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Smart card application protocol data unit
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<p>In the context of <a href="/facts/Smart_card/K7b9lowS">smart cards</a>, an application protocol data unit (APDU) is the communication unit between a <a href="/facts/Card_reader/zql4fN7a">smart card reader</a> and a smart card. The structure of the APDU is defined by <a href="/facts/ISO/IEC_7816/elBdXa4k">ISO/IEC 7816</a>-4 <i>Organization, security and commands for interchange</i>. </p>