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Apache > HTTP Server > Documentation > Version 2.4 > Modules

Apache Module mod_tls

Available Languages:  en 

Description:TLS v1.2 and v1.3 implemented in memory-safe Rust via the rustls library
Status:Experimental
ModuleĀ Identifier:tls_module
SourceĀ File:mod_tls.c
Compatibility:Available in version 2.4.52 and later

Summary

mod_tls is an alternative to mod_ssl for providing https to a server. It's feature set is a subset, described in more detail below. It can be used as a companion to mod_ssl, e.g. both modules can be loaded at the same time.

mod_tls, being written in C, used the Rust implementation of TLS named rustls via its C interface rustls-ffi. This gives memory safe cryptography and protocol handling at comparable performance.

It can be configured for frontend and backend connections. The configuration directive have been kept mostly similar to mod_ssl ones.

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TLS in a VirtualHost context

Listen 443
TLSEngine 443

<VirtualHost *:443>
  ServerName example.net
  TLSCertificate file_with_certificate.pem file_with_key.pem
  ...
</VirtualHost>

The above is a minimal configuration. Instead of enabling mod_tls in every virtual host, the port for incoming TLS connections is specified.

You cannot mix virtual hosts with mod_ssl and mod_tls on the same port. It's either or. SNI and ALPN are supported. You may use several virtual hosts on the same port and a mix of protocols like http/1.1 and h2.

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Feature Comparison with mod_ssl

The table below gives a comparison of feature between mod_ssl and mod_tls. If a feature of mod_ssl is no listed here, it is not supported by mod_tls. The one difference, probably most relevant is the lack for client certificate support in the current version of mod_tls.

Featuremod_sslmod_tlsComment
Frontend TLSyesyes
Backend TLSyesyes
TLS v1.3yes*yes*)with recent OpenSSL
TLS v1.2yesyes
TLS v1.0yes*no*)if enabled in OpenSSL
SNI Virtual Hostsyesyes
Client Certificatesyesno
Machine Certificates for Backendyesyes
OCSP Staplingyesyes**)via mod_md
Backend OCSP checkyesno**)stapling will be verified
TLS version to allowmin-maxmin
TLS ciphersexclusive listpreferred/suppressed
TLS cipher orderingclient/serverclient/server
TLS sessionsyesyes
SNI strictnessdefault nodefault yes
Option EnvVarsexhaustivelimited**)see var list
Option ExportCertDataclient+serverserver
Backend CAfile/dirfile
Revocation CRLsyesno
TLS Renegotiationyes*no*)in TLS v1.2
Encrypted Cert Keysyesno

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TLS Protocols

mod_tls supports TLS protocol version 1.2 and 1.3. Should there ever be a version 1.4 and rustls supports it, it will be available as well.

In mod_tls, you configure the minimum version to use, never the maximum:

TLSProtocol TLSv1.3+

This allows only version 1.3 and whatever may be its successor one day when talking to your server or to a particular virtual host.

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TLS Ciphers

The list of TLS ciphers supported in the rustls library, can be found here. All TLS v1.3 ciphers are supported. For TLS v1.2, only ciphers that rustls considers secure are available.

mod_tls supports the following names for TLS ciphers:

  1. The IANA assigned name which uses `_` to separate parts. Example: TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
  2. The OpenSSL name, using `-` as separator (for 1.2). Example: ECDHE-ECDSA-AES256-SHA384. Such names often appear in documentation. `mod_tls` defines them for all TLS v1.2 ciphers. For TLS v1.3 ciphers, names starting with TLS13_ are also supported.
  3. The IANA assigned identifier, which is a 16-bit numeric value. Example: 0xc024. You can use this in configurations as TLS_CIPHER_0xc024.

You can configure a preference for ciphers, which means they will be used for clients that support them. If you do not configure a preference, rustls will use the one that it considers best. This is recommended.

Should you nevertheless have the need to prefer one cipher over another, you may configure it like this:

TLSCiphersPrefer ECDHE-ECDSA-AES256-SHA384
# or several
TLSCiphersPrefer ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305

If you name a cipher that is unknown, the configuration will fail. If you name a cipher is not supported by rustls (or no longer supported in an updated version of rustls for security reasons), mod_tls will log a WARNING, but continue to work.

A similar mechanism exists, if you want to disable a particular cipher:

TLSCipherSuppress ECDHE-ECDSA-AES256-SHA384

A suppressed cipher will not longer be used. If you name a cipher that is unknown, the configuration will fail. If you name a cipher is not supported by rustls (or no longer supported in an updated version of rustls for security reasons), mod_tls will log a WARNING, but continue to work.

