...

...not be able to decrypt the communications, but they still get your ID. "your ID"? You mean your phone's ID. Goodness gracious, if you were a criminal, you wouldn't go out and steal someone else's Clipper phone, would you? Let's not get too high tech here, just because we have the ability.

Or you could just steal someone else's LEAF, by keeping a copy of it, and use that for spoofing. Then you could have a valid IV too...

The IV is session-dependent, and both ends generate it. We don't know where in the LEAF the chipid is, but if they use a fixed format and don't do a key-dependent permutation of the LEAF bits, it shouldn't be hard to figure out (unless the checksum comes first and they use a block-chaining encryption, in which case you know you lose.) That would let you create rogue LEAFs with known users' chipids, which would be interesting - does anyone want to make 65536 calls to clipperphone@whitehouse.gov :-) ? (Yeah, it's not quite that simple.) (If you do need a lot of data, cellphones are a good source, since the cellphone operators' chipids are likely to be wellknown, though rapidly tapped.) Paranoid-speculation-mode: Of course, if you can forge LEAFs with their chipid, they can forge LEAFs with yours, which could be used to manufacture interesting evidence.... Bill