Java Security

Hi,

I'm writing an application that is going to use RSA encryption/decryption.
I know that there are some problems with encrypting big arrays (error: input too large for RSA cipher), so I created my own function that's parsing the data before the encryption.

And know the problem - it seems that sometimes it works, and sometimes it doesn't.
I mean for the same input array I can get different result - everything goes well or I get

org.bouncycastle.crypto.DataLengthException: input too large for RSA cipher.

And I really don't understand why it sometimes works just fine and sometimes (all the control data is the same -> commented system.outs) throws the exception.

Can anyone help?



Here is the code:

public static byte[] encrypt(byte[] data, CipherParameters key) {
        System.out.println("<--------START--ECRYPTION---------->");
        RSAEngine engine = new RSAEngine();
        engine.init(true, key);

        int blockSize = engine.getOutputBlockSize();
        //System.out.println("blockSize:"+blockSize);

        int numWholeBlocks = data.length / blockSize;
        //System.out.println("numWholeBlocks:"+numWholeBlocks);

        int sizeLastBlock = data.length % blockSize;
        //System.out.println("sizeLastBlock:"+sizeLastBlock);

        int numBlocks;
        if (sizeLastBlock > 0) {
            numBlocks = numWholeBlocks + 1;
        } else {
            //when the size is a multi of a  blockSize
            numBlocks = numWholeBlocks;
            sizeLastBlock=blockSize;
        }
        //System.out.println("numBlocks:"+numBlocks);
        //System.out.println("sizeLastBlock:"+sizeLastBlock);

        byte[] ciphertext = new byte[numBlocks * blockSize];
        //System.out.println("ciphertext.length:"+ciphertext.length);

        byte[] aux;

        int WN = numBlocks - numWholeBlocks;

        for (int i = 0; i < numWholeBlocks; i++) {
            //System.out.println("blockSize: "+blockSize);
            //System.out.println("i*blockSize: "+i*blockSize);
            aux = engine.processBlock(data, i * blockSize, blockSize);
            System.arraycopy(aux, 0, ciphertext, i * blockSize, blockSize);
        }

        for (int i = 0; i < WN; i++) {
            aux = engine.processBlock(data, i * blockSize, sizeLastBlock);
            System.arraycopy(aux, 0, ciphertext, numWholeBlocks * blockSize, blockSize);
        }




        System.out.println("<---------END--ECRYPTION----------->");

        return ciphertext;
    }