GPG error: http://ru.archive.ubuntu.com oneiric Release: The following signatures were invalid:
BADSIG <..> Ubuntu Archive Automatic Signing Key
A error occurred during the signature verification. The repository is not updated and the previous index files will be used.
GPG error: http://extras.ubuntu.com oneiric Release: The following signatures were invalid:
BADSIG <..> Ubuntu Extras Archive Automatic Signing Key
Failed to fetch http://extras.ubuntu.com/ubuntu/dists/oneiric/Release
Some index files failed to download. They have been ignored, or old ones used instead.
Solution (well, workaround):
sudo rm /var/lib/apt/lists/* && sudo rm /var/lib/apt/lists/partial/* && sudo apt-get update
I took it from here