation),
                        </para></listitem>
                        <listitem><para>
			openssl #1467 (kerberos support will be disabled if the openssl version is less than 0.9.8e-beta1) 
                        </para></listitem>
                        <listitem><para>
			openssl #1491 (stop using tls in low memory situations due to the very high risk of openssl crashing or leaking memory).
                        </para></listitem>
			</itemizedlist>
			The bug reports can be viewed at <ulink url="http://rt.openssl.org/">http://rt.openssl.org/</ulink>.
		</para>
	</section>


	<section id="tls.compile">
		<title>Compiling the TLS Module</title>
		<para>
			In most case compiling the TLS module is as simple as:
			<programlisting>
make -C modules/tls
			</programlisting>
			or
			<programlisting>
make modules modules=modules/tls
			</programlisting>
			or (compiling whole Kamailio and the tls module)
			<programlisting>
make all include_modules=tls
			</programlisting>
			.
		</para>
		<para>
			However in some cases the OpenSSL library requires linking with other libraries.
			For example compiling the OpenSSL library with Kerberos and zlib-shared support
			will require linking the TLS module with libkrb5 and libz. In this case just add
			<emphasis>TLS_EXTRA_LIBS</emphasis>="library list" to make's command line. E.g.:
			<programlisting>
make TLS_EXTRA_LIBS="-lkrb5 -lz" all include_modules=tls
			</programlisting>
		</para>
		<para>
			In general, if Kamailio fails to start with a symbol not found error when trying
			to load the TLS module (check the log), it means some needed library was not
			linked and it must be added to <emphasis>TLS_EXTRA_LIBS</emphasis>
		</para>
		<para>
<ulink url="http://wiki.openssl.org/index.php/Elliptic_Curve_Diffie_Hellman">Elliptic Curve Diffie-Hellman (EDCH)</ulink>-Ciphers are only supported in OpenSSL 1.0.0e and later.
		</para>
	</section>

	<section id="tls.low_memory">
		<title>TLS and Low Memory</title>
		<para>
			The Openssl library doesn't handle low memory situations very well. If memory
			allocations start to fail (due to memory shortage), Openssl can crash or cause memory
			leaks (making the memory shortage even worse). As of this writing all Openssl versions
			were affected (including 0.9.8e), see Openssl bug #1491. The TLS module has some
			workarounds for preventing this problem (see <varname>low_mem_treshold1</varname>
			and <varname>low_mem_threshold2</varname>), however starting Kamailio with enough shared
			memory is higly recommended. When this is not possible a quick way to significantly
			reduce Openssl memory usage it to  disable compression (see <varname>tls_disable_compression</varname>).
		</para>
	</section>

	<section id="tls.debugging">
		<title>TLS Debugging</title>
		<para>
			Debugging messages can be selectively enabled by recompiling
			the TLS module with a combination of the following defines:
			<itemizedlist>
				<listitem>
					<para>
						TLS_WR_DEBUG - debug messages for the write/send part.
					</para>
				</listitem>
				<listitem>
					<para>
						TLS_RD_DEBUG - debug messages for the read/receive
						part.
					</para>
				</listitem>
				<listitem>
					<para>
						TLS_BIO_DEBUG - debug messages for the custom BIO.
					</para>
				</listitem>
			</itemizedlist>
		</para>
		<example>
			<title>Compiling TLS with Debug Messages</title>
			<programlisting>
make -C modules/tls extra_defs="-DTLS_WR_DEBUG -DTLS_RD_DEBUG"
			</programlisting>
		</example>
		<para>
			To change the level at which the debug messages are logged,
			change the <varname>tls_debug</varname> module parameter.
		</para>
	</section>

	<section id="tls.known_limitations">
		<title>Known Limitations</title>
		<para>
			The private key must not be encrypted (Kamailio cannot ask you for a password on startup).
		</para>
		<para>
			The TLS certificate verifications ignores the certificate name, subject altname
			and ip extensions, it just checks if the certificate is signed by a recognized CA.
			One can use the select framework to try to overcome this limitation (check in the
			script for the contents of various certificate fields), but this is not only slow,
			but also not exactly standard conforming (the verification should happen during TLS
			connection establishment and not after).
		</para>
		<para>
			TLS specific config reloading is not safe, so for now better don't use it,
			especially under heavy traffic.
		</para>
		<para>
			This documentation is incomplete.
			The provided selects are not documented. A list with all the
			ones implemented by the TLS module can be seen under
			doc/select_list/select_tls.txt or
			or <ulink url="http://sip-router.org/docbook/sip-router/branch/master/select_list/select_list.html#select_list.tls">
			http://sip-router.org/docbook/sip-router/branch/master/select_list/select_list.html#select_list.tls</ulink>.
		</para>
	</section>

	<xi:include href="certs_howto.xml"/>
	<xi:include href="params.xml"/>
	<xi:include href="functions.xml"/>
	<xi:include href="rpc.xml"/>
	<xi:include href="history.xml"/>
	</chapter>
</book>

