Anti-peep password keyboard design with scrolling digital mouse concept

With the development of information technology, various transaction cards and identity cards are increasingly entering people's daily lives. In these activities, it is often necessary to enter a few-digit password or password, namely a personal identification number (PIN) to confirm the identity. At present, a fixed-digit password keypad is used on automatic teller machines (ATMs), savings banks and most stock exchanges. This keypad generally includes 10 numeric keys from 0 to 9 and several function keys such as confirmation. The main defect of this keyboard is that it is easy for thieves to steal the transaction password by observing the trader's password input action or using tools such as micro cameras, causing economic losses to the trader and loss of credibility to the financial institution. This keyboard is also easy to be peeped by people around, causing unnecessary embarrassment to the trader. Therefore, it is required to continuously study new identity confirmation technologies with high confidentiality to prevent PINs from being peeped and stolen by others. In some occasions with high security requirements, such as national security and military command agencies, sound spectrum, fundus image recognition or multiple identity recognition methods can be used. Some technologies, such as fingerprint recognition technology, have large identification errors and high costs. Therefore, the password keyboard with fixed digital positions is still the most widely used password input method. This article introduces a password input method developed based on the concept of mouse, or called password mouse. This password mouse uses a scrolling digital input method and has only 3 to 4 keys. Its output coding structure, digital transmission method and transmission rate are exactly the same as those of the current password keyboard. The biggest difference is that it can completely prevent others from peeping when entering the password.

1 The overall structure and working principle of the keyboard

From the outside, the keyboard consists of two parts: one is the code selection and operation part; the other is the digital display part. Figures 1 (a) and (b) respectively show two appearance diagrams of this keyboard.

Figure 1 Two appearances

The code selection and operation part includes a functional circuit and several operation keys. In addition to the same function keys as the original keyboard, there is also a code selection key (or code selection wheel), which replaces the 10 numbers 0 to 9 on the original keyboard. By scrolling "+" or "-", one of 0 to 9 is selected, and then the input is selected. Figure 2 is its structural block diagram.

Figure 2 Structure diagram

The display part is a digital display tube with one digit, which instantly displays the digital number selected by the code selection key (or code selection wheel). The display part uses optical principles and optical materials to limit the digital display viewing angle.

The above two parts are combined to complete the password input process. The working principle is as follows: At the beginning, the display part of the keyboard will display a random number between 0 and 9. The value of the BCD reversible counter is changed by rotating the wheel. When the wheel rotates forward, the counter counts forward, that is, it counts according to the rule of 0-1-2-3-4-5-6-7-8-9-0; when the wheel rotates reversely, the counter counts reversely, that is, it counts according to the rule of 0-9-8-7-6-5-4-3-2-1-0. While the BCD code counter is counting, the display part instantly displays the value of the counter. When the number to be entered is selected, press the "Select" key, the BCD code is stored in parallel in the latch, and then the BCD code is output at the set transmission rate. After entering all the passwords in sequence, press the "Confirm" key.

The operational flexibility of the keyboard can be further improved by adding other sound and light prompt information.

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2 Keyboard implementation circuit and key technologies

2.1 Hardware Composition

The above functions can be realized by discrete electronic components, single-chip microcomputers, or programmable logic devices. According to current technical conditions, it is more convenient to use single-chip microcomputers to realize the above functions. The compact structure chip AT89C2051 of the 8051 single-chip microcomputer can be wired in a very small area and complete the functions of Figure 2. Since the external input/output leads of AT89C2051 are limited, using software decoding will occupy 7 input/output lines, so a BCD code to 7-segment display code decoder CD4056 is connected between AT89C2051 and the 7-segment LED digital tube.

From the outside, P1.0, P1.1, P1.2, P1.3 and P3.7 are used as the input of five hot keys (only three are used for the mouse type); P3.2 and P3.3 are used as the input interface of the code selection wheel; P1.4, P1.5, P1.6 and P1.7 are used to transmit the BCD code to CD4056 in real time; the output of CD4056 directly drives the 7-segment LED digital tube. P3.5 is a serial communication port, which is used to transmit the determined BCD code.

2.2 Code selection wheel and reversible counter

The code selection wheel is a circular wheel with 12 small holes evenly distributed in a ring shape on the inner diameter. An infrared light-emitting tube and two infrared receiving tubes are installed on the PCB board. The rotation of the wheel will cut the infrared light, and form a signal through the photodiode and the light hole on the wheel. After shaping, the order of the two signal inputs is used to identify the forward and reverse rotation of the wheel.

2.3 Random Number Generator

In order to prevent others from seeing the input password from the input action and pattern, the keyboard always displays a random number between 0 and 9 each time it is started or each time a new code is entered after a code is entered, and then adds/subtracts the count based on this number. The generation of this random number is completed by an internal register of the microcontroller. This register continuously performs high-speed BCD addition counts without carry. When a random number needs to be generated, the current count value is immediately taken out from the register. Since the number is taken after the operator presses the "Confirm" key, it is a random moment, so the number taken out is also a random number between 0 and 9.

3 Viewing angle limitation method

A layer of light-transmitting material with a concave-convex inner plane is placed in front of the display. This layer of material allows the light parallel to the normal direction of the display plane to be emitted without distortion, and causes the light off the center to be scattered, thereby limiting the vertical viewing angle of the display, that is, only allowing the trader to see the content of the display. The current of the display is adjusted to make the brightness of the display a suitable value. The viewing angle of the display in the vertical direction can also be limited by adjusting the distance h between the display surface and the light-transmitting material, as shown in Figure 3.

Figure 3: Partial cross-section of the display

Figure 4 is a diagram of a mouse structure password keyboard made according to the above principle. First, a functional comparison experiment is conducted. The comparison keyboard is a clear code keyboard with fixed code positions produced by a Shenzhen company. When a number between 0 and 9 is entered, the keyboard serially transmits an 8-bit binary code 3X, where X is the number to be transmitted. The keyboard made uses the same encoding and transmission rate, and the receiving end is a computer. After more than 100 inputs of a 6-digit password, the performance of the two is exactly the same.