A simple fingerprint conversion algorithm into code. Optical method on lumen. Ease of use scanner

Digging more and more in the protection and control systems, many of us will eventually pay attention to the biometric identification methods for certain needs.

Biometrics are the methods of automatic identification of man and confirm the personality of a person based on physiological or behavioral characteristics. Examples of physiological characteristics are fingerprints, hand shape, face characteristics, iris, voice characteristics, and obverse features. In the process of technology development, an increasing number of ways appear to identify the human person.

The most popular method of biometric identification is to recognize fingerprints. I think it is so, because it is a relatively cheap and easiest way, tested by time. There are several ways to get a fingerprint with electronics. There are several: optical methods for obtaining a fingerprint image - on the reflection, on the lumen, contactless methods, capacitive fingerprint sensors (semiconductor), radio frequency scanners, scanners using pressure method, thermosmats, ultrasonic method. Each method of obtaining a fingerprint has its advantages and disadvantages, however, mainly the balance of the scanning method is the price - reliability (there is not only effective protection, but also resistance to external factors is distinguished.

The fingerprint scanner of the fingerprint R308 (reference to the store) is optical (reflection method). This method uses the effect of broken full internal reflection (Frusted Total Internal Reflection). The effect lies in the fact that when the light falls on the border of the section of two media, the light energy is divided into two parts - one is reflected from the border, the other penetrates through the border into the second Wednesday. The proportion of reflected energy depends on the angle of falling the light stream. Starting with some values \u200b\u200bof this angle, all light energy is reflected from the border of the section. This phenomenon is called a complete internal reflection. In the case of a contact of a more dense optical medium (finger surface) with a less dense at the point of complete internal reflection, light beam passes through this boundary. Thus, only the beams of light, which fell into certain points of complete internal reflection, will be praised from the border, to which a papillar pattern of the finger was not applied. To capture the resulting light picture of the finger surface, a special image sensor (CMOS or CCD, depending on the sale of the scanner) is used.

For this method You can note the following:

• Some of the cheapest fingerprint scanners with relatively large finger scanning area
• Sensitivity to the contamination of the working surface of the sensor
• Small Protection from Mouling
• Relatively large sizes of the module

So, the fingerprint scanner R308 has the following form:

I would like to disassemble and look at the module from the inside, but the design is made in such a way that carefully unscrew the screws and remove the fee with the elements, because it keeps it from the inside and without the use of the soldering iron it is problematic, so do not try to break the integrity of the module What can lead to the conclusion of it.

This optical fingerprint scanner uses a high-speed digital signal processor as its basis. This module can get an image of the fingerprint, process the image to save or search, save the fingerprint data in your own memory and make a search for the coincidence of the resulting print with the preserved. To connect to akud (system control and access control systems), the module has an UART interface, by which the module receives commands and sends answers to the results of operations. In addition, the module can transfer to another device a fingerprint image obtained using it. The fingerprint scanner is built in such a way that all computing and analytical operations performs itself, but these processes need to be controlled to obtain the practical value of the module. Thus, based on the responses on the results of the execution of the commands, the external microcontroller can build any necessary logic of the operation of the SCOD using the fingerprint scanner.

Fingerprint scanner characteristics R308:

• Supply voltage - 4.5-5 volts
• Operating current - 40 mA
• Interface - UART (TTL Logical Level)
• BAUD RATE - 9600 * N, N \u003d 1 ~ 12, default 57600 BPS
• Time scanning fingerprint - 0.5 sec
• Fingerprint template size - 512 bytes
• False Far Skip Coefficient (False Acceptance Rate) - less than 0.001%
• False refusal factor in FRR access (False Rejection Rate) - less than 0.5%
• Security level - 5
• Medium search time - less than 1 sec
• Fingerprint reading window size - 18x22 mm
• Module size - 55,5x21x20,5 mm
• Range of operating temperatures - -20- + 40 degrees Celsius

To connect to other devices, the R308 has a 6-pin connector:

1. VT - plus a finger detector
2. VIN - plus power module
3. Touch - Finger Detector Signal

The documentation indicates the colors of the loop complete with the module, but in my case the colors did not coincide, therefore it is more reliable to determine the purpose of the numbering contacts indicated on the board near the module connector.

