W: An 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 trusty Release: The following signatures couldn't be verified because the public key is not available:
NO_PUBKEY 16126D3A3E5C1192
W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/trusty/Release
So can any one please give me the right key for this one? , i google it but i didnt find a related thing