The latest upload by BOOSTER (or maybe, someone else?) suggests that 2.71 Firmware has been decrypted.
It weighs in at about 6.7MB.
Haven't tried it yet, and there's no readme included in the archive, but the directories are there.
EDIT: Ok, so I see Dark_AleX has a thread about decrypting 2.60/2.70 or something, I hope this isn't the same