False positives of the fingerprint scanner. Fingerprint scanner on a smartphone: setup and use

Any fingerprint scanner has two functions: obtain an image of the fingerprint and check its pattern against other patterns in the database. Modern smartphones use optical scanners. They work on the same principle as small digital cameras. The picture is taken using a microcircuit consisting of light-sensitive photodiodes and an autonomous lighting source - a matrix of LEDs, which illuminates the patterns on the finger.

When exposed to light, photodiodes create electric charge, capturing a single pixel in a future photo. Depending on the amount of light entering, the color intensity of the pixel changes. The combination of pixels of different intensities forms a fingerprint image on the scanner. Before starting to verify the print, the scanner checks the quality of the image, namely its brightness and clarity. If the photo is too bright or dark, the scanner's shutter speed is adjusted and the process repeats.

Once the fingerprint is received, it is analyzed using special software. The software uses complex algorithms to determine the features of papillary patterns. In total, there are three types of patterns: arc, loop and curl. Having determined the type of pattern, the scanner identifies the endings of the pattern's lines, such as breaks and splits - called minutiae. They are unique and allow one to identify its owner by fingerprint. The scanner determines the position of the minutiae relative to each other in each image: it breaks the print into small blocks of 9x9 pixels, each of which contains a certain number of minutiae. The coordinates of the detected minutiae and their orientation angles are recorded in a vector. Identical blocks from the scanner and images from the database are then compared, and if the patterns in them are identical, then the fingerprints belong to the same owner. It is worth noting that scanners do not analyze every line of the pattern: they only find identical patterns in a small number of blocks and establish similarities based on them.

There are two main types of optical scanners. The first one takes a picture of the desired area of the finger when touching the scanner. This type is used in Apple smartphones, starting with iPhone 5s.

The second type of optical scanner involves running your finger across it. It takes a series of pictures and programmatically merges them together. Such a scanner has found its application in Samsung. But in subsequent models it was replaced by the first type, which is more convenient, but also more expensive due to the need to use a larger matrix.

A common disadvantage of optical scanners is their susceptibility to contamination and scratches. In addition, such a scanner can be deceived using a cast of the phalanx of the finger.

Touch ID began to be installed for the first time on iPhone 5S in 2013. Later, new ones were equipped with a scanner iPhone models, iPad and MacBook Pro.

On this moment There are 2 generations of sensors that are used in Apple technology:

Touch ID 1st generation is used in:

iPhone 5s;
iPhone 6/6 Plus;
iPhone SE;
iPad Air 2;
iPad mini 3/4;
iPad Pro 12.9″ (first generation 2015);
iPad Pro 9.7″;
iPad 2017/2018.

Faster 2nd generation Touch ID is installed in:

iPhone 6S/6S Plus;
iPhone 7/7 Plus;
iPhone 8/8 Plus;
iPad Pro 10.5″;
iPad Pro 12.9″ (second generation 2017);
MacBook Pro 2016/2017.

Generations of sensors differ only in response speed, but not in the degree of fingerprint recognition. The features and techniques described below will work with both generations of Touch ID.

What affects Touch ID?

When it appeared in the iPhone 5s, the fingerprint sensor was head and shoulders above the solutions available from competitors. The developers managed to create a device that correctly reads the owner’s fingerprint quite quickly and with high accuracy.

Two years later, the sensor was improved, reducing the sensor response time by half.

The operation of the sensor is definitely affected by dirt and liquids. Maximum response accuracy is guaranteed when the sensor surface is clean and there is no grease, dirt or water on the finger. Despite this, the scanner requires daily cleaning only under very difficult operating conditions.

Most users don't need to wipe Touch ID or wash and dry their hands before using their smartphone.

What doesn't affect Touch ID?

Sensor operation is not affected by temperature environment and humidity. Even if you use the device in the cold, when the skin on your fingers shrinks a little, a slight change in fingerprints will not have a serious impact on Touch work ID.

The state of the smartphone battery and its charge level do not affect the response speed. Some users mistakenly believe that a sensor with a charged battery works better.

There is no confirmed evidence of Touch ID learning when repeatedly touching the sensor in a menu increases the accuracy of the sensor. IN this menu this is only intended to indicate the entered fingerprint.

How, then, can you improve the accuracy of Touch ID?

The essence of the method is to add several prints of the same finger, but at different angles and in different positions. If the fingerprints of your wife/husband, children or relatives are not entered into your smartphone, you can fill all five slots with your data.

Use either two prints for your non-working hand and three for your working hand, or four for your working hand and one for your non-working hand.

1. Go to Settings – Touch ID & Passcode and remove existing fingerprints.

2. Now add a new fingerprint for the hand with which you most often hold your smartphone. When adding a fingerprint, try to press the top of your fingertip onto the sensor.

