Keystroke Recognition

Keystroke recognition is a behavioral biometric which authenticates (verifies the claimed identity) or identifies an individual (recognizes a valid user) based on their unique typing rhythm. Unlike physiological biometrics, such as fingerprint or iris, where specialized sensors are necessary to collect data, keystroke biometrics utilizes off-theshelf physical keyboards or virtual keyboards in smartphones or PDAs. Thus, keystroke recognition offers a low-cost authentication and is easily deployed in a variety of scenarios. Two events constitute a keystroke event: key down and key up. The key down occurs when the typist presses a key. The key up is associated with the event that occurs when the pressed key is released. Using these two events, a set of intra-key and inter-key features commonly called hold times, delay times and key down-key down times can be extracted. Hold times constitute the finite amount of time a particular key is pressed. Delay times constitute the latency between the release of the current key and the pressing of the next key. Delay times may be negative given that individuals can press the next key prior to releasing the current key. Finally, key down-key down time represents the finite amount of time between successive key down events. While other keystroke events can be extracted (such as key pressure and location of a particular Shift key and special keys such as Alt, Ctrl, etc.), these features are not commonly used as their collection from commercially available keyboards is not straightforward. Keystroke data can come either from a predetermined body of text (fixed-text analysis) or from any unrestricted text (free-text analysis). Fixed-text analysis from strings similar to passwords can be used for one-time authentication. On the other hand, free-text analysis can allow more complex usage scenarios. Given sufficient corpus of user activity, it can support continual user authentication and ensure that an impostor has not gained control of the device. Similar to other behavioral biometrics, keystroke recognition exhibits a phase in which the individual learns the motor skills required to enter text entries. For the fixed text, habituation phase includes the cognitive activity related to string memorization as well as the adaptation of motor