s using DHE need a certificate and key and additional DH-parameters (see <a href="../man3/SSL_CTX_set_tmp_dh_callback.html">SSL_CTX_set_tmp_dh_callback(3)</a>).</p>

<p>A DSA cipher can only be chosen, when a DSA certificate is available. DSA ciphers always use DH key exchange and therefore need DH-parameters (see <a href="../man3/SSL_CTX_set_tmp_dh_callback.html">SSL_CTX_set_tmp_dh_callback(3)</a>).</p>

<p>When these conditions are not met for any cipher in the list (e.g. a client only supports export RSA