President’s Spotlight—April 2021


Source: Carl R. McClary, MS, 2021-22 AAFS President

During the year, we will present monthly presidential spotlights for each section to highlight the latest significant research or improvements within its discipline(s). Examples include cutting-edge technology, standards, or methods that improve the practice. Alternatively, they may show a historical account/timeline of the discipline’s use of innovative technology or research. These are presented to inform all members of how each discipline is responding to the challenges of a modern forensic science world—our theme for the year. The first featured submission is from the Questioned Documents Section.


Source: Timothy Campbell, BSc

Electronic Signatures—Examining a Modern Tradition

What is a handwritten signature but a personal mark of acknowledgement? The signature has been used since time immemorial to authorize transactions, laws, revolutions, or personal correspondence. It is not commonly thought of as a biometric, but it is one of the oldest methods used to identify a person, including their intentions. Indeed, its examination has been a forensic discipline since the 19th century. As we gaze upon one-fifth of the 21st century in the mirror, the Digital Age has brought forth many changes and much work has been done in the past two decades. With the rise of the internet and the corresponding increase in electronic commerce, society needed a way to make trustworthy exchanges in the virtual world.

Since the United States and Canada are major trading partners, both countries enacted legislation to facilitate this in 2000. The Electronic Signatures in Global and National Commerce Act (ESIGN) in the United States and, in Canada, the Personal Information Protection and Electronic Documents Act (PIPEDA) both provide for electronic equivalents to paper-based documents and signatures. The specifications for capturing an electronic signature are laid out in the standard ISO/IEC 19794-7:2014.

Europe has likewise created the EU Regulation 910/2014 for Electronic IDentification, Authentication and trust Services (eIDAS). In October 2020, the European Network of Forensic Handwriting Experts (ENFHEX) released a procedure for the examination of Digitally Captured Signatures (DCS) as Appendix 5 to their Best Practice Manual for the Forensic Examination of Handwriting.

To some people, electronic signature can mean a static JPG image of a scanned ink signature that is digitally added to a contract. There is almost no security in this approach, however, and so it defeats the intended purpose since it can be reused repeatedly without changing. Likewise, an electronic “signature” that is only a cryptographic date and time stamp, without the physical act of signing, is not habitual and can only signal that a button was pressed but not who was operating the computer. There is no way to prove who “signed” the contract. The inherent security of an ink signature resides in the dynamic habitual writing action of the signer and its strength lies in its lack of identical reproduction.

A Forensic Document Examiner (FDE) analyzes the skill, design, and fluency of execution when comparing known and questioned signatures. An inked line can reveal not just a two-dimensional construction, but also the pressure that is imparted on the pen compressing the paper fibers in the vertical dimension. Fortunately, a DCS records this same dynamic information.

To best capture a DCS, a stylus that can detect many pressure levels is used to sign on a tablet resulting in X, Y, and pressure coordinates for every sampling point. The additional benefit to a DCS is the fourth dimension of time. Previously, speed and acceleration could only be inferred without directly witnessing the signature’s execution. Research has repeatedly shown that when one person is attempting to accurately simulate another’s signature, it is done slowly with concentration, whereas a naturally written signature is generally a quick and habitual action. Conversely, if the simulation is quickly written, the design deviates further from the genuine.

When an electromagnetic active stylus technology is used, the invisible movements of the pen in the air are additionally recorded. This non-contact of the stylus above the pad’s surface is captured and shows habitual movement between words, disconnected forms, and start/end motions as well (see Figures 1 and 2). So, there is now an additional feature that the FDE can use that was previously absent, adding another valuable tool to the examiner’s toolbox.

FIGURE 1: A 2D digitally captured signature. The gray lines are the visible portion and the red lines show the airstrokes above the surface of the pad.

 

FIGURE 2: A 3D representation of a digitally captured signature. Each circle is a single sampling point of the written line. X is horizontal and Y is the vertical dimension on the pad, while Z is the pressure applied to the pen. Red circles are the heaviest pressure and blue circles are the airstrokes.

 

Software has been developed to analyze electronic signatures, but without standardization between manufacturers, considerations must be made regarding not just how DCS data is recorded, but also the nature of the data itself since device sensitivity can vary greatly. Advanced research by FDEs is currently underway to normalize this diverse information to allow comparisons between signatures captured on different hardware, such as when a bank makes use of one manufacturer’s device, but the investigator acquires specimens on another.

It is an exciting time to be a Forensic Document Examiner—always a foot in the past, but ever looking forward to the future.