Comment 2 for bug 620576

apt does not depend on gpg so should be happy to operate without keys. Nor does it depend on ubuntu-keyring.

/etc/apt/trusted.gpg normally seems to be generated by ubutnu-keyring postinst.

So I''m not sure what the purpose of the /usr/share/apt/ubuntu-archive.gpg is/was. Is it now superceded?

The practical problem where this bug is an issue is chreating a minimal rootfs or chroot where ubuntu-keyring is not installed.