We present the adaptation of our model for the validation of key distribution and authentication protocols to address specific needs of protocols for electronic commerce. The two models defer in both the threat scenario and in the formalization. We demonstrate the suitability of our adaptation by analyzing a specific version of the Internet Billing Server protocol introduced by Carnegie Mellon University. Our analysis shows that, while the security properties a key distribution or authentication protocol shall provide are well understood, it is often not clear what properties an electronic commerce protocol can or shall provide. Our methods rely on automatic theorem proving tools. Specifically, we used “Otter”, an automatic theorem proving software developed at Argonne National Laboratories.