Deniability

[Robert J. Hansen]

On Tue, 22 Mar 2011 14:37:16 +0000, Jerome Baum <jerome at jeromebaum.com>
wrote:
> Part thought  experiment, part practical  usage. I was thinking  more in
> terms of  a German court  asking me to  turn over evidence --  but then,
> there still might  be a lead pipe involved outside the  scope of a court
> case.

The amount of lead pipe a court can swing at you in many ways exceeds the
amount of lead pipe organized crime can throw at you.  Let's do this
thought experiment again, but this time with a zealous prosecutor who is
sincerely doing what she believes to be her job.  Further, assume you have
a deniable cryptosystem: you can't deny you received the message, but you
can neither prove nor disprove having the ability to read it.

Alice and Bob are plotting a heinous crime -- terrorism, narcotics
trafficking, child exploitation, whatever.  They know their communications
are being monitored and they are using a deniable cryptosystem.  They have
also made plans for what to do if either of them ever gets arrested: they
will do their best to incriminate someone else, so that the surviving
conspirator will have time to go to ground and continue their plans of
skulduggery.

Alice gets picked up by the cops.  Paula Prosecutor interrogates her. 
Alice says, "my co-conspirator was Jerome Baum."  This is a lie, of course,
but all Alice needs to do is give the police someone to chase after for a
few days while Bob goes into hiding.  Alice has sent you some innocuous
messages through a deniable system in order to make you a good candidate
for being made their patsy.

Paula hauls you in.  "Tell us all about your role in $nefarious_crime." 
You tell Paula that you don't have any role in it.  "Prove it.  Show me
those messages."  Um... well, you see, it's like this: it's a deniable
system, which means there's no way I can prove or disprove ever having the
ability to read it.  

Paula is *not* going to say, "oh, well then, I guess I'm out of luck." 
No, Paula is going to assume you're playing games and Paula's going to
start playing hardball the way only a government prosecutor can.  "Okay. 
In that case, we're going to have a forensic accountant crawl over your
bank accounts and tax records, have a squad of detectives crawling over
your personal life, we're going to talk to the media and name you as a
subject of the investigation, and you're going to be racking up a thousand
euros a day of legal fees.  But you can make it stop any time.  Just show
me those messages."

And when you scream, *I CAN'T DO WHAT YOU'RE ASKING ME TO DO!*, Paula will
just look at you and say, "That's not my problem."

Prosecutors play hardball.  I would much rather face a gangster in an
alleyway who wanted to get my secrets via a lead pipe than I would ever
want to face a government prosecutor.  I have better odds with the
gangster.