Module ngx_mail_ssl_module

Planning your ingress-nginx migration? Start here:
kubernetes.nginx.org.

english
русский
news
about
download
security
documentation
faq
books
community
enterprise
community forum (new)
x.com
blog
njs
ingress controller
gateway fabric

Module ngx_mail_ssl_module

Example Configuration
Directives
ssl
ssl_certificate
ssl_certificate_compression
ssl_certificate_key
ssl_ciphers
ssl_client_certificate
ssl_conf_command
ssl_crl
ssl_dhparam
ssl_ecdh_curve
ssl_password_file
ssl_prefer_server_ciphers
ssl_protocols
ssl_session_cache
ssl_session_ticket_key
ssl_session_tickets
ssl_session_timeout
ssl_trusted_certificate
ssl_verify_client
ssl_verify_depth
starttls

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

This module is not built by default, it should be enabled with the
--with-mail_ssl_module
configuration parameter.

This module requires the
OpenSSL library.

Example Configuration

To reduce the processor load, it is recommended to

set the number of
worker processes
equal to the number of processors,

enable the shared session cache,

disable the built-in session cache,

and possibly increase the session lifetime
(by default, 5 minutes):

worker_processes auto;

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;
ssl_session_cache shared:SSL:10m;
ssl_session_timeout 10m;

...
}

Directives

Syntax:

ssl on | off;

Default:

ssl off;

Context:

mail, server

This directive was made obsolete in version 1.15.0
and was removed in version 1.25.1.
The ssl parameter
of the listen directive
should be used instead.

Syntax:

ssl_certificate file;

Default:

—

Context:

mail, server

Specifies a file 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.

Since version 1.11.0,
this directive can be specified multiple times
to load certificates of different types, for example, RSA and ECDSA:

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;

...
}

Only OpenSSL 1.0.2 or higher supports separate
certificate
chains
for different certificates.
With older versions, only one certificate chain can be used.

The value
data:certificate
can be specified instead of the file (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
error log.

Syntax:

ssl_certificate_compression on | off;

Default:

ssl_certificate_compression off;

Context:

mail, server

This directive appeared in version 1.29.1.

Enables TLS 1.3
compression
of server certificates.

The directive is supported when using OpenSSL 3.2 or higher;
the list of supported compression algorithms is provided by the library.

The directive is supported when using BoringSSL;
the list of supported compression algorithms includes
zlib (1.29.3).

Syntax:

ssl_certificate_key file;

Default:

—

Context:

mail, server

Specifies a file with the secret key in the PEM format
for the given server.

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

The value
store:scheme:id
can be specified instead of the file (1.29.0),
which is used to load a secret key with a specified id
and OpenSSL provider registered URI scheme, such as
pkcs11.

The value
data:key
can be specified instead of the file (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
error log.

Syntax:

ssl_ciphers ciphers;

Default:

ssl_ciphers HIGH:!aNULL:!MD5;

Context:

mail, server

Specifies the enabled ciphers.
The ciphers are specified in the format understood by the
OpenSSL library, for example:

ssl_ciphers ALL:!aNULL:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP;

The full list can be viewed using the
“openssl ciphers” command.

The previous versions of nginx used
different
ciphers by default.

Syntax:

ssl_client_certificate file;

Default:

—

Context:

mail, server

This directive appeared in version 1.7.11.

Specifies a file with trusted CA certificates in the PEM format
used to verify client certificates.

The list of certificates will be sent to clients.
If this is not desired, the ssl_trusted_certificate
directive can be used.

Syntax:

ssl_conf_command name value;

Default:

—

Context:

mail, server

This directive appeared in version 1.19.4.

Sets arbitrary OpenSSL configuration
commands.

The directive is supported when using OpenSSL 1.0.2 or higher.

Several ssl_conf_command directives
can be specified on the same level:

ssl_conf_command Options PrioritizeChaCha;
ssl_conf_command Ciphersuites TLS_CHACHA20_POLY1305_SHA256;

These directives are inherited from the previous configuration level
if and only if there are no ssl_conf_command directives
defined on the current level.

Note that configuring OpenSSL directly
might result in unexpected behavior.

Syntax:

ssl_crl file;

Default:

—

Context:

mail, server

This directive appeared in version 1.7.11.

Specifies a file with revoked certificates (CRL)
in the PEM format used to verify
client certificates.
When using intermediate certificates, their CRLs should be
specified in the same file.

Syntax:

ssl_dhparam file;

Default:

—

Context:

mail, server

This directive appeared in version 0.7.2.