3. Add another fingerprint and enter the same finger again, but do most of the touching with the bottom of the fingertip.

4. Add a third print for the same finger, but do not hold the smartphone in your hand with a normal grip, but in the most familiar place, for example, when taking the iPhone out of your pocket.

5. Now you can add two fingerprints for the thumb of the second hand or just one such fingerprint, and the last one to secure the thumb of the main hand in another atypical position, for example, pressing the smartphone in a car holder.

By adding two prints per finger (one for the top of the pad, and the second for the bottom), you can enter a larger area of skin into the device’s memory. By adding a fingerprint in a specific position (out of a pocket, in a holder, or on a table), we train the sensor to apply a common press at a specific angle.

This simple method will minimize the percentage of false positives of the Touch ID sensor.

What is a fingerprint and how can you fool a fingerprint scanner? Essentially, an imprint is papillary patterns on the skin. That is, protrusions and recesses that form a certain pattern. Each person has their own, individual ones.

Formation of papillary patterns

The formation of such patterns occurs around the 12th week of the fetus. At the same time, the nervous system is also formed. The pattern is influenced by many factors. This includes the position of the fetus in the womb, the genetic code, the state of the environment, the mother’s diet, and much more.

The pattern can be restored with minor damage to the epidermis. In this article we will look at whether and how it is possible to fool the fingerprint scanner, as well as how it works on modern phones.

Determining a person's identity by his fingerprint is one of the most reliable methods of identification. More accurate methods include only DNA analysis and retinal scanning.

How does a fingerprint scanner work?

The fingerprint scanner must do two things:

Get pattern image
Check if it matches the fingerprints in the database.

Scanning

Smartphones are now equipped with optical scanners. The principle of their operation is similar to that of a digital camera. A matrix of LEDs illuminates the pattern itself, and a microcircuit of light-sensitive LEDs takes a picture at this time.

When light hits an LED, it produces an electrical charge. Thus, a pixel is formed in the future image of the pattern. The color of the pixel varies depending on how much light hits it.

Pixels of different intensities form a pattern. Before matching the print with the database, the scanner checks the brightness and clarity of the image. If the results are unsatisfactory, the entire image acquisition process is repeated.

Fingerprint analysis

The resulting image is analyzed by software. Recognition occurs using complex algorithms.

All patterns can be divided into three main types:

arc,
loopback
helical.

Once the pattern type is determined, the scanner looks for minutiae. These are the places where the pattern line ends. For example, a line breaks or splits. The uniqueness of a fingerprint lies in the minutes. The scanner recognizes how the minutes are positioned in relation to each other. To do this, the entire drawing is divided into small zones. Each section includes a certain number of minutes. Their location data is recorded.

Similar areas of the fingerprint under study and the database are analyzed. If the patterns are the same, the owner of the fingerprints is the same person. The scanner does not compare absolutely all lines of the pattern. It only looks for similar patterns in blocks and draws conclusions based on this data.

Types of fingerprint scanners

There are two types of optical scanners:

Apple scanners (iPhone 5s and later) take a photo of your finger as it touches the phone screen.
Another type of scanner takes multiple images at once while you swipe the screen. This scanner was used in Samsung Galaxy S5 smartphones. Later the scanner was replaced with the first type. It is more convenient, but at the same time more expensive, since you need to use a large matrix.

All scanners of this type have one drawback: scratches and dirt can damage it.

Surely, many have ever wondered how to fool a fingerprint scanner and is it even possible? The answer is yes. Of course, the company understands now and understood before when creating similar phone functionality that any biometric system can be deceived.

It is enough to make an impression of the phalanx of the finger and touch it to the scanner. In addition, the owner of the phone can be forced to place his finger on the device.

Apple has thought of some security measures for such cases. But still the method has a right to exist. Older iPhone models can be fooled by simply printing a high-resolution photo of your finger.

As you can see, there are several ways to fool the fingerprint scanner. Moreover, if this is difficult to do on iPhones, then on smartphones with Android OS the situation is much simpler.

Not long ago, fingerprint technology was mostly associated with science fiction films. Now, even in budget smartphone Xiaomi has a fingerprint scanner. We will explain to readers the principle of its operation.

The fingerprint scanner (Touch ID) allows user identification based on the unique skin pattern on the fingertip. Each person has his own imprint and “pattern”, which is not repeated even in the case of identical twins.

A fingerprint allows you to identify any person, for example in the case of searching for criminals. As it turns out, Touch ID is also useful for smartphone users. With its help you can protect your smartphone from unauthorized access.

There are several types of scanners currently on the market. They all work on the same principle - the scanner reads the fingerprint of the smartphone owner and, when trying to unlock it, compares the “pattern” with the one that is pre-programmed in the device. If the fingerprint matches, the device will be unlocked. Otherwise an error message will appear.

