How to fix OwnCloud Key Expired Error

If you get an error like W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://download.opensuse.org Release: The following signatures were invalid: KEYEXPIRED 1397815516 W: Failed to fetch http://download.opensuse.org/repositories/isv:/ownCloud:/community/xUbuntu_12.04/Release W: Some index files failed to download. Read more…