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<appref>
<header>
<copyright>
<year>1999</year><year>2018</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
</legalnotice>
<title>ssl</title>
<prepared></prepared>
<docno></docno>
<date></date>
<rev></rev>
<file>ssl_app.sgml</file>
</header>
<app>ssl</app>
<appsummary>The ssl application provides secure communication over
sockets.</appsummary>
<description>
<p>
The ssl application is an implementation of the SSL, TLS and DTLS protocols in Erlang.
</p>
<p>For current statement of standards compliance see the <seealso marker="standards_compliance">User's Guide</seealso>.</p>
</description>
<section>
<title>DEPENDENCIES</title>
<p>The SSL application uses the <c>public_key</c>, <c>asn1</c> and
Crypto application to handle public keys and encryption, hence
these applications must be loaded for the SSL application to work.
In an embedded environment this means they must be started with
<c>application:start/[1,2]</c> before the SSL application is
started.</p>
</section>
<section>
<title>CONFIGURATION</title>
<p>The application environment configuration parameters in this section
are defined for the SSL application. For more information
about configuration parameters, see the
<seealso marker="kernel:application">application(3)</seealso>
manual page in Kernel.</p>
<p>The environment parameters can be set on the command line,
for example:</p>
<p><c>erl -ssl protocol_version "['tlsv1.2', 'tlsv1.1']"</c></p>
<taglist>
<tag><c>protocol_version = </c><seealso marker="ssl#type-protocol">ssl:ssl_tls_protocol()</seealso><c><![CDATA[<optional>]]></c></tag>
<item><p>Protocol supported by started clients and
servers. If this option is not set, it defaults to all
TLS protocols currently supported by the SSL application.
This option can be overridden by the version option
to <c>ssl:connect/[2,3]</c> and <c>ssl:listen/2</c>.</p></item>
<tag><c>dtls_protocol_version = </c><seealso marker="ssl#type-protocol">ssl:dtls_protocol()</seealso><c><![CDATA[<optional>]]></c></tag>
<item><p>Protocol supported by started clients and
servers. If this option is not set, it defaults to all
DTLS protocols currently supported by the SSL application.
This option can be overridden by the version option
to <c>ssl:connect/[2,3]</c> and <c>ssl:listen/2</c>.</p></item>
<tag><c><![CDATA[session_lifetime = integer() <optional>]]></c></tag>
<item><p>Maximum lifetime of the session data in seconds. Defaults to 24 hours which is the maximum
recommended lifetime by <url href="http://www.ietf.org/rfc/5246rfc.txt">RFC 5246</url>. However
sessions may be invalidated earlier due to the maximum limitation of the session cache table.
</p></item>
<tag><c><![CDATA[session_cb = atom() <optional>]]></c></tag>
<item><p>Name of the session cache callback module that implements
the <c>ssl_session_cache_api</c> behavior. Defaults to
<c>ssl_session_cache</c>.</p></item>
<tag><c><![CDATA[session_cb_init_args = proplist:proplist() <optional>]]></c></tag>
<item><p>List of extra user-defined arguments to the <c>init</c> function
in the session cache callback module. Defaults to <c>[]</c>.</p></item>
<tag><c><![CDATA[session_cache_client_max = integer() <optional>]]></c><br/></tag>
<item><p>Limits the growth of the clients session cache, that is
how many sessions towards servers that are cached to be used by
new client connections. If the maximum number of sessions is
reached, the current cache entries will be invalidated
regardless of their remaining lifetime. Defaults to
1000. Recommended ssl-8.2.1 or later for this option to work as intended.</p></item>
<tag> <c><![CDATA[session_cache_server_max = integer() <optional>]]></c></tag>
<item><p>Limits the growth of the servers session cache, that is
how many client sessions are cached by the server. If the
maximum number of sessions is reached, the current cache entries
will be invalidated regardless of their remaining
lifetime. Defaults to 1000. Recommended ssl-8.2.1 or later for this option to work as intended.</p></item>
<tag><c><![CDATA[ssl_pem_cache_clean = integer() <optional>]]></c></tag>
<item>
<p>
Number of milliseconds between PEM cache validations. Defaults to 2 minutes.
</p>
<seealso
marker="ssl#clear_pem_cache-0">ssl:clear_pem_cache/0</seealso>
</item>
<tag><c><![CDATA[bypass_pem_cache = boolean() <optional>]]></c></tag>
<item>
<p>Introduced in ssl-8.0.2. Disables the PEM-cache.
Can be used as a workaround for the PEM-cache bottleneck
before ssl-8.1.1. Defaults to false.
</p>
</item>
<tag><c><![CDATA[alert_timeout = integer() <optional>]]></c></tag>
<item>
<p>
Number of milliseconds between sending of a fatal alert and
closing the connection. Waiting a little while improves the
peers chances to properly receiving the alert so it may
shutdown gracefully. Defaults to 5000 milliseconds.
</p>
</item>
<tag><c><![CDATA[internal_active_n = integer() <optional>]]></c></tag>
<item>
<p>
For TLS connections this value is used to handle the
internal socket. As the implementation was changed from an
active once to an active N behavior (N = 100), for
performance reasons, this option exist for possible tweaking
or restoring of the old behavior (internal_active_n = 1) in
unforeseen scenarios. The option will not affect erlang
distribution over TLS that will always run in active N mode.
Added in ssl-9.1 (OTP-21.2).
</p>
</item>
</taglist>
</section>
<section>
<title>ERROR LOGGER AND EVENT HANDLERS</title>
<p>The SSL application uses the default <seealso
marker="kernel:error_logger">OTP error logger</seealso> to log
unexpected errors and TLS/DTLS alerts. The logging of TLS/DTLS alerts may be
turned off with the <c>log_alert</c> option. </p>
</section>
<section>
<title>SEE ALSO</title>
<p><seealso marker="kernel:application">application(3)</seealso></p>
</section>
</appref>
