Design of electronic password lock system for safe door based on single chip microcomputer

Abstract: Aiming at the high confidentiality and security requirements of the vault door, a new type of electronic password lock for the vault door is designed, which can prevent password leakage and increase the security of the vault. The system consists of a vault door password lock controller and a password generator. The password generator provides the unlocking password, and the probability of password duplication is less than 1/1 000 000. When the unlocking password is entered incorrectly more than three times, the alarm system is activated. The paper introduces the hardware and software implementation ideas of the electronic password lock system for the vault door, and gives the hardware schematic diagram and program flow chart.
Keywords: electronic password lock system for vault door; variable password; password lock controller; password generator0

Introduction
With the rapid growth of social economy, security and anti-theft have become a social problem. Especially for various financial institutions and many enterprises and institutions, in order to facilitate capital turnover, vaults are generally set up. However, in recent years, many major thefts have occurred, such as the theft of 51 million yuan from the vault of the Agricultural Bank of China in Handan, Hebei Province. The security management of the vault has become an issue that cannot be ignored. This paper aims to strengthen the security management of the vault and designs a vault door electronic password lock system in response to the current management defects of the vault. This kind of password lock does not need to change the password, but the unlocking password is different every time. It has high confidentiality. It requires not only a set of random serial numbers, but also a variable password calculated by the password generator. This design is very suitable for situations where the security factor is very high and multiple people are required to manage and participate in unlocking. The unlocking password is different each time, which solves the shortcomings of traditional keyboard-type electronic password locks that are easy to be tried out by others on the keyboard or peeped by bystanders, and the confidentiality is insufficient.

1 Design ideas
The whole design consists of two parts: the vault door password lock controller and the password generator. Both parts have an LCD display module and a keyboard module as interfaces and tools for human-computer dialogue. The difference is that the password lock controller also includes a password identification module and an unlocking control module. The user enters the password information from the keyboard, and the unlocking control module and the alarm system are controlled through the calculation, comparison and judgment of the built-in information. The password generator mainly includes a password generation module. According to the information entered by the user, the password is calculated through a certain algorithm, and the password is fed back to the user through the LCD display.
The password generator is managed by an institution head. When the user needs to open the vault door, the vault door password lock controller first generates a six-digit random code for the user. After the user obtains the random code, he needs to ask the head of the organization for the password. The head of the organization enters the 2-digit random serial number and the 6-digit random code informed by the user on the password generator according to the prompts. The password generator calculates the 6-digit password. The responsible personnel inform the user of the 2-digit random serial number and the 6-digit password. After the user enters the 2-digit serial number and the 6-digit password, the vault door password lock is calculated by the same algorithm. If the password matches correctly, it will be unlocked, otherwise it will not be opened. If the number of incorrect password input exceeds 3 times, the buzzer will sound and the alarm system will be activated. Only by entering the correct system built-in password can the buzzer stop sounding and the alarm system be turned off.
The vault door password lock controller and the password generator have the same built-in password, which can be reset. When resetting, the original password needs to be verified. If it is the same, it can be changed and the new password is saved in the EEP-ROM of the microcontroller. After shutting down, the saved password is not lost. After resetting the built-in password, the same random code and random serial number will result in different unlocking passwords.

2 Introduction to STC12 series microcontrollers and OCM12864
STC12 series microcontrollers are single clock/machine cycle (1T) microcontrollers produced by Hongjing Technology. Compared with ordinary microcontrollers, they have the advantages of high speed/low power consumption/super strong anti-interference/inability to decrypt. They are a new generation of 8051 microcontrollers, and the instruction code is fully compatible with the traditional 8051, but the speed is 8 to 12 times faster. The operating voltage is 3.8 V ~ 2.2 V (3 V microcontroller) / 5.5 V ~ 3.3 V (5 V microcontroller), with 6 16-bit timers, compatible with ordinary 8051 timers or 4 external interrupts, with watchdog and EEPROM functions, and internally integrated MAX810 dedicated reset circuit. Based on the above advantages, this design uses STC12 series microcontrollers.
The LCD display part uses OCM12864 graphic dot matrix LCD module, which has 128×64 dot matrix, can display various characters and graphics, can be directly interfaced with CPU, and has 8-bit standard data bus, 6 control lines and power lines. OCM12864 has its own instruction set. Combined with the interface timing of OCM12864, it can realize the read and write operations of the LCD module. Figure 1 and Figure 2 are the read and write operation timings of OCM12864 respectively. By comparing the read and write operation timings, it can be found that the difference in the read and write operation timings lies in the value of the chip select signal R/W when E is valid. When E is high and R/W is high, the microcontroller performs a read operation; when E is high and R/W is low, the microcontroller performs a write operation. This design uses OCM12864-5 (3 V) and OCM12864-2 (5 V) in OCM12864. According to the read and write operation timing programming provided by Jinpeng Electronics Co., Ltd., the reading and writing of the LCD module can be realized.

