On the security and usability of dual credential authentication in UK online banking

This paper presents the results of a security and usability review of the authentication implementations used by more than 10 UK banks. Our focus is on their use of dual text credentials that combine two passwords, PINs, or challenge questions (and some “partial selection” variations). We model the authentication protocols based upon several deployment choices, such as the credential rules, and use the model to compare the security and usability properties of the implementations. Our results indicate some variation and inconsistency across the UK banking industry, from which we offer some suggestions for improved authentication protocol design.