[http://deb.opera.com/archive.key] didn't work for me a couple of days ago, but a cut and paste of the 2013b code did work.
I just took a look at the content of the file now, and it appears to only contain the 2013b key (not the 2013 one). So either it's been changed since or there was an error with my original key installation
PS, Very very happy with my Opera installation now. Runs significantly faster than my Chrome installation and love the mouse gestures.