ngx_mail_ssl_module.xml

<?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="34">

<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       TLSv1.2 TLSv1.3;
        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
and was removed in version 1.25.1.
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
<link doc="../http/configuring_https_servers.xml" id="chains">certificate
chains</link>
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_compression">
<syntax><literal>on</literal> | <literal>off</literal></syntax>
<default>off</default>
<context>mail</context>
<context>server</context>
<appeared-in>1.29.1</appeared-in>

<para>
Enables TLS 1.3
<link url="https://datatracker.ietf.org/doc/html/rfc8879">compression</link>
of server certificates.
<note>
The directive is supported when using OpenSSL 3.2 or higher;
the list of supported compression algorithms is provided by the library.
</note>
<note>
The directive is supported when using BoringSSL;
the list of supported compression algorithms includes
<literal>zlib</literal> (1.29.3).
</note>
</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>
The value
<literal>store</literal>:<value>scheme</value>:<value>id</value>
can be specified instead of the <value>file</value> (1.29.0),
which is used to load a secret key with a specified <value>id</value>
and OpenSSL provider registered URI <value>scheme</value>, such as
<link url="https://datatracker.ietf.org/doc/html/rfc7512"><literal>pkcs11</literal></link>.
</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>name</value> <value>value</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.
When using intermediate certificates, their CRLs should be
specified in the same file.
</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>

<para>
<note>
When using OpenSSL 1.0.2 or higher,
this directive sets the list of curves supported by the server.
Thus, in order for ECDSA certificates to work,
it is important to include the curves used in the certificates.
</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>TLSv1.2 TLSv1.3</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 or higher is used.
</note>
<note>
The <literal>TLSv1.3</literal> parameter is used by default
since 1.23.4.
</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.
It is also used to automatically generate, store, and
periodically rotate TLS session ticket keys (1.23.2)
unless configured explicitly
using the <link id="ssl_session_ticket_key"/> directive.
</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://datatracker.ietf.org/doc/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>