<?xml version="1.0"?>

<!--
  Copyright (C) 2006, 2007 Anton Yuzhaninov
  Copyright (C) Nginx, Inc.
  -->

<!DOCTYPE module SYSTEM "../../../../dtd/module.dtd">

<module name="Module ngx_mail_ssl_module"
        link="/en/docs/mail/ngx_mail_ssl_module.html"
        lang="en"
        rev="21">

<section id="summary">

<para>
The <literal>ngx_mail_ssl_module</literal> module provides the necessary
support for a mail proxy server to work with the SSL/TLS protocol.
</para>

<para>
This module is not built by default, it should be enabled with
the <literal>--with-mail_ssl_module</literal>
configuration parameter.
<note>
This module requires the <link url="http://www.openssl.org">OpenSSL</link>
library.
</note>
</para>

</section>


<section id="example" name="Example Configuration">

<para>
To reduce the processor load, it is recommended to
<list type="bullet">

<listitem>
set the number of
<link doc="../ngx_core_module.xml" id="worker_processes">worker processes</link>
equal to the number of processors,
</listitem>

<listitem>
enable the <link id="ssl_session_cache_shared">shared</link> session cache,
</listitem>

<listitem>
disable the <link id="ssl_session_cache_builtin">built-in</link> session cache,
</listitem>

<listitem>
and possibly increase the session <link id="ssl_session_timeout">lifetime</link>
(by default, 5 minutes):
</listitem>

</list>

<example>
<emphasis>worker_processes auto;</emphasis>

mail {

    ...

    server {
        listen              993 ssl;

        ssl_protocols       TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers         AES128-SHA:AES256-SHA:RC4-SHA:DES-CBC3-SHA:RC4-MD5;
        ssl_certificate     /usr/local/nginx/conf/cert.pem;
        ssl_certificate_key /usr/local/nginx/conf/cert.key;
        <emphasis>ssl_session_cache   shared:SSL:10m;</emphasis>
        <emphasis>ssl_session_timeout 10m;</emphasis>

        ...
    }
</example>
</para>

</section>


<section id="directives" name="Directives">

<directive name="ssl">
<syntax><literal>on</literal> | <literal>off</literal></syntax>
<default>off</default>
<context>mail</context>
<context>server</context>

<para>
This directive was made obsolete in version 1.15.0.
The <literal>ssl</literal> parameter
of the <link doc="ngx_mail_core_module.xml" id="listen"/> directive
should be used instead.
</para>

</directive>


<directive name="ssl_certificate">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>

<para>
Specifies a <value>file</value> with the certificate in the PEM format
for the given server.
If intermediate certificates should be specified in addition to a primary
certificate, they should be specified in the same file in the following
order: the primary certificate comes first, then the intermediate certificates.
A secret key in the PEM format may be placed in the same file.
</para>

<para>
Since version 1.11.0,
this directive can be specified multiple times
to load certificates of different types, for example, RSA and ECDSA:
<example>
server {
    listen              993 ssl;

    ssl_certificate     example.com.rsa.crt;
    ssl_certificate_key example.com.rsa.key;

    ssl_certificate     example.com.ecdsa.crt;
    ssl_certificate_key example.com.ecdsa.key;

    ...
}
</example>
<note>
Only OpenSSL 1.0.2 or higher supports separate certificate chains
for different certificates.
With older versions, only one certificate chain can be used.
</note>
</para>

<para id="ssl_certificate_data">
The value
<literal>data</literal>:<value>certificate</value>
can be specified instead of the <value>file</value> (1.15.10),
which loads a certificate without using intermediate files.
Note that inappropriate use of this syntax may have its security implications,
such as writing secret key data to
<link doc="../ngx_core_module.xml" id="error_log">error log</link>.
</para>

</directive>


<directive name="ssl_certificate_key">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>

<para>
Specifies a <value>file</value> with the secret key in the PEM format
for the given server.
</para>

