Bug in FPGA?

Bitstreams can always be modified. What this attack enables it to read out from the device (albeit very slowly) in its unencrypted form

This potentially allowing copying of intellectual property and perhaps reverse-engineering, although I suspect reverse engineering a bitstream to anything understandable would be harder than decompiling source code. No fun at all!

Yes, but, the attack requires close and invasive physical access to the target.

As X said, if the attacker has close access to the target you have bigger problems than breaking bit stream encryption.

It does support my unproven law of all security systems - they can be broken - always !

MK