sudo apt-get update

Reading package lists... Done
W: GPG error: https://download.01.org/gfx/ubuntu/17.04/main zesty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 611B903CAB97EA77
W: The repository 'https://download.01.org/gfx/ubuntu/17.04/main zesty InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.