APDUcommandos

APDUcommandos is an informal label sometimes used to refer to the set of APDU commands used in smart card communication. APDU stands for Application Protocol Data Unit, a messaging format defined by ISO/IEC 7816 for exchanging instructions between a card reader and a smart card or secure element. The term APDUcommandos is not an official standard but a colloquial way to discuss the commands that carry instructions and data to and from the card.

A command APDU typically consists of four mandatory fields—CLA (class), INS (instruction), P1 and P2 (parameters)—and may include optional data fields such as Lc (length of command data), Data, and Le (expected length of response). The card responds with a response APDU, which often contains data followed by two status bytes, SW1 and SW2, indicating the result of the operation. Cards may support different command sets and may return additional data through GET RESPONSE.

APDUcommandos are employed across various smart card applications, including financial cards (EMV), SIM and eSIM, government IDs, and mobile device secure elements. Common instructions include SELECT (to choose an application), READ BINARY, UPDATE BINARY, GET RESPONSE, VERIFY (for user authentication), and GENERATE AC (generate the application cryptogram).

Communication protocols between reader and card include T=0 and T=1, with differences in data transfer methods. Cards may support extended length fields and CASE structures (CASE 1–CASE 4), affecting how commands are formed and parsed. Security considerations are central, as APDUs may carry sensitive data and cryptographic operations, often protected by PINs, keys, or secure messaging. Development and testing rely on interfaces such as PC/SC and compatible readers, and on understanding the card’s specific command set.