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Virtual Hosts

mod_tls uses the SNI (Server Name Indicator) to select one of the configured virtual hosts that match the port being served. Should the client not provide an SNI, the first configured virtual host will be selected. If the client does provide an SNI (as all today's clients do), it must match one virtual host (ServerName or ServerAlias) or the connection will fail.

As with mod_ssl, you may specify ciphers and protocol versions for the base server (global) and/or individual virtual hosts that are selected via SNI by the client.

Listen 443
TLSEngine 443

<VirtualHost *:443>
  ServerName example1.net
  TLSCertificate example1-cert.pem
  ...
</VirtualHost>

<VirtualHost *:443>
  ServerName example2.net
  TLSCertificate example2-cert.pem
  ...
  TLSProtocol v1.3+
</VirtualHost>

The example above show different TLS settings for virtual hosts on the same port. This is supported. example1 can be contacted via all TLS versions and example2 only allows v1.3 or later.

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ACME Certificates

ACME certificates via mod_md are supported, just as for mod_ssl. A minimal configuration:

Listen 443
TLSEngine 443
MDomain example.net

<VirtualHost *:443>
  ServerName example.net
  ...
</VirtualHost>
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OCSP Stapling

mod_tls has no own implementation to retrieve OCSP information for a certificate. However, it will use such for Stapling if it is provided by mod_md. See mod_md's documentation on how to enable this.

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TLS Variables

Via the directive TLSOptions, several variables are placed into the environment of requests and can be inspected, for example in a CGI script.

The variable names are given by mod_ssl. Note that these are only a subset of the many variables that mod_ssl exposes.

VariableTLSOptionDescription
SSL_TLS_SNI*the server name indicator (SNI) send by the client
SSL_PROTOCOL*the TLS protocol negotiated
SSL_CIPHER*the name of the TLS cipher negotiated
SSL_VERSION_INTERFACEStdEnvVarsthe module version
SSL_VERSION_LIBRARYStdEnvVarsthe rustls-ffi version
SSL_SECURE_RENEGStdEnvVarsalways `false`
SSL_COMPRESS_METHODStdEnvVarsalways `false`
SSL_CIPHER_EXPORTStdEnvVarsalways `false`
SSL_CLIENT_VERIFYStdEnvVarsalways `false`
SSL_SESSION_RESUMEDStdEnvVarseither `Resumed` if a known TLS session id was presented by the client or `Initial` otherwise
SSL_SERVER_CERTExportCertDatathe selected server certificate in PEM format

The variable SSL_SESSION_ID is intentionally not supported as it contains sensitive information.

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Client Certificates

While rustls supports client certificates in principle, parts of the infrastructure to make use of these in a server are not offered.

Among these features are: revocation lists, inspection of certificate extensions and the matched issuer chain for OCSP validation. Without these, revocation of client certificates is not possible. Offering authentication without revocation is not considered an option.

Work will continue on this and client certificate support may become available in a future release.

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TLSCertificate Directive

Description:adds a certificate and key (PEM encoded) to a server/virtual host.
Syntax:TLSCertificate cert_file [key_file]
Context:server config, virtual host
Status:Experimental
Module:mod_tls

If you do not specify a separate key file, the key is assumed to also be found in the first file. You may add more than one certificate to a server/virtual host. The first certificate suitable for a client is then chosen.

The path can be specified relative to the server root.

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TLSCiphersPrefer Directive

Description:defines ciphers that are preferred.
Syntax:TLSCiphersPrefer cipher(-list)
Context:server config, virtual host
Status:Experimental
Module:mod_tls

This will not disable any ciphers supported by `rustls`. If you specify a cipher that is completely unknown, the configuration will fail. If you specify a cipher that is known but not supported by `rustls`, a warning will be logged but the server will continue.

Example

TLSCiphersPrefer ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305

The example gives 2 ciphers preference over others, in the order they are mentioned.

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TLSCiphersSuppress Directive

Description:defines ciphers that are not to be used.
Syntax:TLSCiphersSuppress cipher(-list)
Context:server config, virtual host
Status:Experimental
Module:mod_tls

This will not disable any unmentioned ciphers supported by `rustls`. If you specify a cipher that is completely unknown, the configuration will fail. If you specify a cipher that is known but not supported by `rustls`, a warning will be logged but the server will continue.

Example

TLSCiphersSuppress ECDHE-ECDSA-CHACHA20-POLY1305

The example removes a cipher for use in connections.

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TLSEngine Directive

Description:defines on which address+port the module shall handle incoming connections.
Syntax:TLSEngine [address:]port
Context:server config
Status:Experimental
Module:mod_tls

This is set on a global level, not in individual <VirtualHost>s. It will affect all <VirtualHost> that match the specified address/port. You can use TLSEngine several times to use more than one address/port.

Example

TLSEngine 443

The example tells mod_tls to handle incoming connection on port 443 for all listeners.

