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 [通信技术]smart card 2 |
gun 发表于 2005/1/14 17:24:36 |
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Is a "smart card" the same plastic card that I use at the ATM? No, probably not. The ATM cards are just plastic cards with a magnetic stripe bearing some information. A Smart Card is really smart. You might ask why?
The old ATM cards and other proprietary magnetic stripe cards do not provide security and do not have any embedded hardware in them. They’re more like an audio tape which can be tampered with! Smart cards are really a Smart Solution to provide security bundled with ease of use. Most Smart cards, if not all, incorporate an integrated circuit chip (ICC) on the plastic card. This ICC is usually a micro-controller with limited computational power and I/O support. ISO uses the term, Integrated Circuit Card (ICC) to identify all those devices where an integrated circuit is contained within an ISO ID1 identification card piece of plastic. The card is 85.6mm x 53.98mm x 0.76mm and is the same as any other standard magnetic stripe card.
Types of Smart Cards
These Integrated Circuit Cards come in two forms when we categorize them based on the way we use tem, contact and contact-less. The former is easily identified due to its characteristic gold connector plate.
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Figure 1
Originally the ISO Standard (7816-2) defined eight contacts, but only 6 are actually used to communicate with the outside world and rest two are marked as RFU (Reserved for future use). The contact-less cards optionally may contain its own power source, however mostly the operating power is provided to the contact-less card by means of an inductive loop that uses low frequency electronic magnetic radiation. The signals needed for communication with the reader devices may be transmitted in a similar way or can use capacitive coupling or even an optical connection (IR).
The Contact card is the most widely used ICC to date largely because of its use as telephone prepayment card. Yes! The SIM card that we you use in our cell phones is just a Smart card without the plastic base. Most contact cards contain only a simple integrated circuit although some also use two chips; the other one is used to perform complex cryptographic computations (which I’ll explain shortly). The chip itself varies considerably between vendors and each takes it own way of programming application for it, but the Java Card™ initiative by Sun has made it a breeze to write Smart Card applications that can be downloaded onto the memory of these cards and can execute on any type of chip which supports the Java Card runtime environment. I’ll come to programming the Smart cards in next article of this series.
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Figure 2
Let us now consider the use of the 6 contacts used by the ICC:
Vcc is the supply voltage that drives the chips and is generally 3 to 5 volts with 10% deviation allowed. It used to be in 5-volt range prior to the recent move towards low power devices to make these cards.
Vss/GND pin is used to provide the substrate or ground reference voltage against which the Vcc potential is measured. It is usually 0 volts.
Reset is the signal line that is used to send the signal to the integrated circuit in order to reset it. This is a complex process that we shall describe later in more detail. There are two ways a card is reset:
Warm Reset: When a Signal is sent through this pin to reset the ICC.
Cold Reset: When the supply voltage is turned off and on again. Ejecting the card out and inserting again will have the same effect.
Clock pin is used to drive the logic of the embedded IC and is also used as the reference for the serial communications synchronization. This pin is provided because the ICC doesn’t have any clock generator onboard and needs this as external input. The card reader device provides this clock. The clock frequency is 5MHz generally but many high end ICCs use frequency multipliers to operate at higher frequencies up to 40 MHz.
Vpp pin is now optional and used only in old cards. Previously it was used for the high voltage signal that is necessary to program the EPROM memory. It was provided with two voltage levels. The lower one (or the idle state) is held down by the Card Reader device, until the higher level (or the active state) is required.
I/O pin is the serial input/output (SIO) connector. This is the signal line by which the underlying circuit receives commands and interchanges data with the outside world. This process will be explained in more detail when we talk about programming applications that receive these commands. | |
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