Java Security

Hi there,
I am struggling to encrypt more than 117 bytes of data with a 1024 bit RSA key.
If I try to encrypt (write to my OutputStreamWriter) 118 Bytes ("A"s) or more, the file I am writing to is just empty and I get an exception whe trying to read it.

I know the encryptable bytes (blocksize) are related to the key length: blocksize = keylength / 8 -11
I also know RSA encryption of large files is discouraged, because it is like 100x slower than for instance AES and was originally only intended to exchange symmetric keys.

Still I need to be able to asymmetrically encrypt at least 5kb of Data.

I am out of ideas here and have no understanding of why the block size is limited (i know from hours of "googling" that it is limited as described above though).

So, I would be very glad If somebody could point out a way how I could encrypt more than 117 bytes (without using a longer key of course).

import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.FileOutputStream;
import java.io.Reader;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.security.PublicKey;
import java.io.IOException;
import java.security.InvalidKeyException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import javax.crypto.*;

public class strchrbty {
	public static void main(String[] args) {
		
		//generate Keys
		
		PublicKey publicKey = null;
		PrivateKey privateKey = null;
		try {
			KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
			kpg.initialize(1024);
			KeyPair kp = kpg.generateKeyPair();
			publicKey = kp.getPublic();
			privateKey = kp.getPrivate();
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		}
		
		//------ENCODE------
		
		try {
			
	    	//initialize cipher
	    	Cipher cipher = Cipher.getInstance("RSA");   
			cipher.init(Cipher.ENCRYPT_MODE, publicKey);    
	    	
			OutputStream cos = new CipherOutputStream(new FileOutputStream("c:\\test.txt"), cipher);
	    	Writer out = new OutputStreamWriter(cos);
	    	
	    	// 1024 bit (key length) / 8 bytes - 11 bytes padding = 117 Bytes Data.
	    	//  for 118 Bytes (or more) Data: c:\\test.txt is empty annd no Data is read.
	    	for(int i = 0; i<117; i++) {
	    		out.write("A");
	    	}
	    	out.close();
	    	cos.close();
	    	
	    } catch (InvalidKeyException e) {
	    	e.printStackTrace(); 	
	    } catch (NoSuchPaddingException e) {
	    	e.printStackTrace(); 		
	    } catch (NoSuchAlgorithmException e) {
	    	e.printStackTrace(); 	
	    } catch (IOException e) {
	    	e.printStackTrace();
	    }
	    
	    //------DECODE------
	    
	    try {
	    	StringBuffer buf = new StringBuffer(); 
	    
	    	Cipher cipher2 = Cipher.getInstance("RSA");  
	    	cipher2.init(Cipher.DECRYPT_MODE, privateKey); 
		
	    	//read char-wise
	    	InputStream cis = new CipherInputStream(new FileInputStream("c:\\test.txt"), cipher2);
    		Reader in = new InputStreamReader(cis);
    		for(int c = in.read(); c != -1; c = in.read()) { 
                buf.append((char)c); 
            }
    		
    		//output
    		System.out.println(buf.toString());
    		
    		in.close();
    		cis.close();
    		
    		
		} catch (InvalidKeyException e) {
	    	e.printStackTrace(); 	
	    } catch (NoSuchPaddingException e) {
	    	e.printStackTrace(); 		
	    } catch (NoSuchAlgorithmException e) {
	    	e.printStackTrace(); 	
		} catch(IOException e) {
        	e.printStackTrace();
        }
		
	}
}

Regards.

Edited by: junghansmega on Sep 10, 2008 3:41 PM
Sorry about the bad autoformating.... It only occurrs in here, in my eclipse it looks fine =(