Intel graphic ppa error after apt-get update

how can i ignore this message?

W: GPG error: https://download.01.org/gfx/ubuntu/16.04/main xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 56A3DEF863961D39
W: The repository 'https://download.01.org/gfx/ubuntu/16.04/main xenial 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.

Its from intel update gfx.

I managed to solve it for Ubuntu 16.04 and 16.10 by running following commands

wget --no-check-certificate https://download.01.org/gfx/RPM-GPG-GROUP-KEY-ilg -O - | sudo apt-key add -
wget --no-check-certificate https://download.01.org/gfx/RPM-GPG-KEY-ilg -O - | sudo apt-key add -
wget --no-check-certificate https://download.01.org/gfx/RPM-GPG-KEY-ilg-2 -O - | sudo apt-key add -
wget --no-check-certificate https://download.01.org/gfx/RPM-GPG-KEY-ilg-3 -O - | sudo apt-key add -
wget --no-check-certificate https://download.01.org/gfx/RPM-GPG-KEY-ilg-4 -O - | sudo apt-key add -

Try to add the key (replace 56A3DEF863961D39 with your missing key):

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 56A3DEF863961D39
sudo apt-get update

References and further reading:

• GPG error: The following signatures couldn't be verified because the public key is not available
• How do I fix the GPG error "NO_PUBKEY"?
• Invalid filename extension in apt sources.list

Open a terminal & run

wget --no-check-certificate https://download.01.org/gfx/RPM-GPG-KEY-ilg-4 -O - | sudo apt-key add -

This will allow updates, you'll get the weak digest algorithm warning but it's just a warning at the moment. (in 16.04