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 [通信技术]smart card 4 |
gun 发表于 2005/1/14 17:28:24 |
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So the chip contains CPU but it’ll need to have some memory if at all it wants to process something and do some computations. Well, the primary use of the IC card had been for the portable storage and retrieval of data but now they provide very advanced security features like storing private keys and certificates for authenticating users to some external system, for example a secure website. Hence another fundamental component of the IC is a memory module. The following list represents the most commonly used memory types:
ROM Read only memory (mask ROM)
EEPROM Electrically erasable PROM
RAM Random access memory
A particular chip may have any combination of these memory types. Each of these memory types possesses particular characteristics that determine their usability in a particular ICC.
The ROM: These types of memories, some times also referred to as persistent non-mutable, are fixed and can’t be changed once manufactured by the semiconductor company. This is a low cost memory, because it occupies minimum space on the silicon substrate and the manufacturing is also less complex.
The EEPROM: This memory is electrically erasable and programmable by the user and can be rewritten many times (about a million times).
All of these memories described above are non-volatile. That is they retain their contents when the power is removed.
The random access memory (RAM): This is the most common one because every single desktop on the planet uses them. This memory is volatile memory and the data content is lost as soon as the power is removed.
The requirement of the memory and its type varies in accordion with the requirement and the place where the smart card is to be employed for example one card utilize a little EEPROM memory (128 - 512 bytes) and a simple memory control logic for a telephone card and in case of ATM transaction or for provision of higher security the smart card may employ CPU, additional coprocessor and RAM, ROM or EEPROM, FLASH ROM with a greater storage capability. Additional co processor is required for encryption process or for carrying out additional calculations. The smart term is associated with these cards because of their capability to perform the calculation with the help of CPU embedded in the chip inside the card during the manufacturing process.
The control logic provides protection system in the card so that it can be used by a fake person in addition with the task of carrying out communication protocols. The ICC has security intrinsically built in and it does provide a tamper resistant domain that is tricky to match with the somewhat larger security boxes that handle cryptographic processes. Different types of ICC can be differentiated on the basis of their content such as given below:
Memory only ICC
Memory with security logic
Memory with CPU
Smart card employs some form of access code for accessing memory through the security logic. The access code size, which is used for the authorized access of the memory may be quite large i.e. 64 bits or more. The use of EEPROM memory is not considered safe for the cards, which are to be used for making the financial transactions as fraudsters can obtain a financial advantage by unauthorized use. The smart card that employs CPU or additional processor for the cryptographic purpose have the associated benefit in regard of security features and can be safely used for the use of transaction or other security concerns safely.
The term application that is widely associated with the Smart Card, implies the software or programs that the IC implements. The program may be in the form of a file manager for organizing the storage and retrieval of data or for carrying out complex calculations. These applications are fully implemented in the logic of the chip. Smart cards employs the communications logic for carrying out the communication with the host, through this logic, chip accepts commands from the card acceptance device (CAD) and receives and transmits the application data. Since the CPU is capable of carrying out complex calculations, the ICC which contains a CPU can handle more sophisticated applications and even multi applications. | |
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