OTP-based disposable electronic wallet RFID card.Pet Management RFID Chip manufacture

　　OTP-based disposable electronic wallet RFID card

　　Electronic wallet is a payment tool commonly used by customers in e-commerce shopping activities. It is a new type of wallet commonly used when shopping for small amounts or purchasing small commodities. There are two concepts of electronic wallets: one is pure software, as long as it is used for online consumption and account management, this type of software is usually connected with bank accounts or bank card accounts; the other is smart stored-value cards for micropayments. The cardholder deposits a certain amount in the card in advance, and the transaction amount is directly deducted from the card during the transaction. Because this type of card does not require the support of a large-scale system like a bank card, it is used in some activities and small transactions. Very extensive, the most representative is the bus card.

　　Electronic wallet smart stored-value cards are generally based on radio frequency identification technology and include three main components: chip, antenna, and packaging. The chip storage value of the electronic wallet can be digital cash and other electronic currency, which can be consumed on the corresponding device, and it can display how much money is in the user's electronic wallet. For example, the public transportation card can be read on the corresponding public transportation card reader. Take out its stored value and consume on it.

　　With the development of e-commerce and technology, the use of electronic wallets has increased. However, the existing smart stored-value cards are all based on EEPROM (Electrically Erasable Programmable Read Only Memory) technology, and its cost is difficult to reduce, which hinders The use of electronic wallets. Utilize low-cost OTP (one time programmable) memory, combine analog circuit and digital circuit to realize a kind of disposable electronic wallet. The basic function of this kind of disposable electronic wallet is to deposit a certain amount into the card when the card is issued, and then the end user consumes the unit value or a multiple of the unit value on the card reader until the amount is consumed. Because the OTP memory can only be programmed once, the internal operation of disposable electronic wallets based on this memory is very different from that of EEPROM-based electronic wallets.

　　2 Functions of disposable electronic wallets

　　Electronic wallet generally includes the following main functions: initializing the wallet, deducting the wallet, adding the wallet and reading the wallet. Initializing the wallet refers to depositing a certain amount of money in the electronic wallet from the card issuer; deducting the wallet is to support the electronic wallet to consume in the specified equipment, and a certain amount is deducted for each consumption; adding the wallet means to recharge the electronic wallet; reading the wallet is Read out the balance of the electronic wallet. The disposable electronic wallet does not have the function of adding a wallet, but other functions are the same as those commonly used electronic wallet cards such as S50 from the user level.

　　2.1 Memory allocation

　　The size of the OTP memory of a disposable electronic wallet is 8KBits, which is mainly divided into two functional areas: one is the operation area for accessing information such as face value and password, and the size is 2KBits; the other is the subtraction area for recording unit value usage. The size is 6KBits, and each Bit in the subtraction area represents a unit value. The operation area is divided into 4 sectors, each sector has 4 blocks, and the size of each block is 128 Bits. The fourth block of each sector stores the password, the first block of sector 0 is written by the card manufacturer to write UID and other data, the second block of sector 0 is written into the data of the face value of the disposable electronic wallet, and other user-defined The data block can write any data by the user.

　　2.2 Initialize the wallet

　　The face value of an electronic wallet refers to the initial amount when the card issuer sends the smart card to the end user. The face value of an electronic wallet based on (OTP memory) is represented by two numbers, such as the unit value U is (32Bits) and the number of times the unit value can be used is T16 (Bits). Its distribution in a block of 128Bits is as follows: Write the data in the format shown in Figure 1. The face value is equal to the unit value U multiplied by the usable times T. If the unit value is 32'd2 and the usable times is 16'd50, the face value is 100. In the subtraction area, each Bit Represents a unit value, a total of 6000 Bits, that is, the maximum number of uses T can be set to 6000, but it can also be any number less than 6000. A block pointer is set for the denomination block, and after this block is written, Program this pointer to 1. After the block pointer is set to 1, no more write operations can be performed on this block, and every time you perform wallet deduction and read wallet operations, you must check whether the block pointer is 1.

　　2.3 Buckle wallet

　　After the one-time electronic wallet has initialized the denomination, it can perform subtraction operations, but it cannot perform addition and recharge operations like S50. The one-time electronic wallet subtraction operation is divided into the following steps: the first step is to pass identity authentication and password verification between the card and the card reader; the second step is to start from the last address (6000th) in the subtraction area, Find the address of the highest programmed bit in reverse order, record it as the third step of LBAddr, accept the subtraction value S from the card reader, divide S by the unit value in the face value area, and get the result quotient Q and remainder R. If If the remainder R is not 0, it means that the subtraction value S is not an integral multiple of the unit value, and the operation fails, otherwise proceed to the next step; the fourth step is to subtract the address FBAddr of the first bit in the subtraction area with LBAddr to obtain the unit value. The number of times UT, if the sum of the quotient Q and the number of uses of the unit value UT is less than or equal to the number of times T in the face value area, proceed to the next step, otherwise stop. In the fifth step, LBAddr adds the quotient Q to get the new programming address NBAddr. After receiving the programming command from the card reader, the value of the bit NBAddr is programmed to be 1, and the subtraction operation successful information is returned to the card reader.

