Do You Believe in Tinker Bell? The Social Externalities of Trust

In the play Peter Pan, the fairy Tinker Bell is about to fade away and die because nobody believes in her any more, but is saved by the belief of the audience. This is a very old meme; the gods in Ancient Greece became less or more powerful depending on how many mortals sacrificed to them. On the face of it, this seems a democratic model of trust; it follows social consensus and crumbles when that is lost. However, the world of trust online is different. People trust CAs because they have to; Verisign and Comodo are dominant not because users trust them, but because merchants do. Two-sided market effects are bolstered by the hope that the large CAs are too big to fail. Proposed remedies from governments are little better; they declare themselves to be trusted and appoint favoured contractors as their bishops. Academics have proposed, for example in SPKI/SDSI, that trust should flow from individual users’ decisions; but how can that be aggregated in ways compatible with incentives? The final part of the problem is that current CAs are not just powerful but all-powerful: a compromise can let a hostile actor not just take over your session or impersonate your bank, but ‘upgrade’ the software on your computer. Omnipotent CAs with invisible failure modes are better seen as demons rather than as gods.