JavaCard OS

Posted: **Mon Jul 11, 2016 1:54 am**

I want to do RSA encryption & decryption in my applet. And my java card supports T=0 protocol. So can I send the data in an APDU command and also to get the encrypted data in the same APDU's response? Must I write two different commands to send the data for encryption and get the encrypted data?

Posted: **Tue Jul 12, 2016 1:55 am**

For T=0 protocol, you can not receive the data in the same APDU response. You should send GET RESPONSE command to get the data.
It's the limitation of T=0 protocol.

Posted: **Tue Jul 12, 2016 4:50 am**

Thanks for your reply.

I also have another question. Here is section of my code. But it can't be able to work. It always threw exception. Could you point me where I made mistake?

Code: Select all

//In constructor
cipherRSA = Cipher.getInstance(Cipher.ALG_RSA_PKCS1, false);

//In Process Method
short len = apdu.setIncomingAndReceive(); // This is the amount of data read from the OS.

while (len < lc) 
        {
            len += apdu.receiveBytes(len);
        }
              case ENCRYPT_HASH_INS:
                    encryptHash(apdu, len);
                    break;
                    
               case GET_ENCRYPT_HASH_INS:
                    getEncryptedHash(apdu);
                    break;

/*********************************************************************/
public void encryptHash( APDU apdu, short length)
     {
          byte [] buffer = apdu.getBuffer();
          cipherRSA.init(rsa_PrivateCrtKey, Cipher.MODE_ENCRYPT);
          short cipherLength = cipherRSA.doFinal(buffer, buffer[ISO7816.OFFSET_CDATA], length, buffer, buffer[ISO7816.OFFSET_CDATA]);
          encyrtedHash = JCSystem.makeTransientByteArray(cipherLength, JCSystem.CLEAR_ON_RESET);
          Util.arrayCopyNonAtomic(buffer, buffer[ISO7816.OFFSET_CDATA], encyrtedHash, (short) 0, length);
     }
/*********************************************************************/     
 public void getEncryptedHash(APDU apdu)
     {
          apdu.setOutgoing();
          apdu.setOutgoingLength((short)encyrtedHash.length );
          apdu.sendBytesLong(encyrtedHash, (short)0, (short)(encyrtedHash.length));
          
     }

Posted: **Wed Jul 13, 2016 1:50 am**

There are some problems in your code.

Try the below code. This code will encrypt your data and send the response in one APDU.

Code: Select all

//In constructor
cipherRSA = Cipher.getInstance(Cipher.ALG_RSA_PKCS1, false);

//In Process Method
short len = apdu.setIncomingAndReceive(); // This is the amount of data read from the OS.

while (len < lc) 
     {
          len += apdu.receiveBytes(len);
     }
           case ENCRYPT_HASH_INS:
                    encryptHash(apdu, len);
                    break;
 
 /*********************************************************************/
public void encryptHash( APDU apdu, short length)
     {
          byte [] buffer = apdu.getBuffer();
          cipherRSA.init(rsa_PrivateCrtKey, Cipher.MODE_ENCRYPT);
          short cipherLength = cipherRSA.doFinal(buffer, ISO7816.OFFSET_CDATA, length, buffer, ISO7816.OFFSET_CDATA);
          
          apdu.setOutgoing();
          apdu.setOutgoingAndSend(ISO7816.OFFSET_CDATA, cipherLen)
          
     }

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