We address the problem of shoulder-surfing attacks on authentication schemes by proposing IllusionPIN (IPIN), a PIN-based authentication method that operates on touchscreen devices. IPIN uses the technique of hybrid images to blend two keypads with different digit orderings in such a way, that the user who is close to the device is seeing one keypad to enter her PIN, while the attacker who is looking at the device from a bigger distance is seeing only the other keypad. The user’s keypad is shuffled in every authentication attempt, since the attacker may memorize the spatial arrangement of the pressed digits. To reason about the security of IPIN, we developed an algorithm which is based on human visual perception and estimates the minimum distance from which an observer is unable to interpret the keypad of the user. We tested our estimations with 84 simulated shoulder-surfing attacks from 21 different people. None of the attacks was successful against our estimations. In addition, we estimated the minimum distance from which a camera is unable to capture the visual information from the keypad of the user. Based on our analysis, it seems practically almost impossible for a surveillance camera to capture the PIN of a smartphone user when IPIN is in use.
@cite_27: 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 additional card readers. Personal identification numbers (PINs) are obtained by shoulder surfing, through the use of mirrors or concealed miniature cameras. Both elements, the PIN and the card, are generally sufficient to give the criminal full access to the victim's account. In this paper, we present alternative PIN entry methods 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 procedure. We also introduce the idea of probabilistic cognitive trapdoor games, which offer resilience to shoulder surfing even if the criminal 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.
@cite_37: A clamping circuit is provided between a differential signal generator (such as a differential amplifier or a comparator) and a control signal generator (such as an integrator and or a proportional amplifier) of an electronic closed loop control system for controlling an air-fuel ratio of the air-fuel mixture supplied to an internal combustion engine. The clamping circuit generates a signal whose maximum and maximum levels are symmetrical with respect to the half value of a potential of a d.c. power source provided for the clamping circuit.
The principle states that it has to be difficult to process the acquired visual information @cite_37 . For example, in one of the cognitive trapdoor games @cite_27 , the user is required to enter her PIN in the following way. The digits on the provided keypad are separated into two sets based on their color; half of them are black, and half of them are white. The user selects the set that the current digit of her PIN belongs to, and then the digits are reassigned to the two color sets. This procedure is repeated until the scheme is able to uniquely determine the correct digit by intersecting the selected sets. Then, the user proceeds to the next digit of her PIN. For an observer, it is extremely difficult, if not impossible, to successfully perform sequential intersections of sets to extract the correct PIN. However, such schemes are usually complex for the users too, with all the inevitable consequences for usability. In addition, recorded material or even repeated observation may reveal the authentication credentials, since all the useful information is observable.