There’s an interesting new paper out of Stanford and NYU, about a system called “PrivAds” that tries to provide behavioral advertising on web sites, without having a central server gather detailed information about user behavior. If the paper’s approach turns out to work, it could have an important impact on the debate about online advertising and privacy.
Advertisers have obvious reasons to show you ads that match your interests. You can benefit too, if you see ads that are relevant to your needs, rather than ones you don’t care about. The problem, as I argued in my Congressional testimony, comes when sites track your activities, and build up detailed files on you, in order to do the targeting.
PrivAds tries to solve this problem by providing behavioral advertising without having any server track you. The idea is that your own browser will track you, and analyze your online activities to build a model of your interests, but your browser won’t reveal this information to anyone else. When a site wants to show you an interest-based ad, your browser will choose the ad from a portfolio of ads offered by the ad service.
The tricky part is how your browser can do all of this without incidentally leaking your activities to the server. For example, the ad agency needs to know how many times each ad was shown. How can you report this to the ad service without revealing which ads you saw? PrivAds offers a solution based on fancy cryptography, so that the ad agency can aggregate reports from many users, without being able to see the users’ individual reports. Similarly, every interaction between your browser and the outside must be engineered carefully so that behavioral advertising can occur but the browser doesn’t telegraph your actions.
It’s not clear at this point whether the PrivAds approach will work, in the sense of protecting privacy without reducing the effectiveness of ad targeting. It’s clear, though, that PrivAds is asking an important question.
If the PrivAds approach succeeds, demonstrating that behavioral advertising does not require tracking, this doesn’t mean that companies will stop wanting to track you — but it does mean that they won’t be able to use advertising as an excuse to track you.