Structure of the data packet transmitted and received by the module:

1. Header - Title, Fixed 0XEF01 (2 bytes)
2. Adder - Fingerprint Scanner Address, Fixed 0xFFFFFFFFFFFFF (4 bytes)
3. Package Identifier - Data Pack Identifier, 01H - Team Package, 02h - Data Package, 07h - Response Package, 08h - Data End Package (1 byte)
4. Package Length - the number of byte of the information packet (includes the sum of the data byte of paragraphs 5 - 6), maximum amount 256 bytes (2 bytes)
5. Package Contents - Useful data
6. Checksum - check sum, arithmetic amount of paragraphs 3-6 (2 bytes)

Fingerprint scanner has 8 basic instructions for controlling it:

1. Scan fingerprint and saving it in a buffer. Returns the confirmation code about the success of the operation.
2. Creating a fingerprint symbol file from the original print and saves it in Charbuffer1 (2). Returns the confirmation code about the success of the operation.
3. Search for a coincidence of a fingerprint in a module library that corresponds to stored in Charbuffer1 or Charbuffer2. Returns the confirmation code about the success of the operation and the fingerprint ID in the module library.
4. Creating a fingerprint model template. Information in Charbuffer1 and Charbuffer2 is combined and combined to obtain more reliable fingerprint data (the imprint in these buffers should belong to one finger). After the operation, the data is saved back to Charbuffer1 and Charbuffer2. Returns the confirmation code about the success of the operation.
5. Saving a fingerprint template from Buffer1 / Buffer2 to Flash MODEL Library Memory. Returns the confirmation code about the success of the operation.
6. Remove the template from the flash memory of the module. Returns the confirmation code about the success of the operation.
7. Clearing the module fingerprint library memory. Returns the confirmation code about the success of the operation.
8. Check the password of the module. Returns the confirmation code about the success of the operation.

In order to search for a fingerprint coincidence in the module library, you must scan a fingerprint and save it in the buffer, generate a character file and place it in Charbuffer and register the team to search for fingerprints (instructions 1, 2, 3).

In order to make a fingerprint in the module's memory you need to get an image of a fingerprint, save it in a buffer and generate a character file saved in charbuffer (repetition of a minimum 2 times and save everything in Charbuffer1 and Charbuffer2), then combine the data in buffers 1 and 2 To obtain a more accurate result and run the Save command to the specified memory location information about the fingerprint (instructions 1, 2, 4, 5).

In the course of the execution of instructions, the module must monitor the correctness and success of execution by means of answers following the commands. This can improve the quality of the program and the accuracy of the specified manipulations with the fingerprint scanner R308.

To evaluate the operation of the module, a demonstration firmware for the STM32 microcontroller is attached, corresponding to the scheme:

The LCD display displays the necessary data to work with the fingerprint scanner, when you turn on the circuit without closed jumpers JMP1 and JMP2, the main program cycle is launched when the microcontroller is waiting for the fingerprint from the scanner and starts searching in the module's memory when it appears. When you turn with a closed jumper JMP1, the complete erasure of the fingerprint library is launched. When you turn with a closed jumper JMP2, add 5 new fingerprints to the module's memory. To add a fingerprint, you need to attach a finger twice to the scanner to save it in the absence of errors when scanning prints.

In addition, the article is attached to the SFGDEMO program. With it, you can get an image of your fingerprint. In addition to the standard operation of adding an imprint in memory, search for coincidences, deleting an imprint from memory (USB-UART adapter is used to connect to the computer).

List of radio elements

Man has always tried to keep his personal information in secret. And it does not surprise it at all - it's personal! With the advent of the first computers, users began to protect their data by passwords and various PIN codes. However, the first computers were not created for home use, but for various manufacturing firms. Let them not have personal information, they kept various algorithms of work, which no one wanted to disclose.

Then computers gradually began to "domesticated", and in parallel it appears and cell Phones. And each person, taking advantage of a combination, known only to him, was able to secure his data. For a long time Different combinations of characters as passwords were used in everyday life. However, the fingerprint scanner comes to replace them. It was popular in America in the mid-90s. The idea was that you can access the device "in one touch". And instead of entering the password every time, the user is just enough to touch the appropriate site.

