Usability and security of out-of-band channels in secure device pairing protocols

Abstract

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.In this paper, we 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. Our work builds on previous research in the usability of pairing methods and the accompanying recommendations for designing user interfaces that minimise human mistakes. Our findings show that the traditional methods of comparing and typing short strings into mobile devices are still preferable despite claims that new methods are more usable and secure, and that user interface design alone is not sufficient in mitigating human mistakes in OOB channels.

Secure and Usable Out-Of-Band Channels for Ad Hoc Mobile Device Interactions

“…The aim of the study was not only to evaluate how usable the methods are but also compare our results with those previous studies. To this regard, we designed our laboratory experiment similarly to [7,8,9].…”

“…Currently proposed OOB channels force one to choose between security and usability. Compare and confirm has been found both a usable and preferred method but also susceptible to security failures [7,8,9]. Other methods such as timing and auxiliary device methods are also susceptible to security failures though they do not offer the same level of usability as compare and confirm.…”

“…Even vigilant users may be distracted, accidentally press a wrong button, or merely miss the comparison. In fact, in their study of pairing methods, Kainda et al [7] reported that some participants were concerned that with compare and confirm it was easy for a security failure to occur because the method did not force them to compare accurately.…”

Mobile Electronic Identity: Securing Payment on Mobile Phones

“…In any case we believe that the use of HISPs in payments should usually be backed up by secondary security as discussed later. 6 digits happens to be the number used in the experiments reported in [35]. 7 A user may simply keep pressing the OK button regardless of what displayed on the mobile phone.…”

“…7 A user may simply keep pressing the OK button regardless of what displayed on the mobile phone. 8 [35] examines ways of performing this comparison and conclusively demonstrates that for security the best approach is for the customer to type the digits of the merchant's digest value into mobile phone, which then compares the two.…”