Specifies a file with DH parameters for DHE ciphers.

By default no parameters are set,
and therefore DHE ciphers will not be used.

Prior to version 1.11.0, builtin parameters were used by default.

Syntax:

ssl_ecdh_curve curve;

Default:

ssl_ecdh_curve auto;

Context:

mail, server

This directive appeared in versions 1.1.0 and 1.0.6.

Specifies a curve for ECDHE ciphers.

When using OpenSSL 1.0.2 or higher,
it is possible to specify multiple curves (1.11.0), for example:

ssl_ecdh_curve prime256v1:secp384r1;

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

Prior to version 1.11.0,
the prime256v1 curve was used by default.

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.

Syntax:

ssl_password_file file;

Default:

—

Context:

mail, server

This directive appeared in version 1.7.3.

Specifies a file with passphrases for
secret keys
where each passphrase is specified on a separate line.
Passphrases are tried in turn when loading the key.

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;
}
}

Syntax:

ssl_prefer_server_ciphers on | off;

Default:

ssl_prefer_server_ciphers off;

Context:

mail, server

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

Syntax:

ssl_protocols
[SSLv2]
[SSLv3]
[TLSv1]
[TLSv1.1]
[TLSv1.2]
[TLSv1.3];

Default:

ssl_protocols TLSv1.2 TLSv1.3;

Context:

mail, server

Enables the specified protocols.

The TLSv1.1 and TLSv1.2 parameters
(1.1.13, 1.0.12) work only when OpenSSL 1.0.1 or higher is used.

The TLSv1.3 parameter (1.13.0) works only when
OpenSSL 1.1.1 or higher is used.

The TLSv1.3 parameter is used by default
since 1.23.4.

Syntax:

ssl_session_cache
off |
none |
[builtin[:size]]
[shared:name:size];

Default:

ssl_session_cache none;

Context:

mail, server

Sets the types and sizes of caches that store session parameters.
A cache can be of any of the following types:

off

the use of a session cache is strictly prohibited:
nginx explicitly tells a client that sessions may not be reused.

none

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.

builtin

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.

shared

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 ssl_session_ticket_key directive.

Both cache types can be used simultaneously, for example:

ssl_session_cache builtin:1000 shared:SSL:10m;

but using only shared cache without the built-in cache should
be more efficient.

Syntax:

ssl_session_ticket_key file;

Default:

—

Context:

mail, server

This directive appeared in version 1.5.7.

Sets a file 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.

If several keys are specified, only the first key is
used to encrypt TLS session tickets.
This allows configuring key rotation, for example:

ssl_session_ticket_key current.key;
ssl_session_ticket_key previous.key;

The file must contain 80 or 48 bytes
of random data and can be created using the following command:

openssl rand 80 > ticket.key

Depending on the file size either AES256 (for 80-byte keys, 1.11.8)
or AES128 (for 48-byte keys) is used for encryption.

Syntax:

ssl_session_tickets on | off;

Default:

ssl_session_tickets on;

Context:

mail, server

This directive appeared in version 1.5.9.

Enables or disables session resumption through
TLS session tickets.

Syntax:

ssl_session_timeout time;

Default:

ssl_session_timeout 5m;

Context:

mail, server

Specifies a time during which a client may reuse the
session parameters.

Syntax:

ssl_trusted_certificate file;

Default:

—

Context:

mail, server

This directive appeared in version 1.7.11.

Specifies a file with trusted CA certificates in the PEM format
used to verify client certificates.

In contrast to the certificate set by ssl_client_certificate,
the list of these certificates will not be sent to clients.

Syntax:

ssl_verify_client
on | off |
optional | optional_no_ca;

Default:

ssl_verify_client off;

Context:

mail, server

This directive appeared in version 1.7.11.

Enables verification of client certificates.
The verification result is passed in the
“Auth-SSL-Verify” header of the
authentication
request.

The optional parameter requests the client
certificate and verifies it if the certificate is present.

The optional_no_ca 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
sent
to the authentication server.

Syntax:

ssl_verify_depth number;

Default:

ssl_verify_depth 1;

Context:

mail, server

This directive appeared in version 1.7.11.

Sets the verification depth in the client certificates chain.

Syntax:

starttls
on |
off |
only;

Default:

starttls off;

Context:

mail, server

on

allow usage of the STLS command for the POP3
and the STARTTLS command for the IMAP and SMTP;

off

deny usage of the STLS
and STARTTLS commands;

only

require preliminary TLS transition.