smart card application protocol data unit
{{Short description|Communication unit between a reader and a smart card}}
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.{{Cite ISO standard
|csnumber=77180
|title=ISO/IEC 7816-4:2020 — Identification cards — Integrated circuit cards
}}
APDU message command-response pair
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){{cite journal
|last=Celer
|first=Victor
|date=2021-12-25
|title=Using the SIMcard as a Security Module (HSM)
|url=https://www.celersms.com/android-SIM-HSM.htm
|journal=CelerSMS
|volume=1
|issue=2
|pages=13–17
|issn=2745-2336
|oclc=1295467772
}} 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).
| class="wikitable"
! colspan="3" | Command APDU |
| Field name
! Length (bytes) ! Description |
|---|
| CLA
| 1 | Instruction class - indicates the type of command, e.g., interindustry or proprietary |
| INS
| 1 | Instruction code - indicates the specific command, e.g., "select", "write data" |
| P1-P2
| 2 | Instruction parameters for the command, e.g., offset into file at which to write the data |
| Lc
| 0, 1 or 3 | Encodes the number (Nc) of bytes of command data to follow 0 bytes denotes Nc=0 1 byte with a value from 1 to 255 denotes Nc with the same length 3 bytes, the first of which must be 0, denotes Nc in the range 1 to 65 535 (all three bytes may not be zero) |
| Command data
| Nc | Nc bytes of data |
| Le
| 0, 1, 2 or 3 | Encodes the maximum number (Ne) of response bytes expected 0 bytes denotes Ne=0 1 byte in the range 1 to 255 denotes that value of Ne, or 0 denotes Ne=256 2 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 65 536 3 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 |
| colspan="3" | Response APDU |
| Response data
| Nr (at most Ne) | Response data |
| SW1-SW2 (Response trailer) | 2 | Command processing status, e.g., 90 00 (hexadecimal) indicates success |
References
{{reflist}}
See also
External links
- [https://web.archive.org/web/20090624235219/http://cheef.ru/docs/iso/ Smartcard ISOs, contents ]
- [https://web.archive.org/web/20090630004017/http://cheef.ru/docs/HowTo/APDU.info Selected list of smartcard APDU commands]
- [https://web.archive.org/web/20090623030155/http://cheef.ru/docs/HowTo/SW1SW2.info Selected list of SW1 SW2 Status bytes]
- [https://web.archive.org/web/20090330082954/http://www.wrankl.de/SCTables/SCTables.html More information about APDU commands and APDU responses]