Backporting documentation commits from trunk (new mod_ssl note about ECC):...

RSA, DSA, and ECC. The number of supported algorithms depends on the

OpenSSL version being used for mod_ssl: with version 1.0.0 or later,

<code>openssl list-public-key-algorithms</code> will output a list

of supported algorithms.

of supported algorithms, see also the note below about limitations

of OpenSSL versions prior to 1.0.2 and the ways to work around them.

</p>

<p>

</p>

</note>

<note>

<title>Default DH parameters when using multiple certificates and OpenSSL

versions prior to 1.0.2</title>

<p>

When using multiple certificates to support different authentication algorithms

(like RSA, DSA, but mainly ECC) and OpenSSL prior to 1.0.2, it is recommended

to either use custom DH parameters (preferably) by adding them to the

first certificate file (as described above), or to order the

<directive>SSLCertificateFile</directive> directives such that RSA/DSA

certificates are placed <strong>after</strong> the ECC one.

</p>

<p>

This is due to a limitation in older versions of OpenSSL which don't let the

Apache HTTP Server determine the currently selected certificate at handshake

time (when the DH parameters must be sent to the peer) but instead always

provide the last configured certificate. Consequently, the server may select

default DH parameters based on the length of the wrong certificate's key (ECC

keys are much smaller than RSA/DSA ones and their length is not relevant for

selecting DH primes).

</p>

<p>

Since custom DH parameters always take precedence over the default ones, this

issue can be avoided by creating and configuring them (as described above),

thus using a custom/suitable length.

</p>

</note>

<example><title>Example</title>

<highlight language="config">

SSLCertificateFile "/usr/local/apache2/conf/ssl.crt/server.crt"