KEYEXPIRED 1217637003

My debian box was unable to update for several months due to the following error when running apt-get update:

W: GPG error: http://mirror.noreply.org etch Release: The following signatures were invalid: KEYEXPIRED 1217637003 KEYEXPIRED 1217637003 KEYEXPIRED 1217637003 KEYEXPIRED 1217637003
W: You may want to run apt-get update to correct these problems

I particularly liked the way it suggests running apt-get update to fix the problem.

First off, if your error message has different key numbers then it's worth checking your debian distro keys are fine by running:

apt-key update

All the solutions I found to this specific key problem were in German but google translate saved the day.
The key in question is related to TOR, this line in /etc/apt/sources.list:

deb http://mirror.noreply.org/pub/tor etch main

The key used to sign the original packages has expired, to get the new one use:

gpg --keyserver keys.gnupg.net --recv 94C09C7F

gpg --export 94C09C7F | apt-key add -

Hopefully your apt-get update/upgrade should now work...