The study of developing Java Card applications for GSM SIM/WIM is included by the authors in various research projects and papers. For signing purpose there is a standard Java card applet that runs within Java Card Virtual Machine from SIM/WIM. In message passing model there is all the time a selected applet/application in the card and when is receiving an APDU Command. A communication process is called failed if there were execution errors (SW1=0圆4 or SW1=0圆5 and SW2 has the error code for execution) or checking errors (SW1=from 0圆7 to 0圆F and SW2 has the code for checking error). The fields SW1 and SW2 are parsed and interpreted together, but a communication process is called complete if there were no problems (SW1=0圆1 and SW2=0x90 or any-0xnn) or if there were only warnings (SW1=0圆2 or SW1=0圆3 and SW2 contains the warning code). The structure for an APDU Response is simple and is shown in the table 2: The fields’ explication for APDU Response is the following: Data Field – has variable length which is determined by the value of the byte field Le from the APDU Command SW1 – has one byte and represent the status word 1 SW2 – has one byte and represent the status word 2.
a host application sends to the CAD but the CAD sends to the applet the same APDU commands with structures and values which respect the standards.
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