You can get the attestation functionality to work in b4 by installing patatt which is now in unstable.
See related request to have a dependency in b4 for patatt: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1000250 -- Anuradha
- Bug#999562: b4: Fails to attest without additional depen... Uwe Kleine-König
- Bug#999562: Patatt is now in unstable Anuradha Weeraman