Fingerprint scanner in Russia

In Russia, such an innovation was not highly distributed in those times. Only on September 20, 2013, when the iPhone 5S was launched, which has a built-in fingerprint scanner and a totality of funds (Touch ID) to ensure its work, a wide group of users was able to evaluate such an interesting technology. After the advent of the smartphone from Cupertino, a bunch of models above the average price segment, which were equipped with a fingerprint scanner. Today even budget smartphones For the most part, have a biometric sensor to identify users.

How safe is the fingerprint scanner?

Despite the fact that human biometric indicators are not so easy to fake, the print scanner is not as safe as it may seem. The Kaspersky Lab team conducted an inspection of the security of this device. It turned out that on some devices information about prints is stored in unencrypted form and in the image format. So theoretically, any application to which you will access the Internet and to local files will be able to transfer information about your prints anywhere. Therefore, Kaspersky recommended to enjoy only proven applications and programs. Be that as it may, at most modern devices, this information is stored in the encoded form and in a reliably protected folder.

Alternatives of fingerprint scanner

Samsung decided to follow Apple example with her touch ID and come up with a unique biometric sensor that can be implemented in a smartphone. The company decided to develop an eye iris scanner. Its essence is that to unlock the device, it is necessary to watch the camera to the system, by analyzing the data obtained, recognized you. She fixes the height of the eye, which is as well as fingerprints, each person is different. However, this type of biometric identification is far from being perfect. The technology requires that more than 90% of the eye iris can be seen. Some people with an Asian eye deal complain that the device asks to open the eyes of the sewn, but due to the anatomical features it is not so easy.

Apple also decided not to stop on the fingerprint scanner by developing Face ID. This combination of programs that analyzes your face and builds its volume virtual model. It, in addition to the unique face relief, also carries information about your eyes, lips and nose. These indicators are stored on a smartphone in the encoded format. But this technology of biometric identification could not guarantee one hundred percent protection. After a week after launching the iPhone X, which first received Face ID, a video was published on the network in which one of the company's specialists with a mask.

Where is located

Most often, two locations are used for the location of the scanner: the "Home" button on the front of the smartphone or the rear cover of the device. Scanner looks like smooth surface, most often a little framed by a small side. Rarely, the dactylconical scanner is embedded in the sideline power button.

How to setup

To customize the fingerprint scanner on the Android device, you need to go to the settings, then select the "lock screen" item (sometimes "lock screen and fingerprint"), click on "fingerprint management" and can safely set up. Namely - add a fingerprint or remove from the memory already brought.

Mostly smartphones can store up to 10 fingerprints (less often less). To put a fingerprint, you need to select the appropriate item and attach a finger to the scanner (without pressing the "Home" buttons if it is built into it), applying your finger in different positions. Also, after the fingerprint of the finger in the memory of the device, it is desirable to assistent with him any name, in order not to get confused if several prints are entered into the system.

All the existing fingerprint scanners for the physical principles used today can be allocated in three groups:

• optical;
• silicon (or semiconductor);
• ultrasound.

Optical scanners

The operation of optical scanners is based on an optical method for obtaining an image. By type of technologies used, the following groups of optical scanners can be distinguished:

1. Ftir scanners - Devices that use the effect of broken full internal reflection (FrustratedTotalInternalReflection, FTIR).

When the light is dropped on the border of the two media, the light energy is divided into two parts: one is reflected from the border, the other - penetrates through the border of the partition in the second environment. The proportion of reflected energy depends on the angle of fall. Starting with some of its magnitude, all light energy is reflected from the border of the section. This phenomenon is called full internal reflection. However, when contacting a more dense optical medium (in our case, the surface of the finger) with less dense (in practical implementationAs a rule, the surface of the prism) at the point of complete internal reflection, the light beam passes through this border. Thus, only light beams will be puzzled from the border, which fell into such points of complete internal reflection, to which the grooves of the papillary surface of the finger surface were applied. To fix the resulting light picture of the finger surface, a special chamber is used (CCD or CMOS, depending on the sale of the scanner).

2. Wholesale equestrian Scanners (Fiber Optic Scanners) - It is a fiber optic matrix, each of the fibers of which ends with a photocell.

The sensitivity of each photocell allows you to fix the residual light passing through the finger at the point of touching the relief of the finger to the surface of the scanner. The fingerprint image is formed according to each of the elements.

3. Electro-optical scanners (electro-optical.scanners) Based on the use of a special electro-optical polymer, which includes a light-emitting layer.

