Strange data received from java smart card APDU?

Question

I can send most data from the smart card without a problem. I noticed i always need to remove the first 6 bytes in the APDU to get the real data for some reason.

However, when sending one particular data, it's very hard to know where the data is in the APDU.

This is the code of the Java smartcard simulator:

data = new byte[] {(byte)0x6302}; 
apdu.setOutgoing();
apdu.setOutgoingLength((short) data.length);
apdu.sendBytesLong(data, (short) 0, (short) data.length);

The data expected to be sent/received is:

{0x2}

However, the data received in the middleware response APDU is:

responseApdu.getData():

{0x80, 0x32, 0x0, 0x0, 0x8, 0x0, 0x0, 0x1, 0x5c, 0x6, 0xf9, 0x63, 0x33, 0x1, 0x2, 0x90, 0x0}

I also tried logging the APDU that is sent by the java card simulator; it is the following data:

SendAPDU() data (apdu.getBuffer()):

{0x2, 0x32, 0x0, 0x0, 0x8, 0x0, 0x0, 0x1, 0x5c, 0x6, 0xf9, 0x63, 0x33, 0x0, ..... (all 0x0 after this point)}

Offset CDATA: 5

Can somebody help me understand why the data sent (or read before even sending) is so different from the actual data sent? Is it some kind of padding? How can I get the original data sent?

your statement data = new byte[] {(byte)0x6302}; creates a byte array with only one byte element 0x02. Is it really what you want? — nandsito
@nandsito It is, it's a small message to let the middleware know to send specific data back to the java card. However, I'm unable to retrieve the 0x02 from the middleware (see output). — Kevin Van Ryckegem
Your command has a first byte (the CLA byte) set to 0x02. That means that you use logical channel 3. That's not something that is likely to work and I wonder why that first byte has such a value. The response looks like an altered command APDU followed by the response, including length and status word; I don't see an immediate explanation for that. Setting the CLA byte to 0x00 or 0x80 may however be worth trying. — Maarten Bodewes

JavaCardOS JavaCardOS · Accepted Answer · 2017-05-15T02:01:44

Change code to:

data = new byte[] {(byte) 0x63, (byte) 0x02}; 
apdu.setOutgoing();
apdu.setOutgoingLength((short) data.length);
apdu.sendBytesLong(data, (short) 0, (short) data.length);

The data bytes { 0x63, 0x02 } will be sent out.

And the data you mentioned in your question:

The Response APDU data is:

responseApdu.getData():
{0x80, 0x32, 0x0, 0x0, 0x8, 0x0, 0x0, 0x1, 0x5c, 0x6, 0xf9, 0x63, 0x33, 0x1, 0x2, 0x90, 0x0}

Means command data is: { 0x80, 0x32, 0x0, 0x0, 0x8, 0x0, 0x0, 0x1, 0x5c, 0x6, 0xf9, 0x63, 0x33, 0x1};, and response data is: { 0x2, 0x90, 0x0 };

The apdu buffer is:

SendAPDU() data (apdu.getBuffer()):
{0x2, 0x32, 0x0, 0x0, 0x8, 0x0, 0x0, 0x1, 0x5c, 0x6, 0xf9, 0x63, 0x33, 0x0, ..... (all 0x0 after this point)}
Offset CDATA: 5

Means the data byte 0x02 will be sent (the sent length is 1 byte), the SW 0x9000 ({ 0x90, 0x00 }) will be sent after this byte. The Offset CDATA is not used when outgoing. And other data bytes in the APDU buffer is your APDU commands, the first byte is overwrite by the outgoing bytes (Here only 1 byte, 0x02).

Note: process of APDU.sendBytesLong(data, offset, length):

1). Copy data with offset and length to APDU buffer;

2). Send data using APDU buffer;

3). Send SW;

Strange data received from java smart card APDU?

1 Answers