<para>
The value
<literal>engine</literal>:<value>name</value>:<value>id</value>
can be specified instead of the <value>file</value> (1.7.9),
which loads a secret key with a specified <value>id</value>
from the OpenSSL engine <value>name</value>.
</para>

<para id="ssl_certificate_key_data">
The value
<literal>data</literal>:<value>key</value>
can be specified instead of the <value>file</value> (1.15.10),
which loads a secret key without using intermediate files.
Note that inappropriate use of this syntax may have its security implications,
such as writing secret key data to
<link doc="../ngx_core_module.xml" id="error_log">error log</link>.
</para>

</directive>


<directive name="ssl_ciphers">
<syntax><value>ciphers</value></syntax>
<default>HIGH:!aNULL:!MD5</default>
<context>mail</context>
<context>server</context>

<para>
Specifies the enabled ciphers.
The ciphers are specified in the format understood by the
OpenSSL library, for example:
<example>
ssl_ciphers ALL:!aNULL:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP;
</example>
</para>

<para>
The full list can be viewed using the
“<command>openssl ciphers</command>” command.
</para>

<para>
<note>
The previous versions of nginx used
<link doc="../http/configuring_https_servers.xml" id="compatibility">different</link>
ciphers by default.
</note>
</para>

</directive>


<directive name="ssl_client_certificate">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>
<appeared-in>1.7.11</appeared-in>

<para>
Specifies a <value>file</value> with trusted CA certificates in the PEM format
used to <link id="ssl_verify_client">verify</link> client certificates.
</para>

<para>
The list of certificates will be sent to clients.
If this is not desired, the <link id="ssl_trusted_certificate"/>
directive can be used.
</para>

</directive>


<directive name="ssl_conf_command">
<syntax><value>command</value></syntax>
<default/>
<context>mail</context>
<context>server</context>
<appeared-in>1.19.4</appeared-in>

<para>
Sets arbitrary OpenSSL configuration
<link url="https://www.openssl.org/docs/man1.1.1/man3/SSL_CONF_cmd.html">commands</link>.
<note>
The directive is supported when using OpenSSL 1.0.2 or higher.
</note>
</para>

<para>
Several <literal>ssl_conf_command</literal> directives
can be specified on the same level:
<example>
ssl_conf_command Options PrioritizeChaCha;
ssl_conf_command Ciphersuites TLS_CHACHA20_POLY1305_SHA256;
</example>
These directives are inherited from the previous configuration level
if and only if there are no <literal>ssl_conf_command</literal> directives
defined on the current level.
</para>

<para>
<note>
Note that configuring OpenSSL directly
might result in unexpected behavior.
</note>
</para>

</directive>


<directive name="ssl_crl">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>
<appeared-in>1.7.11</appeared-in>

<para>
Specifies a <value>file</value> with revoked certificates (CRL)
in the PEM format used to <link id="ssl_verify_client">verify</link>
client certificates.
</para>

</directive>


<directive name="ssl_dhparam">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>
<appeared-in>0.7.2</appeared-in>

<para>
Specifies a <value>file</value> with DH parameters for DHE ciphers.
</para>

<para>
By default no parameters are set,
and therefore DHE ciphers will not be used.
<note>
Prior to version 1.11.0, builtin parameters were used by default.
</note>
</para>

</directive>


<directive name="ssl_ecdh_curve">
<syntax><value>curve</value></syntax>
<default>auto</default>
<context>mail</context>
<context>server</context>
<appeared-in>1.1.0</appeared-in>
<appeared-in>1.0.6</appeared-in>

<para>
Specifies a <value>curve</value> for ECDHE ciphers.
</para>

<para>
When using OpenSSL 1.0.2 or higher,
it is possible to specify multiple curves (1.11.0), for example:
<example>
ssl_ecdh_curve prime256v1:secp384r1;
</example>
</para>

<para>
The special value <literal>auto</literal> (1.11.0) instructs nginx to use
a list built into the OpenSSL library when using OpenSSL 1.0.2 or higher,
or <literal>prime256v1</literal> with older versions.
</para>

