Wednesday, November 14, 2007

I'm Spartacus!

It's one of the great scenes in film, one, if you're like me, you've seen even though you haven't actually seen the film itself. After wreaking havoc against the Roman armies, Spartacus and his followers are finally defeated and captured. It's clear that Spartacus is destined to die a horrible death -- if only the Romans can figure out who he is.

To get his followers to rat Spartacus out, the Romans promise leniency to the person who will identify him. Instead, those assembled stand up one by one and shout "I'm Spartacus!"

That's anonymity in a nutshell. Spartacus might be anyone in the crowd. If the idea was to single Spartacus out, the Romans are no closer than they were to begin with. When you use an anonymizer, you're in much the same situation. It's not hard to establish that you might be the person who engaged in some particular interaction, but if the anonymizer is doing its work, there's no way to tell that it was you in particular and not some other user. Everyone's in the same boat.

This "everyone's in the same boat" factor lends anonymity a peculiar flavor. Looking at it from that angle, why would I use such a service if I didn't feel I had more to lose than the average user? This in turn will tend to throw the average user in with a fairly interesting crowd. I'm guessing here, of course. There aren't a lot of reliable usage statistics available.

I'm also guessing that most people using anonymizers aren't up to anything particularly nefarious and either value privacy on principle or just like the concept. How does that square with the previous point? Probably most people figure there's safety in numbers. Whatever those involved stand to lose, there is presumably a smaller chance they will lose it than if each operated alone.

"Sure, there may be some bad apples in the crowd, but they can't arrest all of us just to find them. And if they come for me, I can prove I'm not up to anything bad."

At which point it might be worth pointing out that in the film, Spartacus and his followers end up crucified.

(A side note: Not only do the Romans know no more than when they started, everyone now knows this. It's a neat case of common knowledge in action. By contrast, in the classic "question them separately" scenario, the person being interrogated has no idea who has said what to whom.)

(Another side note: The real Spartacus most likely died in battle. The whole scene is just a nice bit of dramatic license.)

[And finally ... this later post in the anonymity thread references LaTanya Sweeny's work in anonymity, specifically the notion of an "anonymity set", which formalizes the intuition that the more people you could be mistaken for, the more anonymous you are. Another later post references Alessandro Acquisti, Roger Dingledine and Paul Syverson's work on the economics of anonymity, drawing on the economic notion of a public good.]

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