Click-through nonrepudiation

  One drawback of all our previous schemes is that while they enable a referrer to detect hit shaving, they do not arm the referrer with any evidence to present to a third party in the case of a dispute. So, in the extreme, the webmaster of site B can repudiate some or all referrals, including any acknowledgements it sent, and refuse to pay certain referrers. While these referrers are thus likely to leave B's click-through program, there is nothing that they can do to bring third-party leverage on the dispute. In this section we extend the technique in Section 4.1 to enable B to pass nonrepudiable acknowledgements to the referrer. Again, any failure of B to cooperate is quickly detectable by the referring site A (if combined with the techniques of Sections 2 and 3), and so the webmaster of A can immediately take action to avert a dispute, rather than wait until, say, the end of the month to find out that B will not pay her.