Interestingly, scanners do not analyze the entire fingerprint pattern. Only some of the characteristic features or patterns are tested. This is, for example, branching, bifurcation or tearing off fingerprints.

Scanners convert the image into a template (template), and using an algorithm they compare the distance between curves and lines. This makes the verification process much shorter than if you had to analyze the entire fingerprint.

Algorithms confirm the fingerprint if approximately 40% of the minutes match the saved drawing. In practice, this is sufficient to identify a specific user and ensure fault tolerance.

Minutes (or “Galton’s points”) are areas of the skin pattern (points) that are unique for each finger, which show in which places the papillary lines merge, bifurcate or break off.

Types of fingerprint scanners

1. Optical scanner"captures" the entire finger panel and uses a CCD sensor (like most cameras) to do so. In areas where light does not reach (ridges), the sensor records "black" pixels, creating an accurately displayed image of the finger. Often optical scanners have a built-in light source (usually LED) to make the image as transparent as possible.

2. Capacitive scanner– instead of a matrix, special miniature capacitor circuits (capacitive sensors) are used. When we put our finger on this reader, the capacitance of the individual capacitors instantly changes. Capacitive scanners are much more accurate and more efficient than optical scanners because they are harder to fool.

3. Thermal scanner– it works similarly to a capacitive reader, but instead of microcapacitors they use microscopic thermal sensors that detect the temperature difference between the ridges and lobes of the finger pad. Such a scanner cannot be fooled by an imitation of a finger (i.e., a fragment with skin).

4. Ultrasound scanner– uses the phenomenon of diffraction, i.e. reflection and scattering of sound waves. When we put our finger on the reader, it begins to generate inaudible sounds for us. The behavior of sound waves at the points of contact of the “ridge” of the print pad with the scanner is completely different than in the “cavities” (where there is air). This allows the ultrasound scanner to create an accurate fingerprint of your fingerprint.

Which fingerprint scanner is better?

Currently the majority Xiaomi smartphones use capacitive readers, for example popular Redmi Note 3 or Mi 5. However, much hope lies in ultrasonic scanners installed directly under the display, and this technology is likely to be most popular in the near future.

Touch function Smartphone ID, although very secure, is not 100% secure. With the right technology and tools, it is possible to create a fingerprint that can fool the scanner.

So what is a fingerprint scanner?

This is a type of biometric security technology that uses a combination of hardware and software methods to recognize the user's fingerprint. It identifies and authenticates a person's fingerprints to allow or deny access to a smartphone, app, and other places that need protection from unwanted interference. There are many other ways to protect yourself personal information, such as: biometrics, iris scanning, retinal scanning, facial feature scanning, and so on, right down to a special blood or gait test. By the way, gait analysis was demonstrated in the Mission Impossible film series with Tom Cruise. Some smartphones even use an iris scanner, but the implementation of this feature is naturally far from ideal. Why a fingerprint scanner? It's simple: fingerprint scanning boards are quite cheap and easy to manufacture and use. Touch the scanner and your Redmi Note 3 is instantly unlocked and ready to use.

Just as there are different types of biometric security technologies, the types of fingerprint scanners have different technologies and methods of implementation. There are three types of fingerprint scanners:

Optical scanners;
Capacitive scanners;
Ultrasound scanners.

Optical scanners

Optical fingerprint scanners are the oldest method of capturing and comparing fingerprints. As you might guess from the name, this method is based on capturing an optical image of a fingerprint. Essentially, it is a photograph of a fingerprint that, once captured, is processed using special algorithms to detect unique patterns on the surface, such as ridges and unique curls, by analyzing the lightest and darkest areas of the image.

Just like a smartphone camera, these sensors have a finite resolution and the higher the resolution, the finer pattern details the sensor can discern on your finger, the greater the security. However, these sensors have much higher contrast than a typical camera. They typically have a very high number of diodes per inch to capture images at close range. But when you put your finger on the scanner, its camera doesn’t see anything, because it’s dark, you object. Right. Therefore, optical scanners also have entire arrays of LEDs as a flash to illuminate the scanning area. Obviously, this design is too bulky for a phone, where the thinness of the body plays an important role.

The main disadvantage of optical scanners is that they are quite easy to fool. Optical scanners only capture 2D images. Many have seen how, with the help of simple manipulations with the same PVA glue or simply with a high-quality photograph, a scanner is hacked and access to your important documents or cats is obtained. Therefore, this type of security is not suitable for smartphones.

Just as you can now find smartphones with resistive screens, you may also find optical fingerprint scanners. They are still used in many areas, except those where real security is needed. IN Lately With the advancement of technology and the increasing demand for more advanced security, smartphones have unanimously adopted and are using capacitive scanners. They will be discussed below.