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TLSHonorClientOrder Directive

Description:determines if the order of ciphers supported by the client is honored
Syntax:TLSHonorClientOrder on|off
Default:TLSHonorClientOrder on
Context:server config, virtual host
Status:Experimental
Module:mod_tls

TLSHonorClientOrder determines if the order of ciphers supported by the client is honored.

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TLSOptions Directive

Description:enables SSL variables for requests.
Syntax:TLSOptions [+|-]option
Context:server config, virtual host, directory, .htaccess
Status:Experimental
Module:mod_tls

TLSOptions is analog to SSLOptions in mod_ssl. It can be set per directory/location and `option` can be:

Adding variables to a request environment adds overhead, especially when certificates need to be inspected and fields extracted. Therefore most variables are not set by default.

You can configure TLSOptions per location or generally on a server/virtual host. Prefixing an option with `-` disables this option while leaving others unchanged. A `+` prefix is the same as writing the option without one.

The `Defaults` value can be used to reset any options that are inherited from other locations or the virtual host/server.

Example

<Location /myplace/app>
  TLSOptions Defaults StdEnvVars
  ...
</Location>
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TLSProtocol Directive

Description:specifies the minimum version of the TLS protocol to use.
Syntax:TLSProtocol version+
Default:TLSProtocol v1.2+
Context:server config, virtual host
Status:Experimental
Module:mod_tls

The default is `v1.2+`. Settings this to `v1.3+` would disable TLSv1.2.

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TLSProxyCA Directive

Description:sets the root certificates to validate the backend server with.
Syntax:TLSProxyCA file.pem
Context:server config, virtual host, proxy section
Status:Experimental
Module:mod_tls

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TLSProxyCiphersPrefer Directive

Description:defines ciphers that are preferred for a proxy connection.
Syntax:TLSProxyCiphersPrefer cipher(-list)
Context:server config, virtual host, proxy section
Status:Experimental
Module:mod_tls

This will not disable any ciphers supported by `rustls`. If you specify a cipher that is completely unknown, the configuration will fail. If you specify a cipher that is known but not supported by `rustls`, a warning will be logged but the server will continue.

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TLSProxyCiphersSuppress Directive

Description:defines ciphers that are not to be used for a proxy connection.
Syntax:TLSProxyCiphersSuppress cipher(-list)
Context:server config, virtual host, proxy section
Status:Experimental
Module:mod_tls

This will not disable any unmentioned ciphers supported by `rustls`. If you specify a cipher that is completely unknown, the configuration will fail. If you specify a cipher that is known but not supported by `rustls`, a warning will be logged but the server will continue.

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TLSProxyEngine Directive

Description:enables TLS for backend connections.
Syntax:TLSProxyEngine on|off
Context:server config, virtual host, proxy section
Status:Experimental
Module:mod_tls

TLSProxyEngine is analog to SSLProxyEngine in mod_ssl.

This can be used in a server/virtual host or <Proxy> section to enable the module for outgoing connections using mod_proxy.

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TLSProxyMachineCertificate Directive

Description:adds a certificate and key file (PEM encoded) to a proxy setup.
Syntax:TLSProxyMachineCertificate cert_file [key_file]
Context:server config, virtual host, proxy section
Status:Experimental
Module:mod_tls

The certificate is used to authenticate against a proxied backend server.

If you do not specify a separate key file, the key is assumed to also be found in the first file. You may add more than one certificate to a proxy setup. The first certificate suitable for a proxy connection to a backend is then chosen by rustls.

The path can be specified relative to the server root.

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TLSProxyProtocol Directive

Description:specifies the minimum version of the TLS protocol to use in proxy connections.
Syntax:TLSProxyProtocol version+
Default:TLSProxyProtocol v1.2+
Context:server config, virtual host, proxy section
Status:Experimental
Module:mod_tls

The default is `v1.2+`. Settings this to `v1.3+` would disable TLSv1.2.

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TLSSessionCache Directive

Description:specifies the cache for TLS session resumption.
Syntax:TLSSessionCache cache-spec
Context:server config
Status:Experimental
Module:mod_tls

This uses a cache on the server side to allow clients to resume connections.

You can set this to `none` or define a cache as in the SSLSessionCache directive of mod_ssl.

If not configured, `mod_tls` will try to create a shared memory cache on its own, using `shmcb:tls/session-cache` as specification. Should that fail, a warning is logged, but the server continues.

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TLSStrictSNI Directive

Description:enforces exact matches of client server indicators (SNI) against host names.
Syntax:TLSStrictSNI on|off
Default:TLSStrictSNI on
Context:server config
Status:Experimental
Module:mod_tls

Client connections using SNI will be unsuccessful if no match is found.

Available Languages:  en 

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