Security and Usability

Chapter Sixteen. Making the Impossible Easy: Usable PKI

Dirk Balfanz, Glenn Durfee, and D. K. Smetters

THE WIDESPREAD PERCEPTION THAT USABILITY AND SECURITY ARE AT ODDS WITH ONE ANOTHER OFTEN leads systems designers to shun powerful security technologies. A quintessential example is provided by public key infrastructure (PKI) technology: despite the high degree of security PKI technology can provide, designers frequently avoid this technology because of its notoriously complex deployment and the incomprehensibility of such an infrastructure to end users.

This chapter explains how by designing usability in from the start, one can make PKI-based systems easy to deploy and use. The resulting systems, however, are not large, general-purpose infrastructures, but PKIs that are small, dedicated, easy to set up, and application specific. We refer to these as instant PKIs (iPKIs). Several case studies illustrate interaction paradigms for building such usable, secure iPKIs.

Public Key Infrastructures

Before the invention of public key cryptography, methods for secure digital communications were all but unavailable to mainstream computer users. The reason for this was the difficult problem of key distribution : for Alice to send a secure message to Bob, they first would have to agree on a shared secret (e.g., a key or password). The only way to do this would be for Alice (or Bob, or a third party) to generate such a key and then deliver that key to Bob (or Alice, or both). While in transit, the ...