[ixdchtom] Unwritable files in the approx cache

Symptom: aptitude full-upgrade says "Untrusted packages could compromise your system's security."

There is no Release.gpg in /var/lib/apt/lists

aptitude update reports "Ign" when attempting to download Release.gpg

I was using the "approx" package cache proxy. Go to the approx server and see that in /var/cache/approx "Release.gpg" is a zero-byte file with 0000 permissions. This is Debian bug 655986.

find . -perm 0000 -type f -exec rm '{}' \;

and the problem is solved.