Modification of the relative distance for free text keystroke authentication

Unlike many other biometrics, keystroke authentication does not require any additional hardware. Pressing time of keystrokes is the main source of information and can be extracted continuously during an ongoing session, even after the login time. The relative distance, which is a common measure in this field, is defined based on the relative typing speed of different digraphs. To improve the accuracy of authentication based on this measure, we propose to assign a weight to each digraph depending on its typing speed reliability; this expands the effectiveness of reliable digraphs in distance computation. The proposed method is tested on 315 typing samples of 21 users. The results show that our method will improve the accuracy in both forms of FAR and FRR measures.