Here is logs on my Debian 9 system: Use the following command to list all keys configured for apt on your system. You will see the expired key like this.


Now, update the expired key by running the below command. Here 8C718D3B5072E1F5 is the key was expired on my system. You must change 8C718D3B5072E1F5 with the expired key on your system.

How to Solve an Expired Key  EXPKEYSIG  with Apt   TecAdmin - 91