Random data generator applet returns `0x6F00` - javacard

Question

I wrote the below program to generate random numbers of different lengths, using two different algorithms (ALG_SECURE_RANDOM and ALG_PSEUDO_RANDOM).
P1 and P2 in the APDU command specify the algorithm and the random length in order.
P1 = 0X01 : ALG_SECURE_RANDOM
P1 = 0X02 : ALG_PSEUDO_RANDOM
P2 = Random number length
public class RandGen extends Applet {
byte[] generatedArray;
byte[] generatedRandom;
RandomData randomDataSecure = RandomData
.getInstance(RandomData.ALG_SECURE_RANDOM);
RandomData randomDataPseudo = RandomData
.getInstance(RandomData.ALG_PSEUDO_RANDOM);
private RandGen() {
}
public static void install(byte bArray[], short bOffset, byte bLength)
throws ISOException {
new RandGen().register();
}
public void process(APDU apdu) throws ISOException {
if (selectingApplet()) {
return;
}
byte[] buffer = apdu.getBuffer();
generatedArray = JCSystem.makeTransientByteArray(
(short) buffer[ISO7816.OFFSET_P2], JCSystem.CLEAR_ON_DESELECT);
switch (buffer[ISO7816.OFFSET_P1]) {
case (0x01):
generatedRandom = secureRandomGenerator(apdu);
break;
case (0x02):
generatedRandom = pseudoRandomGenerator(apdu);
break;
default:
return;
}
Util.arrayCopyNonAtomic(generatedRandom, (short) 0, buffer, (short) 0,
(short) ISO7816.OFFSET_P2);
apdu.setOutgoingAndSend((short) 0, (short) ISO7816.OFFSET_P2);
}
public byte[] secureRandomGenerator(APDU apdu) {
byte[] buffer = apdu.getBuffer();
randomDataSecure.generateData(generatedArray, (short) 0,
(short) buffer[ISO7816.OFFSET_P2]);
return generatedArray;
}
public byte[] pseudoRandomGenerator(APDU apdu) {
byte[] buffer = apdu.getBuffer();
randomDataPseudo.generateData(generatedArray, (short) 0,
(short) buffer[ISO7816.OFFSET_P2]);
return generatedArray;
}
}
The CAP file generated and uploaded on the card successfully, but when I send APDU commands to the card, I receive the 0X6F00 status word :
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000202
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 02 02
Received (SW1=0x90, SW2=0x00)
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000102
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 01 02
Received (SW1=0x6F, SW2=0x00)
Is there something wrong in my applet?
Update:
Based on dear #Vojta's answer, I replace
Util.arrayCopyNonAtomic(generatedRandom, (short) 0, buffer, (short) 0,
(short) ISO7816.OFFSET_P2);
apdu.setOutgoingAndSend((short) 0, (short) ISO7816.OFFSET_P2);
With following lines in process() method :
Util.arrayCopyNonAtomic(generatedRandom, (short) 0, buffer, (short) 0,
(short) buffer[ISO7816.OFFSET_P2]);
apdu.setOutgoingAndSend((short) 0, (short) buffer[ISO7816.OFFSET_P2]);
Now I have a weird output in OpenSC-Tool output :
Secure random generator :
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000110
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 01 10
Received (SW1=0x90, SW2=0x00):
B8 1F 80 25 A2 8E 25 30 F8 22 F8 40 0F AE B0 6C ...%..%0.".#...l
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 .....
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000110
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 01 10
Received (SW1=0x6F, SW2=0x00)
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000110
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 01 10
Received (SW1=0x90, SW2=0x00):
F6 45 A9 0C 0C 3B 3A 5A 5F DC A8 36 .E...;:Z_..6
Pseudo random generator :
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000210
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 02 10
Received (SW1=0x90, SW2=0x00):
37 FD FC 67 EB 9E 21 00 6B E9 44 A7 21 3F 31 9A 7..g..!.k.D.!?1.
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 .......
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000210
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 02 10
Received (SW1=0x6F, SW2=0x00)
OSC: opensc-tool.exe -s 00a404000b0102030405060708090000 -s 00000210
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 0B 01 02 03 04 05 06 07 08 09 00 00
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 02 10
Received (SW1=0x90, SW2=0x00):
72 FE 48 1B 9A A0 BD 2D DF F9 E7 F8 58 CF B7 C0 r.H....-....X...
00 00 00 00 00 00 00 00 00 00 00 ...........
Why I have different output for a single command?

Answer 1

There is a little bug in your code. You want
Util.arrayCopyNonAtomic(generatedRandom, (short) 0, buffer, (short) 0,
(short) buffer[ISO7816.OFFSET_P2]);
instead of
Util.arrayCopyNonAtomic(generatedRandom, (short) 0, buffer, (short) 0,
(short) ISO7816.OFFSET_P2);
General rule: ALWAYS surround the content of your process method with a try-catch block and set status words according to the type and reason of the exception. Otherwise you get only 6F00 and you do not know what really happened. If you followed this rule, you would know that ArrayIndexOutOfBoundsException was thrown.
Answer to update:
Weird output is caused by the fact, that
Util.arrayCopyNonAtomic(generatedRandom, (short) 0, buffer, (short) 0,
(short) buffer[ISO7816.OFFSET_P2]);
apdu.setOutgoingAndSend((short) 0, (short) buffer[ISO7816.OFFSET_P2]);
overwrites the buffer[ISO7816.OFFSET_P2] with some random value and then this value is used on the next line. You should store buffer[ISO7816.OFFSET_P2] in RAM in the beginning of the process method:
final byte p2 = buffer[ISO7816.OFFSET_P2];
Answer to comment below:
You have troubles for P2 >= 0x80, because of casting byte to short. Unfortunately, JavaCard handles byte as signed, that is why your length for P2 >= 0x80 is negative. You could easily avoid this by:
final short outputLen = (short) (buffer[ISO7816.OFFSET_P2] & 0xFF);

Answer 2

command not supported
You have the wrong instruction joining together.