ISO/IEC 7816-4

ISO/IEC 7816-4 defines the APDU (Application Protocol Data Unit) command structure for interacting with smart card applications. Originally designed for contact smart cards, this standard is equally critical for contactless NFC applications via ISO 14443-4. It specifies SELECT, READ BINARY, UPDATE BINARY, and authentication commands used by NFC Forum Type 4 tags, payment cards, and identity credentials. APDU commands form the application layer of all high-security NFC interactions.