On Freitag, 13. Januar 2023 18:18:21 CET tor wrote:

the backport of obfs4proxy seems to be unsigned

Backports has been an official Debian service since ~2010 and the packages are signed with the debian-archive-keyring.

I needed to use: deb [trusted=yes] http://deb.debian.org/debian bullseye-backports main

No, then you have configured something wrong, or you don't have a Debian system.

Raspbian != Debian and, like Ubuntu, must first import the debian-archive- keyring: https://packages.debian.org/bullseye/debian-archive-keyring