The purpose of a simple RFID system is to enable data to be transmitted by a mobile device, called a tag, which is read by an RFID reader and processed according to the needs of a particular application. The data transmitted by the tag may provide identification or location information or specifics about the product tagged, such as price, color, date of purchase, and so on, depending on the particular installation and design goal of the system as implemented.
In a typical RFID system, individual objects are equipped with a small, inexpensive tag. The tag contains at least a digital memory chip with a unique identifier (UID) along with an RF interface. Many modern tags contain additional features such as user-programmable memory and cryptographic hardware for authentication and/or transport level encryption. The interrogator, an antenna packaged with a transceiver and decoder, emits and powers the RFID tag so the transceiver can read and write data to the tag. When an RFID tag passes through the electromagnetic zone, it detects the reader's activation signal.
You can compare this to a flashlight and mirror. The flashlight emits energy in the form of light. The mirror reflects the energy and sends the light back toward the source. Similarly, the RFID reader will send out an RF signal, which the tag uses as a source of energy to power the onboard antenna and transmit data back.
After the reader receives the data from the RFID tag, it decodes the data encoded in the tag's onboard integrated circuit and then passes the data to the host computer for additional data processing and business logic decisions. The application software on the reader or middleware processes the data and may possibly perform various functions to identify collisions and other performance issues.
RFID tags are available in a variety of forms. Some of them simply have a factory preprogrammed unique ID. Others provide write-once or even rewritable user memory for arbitrary data. In addition, some tags implement cryptography based on state machines and hard-wired logic. Finally, some tags are actually cryptographic smartcards with a contactless interface. Such smartcards can provide 3DES (a block cipher created by using the Data Encryption Standard (DES) cipher three times consecutively) and RSA cryptography and feature built-in CPUs with operating systems and user applications— even Java cards with contactless (ISO 14443) RFID interfaces exist.
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