The New Mykotronix phones...

Okay, let's suppose that the NSA/NIST/Mykotronix Registered
Key system becomes standard and I'm able to buy such a system
from my local radio shack. Every phone comes with a built in
chip and the government has the key to every phone call. 
I go and buy a phone and dutifully register the key. 

What's to prevent me from swapping phones with a friend or 
buying a used phone at a garage sale? Whooa. The secret registered
keys just became unsynchronized. When the government comes 
to listen in, they only receive gobbledly-gook because the 
secret key registered under my name isn't the right one. 

That leads me to conjecture that:

1) The system isn't that secure. There are just two master keys
that work for all the phones in the country. The part about
registering your keys is just bogus. 

or 

2) The system is vulnerable to simple phone swapping attacks
like this. Criminals will quickly figure this out and go to
town.

In either case, I think we need to look at this a bit deeper.

-Peter Wayner

Peter Wayner says:

> What's to prevent me from swapping phones with a friend or 
> buying a used phone at a garage sale? Whooa. The secret registered
> keys just became unsynchronized. When the government comes 
> to listen in, they only receive gobbledly-gook because the 
> secret key registered under my name isn't the right one. 

Perhaps you can deduce which chip is doing the encryption by
identification data transmitted by the chip down the line -- they
might identify themselves, making it impossible for you to avoid
having them figure out which pair of keys registered with the Ministry
of Truth and the Ministry of Love are to be used to listen in on your
conversation. After all, they keys are registered by the
manufacturer...

Perry

PS We all remember the Ministry of Love and the Ministry of Truth,
don't we? This proposal was, of course, created by a group spun off
from the Ministry of Peace, a.k.a. No Such Agency.

Date: Fri, 16 Apr 1993 14:54 CDT
    From: Peter Wayner <pcw@access.digex.com>

    Okay, let's suppose that the NSA/NIST/Mykotronix Registered
    Key system becomes standard and I'm able to buy such a system
    from my local radio shack. Every phone comes with a built in
    chip and the government has the key to every phone call. 
    I go and buy a phone and dutifully register the key. 

    What's to prevent me from swapping phones with a friend or 
    buying a used phone at a garage sale? Whooa. The secret registered
    keys just became unsynchronized. When the government comes 
    to listen in, they only receive gobbledly-gook because the 
    secret key registered under my name isn't the right one. 

Knowing nothing except what I've read on the net today, I suppose that
while scrambling the phone conversation the chip inserts in the data
stream some ID (perhaps once per second) to tell the govt. which chip is
doing the scrambling.  This would allow multiple trapdoor keys (as
claimed) and also there would be no need for phone users to register.
The chip might also insert the number of the phone originating and/or
receiving the call, though presumably the wiretappers would already know
this.

-- Peter Meyer