Using digital signatures

  If there is a well-known public key for authenticating site B via digital signatures (e.g., [RSA78]), then one approach for B to provide nonrepudiable acknowledgements to A is for B to pass a digital signature to A as part of the click-through protocol. This signature could sign a tuple containing the IP address of the user, the time and date of the referral, the page to which the referral was made, and the referring page. A can then retain this signed tuple for use in a dispute with B later, if necessary. Like in Section 4.1, B can create this signature in serve.cgi and include it within pageB.html, to be passed as an argument to a CGI script on site A by the user's browser when pageB.html loads.

A drawback of this approach is that it requires B to compute a digital signature per referral, which must be done on its critical path for servicing the user's request. Because digital signatures, particularly RSA signatures [RSA78], tend to be computationally intensive, the additional computational load imposed by these signatures may be prohibitive if B is a very busy server.