There seems to be a problem with your archive key:
elgar:~# apt-get update
Hit http://ftp.de.debian.org unstable InRelease
Get:1 http://www.freewrt.org cross InRelease [13.2 kB]
Hit http://ftp.debian-ports.org unstable InRelease
Hit http://ftp.debian-ports.org unreleased InRelease
Hit http://ftp.de.debian.org unstable/main Sources
Hit http://ftp.debian-ports.org unstable/main m68k Packages
Hit http://www.freewrt.org cross/main m68k Packages
Ign http://ftp.debian-ports.org unstable/main Translation-en
Ign http://www.freewrt.org cross/main Translation-en
Hit http://ftp.debian-ports.org unreleased/main m68k Packages
Ign http://ftp.debian-ports.org unreleased/main Translation-en
Fetched 13.2 kB in 14s (882 B/s)
Reading package lists... Done
elgar:~# debootstrap --variant=buildd
--include=apt,wtf-debian-keyring,debian-ports-archive-keyring sid
rg/chroots/buildd/unstable/ http://www.freewrt.org/~tg/dp
I: Retrieving InRelease
I: Checking Release signature
E: Release signed by unknown key (key id F7E974E9405422DD)
elgar:~# keyid=F7E974E9405422DD ; gpg --keyserver subkeys.pgp.net
--recv-key $keyid ; gpg --armor --expo
$keyid | apt-key add -
gpg: requesting key 405422DD from hkp server subkeys.pgp.net
gpg: key 405422DD: public key "Thorsten Glaser (Package signing key
for wtf debs) <tg@freewrt.org>" impo
ed
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
OK
elgar:~# debootstrap --variant=buildd
--include=apt,wtf-debian-keyring,debian-ports-archive-keyring sid
rg/chroots/buildd/unstable/ http://www.freewrt.org/~tg/dp
I: Retrieving InRelease
I: Checking Release signature
E: Release signed by unknown key (key id F7E974E9405422DD)