$ sudo DIST=sid ARCH=i386 pbuilder create
[sudo] password for u:
I: Distribution is unstable.
I: Current time: Mon Mar 17 09:37:53 EDT 2014
I: pbuilder-time-stamp: 1395063473
I: Building the build environment
I: running debootstrap
/usr/sbin/debootstrap
I: Retrieving Release
I: Retrieving Release.gpg
I: Checking Release signature
E: Release signed by unknown key (key id 8B48AD6246925553)
E: debootstrap failed
W: Aborting with an error
I: cleaning the build env
I: removing directory /var/cache/pbuilder/build//8688 and its subdirectories

sudo apt-get install debian-archive-keyring

sudo DIST=sid ARCH=i386 pbuilder create --debootstrapopts
--keyring=/usr/share/keyrings/debian-archive-keyring.gpg