Module ngx_http_ssl_module

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Module ngx_http_ssl_module

Example Configuration
Directives
ssl
ssl_buffer_size
ssl_certificate
ssl_certificate_cache
ssl_certificate_compression
ssl_certificate_key
ssl_ciphers
ssl_client_certificate
ssl_conf_command
ssl_crl
ssl_dhparam
ssl_early_data
ssl_ecdh_curve
ssl_ech_file
ssl_key_log
ssl_ocsp
ssl_ocsp_cache
ssl_ocsp_responder
ssl_password_file
ssl_prefer_server_ciphers
ssl_protocols
ssl_reject_handshake
ssl_session_cache
ssl_session_ticket_key
ssl_session_tickets
ssl_session_timeout
ssl_stapling
ssl_stapling_file
ssl_stapling_responder
ssl_stapling_verify
ssl_trusted_certificate
ssl_verify_client
ssl_verify_depth
Error Processing
Embedded Variables

The ngx_http_ssl_module module provides the
necessary support for HTTPS.

This module is not built by default, it should be enabled with the
--with-http_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
keep-alive
connections,

enable the shared session cache,

disable the built-in session cache,

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

worker_processes auto;

http {

...

server {
listen 443 ssl;
keepalive_timeout 70;

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:

http, 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_buffer_size size;

Default:

ssl_buffer_size 16k;

Context:

http, server

This directive appeared in version 1.5.9.

Sets the size of the buffer used for sending data.

By default, the buffer size is 16k, which corresponds to minimal
overhead when sending big responses.
To minimize Time To First Byte it may be beneficial to use smaller values,
for example:

ssl_buffer_size 4k;

Syntax:

ssl_certificate file;

Default:

—

Context:

http, server

Specifies a file with the certificate in the PEM format
for the given virtual 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 443 ssl;
server_name example.com;

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.

Since version 1.15.9, variables can be used in the file name
when using OpenSSL 1.0.2 or higher:

ssl_certificate $ssl_server_name.crt;
ssl_certificate_key $ssl_server_name.key;

Note that using variables implies that
a certificate will be loaded for each SSL handshake,
and this may have a negative impact on performance.

The value
data:$variable
can be specified instead of the file (1.15.10),
which loads a certificate from a variable
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.

It should be kept in mind that due to the SSL/TLS protocol limitations,
for maximum interoperability with clients that do not use
SNI,
virtual servers with different certificates should listen on
different
IP addresses.

Syntax:

ssl_certificate_cache off;
ssl_certificate_cache
max=N
[inactive=time]
[valid=time];

Default:

ssl_certificate_cache off;

Context:

http, server

This directive appeared in version 1.27.4.

Defines a cache that stores
SSL certificates and
secret keys
specified with variables.

The directive has the following parameters:

max

sets the maximum number of elements in the cache;
on cache overflow the least recently used (LRU) elements are removed;

inactive

defines a time after which an element is removed from the cache
if it has not been accessed during this time;
by default, it is 10 seconds;

valid

defines a time during which
an element in the cache is considered valid
and can be reused;
by default, it is 60 seconds.
Certificates that exceed this time will be reloaded or revalidated;

off

disables the cache.

Example:

ssl_certificate $ssl_server_name.crt;
ssl_certificate_key $ssl_server_name.key;
ssl_certificate_cache max=1000 inactive=20s valid=1m;

Syntax:

ssl_certificate_compression on | off;

Default:

ssl_certificate_compression off;

Context:

http, 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:

http, server

Specifies a file with the secret key in the PEM format
for the given virtual 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:$variable
can be specified instead of the file (1.15.10),
which loads a secret key from a variable 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.

Since version 1.15.9, variables can be used in the file name
when using OpenSSL 1.0.2 or higher.

Syntax:

ssl_ciphers ciphers;

Default:

ssl_ciphers HIGH:!aNULL:!MD5;

Context:

http, 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:

http, server

Specifies a file with trusted CA certificates in the PEM format
used to verify client certificates and
OCSP responses if ssl_stapling is enabled.

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:

http, 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:

http, server

This directive appeared in version 0.8.7.

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:

http, 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_early_data on | off;

Default:

ssl_early_data off;

Context:

http, server

This directive appeared in version 1.15.3.

Enables or disables TLS 1.3
early data.

The directive is supported when using OpenSSL 1.1.1 or higher (1.15.4) and
BoringSSL.

Requests sent within early data are subject to
replay attacks.
To protect against such attacks at the application layer,
the $ssl_early_data variable
should be used.

proxy_set_header Early-Data $ssl_early_data;

OpenSSL built-in replay protection is disabled,
because it interferes with session resumption.
It can be turned back if deemed necessary.

ssl_conf_command Options AntiReplay;

Syntax:

ssl_ecdh_curve curve;

Default:

ssl_ecdh_curve auto;

Context:

http, 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_ech_file file;

Default:

—

Context:

http, server

This directive appeared in version 1.29.4.

