A PIN-entry method resilient against shoulder surfing

Abstract

Magnetic stripe cards are in common use for electronic payments and cash withdrawal. Reported incidents document that criminals easily pickpocket cards or skim them by swiping them through ad-ditional card readers. Personal identification numbers (PINs) are obtained by shoulder surfing, through the use of mirrors or con-cealed miniature cameras. Both elements, the PIN and the card, are generally sufficient to give the criminal full access to the vic-tim’s account. In this paper, we present alternative PIN entry meth-ods to which we refer as cognitive trapdoor games. These methods make it significantly harder for a criminal to obtain PINs even if he fully observes the entire input and output of a PIN entry proce-dure. We also introduce the idea of probabilistic cognitive trapdoor games, which offer resilience to shoulder surfing even if the crim-inal records a PIN entry procedure with a camera. We studied the security as well as the usability of our methods, the results of which we also present in the paper