ABSTRACT
The aim of this paper is to describe the implementation of a lowpower,low-cost 16-bit RISC microcontroller that will act as thecore of a stand-alone security system. The controller is designedto provide moderate-high security at very low cost and to be ableto operate independent of a database. It is designed using 1.5-mSCMOS process from MOSIS and operates at a frequency of 12.5MHz.
KeywordsCard readers, ASICs, security systems, low-power
1. INTRODUCTION
Current access control systems that authorize access to a buildingor a room are either relatively insecure or costly to implement andset up. Many of the security systems used to provide secure accessto a site require database access to check the authentication statusof the user, which requires the system to have networkcompatibility. This increases not only the setup cost of thesecurity system but also the implementation cost of themicrocontroller used in the security system. Besides, such systemsare vulnerable to network failures and congestion, which may bequite disconcerting to the users if not critical to the security andsuccessful operation of the system. On the other hand, many ofthe existing stand-alone systems fail to provide a high level ofsecurity. These systems usually only consist of a single cardreader. If the card user is authorized to access the site, access willbe granted without requiring any further identification. There aresystems that require some kind of identification, such asfingerprint matching, but these systems are too costly toimplement.The aim of this paper is to present a microcontroller thatwill provide high security without the need for any databaseaccess, hence eliminating the high cost disadvantage of a networkbasedsystem but providing a moderate to high level of securitydepending on the data encryption algorithm used. Themicrocontroller is designed for consumers that need moderate tohigh degree of security without the need for a networked accesscontrol system. The microprocessor is also designed as a lowpower system using the low power static CMOS design withseveral chip-specific low-power components and features.
2. OPERATION
The microcontroller-based system described in this paper is to beset up at the site which needs authorization before entry. The userneeds to swipe his/her card through the card reader and then entera 4-digit PIN on the keypad in order to enter the site. The users ofthe site are to be given a card, which is preloaded with a 32-bit.When the card is swiped, the data on the card is read serially viaan RS-232 interface into two special registers inside themicrocontroller. After reading in the data, the controller waits forthe user to enter the 4-digit PIN. If the PIN is not entered in aspecific amount of time determined by the program running on themicrocontroller, the card reader ignores the data in the cardregisters and waits for another swipe. If the PIN is entered in time,the microcontroller reads in the PIN via the serial RS-232interface, converts each digit to a 4-bit number in two’scomplement and stores the whole PIN in a single special register.Then the controller operates on the input data from the card aswell as the PIN and carry out a decryption process. If the result ofthe decryption matches the processed PIN entered by the user,access to the site will be granted by sending an “open” signal tothe door which lasts for 10 seconds.
2.1 Data Encryption/Decryption Algorithms
It is obvious that the security of such a system highly depends onthe encryption algorithm used in the process of assigning PIN’s tothe site users. The requirement of a PIN (password) after the userswipes the card is an important high-security feature of thesystem. In case the card is stolen or lost, any unauthorized userwill not be able to enter the system without the acknowledgmentof the password. This feature is similar to the authenticationmechanisms used in the bank ATM’s to provide more securitythan a bare card reader, but different from the ATM’s in that itdoes not require a network for access authorization


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