Random Privacy

[Eric Cordian]

Tim wrote:

> Not a new idea. Ted Nelson (IIRC) wrote about using coin flips to 
> randomize AIDS poll questions. ("Have you engaged in unprotected sex?" 
> Flip a coin and XOR it with your actual answer.) I remember talking to 
> Eric Hughes, Phil Salin, and others around 1990-91 about this.

[snip]

> The idea is that the
> pollee XORs his answer with a random bit. His answer then doesn't
> _implicate_ him, but overall statistics can still be deduced from a
> large enough sample. 

Uh, excuse me?!

I can see how such an idea works if you add a random variable with a known
mean to the data.  A researcher could do this before storing the data, in
order to protect the confidentiality of individual respondents, and still
be able to compute aggregate statistics.

However, if you XOR a bit with a random bit, you have something equally
likely to be in either state.  Even a large collection of yes/no responses
XORed with random bits is indistinguishable from random data.

So I am afraid I must give the prior message my coveted "Silliest Thing
Said On the Internet This Week" award.  <Chortle>

-- 
Eric Michael Cordian 0+
O:.T:.O:. Mathematical Munitions Division
"Do What Thou Wilt Shall Be The Whole Of The Law"