Not encrypted.

When the video editor that comes with Knoppix appeared unsuitable, I Googled for others and then went to AvidEmux.org and tried to follow the instructions there (and then elsewhere). I think that the repository you mentioned is one I used.

Given that Software Center has never worked, the problem that I'm finding repeatedly is not finding some well-known piece of software (the Opera browser is another example...and that one's world-famous) either in Synaptic or via apt-get. Googling led me to edit things like sources.list and sources.list.d (the difference never explained, in those step-by-steps) and adding whatever repository was described. As a DIY beginner, I feel like a blind man in a dark room.

In trying to solve the problem that is the topic of this post, I created a fresh installation of Knoppix, only to find that Software Center, again, does not work (I click the menu choice and nothing happens).

At least, my Etch-a-Sketch does something when I turn one of its knobs!