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<appref>
  <header>
    <copyright>
      <year>1999</year><year>2020</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 <seeguide marker="standards_compliance">User's Guide</seeguide>.</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 
    <seeerl marker="kernel:application">application(3)</seeerl>
    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><seetype marker="ssl#tls_version">ssl:tls_version()</seetype> |
        [<seetype marker="ssl#tls_version">ssl:tls_version()</seetype>] <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, more might be configurable, 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><seetype marker="ssl#dtls_version">ssl:dtls_version()</seetype> |
        [<seetype marker="ssl#dtls_version">ssl:dtls_version()</seetype>] <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, more might be configurable, 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> Deprecated Since OTP-23.3 replaced by <c>client_session_cb</c>
      and <c>server_session_cb</c>
      </p></item>

      <tag><c><![CDATA[client_session_cb = atom() <optional>]]></c></tag>
      <item><p> Since OTP-23.3 Name client of the session cache callback module that implements
      the <c>ssl_session_cache_api</c> behavior. Defaults to
      <c>ssl_client_session_cache_db</c>.</p></item>


      <tag><c><![CDATA[server_session_cb = atom() <optional>]]></c></tag>
      <item><p>Since OTP-23.3 Name of the server session cache callback module that implements
      the <c>ssl_session_cache_api</c> behavior. Defaults to
      <c>ssl_server_session_cache_db</c>.</p></item>

      <tag><c><![CDATA[session_cb_init_args = proplist:proplist() <optional>]]></c></tag>

      <item><p>Deprecated Since OTP-23.3 replaced by <c>client_session_cb_init_args</c>
      and <c>server_session_cb_init_args</c></p></item>

      <tag><c><![CDATA[client_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[server_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>
	<seemfa
	    marker="ssl#clear_pem_cache/0">ssl:clear_pem_cache/0</seemfa>
	
      </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>

      <tag><c><![CDATA[server_session_tickets_amount = integer() <optional>]]></c></tag>
      <item>
	<p>
	  Number of session tickets sent by the server. It must be greater than 0.
	  Defaults to 3.
	</p>
      </item>

      <tag><c><![CDATA[server_session_ticket_lifetime = integer() <optional>]]></c></tag>
      <item>
	<p>
	  Lifetime of session tickets sent by the server. Servers must not use
	  any value greater than 604800 seconds (7 days). Expired tickets are automatically removed.
	  Defaults to 7200 seconds (2 hours).
	</p>
      </item>

      <tag><c><![CDATA[server_session_ticket_store_size = integer() <optional>]]></c></tag>
      <item>
	<p>
	  Sets the maximum size of the server session ticket store (stateful tickets).
	  Defaults to 1000. Size limit is enforced by dropping old tickets.
	</p>
      </item>

      <tag><c><![CDATA[server_session_ticket_max_early_data = integer() <optional>]]></c></tag>
      <item>
	<p>
	  Sets the maximum size of the early data that the server accepts and also configures
	  its NewSessionTicket messages to include this same size limit in their
	  early_data_indication extension.
	  Defaults to 16384. Size limit is enforced by both client and server.
	</p>
      </item>

      <tag><c><![CDATA[client_session_ticket_lifetime = integer() <optional>]]></c></tag>
      <item>
	<p>
	  Lifetime of session tickets in the client ticket store. Expired tickets are
	  automatically removed. Defaults to 7200 seconds (2 hours).
	</p>
      </item>

      <tag><c><![CDATA[client_session_ticket_store_size = integer() <optional>]]></c></tag>
      <item>
	<p>
	  Sets the maximum size of the client session ticket store.
	  Defaults to 1000. Size limit is enforced by dropping old tickets.
	</p>
      </item>
    </taglist>
  </section>

  <section>
    <title>ERROR LOGGER AND EVENT HANDLERS</title>

    <p>The SSL application uses <seeerl
    marker="kernel:logger">OTP logger</seeerl>.
    TLS/DTLS alerts are logged on notice level. Unexpected
    errors are logged on error level. These log entries
    will by default end up in the default Erlang log.
    The option <c>log_level</c> may be used to in run-time to set
    the log level of a specific TLS connection, which is
    handy when you want to use level debug to inspect the
    TLS handshake setup.    
    </p>
  </section>

  <section>
    <title>SEE ALSO</title>
	<p><seeerl marker="kernel:application">application(3)</seeerl></p>
  </section>
  
</appref>