3 Hardware Design
The system hardware design consists of two parts: password generator hardware design and password lock controller hardware design.
3.1 Password generator hardware design
The STC12 series microcontroller STC12LE5410AD (3 V microcontroller) is the core, and the structural block diagram is shown in Figure 3. Its functional module is mainly composed of four parts: power circuit module, keyboard circuit, LCD display module and indication control module.

The power module is designed with dual power switching, that is, it can be powered by the USB interface or by the battery. The voltage drawn from the USB or battery is 5 V, and then it is stabilized by the 1117-33 voltage regulator to provide 3.3V voltage for the CPU. The P1 port of STC12LE5410AD is connected to the keyboard circuit, and P3.6 is connected to the LED light as the indicator light of the system. P3.0 is connected to the data/instruction pin RS of OCM12864 to realize data/instruction selection. When RW=1, data DB0-DB7 will be sent to the display RAM; when RW=0, data DB0-DB7 will be sent to the instruction register for execution. The read/write selection R/W of the data is controlled by P3.4. E is the read/write enable terminal of the LCD screen of OCM12864, and the left and right half screens of OCM12864 are selected through P3.2 and P3.3 of STC12LE5410AD. In addition, V0 is the adjustment voltage of LCD, which must be connected to 10k potentiometer together with VEE to adjust the contrast of LCD screen.
3.2 Hardware Design of Safe Deposit Door Password Lock Controller
Taking STC12C5410AD (5V single chip microcomputer) of STC12 series as the core, the structure block diagram is shown in Figure 4, which mainly includes power supply circuit module, LCD display driver module, keyboard circuit module, alarm output module, serial communication module for communication with STC12C2052AD, and unlocking control circuit.

In this system, the power supply circuit module is mainly composed of a 12 V transformer and a LM7805 voltage regulator circuit to provide voltage for the CPU. Since STC12C5410AD is a 5 V single-chip microcomputer, the LCD display module also uses a 5 V OCM12864-2 LCD module. The 8-bit standard data bus is connected to the P2 port of the single-chip microcomputer STC12C5410AD; the read/write selection pin R/W is connected to P3.3; the read/write enable pins CS1 and CS2 are connected to P3.7 and P3.5 respectively; RS is connected to P3.4 to control the selection of data/instructions. The system includes an alarm output circuit. When the wrong password is entered three times in a row, the buzzer alarms to warn and activates the alarm system. No operation can be performed until the correct built-in password is entered to turn off the alarm system. In this system, the input and display parts are separated from the unlocking control circuit. Two boards are made during PCB production. Serial communication is used to realize the communication between the two boards, so that the result of password comparison can be transmitted to STC12C2052AD to realize the control of the mechanical lock.

4 Software Design
4.1 Implementation of Password Algorithm
The password algorithm is one of the most important parts of this design. When the user uses the password lock to unlock, the password entered each time is different. The password is mainly calculated by a random code, a built-in password and a random sequence number through a certain algorithm. The
random code directly implemented by the mad(); statement of the C51 language has a certain random order. The random code sequence obtained after each startup is basically the same, which belongs to a pseudo-random code. Therefore, for confidentiality products, the use of rand(); statement has defects. This design uses a timer to implement a random sequence. The timer is set to mode 2, which is an 8-bit counter that can be automatically reloaded, with an initial value of 100. After the password lock controller is turned on, the timer starts timing. The user generates an interrupt by pressing the key three times, reads the value of the lower eight bits of the timer, converts it to decimal, and takes the lower two bits to store in two elements of a predefined 6-bit array. The three key presses generate a total of three 2-digit random codes, forming a 6-digit random code. The probability of repetition of this random code is very small, which is 1/1 000 000. Therefore, the sampling of the timer can achieve true random code.
The user generates a 2-digit random serial number, and generates a password through a certain algorithm with the random code and the built-in password of the password generator. The password lock controller calculates the password based on the random serial number and password entered by the user, the random serial number, the random code, and the built-in password, using the same algorithm as the password generated by the password generator, and compares it with the password entered by the user for verification. The
STC microcontroller has its own EEPROM, which is used to store passwords. The password is not lost after the power is turned off, and the password can be changed at will. The password for each unlock is different, which can effectively prevent malicious peeping behavior, and can clearly identify the people entering and leaving the vault, and there is no need to change the password frequently, which is convenient for management.
4.2 Password lock controller program flow chart

5 Conclusion
The electronic password lock system for the vault door designed in this paper solves the management and separation of passwords in the "one password, two keys and three separations" of the vault door management. The power-on password is different each time, which effectively prevents password leakage and enhances the security of vault management. This electronic password lock system can not only be used for vault doors, but also for other products or places that require high confidentiality. Moreover, one password generator can be equipped with several password lock controllers for easy management.