When applying a finger to the scanner, the heterogeneity of the electric field at its surface (the potential difference between the tubercles and depressions) is reflected in the glow of this layer so that it highlights the fingerprint. Then the array of photodiodes of the scanner converts this glow into a digital view.

4. Optical transit scanners (sweepoptical.scanners) Overall similar to FTIR devices.

Their peculiarity is that the finger is needed not to simply apply to the scanner, but to spend it through a narrow strip - the reader. When the finger moves along the scanner surface, a series of instant pictures (frames) is made. At the same time, neighboring frames are removed with some imposition, i.e. they overlap each other, which makes it possible to significantly reduce the size of the prism used and the scanner itself. For forming (more precisely assembly) Images of fingerprint during its movement on the scanning surface frames, specialized software.

5. Roller scanners (rOLLER-style.scanners). In these miniature devices, the scanning of the finger occurs when the finger of a transparent thin-walled rotating cylinder (roller) is rolling.

During the movement of the finger on the surface of the roller, a series of instant pictures (frames) fragment of a papillary pattern in contact with the surface is made. Similarly, the lengthy scanner adjacent frames are removed with the imposition, which allows you to collect without distortion full image Fingerprint. When scanning, the simplest optical technology is used: inside the transparent cylindrical roller are a static light source, lens and a miniature chamber. The image of the illuminated portion of the finger focuses the lens on the sensitive element of the chamber. After a complete "scrolling" of the finger, "the picture is going". His imprint.

6. Contactless scanners (touchlessscanners). They do not require direct finger contact with the surface of the scanning device.

The finger is applied to the hole in the scanner, several light sources highlight it from the bottom from different sides, in the center of the scanner there is a lens, through which the collected information is projected into a CMOS camera, converting the data obtained into the fingerprint image.

Semiconductor (Silicon) Scanners

At the heart of these scanners, use to obtain an image of the finger surface of the properties of semiconductors, changing in the contact places of the creases of the papillary pattern with the surface of the scanner. Currently, there are several technologies for the implementation of semiconductor scanners.

1. Capacitive scanners (capacitivescanners) - The most widespread type of semiconductor scanners, in which to obtain an image of the fingerprint used the effect of changes in the PN transition capacity semiconductor device When contacting the crest of a papillary pattern with a semiconductor matrix element.

There are modifications of the described scanner in which each semiconductor element in the scanner matrix acts as a single condenser plate, and the finger is the other. When the finger is applied to the sensor between each sensitive element and the protrusion-depressing papillary pattern, a certain container is formed, the value of which is determined by the distance between the surface of the finger and the element. The matrix of these tanks is converted into the fingerprint image.

2. Pressure sensitive scanners (pressurescanners)- These devices use sensors consisting of a piezoelectric matrix.

When the finger is applied to the scanning surface, the protrusions of the papillary pattern have pressure on some subset of the surface elements, respectively, no pressure is not supplied. The matrix of the voltage obtained from piezoelectric elements is converted into the image of the finger surface.

3. Thermo scanners (thermal.scanners) - They use sensors that consist of pyroelectric elements that allow you to fix the temperature difference and convert it to voltage (this effect is also used in infrared chambers).

When applying a finger to the sensor on the temperature of the papillary patterns touched to the pyroelectric elements, the temperature map of the surface of the finger is built and is converted into a digital image.

These types of scanners are the most common. In all given semiconductor scanners, a sensitive trace element matrix is \u200b\u200bused (the type of which is determined by the implementation method) and the transducer of their signals into digital form. Thus, the generalized scheme of the operation of the presented semiconductor scanners can be demonstrated as follows:

4. Radio frequency scanners (RfFieldscanners)- In such scanners, a matrix of elements is used, each of which works as a small antenna.

The sensor generates a weak radio signal and sends it to the scanned surface of the finger. Each of the sensitive elements takes a signal reflected from the papillary pattern. The magnitude of the electronic driving force induced in each micronenchine depends on the presence or absence of the crest of the papillary pattern into close. The voltage matrix thus obtained is converted into a digital fingerprint image.

5. Broaching thermo scanners (thermal.sweepscanners) - A variety of thermo scanners, in which for scanning (as well as in optical lengthy scanners), it is necessary to spend your finger on the surface of the scanner, and not just attach it.

6. Capacitive transit scanners (capacitivesweepscanners) - Use a similar way to frame-cut fingerprint image, but each image frame is obtained using a capacitive semiconductor sensor.