　　In the operation steps of debiting the wallet, first find the address of the first programmed Bit (the last one is the last) in the reverse order, and then calculate the unit value of the e-wallet in a sequential manner according to this address The number of uses (ie, the amount of money consumed); if the conditions for re-consumption are established, the programmed address of this consumption is calculated again in a sequential manner, and finally the address is programmed to 1 (the initial value of all Bits is 0). In this way, every time you do subtraction, no matter how many times the subtraction value s is than the unit value, only one bit is programmed. In the OTP used in this design, programming a bit of data only takes about 200μs, while the traditional method based on EEPROM needs to program 1281 A bit of data takes about 4ms, which greatly reduces the programming time. The whole process is shown in Figure 3.

　　2.4 Read wallet

　　Reading the wallet means reading out the balance. This is the most basic operation in an electronic wallet. It is completed in three steps: the first step is to pass identity authentication and password verification between the card and the card reader; the second step, Starting from the last address in the subtraction area, search for the address of the highest programmed bit in reverse order, denoted as LBAddr; in the third step, subtract the address FBAddr of the first bit in the subtraction area from LBAddr to get the unit value Use times UT, and subtract UT from the available times T in the subtraction area to get the unused times RT of the e-wallet unit value; the fourth step, multiply U by RT to get the balance R, and then return it to the card reader.

　　2.5 Other

　　In addition to the function of a disposable electronic wallet, this design also has a total of 10 blocks of storage space for users to store other information, which can be used as a storage card with encryption function. At the same time, each sector corresponds to a cipher block, and each cipher block corresponds to a cipher pointer. When the password pointer is zero, the password used for encryption verification is the default password, which is automatically given by the digital circuit. After the user has programmed the cipher block, the corresponding cipher pointer will be programmed at the same time, and then the password written by the user will be used for the encryption verification operation.

　　3 The realization of electronic wallet

　　The disposable electronic wallet adopts the ISO/IEC 14443 TypeA protocol and is compatible with the popular MifareOne series of commands on the market. Except that the INCREMENT and RESTORE commands are not supported, the other command formats are the same as S50 or compatible cards. Including the analog circuit, the chip of the disposable electronic wallet is shown in Figure 4.

　　Figure 4 Overall block diagram of the chip

　　In the analog circuit, the function of the rectifier circuit is to convert the AC voltage of the RF signal coupled in the card reader into a DC power supply voltage, and add a voltage stabilizing circuit after the rectifier circuit to prevent the DC voltage from being too high; the power-on reset circuit is The digital circuit generates a reset signal to reset all registers of the digital circuit when the card enters the effective magnetic field range of the card machine; the demodulation circuit demodulates the data signal in the carrier as the signal input of the digital circuit; the modulation circuit is based on The signal returned by the digital circuit modulates the antenna and returns the signal to the card reader; the clock shaping circuit shapes the clock signal divided by 13.56M in the carrier and supplies it to the digital circuit.

　　In the digital circuit, the receiving module mainly translates the signal encoded by the 14443 TypeA protocol into binary code, and provides various frequency division clocks for subsequent modules; the function of the data processing module is mainly instruction decoding, 0TP memory for reading and writing operations , The state of the card is transferred; the encryption unit uses the stream cipher to encrypt the data, except for the commands specified by 14443 TypeA, the communication of other commands are encrypted; the output module returns a signal to the card reader in the format specified by the 14443 TypeA protocol.

　　In terms of memory, it uses Kailu's patented technology XPM memory. XPM adopts the principle of breakdown of the oxide layer to achieve one write and multiple reads. Compared with the use of EEP-ROM in conventional RFID, this kind of memory can be realized under conventional CMOS process, its cost is lower than EEPROM process, and the data storage capacity can reach more than 50 years, while the data storage capacity of EEPROM is less than 10 years . XPM's storage mechanism makes it less susceptible to data loss due to external interference (such as lasers, microwaves) like EEPROM, making it particularly suitable for applications in security areas such as bus cards and electronic passports.

　　4 Conclusion

　　A one-time electronic wallet RFID card is implemented in the 14443 TypeA protocol. This one-time electronic wallet is based on OTP memory, the instructions and encryption methods are compatible with the commonly used S50 in the market, and can be easily applied to existing card reader systems. The basic principle of a disposable electronic wallet is that each Bit in the subtraction area represents the use of a unit value. Based on this, the expression method of the disposable electronic wallet face value, the implementation steps of deducting the wallet and the operation method of reading the balance are given. The disposable electronic wallet was realized under the process conditions of SMIC 0.18/μm, and the tape-out test was successful.

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