Wednesday, May 22, 2013

CCID descriptor statistics: bClassGetResponse

Article from the serie "CCID descriptor statistics"

The bClassGetResponse field is a number value from the USB CCID descriptor:
Significant only for CCID that offers an APDU level for exchanges.

Indicates the default class value used by the CCID when it sends a Get Response command to perform the transportation of an APDU by T=0 protocol.

Value FFh indicates that the CCID echoes the class of the APDU.

0xFF15159.45 %
0x0010340.55 %

The statistics here are the same as for the bClassEnvelope field.

All the readers have bClassEnvelope = bClassGetResponse set to either 0x00 or 0xFF.
It is not surprising to have bClassEnvelope = bClassGetResponse since the two fields are used to manage APDU (short or extended) with T=0 cards.