7. Radiofrequency broaching scanners (RfFieldsweepscanners) - Similar to capacitive, but use radio frequency technology.

Ultrasound scanners

Ultrasonic scanning - It is a scanning of the surface of the finger with ultrasonic waves and measuring the distance between the source of waves and the depressions and protrusions on the surface of the finger on the echo reflected from them. The quality of the image obtained in this way is 10 times better than the method obtained by any other presented on the biometric market method. In addition, it is worth noting that this method It is almost completely protected from dummy, because it allows you to receive some additional characteristics of the finger in addition to the fingerprint (for example, a pulse inside the finger).

Examples of fingerprint scanners

The main application of fingerprint recognition technology is protection against unauthorized access. More often used in security systems and accounting systems for employees.

To control access, fingerprint scanners are embedded in laptops, cell phones, external drives, Flash cards, etc. etc.

We live in the era of total penetration digital technology In all areas of life, we make purchases on the Internet, you store money on cards, virtual accounts, and personal photos and documents - in network storage. At the same time, the protection of personal data becomes relevant than ever. After all, the access of intruders to personal information can threaten us with great problems. A smartphone becomes especially vulnerable in this regard, with which authorization in many online services occurs. It is easy to lose, relatively good to get temporary access to it. In most cases, passwords are used to protect data in smartphones graphic keys. But it is not always safe and convenient. New stage safe modern gadgets Biometric protection becomes based on the uniqueness of some parts of our body. For example - a rainbow shell and retina, face geometry, voice, fingerprints. The use of the biometric authentication process is reliable and convenient protection. After all, such a "password" is impossible to forget, peel, it is extremely difficult to fake and he is always "at hand"))).

In the second type of optical scanner, we must carry a finger across the scanner. The scanner makes a series of snapshots and programmatically combine them into one. This method is called long (swipe). It was implemented by Samsung in Galaxy S5. But in the following models, she refused this method. Due to the need to use a larger matrix for a complete picture of the fingerprint, the first type of optical scanner is more expensive than the extensive, but at the same time more convenient for the end user. The general disadvantage of optical scanners is exposure to pollution, scratches, the influence of the physical condition of the finger (humidity, for example). In addition, such a scanner can be deceived using a picture of a fingerprint that successfully demonstrated a Chaker Group of Chaos Computer Club. They photographed in high resolution of the fingerprint on the glass, printed it on laser printer, poured with liquid latex and after drying such a cast was recognized by the scanner system as a native. Thus managed to bypass the protection of the children and Samsung, and Apple.

2. Semiconductor. Based on the properties of semiconductors to change their properties in places of contact. Such scanners are capacitive, radio frequency, thermal. In modern smartphones, semiconductor space scanners did not find. Probably due to the complexity of the introduction, given the small dimensions of mobile gadgets, as well as high costs. The big plus of this technology is that it will not deceive it with the help of the cast.

3. Ultrasonic. In my opinion, the most promising method of work of the fingerprint scanner. Ultrasonic scanners use the principle of medical ultrasound in order to create a visual image of a fingerprint. Sound waves are generated using piezoelectric converters. Next, they fall on the finger and the echo reflected from it is fixed with special sensors. Unlike optical images, these scanners use very high sound waves frequencies that can penetrate the epidermal layer of the skin. And he has a unique structure.

This eliminates the need for clean, dry, intact finger. The ultrasound scanner cannot be fooled by the imprint with a picture, as it forms a 3D-picture of the structure of the skin, and also knows how to fix the pulse. In March of this year, Qualcomm presented its development on the basis of this technology and rumors that for the first time we will see its implementation in smartphone Xiaomi. Mi5.

Next, let's affect the topic of the program and hardware implementation of the fingerprint scanner in different systems. For the first time Apple introduced biometric method Identification in iPhone 5S under the Touch ID brand. It was an optical scanner based on a resolution of 500 PPI. It was built into the "HOME" button and covered with sapphire glass resistant to scratches.

The coprocessor responded for processing the scanned imprint, and the transformed digital code was already stored only in a special isolated storage. With the iPhone 5S fingerprint scanner, you can only unlock your smartphone and logged in iTunes. He did not support third-party applications. Already in iOS 8, payment was implemented with using touch ID in ApplePay, it has the opportunity to use a scanner to protect third-party data.

