That works!
I tried it with jessie-backports as well, and I got:
root@kmac:~# apt update
Ign http://archive.debian.org jessie InRelease
Get:1 http://archive.debian.org jessie-backports
InRelease [166 kB]
W: There is no public
key available for the following key IDs:
8B48AD6246925553
E: Release file for http://archive.debian.org/debian/dists/jessie-backports/InRelease is expired (invalid
since 424d 14h 54min 36s). Updates for this repository will
not be applied.
Any
clues as to how to deal with that?