Smart card application protocol data unit

In the context of smart cards, an application protocol data unit (APDU) is the communication unit between a smart card reader and a smart card. The structure of the APDU is defined by ISO/IEC 7816-4 Organization, security and commands for interchange.0 bytes denotes Nc=01 byte with a value from 1 to 255 denotes Nc with the same value3 bytes, the first of which must be 0, denotes Nc in the range 1 to 65 535 (all three bytes may not be zero)0 bytes denotes Ne=01 byte in the range 1 to 255 denotes that value of Ne, or 0 denotes Ne=2562 bytes (if extended Lc was present in the command) in the range 1 to 65 535 denotes Ne of that value, or two zero bytes denotes 65 5363 bytes (if Lc was not present in the command), the first of which must be 0, denote Ne in the same way as two-byte Le In the context of smart cards, an application protocol data unit (APDU) is the communication unit between a smart card reader and a smart card. The structure of the APDU is defined by ISO/IEC 7816-4 Organization, security and commands for interchange. There are two categories of APDUs: command APDUs and response APDUs. A command APDU is sent by the reader to the card – it contains a mandatory 4-byte header (CLA, INS, P1, P2) and from 0 to 65 535 bytes of data. A response APDU is sent by the card to the reader – it contains from 0 to 65 536 bytes of data, and 2 mandatory status bytes (SW1, SW2).