In smartphones on the operating system Android scanner Fingerprints first appeared in Motorola ATRIX 4G, but due to the inconvenience of implementation, a few users were used. The flagship became a high-quality breakthrough Samsung Galaxy S5. In it, using the fingerprint scanner, it was possible not only to unlock the smartphone, but also logged in payment payPal system. Also, the functionality of the scanner could use third-party applications. But because of the method of scanning a fingerprint (long) solution in the Samsung S5 losing the Touch ID.

In connection with the features of operating systems, Apple's decision in terms of protection against hacking malware is more reliable.

It is worth saying that Android systems up to the 6th version there was no native support for such a way of authentication, and only in Android Marshmallow. Google has implemented support for the fingerprint scanner directly into the system. IN new version The developers are easier to implement applications to work with the scanner, as it is enough to add support for the system API. Wenders do not need to create from scratch or adapt ready-made software solutions, often ne. better quality or low convenience.

On the this moment The fingerprint scanner module is no longer the privilege of the flagships of the leading players of the smartphone market. Almost all manufacturers picked up this fashion, and the scanner began to appear even in budget models. Developers are experimenting with the placement of this module ("Home" button, turn on / off, under the main chamber), with the software and functionality.

But today, such a biometric protection system would not be recommended to use for payments, storing important personal information. The proof of this is examples of hacking with the help of the casts of the fingers and the touch ID, and the scanners on the Android-e. Perhaps the development based on ultrasound scan will correct this problem. But as the method of unlocking the smartphone - to protect against excessive curiosity of third parties, the fingerprint scanner is perfect.

So what is the fingerprint scanner?

This type of biometric security technology, which uses a combination of hardware and software methods Launch of the fingerprint of the user. He identifies and checks the authenticity of the fingerprint of man to allow or prohibit access to the smartphone, an application and other places that need to protect against unwanted interference. There are many other ways to protect personal information, such as: biometrics, scanning of the iris, scanning the retina, scan feathers, and so on until the quality of blood analysis or gait. By the way, the analysis of the gait was demonstrated in the film of the Mission Impressive film with Tom Cruise. In some smartphones, the scanner of the iris, but the realization of this feature is naturally far from ideal. Why exactly the scanner of prints? Everything is simple: boards for scanning prints are rather cheap and easy both in the manufacture and use. Touch the scanner and your Redmi Note 3 is instantly unlocked and ready to work.

As exist different types biometric safety technologies and fingerprint scanners have different technologies and ways to implement. There are three types of print scanners:

1. Optical scanners;
2. Capacitive scanners;
3. Ultrasound scanners.

Optical scanners

Optical fingerprint scanners are the oldest capture and fingerprint comparison method. As it is easy to guess from the name, this method is based on capturing an optical print image. In fact, this is a photo of a fingerprint, which is processed after the capture using special algorithms to detect unique patterns on the surface, such as ridges and unique curls, analyzing the brightest and dark areas of the image.

As well as the camera in the smartphone, these sensors have a final resolution and the higher this permission, the smallest details of the pattern the sensor can distinguish on your finger, the higher the safety. Nevertheless, the sensors of these sensors have a much larger contrast than the usual camera. As a rule, they have a very large number of diodes on an inch to capture the image at close range. But when you apply your finger to the scanner, then his camera does not see anything, because you are dark, you. Right. Therefore, optical scanners also have entire arrays of LEDs as a flash to illuminate the scan area. Obviously, this design is too cumbersome for the phone where the subtlety of the case plays an important role.

The main disadvantage of optical scanners is that they are quite easy to deceive. Optical scanners capture only 2D image. Many have seen how with the help of uncomplicated manipulations with the same PVA glue or simply with high-quality photography the scanner is collected and access to your important documents or kits is obtained. Therefore, this type of security is not suitable for smartphones.

As well as now you can find smartphones with a resistive screen, you can meet optical fingerprint scanners. They are still used in many areas, except for those who need real security. IN lately With the development of technologies and an increase in demand for more serious safety, smartphones unanimously accepted and use capacitive scanners. We will talk about them below.

