News Flash: Clipper Bug?

[Peter Wayner]

>
>My friend Matt Blaze at Bell Labs showed that you can forge LEAFs on
>Tessera cards so that you can use Skipjack without anyone being able
>to get the key you are using. Its a slick piece of work -- slick
>enough that it made the front page of today's New York Times. I'm not
>sure how practical it is, but its extraordinarily noteworthy.

Please explain how to forge the LEAFs. I presume that this doesn't 
involve super-encryption.