Encrypt all the things!

Neither--well, it's wrong with a question mark, as it's not a question/question tag but part of an indicative sentence. It's not wrong in, for instance: «Ce n'est pas possible.» or «Ceci n'est pas une pipe.» or some such use.

While the form of the question tag is fixed, you *can* ask questions without the inversion in colloquial French, but you need at least one object. «Ce n'est pas le train à Avignon?» This mostly follows on from what someone else has just said and can effectively be a shortened form of something like «Voulez-vous dire que ... ?».

All that said, there's a lot of bad French spoken, as every language is spoken badly much of the time, and someone may well come along in a moment to say it has become colloquial since I last looked. :)