Specifies a file with encrypted ClientHello configuration
(ECHConfig) in the
PEM
format used to enable TLS 1.3
ECH
in shared mode.

The directive is currently supported only when using OpenSSL
ECH
feature branch.

Syntax:

ssl_key_log path;

Default:

—

Context:

http, server

This directive appeared in version 1.27.2.

Enables logging of client connection SSL keys
and specifies the path to the key log file.
Keys are logged in the
SSLKEYLOGFILE
format compatible with Wireshark.

This directive is available as part of our
commercial subscription.

Syntax:

ssl_ocsp on |
off |
leaf;

Default:

ssl_ocsp off;

Context:

http, server

This directive appeared in version 1.19.0.

Enables OCSP validation of the client certificate chain.
The leaf parameter
enables validation of the client certificate only.

For the OCSP validation to work,
the ssl_verify_client directive should be set to
on or optional.

To resolve the OCSP responder hostname,
the resolver directive
should also be specified.

Example:

ssl_verify_client on;
ssl_ocsp on;
resolver 192.0.2.1;

Syntax:

ssl_ocsp_cache
off |
[shared:name:size];

Default:

ssl_ocsp_cache off;

Context:

http, server

This directive appeared in version 1.19.0.

Sets name and size of the cache
that stores client certificates status for OCSP validation.
The cache is shared between all worker processes.
A cache with the same name can be used in several
virtual servers.

The off parameter prohibits the use of the cache.

Syntax:

ssl_ocsp_responder url;

Default:

—

Context:

http, server

This directive appeared in version 1.19.0.

Overrides the URL of the OCSP responder specified in the
“Authority
Information Access” certificate extension
for validation of client certificates.

Only “http://” OCSP responders are supported:

ssl_ocsp_responder http://ocsp.example.com/;

Syntax:

ssl_password_file file;

Default:

—

Context:

http, 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:

http {
ssl_password_file /etc/keys/global.pass;
...

server {
server_name www1.example.com;
ssl_certificate_key /etc/keys/first.key;
}

server {
server_name www2.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:

http, 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:

http, server

Enables the specified protocols.

If the directive is specified
on the server level,
the value from the default server can be used.
Details are provided in the
“Virtual
server selection” section.

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_reject_handshake on | off;

Default:

ssl_reject_handshake off;

Context:

http, server

This directive appeared in version 1.19.4.

If enabled, SSL handshakes in
the server block will be rejected.

For example, in the following configuration, SSL handshakes with
server names other than example.com are rejected:

server {
listen 443 ssl default_server;
ssl_reject_handshake on;
}

server {
listen 443 ssl;
server_name example.com;
ssl_certificate example.com.crt;
ssl_certificate_key example.com.key;
}

Syntax:

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

Default:

ssl_session_cache none;

Context:

http, 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
virtual 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:

http, 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:

http, 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:

http, server

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

Syntax:

ssl_stapling on | off;

Default:

ssl_stapling off;

Context:

http, server

This directive appeared in version 1.3.7.

Enables or disables
stapling
of OCSP responses by the server.
Example:

ssl_stapling on;
resolver 192.0.2.1;

For the OCSP stapling to work, the certificate of the server certificate
issuer should be known.
If the ssl_certificate file does
not contain intermediate certificates,
the certificate of the server certificate issuer should be
present in the
ssl_trusted_certificate file.

For a resolution of the OCSP responder hostname,
the resolver directive
should also be specified.

Syntax:

ssl_stapling_file file;

Default:

—

Context:

http, server

This directive appeared in version 1.3.7.

When set, the stapled OCSP response will be taken from the
specified file instead of querying
the OCSP responder specified in the server certificate.

The file should be in the DER format as produced by the
“openssl ocsp” command.

Syntax:

ssl_stapling_responder url;

Default:

—

Context:

http, server

This directive appeared in version 1.3.7.

Overrides the URL of the OCSP responder specified in the
“Authority
Information Access” certificate extension.

Only “http://” OCSP responders are supported:

ssl_stapling_responder http://ocsp.example.com/;

Syntax:

ssl_stapling_verify on | off;

Default:

ssl_stapling_verify off;

Context:

http, server

This directive appeared in version 1.3.7.

Enables or disables verification of OCSP responses by the server.

For verification to work, the certificate of the server certificate
issuer, the root certificate, and all intermediate certificates
should be configured as trusted using the
ssl_trusted_certificate directive.

Syntax:

ssl_trusted_certificate file;

Default:

—

Context:

http, server

This directive appeared in version 1.3.7.

Specifies a file with trusted CA certificates in the PEM format
used to verify client certificates and
OCSP responses if ssl_stapling is enabled.

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:

http, server

Enables verification of client certificates.
The verification result is stored in the
$ssl_client_verify variable.

The optional parameter (0.8.7+) requests the client
certificate and verifies it if the certificate is present.

The optional_no_ca parameter (1.3.8, 1.2.5)
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 the
$ssl_client_cert variable.

