Apache HTTP Server Version 2.5
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Description: | TLS v1.2 and v1.3 implemented in memory-safe Rust via the rustls library |
---|---|
Status: | Experimental |
Module Identifier: | tls_module |
Source File: | mod_tls.c |
Compatibility: | Available in version 2.4.52 and later |
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.
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.
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.
Feature | mod_ssl | mod_tls | Comment |
---|---|---|---|
Frontend TLS | yes | yes | |
Backend TLS | yes | yes | |
TLS v1.3 | yes* | yes | *)with recent OpenSSL |
TLS v1.2 | yes | yes | |
TLS v1.0 | yes* | no | *)if enabled in OpenSSL |
SNI Virtual Hosts | yes | yes | |
Client Certificates | yes | no | |
Machine Certificates for Backend | yes | yes | |
OCSP Stapling | yes | yes* | *)via mod_md |
Backend OCSP check | yes | no* | *)stapling will be verified |
TLS version to allow | min-max | min | |
TLS ciphers | exclusive list | preferred/suppressed | |
TLS cipher ordering | client/server | client/server | |
TLS sessions | yes | yes | |
SNI strictness | default no | default yes | |
Option EnvVars | exhaustive | limited* | *)see var list |
Option ExportCertData | client+server | server | |
Backend CA | file/dir | file | |
Revocation CRLs | yes | no | |
TLS Renegotiation | yes* | no | *)in TLS v1.2 |
Encrypted Cert Keys | yes | no |
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.
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:
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
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.
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.
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.
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>
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.
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.
Variable | TLSOption | Description |
---|---|---|
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_INTERFACE | StdEnvVars | the module version |
SSL_VERSION_LIBRARY | StdEnvVars | the rustls-ffi version |
SSL_SECURE_RENEG | StdEnvVars | always `false` |
SSL_COMPRESS_METHOD | StdEnvVars | always `false` |
SSL_CIPHER_EXPORT | StdEnvVars | always `false` |
SSL_CLIENT_VERIFY | StdEnvVars | always `false` |
SSL_SESSION_RESUMED | StdEnvVars | either `Resumed` if a known TLS session id was presented by the client or `Initial` otherwise |
SSL_SERVER_CERT | ExportCertData | the selected server certificate in PEM format |
The variable SSL_SESSION_ID
is intentionally not supported as
it contains sensitive information.
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.
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.
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.
TLSCiphersPrefer ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305
The example gives 2 ciphers preference over others, in the order they are mentioned.
Description: | defines ciphers that are not to be used. |
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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.
TLSCiphersSuppress ECDHE-ECDSA-CHACHA20-POLY1305
The example removes a cipher for use in connections.
Description: | defines on which address+port the module shall handle incoming connections. |
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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.
TLSEngine 443
The example tells mod_tls to handle incoming connection on port 443 for all listeners.
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.
Description: | enables SSL variables for requests. |
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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.
<Location /myplace/app> TLSOptions Defaults StdEnvVars ... </Location>
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.
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 |
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.
Description: | defines ciphers that are not to be used for a proxy connection. |
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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.
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
.
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.
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.
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.
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.
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