Security and usability engineering with particular attention to electronic mail

Support for strong electronic mail security is widely available yet only few communicants appear to make use of these features. Apparently, the operational overhead of security outweighs its perceived benefits. Towards increasing the benefits versus overhead ratio we follow an approach that considers security and usability tradeoffs from the outset. We separate key exchange from binding keys to identities. The best effort key exchange and key maintainance scheme that we devise operates transparently for the user. We also describe complementary visualization and interaction techniques that communicate the security state of sent and received mail to users in a non-intrusive fashion. Towards a practical assessment of the overheads of binding keys to identities, we conducted a quantitative analysis of users’ mail behavior of which we present the results. We argue that for individual non-commercial users, out-of-band verification of keys could be more economical than building trust in public key certificates issued by third parties.