Hello Shashank, this error appears when you dont have the pub_key for your Update Tool package, i suggest to download it, please try:
wget https://download.01.org/gfx/RPM-GPG-GROUP-KEY-ilg
sudo apt-key add RPM-GPG-GROUP-KEY-ilg
gpg error : no pub_key
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01 Staff (not verified)
01 Staff (not verified)
Oct 06, 2017 - 10:21am
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.
ive tried installing the intel graphic driver update tool n i get this error
please help