Handwritten Biometric Systems and Their Robustness Evaluation: a Survey

Handwriting has been a popular biometric modality for decades in the fields of forensics and security. In forensic analysis, criminal justice usually relies on a writer identifier in conjunction with an expert to determine the authorship of handwritten materials, for example, threat letters. While in security applications, handwriting verification systems are expected to verify whether a user is indeed the one as he or she claims. For security purposes, it is a relatively new idea to use handwriting for biometric key generation (BKG). BKG uses error-corrected feature values to generate cryptographic keys. It has stronger security requirements than verification systems in that it assumes the internal information to be exposed to adversaries while leaking no useful information about users’ biometric. In this paper, we first describe several techniques in the field of writer identification and verification since 1993 [1]. Then we explain the common ways of evaluating writer identification systems and writer verification systems. Next, we discuss several biometric cryptographic key generation schemes and techniques on how they are usually evaluated. Finally, we discuss some papers addressing the shortcomings in considering the robustness in the context of BKG systems. In these papers, the authors propose several new techniques in evaluating the robustness of the handwritten biometric systems and show that adversaries might be more destructive than they are usually reported in the literature.