Can We Build a Distributed Trust Network?

Mathew Ingram posted an interview with Craig Newmark (the Craig of craigslist fame) in which the latter argued that what the web needs is a “distributed trust network” to manage our online reputations. As it happens, this is an idea that has occupied me for several years. So I figured it was about time that I shared my thoughts on the subject.

When we think of how trust works online, two of the most prominent examples are Google’s PageRank measure and eBay’s feedback scores. But neither of these measures addresses what I think Craig has in mind. PageRank is a great way of using citation analysis to determine the most authoritative citations, but the trust in a page should consider its out-links (i.e., can we trust the page not to point us to untrustworthy ones?) and not just its in-links. eBay’s feedback scores have a different problem: they count positive and negative ratings without considering the social network of buyers and sellers–and approach that is vulnerable to fraud through shill ratings. Incidentally,LinkedIn recommendations have a similar weakness if viewed in strictly quantitative terms…

But I digress. Propagation of trust does seem like the perfect application to build on top of social networks. Consider any problem that involves getting advice to inform a decision. If we regularly solicit advice from our first-degree connections, then we should be able to learn over time whose advice we can trust. We can then vouch for these connections, which offers the connections who trust us a basis for trusting their second-degree connections through us. And so forth through our social network. Of course, trust is not irrevocable: loss of trust should propagate similarly.

I’ve talked about this problem with two of the leading experts on social networks, Jon Kleinberg and Prabhakar Raghavan, and as far as I know no one has built a system along these principles. In economic terms, I envision a system where a person’s reputation truly is his or her coin. One person might think of bribing one another to exploit the latter’s established reputation, but a rational person with a strong reputation would demand an exorbitant bribe to put that reputation at risk.

Of course, a lot of information would have to propagate throughout the social network–and be stored–for this system to work. Regardless of how the information is abstracted, such a reputation index would raise thorny privacy issues. Nonetheless, I don’t know if we can build a reputation system that is entirely privacy-preserving–since reputation is an inherently public mechanism. In addition, any such system would have to consider the implications of defamation laws. These are some major hurdles!

Nonetheless, I agree wholeheartedly with Craig that a distributed trust network could be “the killingest of killer apps”. I just hope we can find a way to build and use it!

Note: Chris Rines suggested I look at Advogato’s Trust Metric, and a quick investigation led me to the Wikipedia entry for trust metric. Looks like I have some homework to do!

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