Capacitive scanners

This is the most common type of fingerprint scanner today. As the name suggests, the capacitor is the main scanning module in a capacitive scanner. Instead of creating a traditional fingerprint image, capacitive scanners use arrays of tiny capacitor circuits to collect fingerprint data. Capacitors store electrical charge and, if you place your finger on the surface of the scanner, the amount accumulated in the capacitor will be slightly changed in those places where the ridge on the pattern touches the plate, and will remain relatively unchanged where the depressions on the pattern are opposite. Integrator circuit operational amplifier is used to track these changes, which can then be recorded using an A/D converter.

Once the fingerprint data has been captured, the data is converted into digital data and searched for distinctive and unique attributes of the fingerprint, which in turn can be stored for comparison at a later stage. The main advantage of this technology is that it is much better than optical scanners. The results of the scan cannot be reproduced with the image and it is incredibly difficult to deceive using prosthetics, that is, a cast of the fingerprint. As written above, this is because when a fingerprint is recognized, slightly different data is recorded, namely, changes in the charge on the capacitor. The only real security threat comes from any hardware or software tampering.

Capacitive fingerprint scanners use fairly large arrays of these capacitors, usually hundreds, if not thousands, in one scanner. This allows for a highly detailed image of the ridges and valleys of the fingerprint. Just like in optical scanners, more capacitors provide more a high resolution scanner, increasing the accuracy of recognition and, accordingly, the level of security, down to the recognition of the smallest dots.

Due to the larger number of components in the fingerprint recognition circuit, capacitive scanners are usually slightly more expensive than optical scanners. In early iterations of capacitive scanners, many manufacturers tried to reduce cost by reducing the number of capacitors needed for fingerprint recognition. Such solutions were almost always not very successful and many users complained about the quality of recognition, because they had to put their finger on it several times to scan the fingerprint. Fortunately, these days this technology has already been brought to mind and even picky user will be satisfied. It is worth noting that if your finger is dirty or too wet/greasy, then the capacitive scanner will sometimes not be able to recognize the fingerprint. However, do they still wash their hands? :)

Ultrasound scanners

Ultrasonic fingerprint scanners are currently the latest technologies fingerprint recognition. First this type scanner was used in the Le Max Pro smartphone. This phone uses technologies from the American company Qualcomm with its Sense ID.

An ultrasonic scanner uses an ultrasonic transmitter and receiver to recognize a fingerprint. The ultrasound pulse is transmitted directly to the finger, which is placed in front of the scanner. Some of this impulse is absorbed, and some returns to the receiver and is further recognized depending on the ridges, valleys and other details of the fingerprint that are unique to each finger. In ultrasound scanners, a sensor that detects mechanical stress is used to calculate the intensity of the returning ultrasonic pulse at various points on the scanner. Scanning for a longer period of time allows for additional fingerprint depth data to be captured, resulting in highly detailed 3D images of the scanned fingerprint. The use of 3D technology in this scanning method makes it the safest alternative to capacitive scanners. The only disadvantage of this technology is that at the moment it has not yet been developed and is too expensive. The first smartphones with such scanners are pioneers in this area. For the same reason, Xiaomi did not use an ultrasonic scanner in its flagship Mi5.

Fingerprint processing algorithms

Although most fingerprint scanners are based on very similar hardware principles, additional components and software may play an important role in fingerprint recognition. Different manufacturers use several different algorithms that will be most “convenient” for specific model processor and operating system. Accordingly, the speed and accuracy of identifying key fingerprint characteristics may vary between manufacturers.

Typically, these algorithms look for where ridges and troughs end, intersect, and split into two. Collectively, the features of a print's pattern are called “minutiae.” If the scanned fingerprint matches several “little things”, it will be considered a match. What is this for? Instead of comparing entire fingerprints each time, minute-by-piece comparisons reduce the amount of processing power required to process and identify each fingerprint. Also this method helps to avoid mistakes when scanning a fingerprint and, most importantly, it becomes possible to place your finger not completely. You never put your finger exactly right, do you? Of course not.

This information should be stored in a secure location on your device and far enough away from code that could potentially compromise the reliability of the scanner. Instead of storing user data online, the processor securely stores fingerprint information on the physical chip in a TEE (Trusted Execution Environment). This secure zone is also used for other cryptographic processes and directly accesses security hardware platforms, such as the same fingerprint scanner, to prevent any software surveillance and any intrusion. These algorithms different manufacturers may differ or be organized in different ways, for example, Qualcomm has the Secure MCM architecture, and Apple has the Secure Enclave, but they are all based on the same principle of storing this information in a separate part of the processor.

Fingerprint scanners have become a fairly secure alternative to remembering countless logins and passwords, and for secure payment transactions, scanners will eventually become a very common and important security tool.

Products that may interest you:

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Global Version means that the product is released for the global market and meets international quality standards.