Capacitive scanners

This is the most common type of fingerprint scanner to date. As can be seen from the name, the condenser is the main module for scanning in the capacitive scanner. Instead of creating a traditional image of a fingerprint, capacitive scanners use the arrays of the condenser's tiny circuits to collect print data. Condensants store electric charge And, applying a finger to the surface of the scanner, accumulated in the capacitor will be slightly changed in those places where the crest on the pattern is touched by the plate, and will remain relatively unchanged, where the opposite is depressed on the pattern. Integrator scheme operational amplifier Used to track these changes, which can then be written using a converter into analog-digital.

After the print data was captured, the data are transformed into digital and already search for distinguishing and unique fingerprint attributes, which in turn can be saved for comparison at a later stage. The main plus of this technology is that it is much better than optical scanners. Scan results cannot be reproduced with the image and it is incredibly difficult to deceive with prosthetics, that is, the impression of the imprint. As written above, it is because when the print recognition, several other data are written, namely, the charge changes on the condenser. The only real security threat comes from any hardware or software intervention.

In capacitive print scanners, use enough large arrays These capacitors are usually a centurion, if not thousands in one scanner. This allows with a high degree to detail the image of the ridges and a fingerprint. As in the optical scanners, a larger number of capacitors provide a higher scanner resolution, increasing the recognition accuracy and, accordingly, the level of security, up to the recognition of the smallest dots.

Due to the larger number of components in the printing chain, capacitive scanners are usually a bit more expensive than optical. In the early iterations of capacitive scanners, many manufacturers tried to reduce the cost, reducing the number of capacitors needed to recognize the imprint. Such solutions were almost always not very successful and many users complained about the quality of recognition, because it was necessary to apply a finger several times to scan the imprint. Fortunately, in our days, this technology has already been brought to mind and even the pick-up user will remain satisfied. It is worth noting that if the finger is dirty or too wet / fat, then the capacitive scanner will sometimes not recognize the imprint. However, still wash your arms? :)

Ultrasound scanners

Ultrasonic fingerprint scanners are currently new technologies Fingerprint recognition. For the first time this type The scanner was used in the LE MAX Pro smartphone. This phone uses the American company Qualcomm technology with its Sense ID.

To recognize the imprint, ultrasonic scanner uses an ultrasonic transmitter and receiver. Ultrasonic impulse is transmitted directly to the finger, which is placed in front of the scanner. Part of this pulse is absorbed, and the part returns to the receiver and is further recognized depending on the ridges, depressions and other parts of the imprint, which are unique for each finger. In ultrasonic scanners, the sensor that detects the mechanical voltage is used to calculate the intensity of the returning ultrasonic pulse at different points on the scanner. Scanning for a longer time allows you to recognize additional data on the depth deposit depth, which will be captured, and will result in a very detailed 3D image of the scanned fingerprint. The use of 3D technology in this scanning method makes it the safest alternative to capacitive scannes. The only minus of this technology is that at the moment it is not yet worked out and too expensive. The first smartphones with such scanners are pioneers in this area. For the same reason, Xiaomi did not use the ultrasound scanner in its MI5 flagship.

Fingerprint processing algorithms

Although most print scanners are based on very similar hardware principles, additional components and software can play an important role in the recognition of prints. Various manufacturers use several different algorithms that will be the most "convenient" for specific model Processor I. operating system. Accordingly, different manufacturers determine key characteristics of fingerprints may vary in speed and accuracy.

As a rule, these algorithms are searched for where the ridges and depressions end, intersect and divided into two parts. In the aggregate, the characteristics of the print pattern are called "trifles". If the scanned imprint corresponds to several "trifles", then it will be considered as a coincidence. What is this for? Instead of comparing whole prints each time, comparing for "small things" decreases the amount of spent computing power required for processing and identifying each fingerprint. Also, this method helps to avoid errors when scanning a print and, most importantly, it becomes possible to apply the finger not completely. After all, you never attach your finger exactly? Of course not.

This information should be stored in a safe place on your device and sufficiently distance from the code that can potentially jeopardize the reliability of the scanner. Instead of storing user data on the Internet, the processor reliably stores information on the print on the physical chip in the TEE (trusted environment for tasks). This secure zone is also used for other cryptographic processes and directly refers to protective hardware platforms, such as the same print scanner to prevent any software surveillance and any invasion. These algorithms of U. different manufacturers They may differ or are organized in different ways, for example, Qualcomm is a Secure MCM architecture, and Apple is Secure Enclave, but they are all based on the same principle of storing this information in a separate part of the processor.