I'm using uddeIM 3.8 on CB 2.0.12. When I select "Strong Encryption" in the backend and then try to send a private message (entering subject, message, and password), it hangs and shows only a blank page. It goes thru if no password is entered but this is the same as simple obfuscation. I see in the code it is probably hanging on the line -

$cm = uddeIMencrypt($savemessagecopy,$thepass,$cipher);

, because no entry gets into the database table.

Maybe encryption is not available on your setup. In that case you can only use obfuscating instead.

I dug a little deeper. That function calls another one -

$td = mcrypt_module_open(MCRYPT_3DES, '', MCRYPT_MODE_CFB, '');

, which appears to be expected in core Joomla (reference to it in com_joomlaupdate) and is a PHP extension. On Fedora 21, the package php-mcrypt is not installed by default. When I installed it, "strong encryption" started working.

Thanks.