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APDU.md

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Application Protocol Data Unit (APDU)

The communication protocol used by BOLOS to exchange APDU is very close to ISO 7816-4 with a few differences:

  • Lc length is always exactly 1 byte
  • No Le field in APDU command
  • Maximum size of APDU command is 260 bytes: 5 bytes of header + 255 bytes of data
  • Maximum size of APDU response is 260 bytes: 258 bytes of response data + 2 bytes of status word

Status words tend to be similar to common APDU responses in the industry.

Command APDU

Field name Length (bytes) Description
CLA 1 Instruction class - indicates the type of command
INS 1 Instruction code - indicates the specific command
P1 1 Instruction parameter 1 for the command
P2 1 Instruction parameter 2 for the command
Lc 1 The number of bytes of command data to follow (a value from 0 to 255)
CData var Command data with Lc bytes

Response APDU

Field name Length (bytes) Description
RData var Reponse data (can be empty)
SW 2 Status word containing command processing status (e.g. 0x9000 for success)