<para>
<note>
Prior to version 1.11.0,
the <literal>prime256v1</literal> curve was used by default.
</note>
</para>

</directive>


<directive name="ssl_password_file">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>
<appeared-in>1.7.3</appeared-in>

<para>
Specifies a <value>file</value> with passphrases for
<link id="ssl_certificate_key">secret keys</link>
where each passphrase is specified on a separate line.
Passphrases are tried in turn when loading the key.
</para>

<para>
Example:
<example>
mail {
    ssl_password_file /etc/keys/global.pass;
    ...

    server {
        server_name mail1.example.com;
        ssl_certificate_key /etc/keys/first.key;
    }

    server {
        server_name mail2.example.com;

        # named pipe can also be used instead of a file
        ssl_password_file /etc/keys/fifo;
        ssl_certificate_key /etc/keys/second.key;
    }
}
</example>
</para>

</directive>


<directive name="ssl_prefer_server_ciphers">
<syntax><literal>on</literal> | <literal>off</literal></syntax>
<default>off</default>
<context>mail</context>
<context>server</context>

<para>
Specifies that server ciphers should be preferred over client ciphers
when the SSLv3 and TLS protocols are used.
</para>

</directive>


<directive name="ssl_protocols">
<syntax>
    [<literal>SSLv2</literal>]
    [<literal>SSLv3</literal>]
    [<literal>TLSv1</literal>]
    [<literal>TLSv1.1</literal>]
    [<literal>TLSv1.2</literal>]
    [<literal>TLSv1.3</literal>]</syntax>
<default>TLSv1 TLSv1.1 TLSv1.2</default>
<context>mail</context>
<context>server</context>

<para>
Enables the specified protocols.
<note>
The <literal>TLSv1.1</literal> and <literal>TLSv1.2</literal> parameters
(1.1.13, 1.0.12) work only when OpenSSL 1.0.1 or higher is used.
</note>
<note>
The <literal>TLSv1.3</literal> parameter (1.13.0) works only when
OpenSSL 1.1.1 built with TLSv1.3 support is used.
</note>
</para>

</directive>


<directive name="ssl_session_cache">
<syntax>
    <literal>off</literal> |
    <literal>none</literal> |
    [<literal>builtin</literal>[:<value>size</value>]]
    [<literal>shared</literal>:<value>name</value>:<value>size</value>]</syntax>
<default>none</default>
<context>mail</context>
<context>server</context>

<para>
Sets the types and sizes of caches that store session parameters.
A cache can be of any of the following types:
<list type="tag">

<tag-name><literal>off</literal></tag-name>
<tag-desc>
the use of a session cache is strictly prohibited:
nginx explicitly tells a client that sessions may not be reused.
</tag-desc>

<tag-name><literal>none</literal></tag-name>
<tag-desc>
the use of a session cache is gently disallowed:
nginx tells a client that sessions may be reused, but does not
actually store session parameters in the cache.
</tag-desc>

<tag-name id="ssl_session_cache_builtin"><literal>builtin</literal></tag-name>
<tag-desc>
a cache built in OpenSSL; used by one worker process only.
The cache size is specified in sessions.
If size is not given, it is equal to 20480 sessions.
Use of the built-in cache can cause memory fragmentation.
</tag-desc>

<tag-name id="ssl_session_cache_shared"><literal>shared</literal></tag-name>
<tag-desc>
a cache shared between all worker processes.
The cache size is specified in bytes; one megabyte can store
about 4000 sessions.
Each shared cache should have an arbitrary name.
A cache with the same name can be used in several
servers.
</tag-desc>

</list>
</para>

<para>
Both cache types can be used simultaneously, for example:
<example>
ssl_session_cache builtin:1000 shared:SSL:10m;
</example>
but using only shared cache without the built-in cache should
be more efficient.
</para>

</directive>


<directive name="ssl_session_ticket_key">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>
<appeared-in>1.5.7</appeared-in>

