[Cryptography] tamper-evident crypto? (was: BULLRUN)

[Richard Clayton]

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In message <52291A36.9070608 at av8n.com>, John Denker <jsd at av8n.com>
writes

>To say the same thing the other way, I was always amazed that the
>Nazis were unable to figure out that their crypto was broken during 
>WWII.  There were experiments they could have done, such as sending
>out a few U-boats under strict radio silence and comparing their 
>longevity to others.

In fact the Nazis did have many suspicions that Enigma was compromised,
no more so (this from memory, the books with the fuller account are on a
shelf several thousand miles away from my current desk) than in the
Python incident where the Devonshire was sent to sink a German U-boat
refuelling boat ... and the Dorsetshire turned up at the same place by
chance and chipped in.

The subsequent German inquiry (two enemy ships appearing over the
horizon heading straight for your refuelling point in the middle of the
empty South Atlantic is deeply worrying) relied upon them reading our
North Atlantic convoy traffic (they were breaking Allied codes at that
point in the war) where they found no evidence of Enigma acquired
information being used to avoid U-boat movements. This was because their
inquiry happened to coincide with a short period during which we were
not reading their traffic!  The inquiry concluded that Enigma was not
broken (which was strictly correct at that moment) and it carried on
being used. Such are the random chances, good and bad, which occur in
the real world.

Of course there were improvements made to Enigma throughout the war both
to the hardware and also to operating procedures... it was harder to
break in 1945 than 1939.

>So my question is:  What would we have to do to produce /tamper-evident/
>data security?
>
>As a preliminary outline of the sort of thing I'm talking about, you
>could send an encrypted message that says 
>  "The people at 1313 Mockingbird Lane have an 
>   enormous kiddie porn studio in their basement."
>and then watch closely.  See how long it takes until they get raided.

you will have noted the requirement for some of the agencies who have
been given NSA material (such as telco metadata) to recreate it for the
benefit of their court cases ...

so you'd probably fail to observe any background activity that tested
whether this information was plausible or not (assuming that the NSA
considered this issue important enough to pursue); and then some chance
event would occur that caused someone from Law Enforcement (or even a
furnace maintenance technician) to have to look in the basement.

You'd be left saying "this proves it" and everyone else will be spending
their time commenting on whether your particular style of tinfoil hat
appeared sartorially suitable

- -- 
richard                                              Richard Clayton

They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety.         Benjamin Franklin

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