Module ngx_http_ssl_module

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.

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 TLSv1.1 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;

        ...
    }

ssl off;

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.

ssl_buffer_size 16k;

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;

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 HTTPS protocol limitations for maximum interoperability virtual servers should listen on different IP addresses.

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 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.

ssl_ciphers HIGH:!aNULL:!MD5;

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.

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.

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.

Specifies a file with revoked certificates (CRL) in the PEM format used to verify client certificates.

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.

ssl_early_data off;

Enables or disables TLS 1.3 early data.

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;

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

ssl_ecdh_curve auto;

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.

ssl_ocsp off;

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;

ssl_ocsp_cache off;

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.

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/;

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;
    }
}

ssl_prefer_server_ciphers off;

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

ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3;

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.

ssl_reject_handshake off;

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;
}

ssl_session_cache none;

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.

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.

ssl_session_tickets on;

Enables or disables session resumption through TLS session tickets.

ssl_session_timeout 5m;

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

ssl_stapling off;

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.

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.

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/;

ssl_stapling_verify off;

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.

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.

ssl_verify_client off;

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.

ssl_verify_depth 1;

Sets the verification depth in the client certificates chain.

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.

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_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_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).