<para>
Sets a <value>file</value> with the secret key used to encrypt
and decrypt TLS session tickets.
The directive is necessary if the same key has to be shared between
multiple servers.
By default, a randomly generated key is used.
</para>

<para>
If several keys are specified, only the first key is
used to encrypt TLS session tickets.
This allows configuring key rotation, for example:
<example>
ssl_session_ticket_key current.key;
ssl_session_ticket_key previous.key;
</example>
</para>

<para>
The <value>file</value> must contain 80 or 48 bytes
of random data and can be created using the following command:
<example>
openssl rand 80 > ticket.key
</example>
Depending on the file size either AES256 (for 80-byte keys, 1.11.8)
or AES128 (for 48-byte keys) is used for encryption.
</para>

</directive>


<directive name="ssl_session_tickets">
<syntax><literal>on</literal> | <literal>off</literal></syntax>
<default>on</default>
<context>mail</context>
<context>server</context>
<appeared-in>1.5.9</appeared-in>

<para>
Enables or disables session resumption through
<link url="https://tools.ietf.org/html/rfc5077">TLS session tickets</link>.
</para>

</directive>


<directive name="ssl_session_timeout">
<syntax><value>time</value></syntax>
<default>5m</default>
<context>mail</context>
<context>server</context>

<para>
Specifies a time during which a client may reuse the
session parameters.
</para>

</directive>


<directive name="ssl_trusted_certificate">
<syntax><value>file</value></syntax>
<default/>
<context>mail</context>
<context>server</context>
<appeared-in>1.7.11</appeared-in>

<para>
Specifies a <value>file</value> with trusted CA certificates in the PEM format
used to <link id="ssl_verify_client">verify</link> client certificates.
</para>

<para>
In contrast to the certificate set by <link id="ssl_client_certificate"/>,
the list of these certificates will not be sent to clients.
</para>

</directive>


<directive name="ssl_verify_client">
<syntax>
    <literal>on</literal> | <literal>off</literal> |
    <literal>optional</literal> | <literal>optional_no_ca</literal></syntax>
<default>off</default>
<context>mail</context>
<context>server</context>
<appeared-in>1.7.11</appeared-in>

<para>
Enables verification of client certificates.
The verification result is passed in the
<header>Auth-SSL-Verify</header> header of the
<link doc="ngx_mail_auth_http_module.xml" id="auth_http">authentication</link>
request.
</para>

<para>
The <literal>optional</literal> parameter requests the client
certificate and verifies it if the certificate is present.
</para>

<para>
The <literal>optional_no_ca</literal> parameter
requests the client
certificate but does not require it to be signed by a trusted CA certificate.
This is intended for the use in cases when a service that is external to nginx
performs the actual certificate verification.
The contents of the certificate is accessible through requests
<link doc="ngx_mail_auth_http_module.xml"
      id="auth_http_pass_client_cert">sent</link>
to the authentication server.
</para>

</directive>


<directive name="ssl_verify_depth">
<syntax><value>number</value></syntax>
<default>1</default>
<context>mail</context>
<context>server</context>
<appeared-in>1.7.11</appeared-in>

<para>
Sets the verification depth in the client certificates chain.
</para>

</directive>


<directive name="starttls">
<syntax>
  <literal>on</literal> |
  <literal>off</literal> |
  <literal>only</literal></syntax>
<default>off</default>
<context>mail</context>
<context>server</context>

<para>
<list type="tag">

<tag-name><literal>on</literal></tag-name>
<tag-desc>
allow usage of the <literal>STLS</literal> command for the POP3
and the <literal>STARTTLS</literal> command for the IMAP and SMTP;
</tag-desc>

<tag-name><literal>off</literal></tag-name>
<tag-desc>
deny usage of the <literal>STLS</literal>
and <literal>STARTTLS</literal> commands;
</tag-desc>

<tag-name><literal>only</literal></tag-name>
<tag-desc>
require preliminary TLS transition.
</tag-desc>

</list>
</para>

</directive>

</section>

</module>