Usability and Security of Out-Of-Band Channels in Secure Device Pairing Protocols

Initiating and bootstrapping secure, yet low-cost, ad-hoc transactions is an important challenge that needs to be overcome if the promise of mobile and pervasive computing is to be fulfilled. For example, mobile payment applications would benefit from the ability to pair devices securely without resorting to conventional mechanisms such as shared secrets, a Public Key Infrastructure (PKI), or trusted third parties. A number of methods have been proposed for doing this based on the use of a secondary out-of-band (OOB) channel that either authenticates information passed over the normal communication channel or otherwise establishes an authenticated shared secret which can be used for subsequent secure communication. A key element of the success of these methods is dependent on the performance and effectiveness of the OOB channel, which usually depends on people performing certain critical tasks correctly.

I will present the results of a comparative usability study on methods that propose using humans to implement the OOB channel and argue that most of these proposals fail to take into account factors that may seriously harm the security and usability of a protocol.

This is joint work with Ivan Flechais and A.W. Roscoe