In the past I’ve tried to hack the release file with sed, this works better. Namely my local repo’s packages files were not in the Release file, and apt was getting upset about that now that I’m using signatures (SecureApt).

Somewhere make an apt-release.conf (copied and modified from here):

APT::FTPArchive::Release::Codename “etch”;
APT::FTPArchive::Release::Origin “localhost.example.com”;
APT::FTPArchive::Release::Components “main”;
APT::FTPArchive::Release::Label “Local Debian Repository”;
APT::FTPArchive::Release::Architectures “i386 amd64”;
APT::FTPArchive::Release::Suite “stable”;

The use apt-ftparchive to create the release file:

apt-ftparchive release -c /path/to/apt-release.conf \
/path/to/etch \
> /path/to/etch/Release

Then sign it: (you do have a local key and all that jazz, right?)

gpg -b /path/to/etch/Release
mv /path/to/etch/Release.sig /path/to/etch/Release.gpg

Should work fine for ubuntu too.