## 5 Methodology, Experiment Design, and Data Analysis
### Experiment
#### 5.2.3 Procedure and Discussion  
Subjects began by signing a consent form that stated that they were asked to enroll in a fingerprint-based biometric system and then verified their identity by providing their fingerprint. This step was important in testing the capability of the system in matching fingerprints correctly. Participants were then requested to create a fake fingerprint for themselves and to try to dupe the system. Some Play-Doh was given to each participant, and they were taught how to reconstruct their fingerprint from a latent image remaining on a glass surface obtained when they enrolled. Each participant was then asked to place the fake fingerprint on the sensor. The fake fingerprints were then randomly assigned to other participants to try and fool the system. In this case, a participant enrolls, creates a fake fingerprint, and tests it. If it is successful in deceiving a traditional fingerprint-based biometric system, we assign the fake fingerprint to an attacker to try to fool the system by using the assigned fake fingerprint. This is important in evaluating the MFAS functioning between subjects, even when using the same fake fingerprint.  
We then informed each participant of the privacy implications if one's fingerprint details are revealed, since anyone can then reconstruct a fake fingerprint based on theirs and then impersonate them using the fake fingerprint. Then, we told the participants that they now needed to allow us to publish their fingerprint in our research paper; if permission was denied, their participation would not be approved. This step was important in creating the unwillingness of providing a fingerprint and then comparing it with the first fingerprint they provided when enrolling and hoping to win the gift card. After the participants provided their fingerprints again, we informed them that no fingerprint would actually be published but that this was done to create the state of unwillingness and compare it with the opposite state of willingness which was needed to build a system that prevents coerced fingerprints in the MFAS.  
By the end of the experiment, we obtained the necessary fingerprints and the micro-movement characteristics of the following conditions:  
1. Enrollment with willingness behavior
2. Fake fingerprint used by the legitimate user
3. Fake fingerprint used by an attacker
4. Unwillingness fingerprint behavior  
In each of the four cases, participants participated once with a dry fingerprint and then with a wet fingerprint to detect if the skin condition would affect the results of the MFAS. They then participated again after we placed a drop of water on the glass surface, in dry skin and wet skin conditions, to see if the surface condition affected the results of the MFAS. A total of four trials were performed per participant. To ensure that the sequence of the conditions did not affect the results of evaluating the MFAS, we randomized the sequence of the conditions per each participant. Some started with dry skin and a dry surface, while others started with wet skin and a wet surface.  
The participation in each of the conditions collected the overall shape of the fingerprint and the six features listed in the MFAS design, including the following:  
1. The sequence and location of the features appearing over time
2. The duration of fingerprint formation, the acceleration between each captured image, and the standard deviation
3. The angle of the fingerprint formation
4. Contour shape changes detection
5. Fingerprint direction of changes
6. Fingerprint micro-movement while stationary  
Figure 5 depicts the smartphone and glass surface setup and the fingerprint capture over time. Table 2 summarizes the trials per participant in each of the conditions where, during the unwillingness trials, 17 out of 24 participants participated hesitantly.  
Figure 5: The setup of the experiment with the smartphone camera pointed toward a glass surface for capturing the fingerprint over time.