Comment 1 for bug 1397462

I was able to verify the trust path entirely by hand, starting with the http://pl.archive.ubuntu.com/ubuntu/dists/precise/Release and http://pl.archive.ubuntu.com/ubuntu/dists/precise/Release.gpg files, downloading the precise amd64 lame package, and verifying that the sha256 for the downloaded package is 378656d3725af0541bf9ecc6439d43172b9f5fc8eb7b66ec5bf37b3211cfc842 as listed in the http://pl.archive.ubuntu.com/ubuntu/dists/precise/universe/binary-amd64/Packages.bz2 file.

Do you have the correct ubuntu-keyring package installed for your release?

Thanks