In the world of security, there seemed to be no shortage of how to secure our asset. We have facial recognition devices that can recognise and grant access to only the pre-programmed face or faces. There is the iris recognition retinal scan like that found in Samsung S8 phones and other devices that can scan the irises of the user and thereby grant access to a device usage or access.

These are part of a biometric identification system which uses a part of the human body as a password to unlock or grant access. There are others which include palm, voice authentication system, and fingerprint recognition system. Out of these security/identification methods, the fingerprint is the most popular biometric system of choice.

It is the most popular for some reasons. The main one is its ability to remain the same (though there may be subtle changes) and unique for each user when compared to other processes such as voice, signature, etc. which often changes with time, hence the need for an update. Another is its low power consumption therefore easily deployed in portable devices such as phones, USB flash drives, laptops, etc.

A Little History of the Fingerprint Technology

The fingerprint technology dates back to the late 19th century. All through the 1800s, there were interests in the use of fingerprint. But the first person to observe and document (in a scientific basis) the use of a fingerprint as a means of identification was Sir Francis Galton in 1888. He later published a book in 1892, Fingerprints which made the first classification made for fingerprints which will be a significant resource for forensic science/investigation.

Fast forward to 1946, the F.B.I manually processed over 100 million fingerprint cards, a figure that jumped to twice the number in 1971. You can imagine the efforts that go into manually looking through the cards.

By 1999, managing the large cache of about 33 million records of criminals becomes easier as the FBI now had a computerised system known as the Automated Fingerprint ID System (AFIS) technology. With the system you can get a match in minutes.

Today the AFIS system has up to 40 million records and handles 70,000 queries daily.

How a fingerprint scanner work

The fingers and thumbs are not smooth; there are some raised rough patterns (ridges) which enables a firm grip that runs all through it. Each person, has a unique pattern, as determined by the DNA, which encodes a unique design for each. Are there chances that two individuals could bear the same fingerprint? Well, theoretically there is, the fingerprint expert, Sir Francis Galton, put the probability of that happening to one in 64 bilion. That is eight times the number of people we currently have on earth. That is a very big odd which does not even favour identical twins as their fingerprints are just as unique as everyone else.

So, what a scanner does is similar to taking a photo of the finger's ridges and valleys. But this is no ordinary photograph; it works by shining a bright light, much as a photocopier does when taking a digital picture of the fingers.

An array of LED bulbs creates a very bright light. The image sensor usually a charge coupled device (CCD) or CMOS captures the reflected image from the finger. The capture duration usually determines how sharp and clear the fingerprint will be. Other software determines if the image of the fingerprint is ok or to be discarded.
Oil, dirt, or skin damage determine if a particular scanner can capture a fingerprint.

There is another type of fingerprint capture technology that does not convert reflected light into electronic signals. This type requires the use of capacitive sensors. These are the types you see on mobile phones, etc.

In the capacitive sensors, the fingerprint raised surface (ridges) and grooves (valleys) produce different electric signals at different parts of the finger.

The scanner processor then builds a digital image of the different voltage output corresponding to both the ridge and valley of the finger.

It has an advantage of being more accurate than a fingerprint optical scanner in producing a fingerprint aside from being more compact and low energy consumption.

The other day I mistakenly tried to unlock my phone using the left index finger, and it was unsuccessful. It only opened when I tried the right index finger. All the fingers have different unique, distinctive features, and the sophisticated scanner knows how to pick the differences.

Using a dead finger to unlock a device

Can I hack off a human finger and use it to unlock either a device, gain access to a secured location, etc.?

In the 1997 movie, Gattaca, Ethan Hawk was able to cheat a fingerprint and DNA scan when he concealed a drop of blood behind a cut off finger skin.

But in reality, the truth is that such an attempt is likely to fail.

On March 23, 2018, a 30-year-old Linus Phillip was shot and killed by police in Largo Florida in the USA outside of a store for refusal to stop for a search while attempting to flee from police.

He uses an iPhone which after 48-hour last access requires a password, but the police were able to get to the body before the time elapsed. But it was already too late; his finger was unable to unlock his phone to aid the police in their investigation.

But, fingerprints are not supposed to change. Or do they vary in death?

Ghoulish science

A research shows that even though fingerprints is something we see as unchangeable, that over time that the ridges in a person's fingers, experience little changes after some time. That is what makes identification less reliable after many years.

A dead finger on the other hand experiences degradation as a result of either desiccation or deterioration.

But the medical examiners can remove the finger and apply the technique of thanatopractical processing. This process involves taking bodily fluid from another part of the body to restore volume in the fingers to improve the ridge and valley prominence to get a higher quality print from the deceased.

But that can only help in identifying a Jane or John Doe, and it may not work in unlocking a capacitive sensor fingerprint scanner.

The reason is simple; the body has some small electrical charges running through it. That is why, unless you are using a special capacitive stylus pen, the capacitive touchscreen of your phone won't respond to other devices that touch it.

The iPhone's Touch ID ensures only a finger that is alive can unlock the fingerprint-locked phone. This information, I think, is excellent news, at least iPhone users will have one less thing to worry about- nobody will go around hacking off their fingers to access their phone.

REFERENCES

1. History of Fingerprint
2. AFIS Technology
3. How Fingerprint Scanner Work
4. Capacitive Sensing
5. Do a Person’s Fingerprints Change After Death?