Apt-get : NO_PUBKEY / GPG error in debian

In computers based on a Debian operating system that uses Linux kernel, error messages may come up like ‘NO_PUBKEY‘.This happens while using the Apt-Get command line tool and this error is associated with the tool’s update feature. The new feature in the Apt-Get package management tool guarantees the authenticity of the server before updating the Debian OS. That’s why the error ‘NO_PUBKEY‘ pops up. This problem can be solved by keying in the appropriate commands.

[Debian] Apt-get : NO_PUBKEY / GPG error

IssuWhen updating the Debian based system, apt-get may display an error message like: 

W: GPG error: ftp://ftp.debian.org/ testing Release:       
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 010908312D230C5F      

W: There is no public key available for the following key IDs:      
010908312D230C5F

This is a new feature of the apt-get system that guarantees the authenticity of servers for updating Debian.

Solution
Simply type the following commands, taking care to replace the number below with that of the key that was displayed in the error message:

gpg --keyserver pgpkeys.mit.edu --recv-key  010908312D230C5F      
gpg -a --export 010908312D230C5F | sudo apt-key add -