Syntax:

ssl_verify_depth number;

Default:

ssl_verify_depth 1;

Context:

http, server

Sets the verification depth in the client certificates chain.

Error Processing

The ngx_http_ssl_module module supports several
non-standard error codes that can be used for redirects using the
error_page directive:

495

an error has occurred during the client certificate verification;

496

a client has not presented the required certificate;

497

a regular request has been sent to the HTTPS port.

The redirection happens after the request is fully parsed and
the variables, such as $request_uri,
$uri, $args and others, are available.

Embedded Variables

The ngx_http_ssl_module module supports
embedded variables:

$ssl_alpn_protocol

returns the protocol selected by ALPN during the SSL handshake,
or an empty string otherwise (1.21.4);

$ssl_cipher

returns the name of the cipher used
for an established SSL connection;

$ssl_ciphers

returns the list of ciphers supported by the client (1.11.7).
Known ciphers are listed by names, unknown are shown in hexadecimal,
for example:

AES128-SHA:AES256-SHA:0x00ff

The variable is fully supported only when using OpenSSL version 1.0.2 or higher.
With older versions, the variable is available
only for new sessions and lists only known ciphers.

$ssl_client_escaped_cert

returns the client certificate in the PEM format (urlencoded)
for an established SSL connection (1.13.5);

$ssl_client_cert

returns the client certificate in the PEM format
for an established SSL connection, with each line except the first
prepended with the tab character;
this is intended for the use in the
proxy_set_header directive;

The variable is deprecated,
the $ssl_client_escaped_cert variable should be used instead.

$ssl_client_fingerprint

returns the SHA1 fingerprint of the client certificate
for an established SSL connection (1.7.1);

$ssl_client_i_dn

returns the “issuer DN” string of the client certificate
for an established SSL connection according to
RFC 2253 (1.11.6);

$ssl_client_i_dn_legacy

returns the “issuer DN” string of the client certificate
for an established SSL connection;

Prior to version 1.11.6, the variable name was $ssl_client_i_dn.

$ssl_client_raw_cert

returns the client certificate in the PEM format
for an established SSL connection;

$ssl_client_s_dn

returns the “subject DN” string of the client certificate
for an established SSL connection according to
RFC 2253 (1.11.6);

$ssl_client_s_dn_legacy

returns the “subject DN” string of the client certificate
for an established SSL connection;

Prior to version 1.11.6, the variable name was $ssl_client_s_dn.

$ssl_client_serial

returns the serial number of the client certificate
for an established SSL connection;

$ssl_client_sigalg

returns the
signature algorithm
for the client certificate for an established SSL connection (1.29.3).

The variable is supported only when using OpenSSL version 3.5 or higher.
With older versions, the variable value will be an empty string.

The variable is available only for new sessions.

$ssl_client_v_end

returns the end date of the client certificate (1.11.7);

$ssl_client_v_remain

returns the number of days
until the client certificate expires (1.11.7);

$ssl_client_v_start

returns the start date of the client certificate (1.11.7);

$ssl_client_verify

returns the result of client certificate verification:
“SUCCESS”, “FAILED:reason”,
and “NONE” if a certificate was not present;

Prior to version 1.11.7, the “FAILED” result
did not contain the reason string.

$ssl_curve

returns the negotiated curve used for
SSL handshake key exchange process (1.21.5).
Known curves are listed by names, unknown are shown in hexadecimal,
for example:

prime256v1

The variable is supported only when using OpenSSL version 3.0 or higher.
With older versions, the variable value will be an empty string.

$ssl_curves

returns the list of curves supported by the client (1.11.7).
Known curves are listed by names, unknown are shown in hexadecimal,
for example:

0x001d:prime256v1:secp521r1:secp384r1

The variable is supported only when using OpenSSL version 1.0.2 or higher.
With older versions, the variable value will be an empty string.

The variable is available only for new sessions.

$ssl_early_data

returns “1” if
TLS 1.3 early data is used
and the handshake is not complete, otherwise “” (1.15.3).

$ssl_ech_outer_server_name

returns the public server name requested through
SNI
if TLS 1.3 ECH was accepted,
otherwise “” (1.29.4);

$ssl_ech_status

returns the result of TLS 1.3 ECH processing:
“FAILED”,
“BACKEND”,
“GREASE”,
“SUCCESS”, or
“NOT_TRIED” (1.29.4);

The variable is currently supported only when using OpenSSL
ECH feature branch
and is therefore subject to change.
The variable value will otherwise be an empty string.

$ssl_protocol

returns the protocol of an established SSL connection;

$ssl_server_name

returns the server name requested through
SNI
(1.7.0);

$ssl_session_id

returns the session identifier of an established SSL connection;

$ssl_session_reused

returns “r” if an SSL session was reused,
or “.” otherwise (1.5.11).

$ssl_sigalg

returns the
signature algorithm
for the server certificate for an established SSL connection (1.29.3).

The variable is supported only when using OpenSSL version 3.5 or higher.
With older versions, the variable value will be an empty string.

The variable is available only for new sessions.