A RSA cipher can only be chosen, when a RSA certificate is available.
RSA export ciphers with a keylength of 512 bits for the RSA key require
a temporary 512 bit RSA key, as typically the supplied key has a length
-of 1024 bit. RSA ciphers using EDH need a certificate and key and
-additional DH-parameters.
+of 1024 bit (see
+L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
+RSA ciphers using EDH need a certificate and key and additional DH-parameters
+(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
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.
+DSA ciphers always use DH key exchange and therefore need DH-parameters
+(see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
When these conditions are not met for any cipher in the list (e.g. a
client only supports export RSA ciphers with a asymmetric key length
L<ssl(3)|ssl(3)>, L<SSL_get_ciphers(3)|SSL_get_ciphers(3)>,
L<SSL_CTX_use_certificate(3)|SSL_CTX_use_certificate(3)>,
+L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
+L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
L<ciphers(1)|ciphers(1)>
=cut