live-build/debootstrap for Raspbian image cannot verify releases

I am trying to use live-build 5.0 on Debian squeeze to build a Raspbian live image. The "sudo lb build" command fails at the step:

I: Checking Release signature
E: Release signed by unknown key (key id 9165938D90FDDD2E)

The contents of "auto/config" are here: https://gist.github.com/detly/54e07c56f68b9d2ed066

I have tried:

- installing the Raspbian repo key using "sudo apt-key add"
- manually installing raspbian-archive-keyring_20120528.2_all.deb
- adding the Raspbian key to config/archives/raspbian.key.(binary|chroot) (ie. from /usr/share/keyrings/raspbian-archive-keyring.gpg)
- prepending DEBOOTSTRAP_OPTIONS="--keyring=/usr/share/keyrings/raspbian-archive-keyring.gpg" to "lb config" and "lb build"
- same, but for "/etc/apt/trusted.gpg"

None of it worked. What do I need to do to tell debootstrap to use a different keyring? (I don't really want to tell it not to verify anything at all...)

I realise Raspbian questions might not be strictly on topic, and I apologise if that's the case, but I feel like it's a simple question of how debootstrap is verifying its downloads, and this seems like a good place to ask about that.

Cheers,
Jason Heeris