I Googled and Googled and I just cannot find a solution to this problem:

sudo apt-get install <whatever>

Gives me:

WARNING: The following packages cannot be authenticated!

and

Install these packages without verification [y/N]?

I cannot find a decent solution.

The closest I got was to run:

sudo apt-get install debian-keyring debian-archive-keyring

But then, even thought, and against my good judgment I agreed to install the package without confirmation, I get:

(I replaced http with XXXX because of forum limitations).

Install these packages without verification [y/N]? y
Err XXXX://il.archive.ubuntu.com gutsy/universe debian-archive-keyring 2007.02.19-0.1
  404 Not Found
Err XXXX://il.archive.ubuntu.com gutsy/universe debian-keyring 2005.05.28
  404 Not Found
Failed to fetch XXXX://il.archive.ubuntu.com/ubuntu/pool/universe/d/debian-archive-keyring/debian-archive-keyring_2007.02.19-0.1_all.deb  404 Not Found
Failed to fetch XXXX://il.archive.ubuntu.com/ubuntu/pool/universe/d/debian-keyring/debian-keyring_2005.05.28_all.deb  404 Not Found
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Trying to run apt-get update also does not help: I get tons of "404 Not Found" errors.

Can someone please direct me to a good solution to this problem?

I cannot understand why this issue is not better documented.

There must be a simple solution which allows me to update my list of sources or whatever.