As said, please post the terminal output. A manpage reference is not very useful, the error code is
That said, it sounds like your missing some keys. We will know for sure when you post the code. On the off chance I am right, run these lines in terminal (one line at a time).
sudo apt clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt update
And welcome to our forums