Abhi Ram

Paul Clapham wrote: outputfile.println(cipherText);

Right. So not only do you throw away all of the cipher text except the last line when you read it, when you write it you're appending an unnecessary line-end character.

But really your cipher text isn't a series of lines anyway, is it? It's just a series of characters. So you should really stop treating it as lines. Don't use any methods which write lines or read lines, just write all the characters to the file and then read them all back.

if i use character stream, when i read from file I am getting it as Integer. Again I need to do conversion

Can you give example

@paul - It is not series of lines , just a series of characters.

ok , I will write characters to the file and then read them back

Thanks , will let you know

Here is the code when user clicks send button - I do encrypt and store in file

cipherText = encrypt(originalText, publicKey); File ashwini = new File("cipher.txt"); FileWriter fwriter = null; try { fwriter = new FileWriter("cipher.txt",true); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } PrintWriter outputfile=new PrintWriter(fwriter); outputfile.println(cipherText); outputfile.close(); pw.println(cipherText);

Yes Paul thats my goal

Basically when i encrypt the text , i store it in file (cipher.txt) to later use it to decrypt it

also can you tell me how to store value in global variable which I can use later rather then in file

I corrected my mistake in above code and made below changes but getting different error

Error"Not PKCS#1 block type 2 or Zero padding" exception "

Run ChatClient.java - Dialog box is shown where user enters username. Then private key and public key are generated and stored in C:/username/publickey,C:/username/privatekey.

Above step repeats when we run ChatClient.java again.

Then user1 sends message to User2 in encrypted form using User2 public key (Which is working fine)(after encryption , message is stored in text file) then User2 clicks decrypt button which decrypts the text (reads the encrypted text from file) using User 2 private key then display in textarea.

When I trying to decrypt I am getting "Not PKCS#1 block type 2 or Zero padding" exception

public static byte[] encrypt(String text, PublicKey key) throws { // get an RSA cipher object and print the provider final Cipher cipher = Cipher.getInstance(ALGORITHM); // encrypt the plain text using the public key cipher.init(Cipher.ENCRYPT_MODE, key); byte[] cipherText = cipher.doFinal(text.getBytes("UTF8")); return org.apache.commons.codec.binary.Base64.encodeBase64(cipherText); } public static String decrypt(String text, PrivateKey key) throws { byte[] dectyptedText = null; // get an RSA cipher object and print the provider final Cipher cipher = Cipher.getInstance(ALGORITHM); // decrypt the text using the private key cipher.init(Cipher.DECRYPT_MODE, key); byte[] byteCipherText =org.apache.commons.codec.binary.Base64.decodeBase64(text): byte[] cipherData = cipher.doFinal(byteCipherText); return new String(dectyptedText); } private void btnDecryptActionPerformed(ActionEvent evt) throws { String name11 = this.getTitle(); String test90 = null; String PRIVATE_KEY_FILE = "C:/keys/"+name11+"/private.key"; BufferedReader in = null; try { in = new BufferedReader(new FileReader("cipher.txt")); } catch (FileNotFoundException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } try { while(in.ready()) { String stest= in.readLine(); test90 = stest; } } catch (IOException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } ObjectInputStream inputStream = null; try { inputStream = new ObjectInputStream(new FileInputStream(PRIVATE_KEY_FILE)); } catch (FileNotFoundException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } catch (IOException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } PrivateKey privateKey = null; try { privateKey = (PrivateKey) inputStream.readObject(); } catch (ClassNotFoundException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } catch (IOException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } try { inputStream = new ObjectInputStream(new FileInputStream(PRIVATE_KEY_FILE)); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } try { PrivateKey privatekey = (PrivateKey) inputStream.readObject(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } String plainText; // byte[] test100 = test90.getBytes(); // out.println(test100); plainText = decrypt(test90, privateKey); (Getting Error Here) decryptText.append(plainText); }

How to edit my original post ?

Sorry for small image

So in my chat application (As you can see two GUI with same GUI components)

In Client A - user types text and clicks send button, which will display the encrypted text in Text Area in Client B.

This is done using following line

pw.println("Encrypted Text:-"+ciphertext);

where pw is pw = new PrintWriter(client.getOutputStream(),true);

There is decrypted button in my GUI, which when clicked would display the text in another text area named decryptedtext. I do this by decryptText.setText(text2);

I have added listners to each button and in action performed i choose what to displayed based on which button clicked

RSAEncryption rsa=new RSAEncryption(1024); String text1 = tfInput.getText(); // String ciphertext = rsa.encrypt(text1); String userInput; BigInteger plaintext = new BigInteger(text1.getBytes()); BigInteger ciphertext = rsa.encrypt(plaintext); BigInteger plaintext1 = rsa.decrypt(ciphertext); String text2 = new String(plaintext1.toByteArray()); if ( evt.getSource() == btnExit ) { pw.println("end"); // send end to server so that server know about the termination System.exit(0); } else if(evt.getSource() == btnDecrypt) { decryptText.setText(text2); } else { // send message to server pw.println("Encrypted Text:-"+ciphertext); } }


Now problem is : When user clicks Decrypt button (in Client A button i.e where we click send button) it displays the text in textarea (decrypttext) but if i click same Decrypt button in Client B(where it displays the text sent from Client A) nothing is getting displayed. How to make it work in both windows

Thanks Richard - That makes sense

Can you explain second problem(in my second post)

Thanks Paul

I understood the mistake I am making I.E

I am encrypting using RSA public key but while decrypting I using different key. Thats why different output.

Which brings me to different problem

Please take a look at the image

I created a Simple RSA enabled chat application in java.

Message sent from Client A (or Client B) in encrypted form, the encrypted message is displayed on Client B (or Client A if sent from B) text area in encrypted form. User clicks decrypt button on client B then we will get the value from text area () then perform necessary cleaning then decrypt Problem: text2 is not in readable format (Look the attached Image ).

I have attached ChatClient.java ( where GUI and rsa code runs) and Chatserver( to run the server)



Chat Client
import java.io.*; import java.security.SecureRandom; import java.util.*; import java.math.BigInteger; import java.net.*; import javax.swing.*; import java.awt.*; import java.awt.event.*; import static java.lang.System.out; public class ChatClient extends JFrame implements ActionListener { String uname; PrintWriter pw; BufferedReader br; JTextArea taMessages; JTextArea decryptText; JTextField tfInput; JButton btnSend,btnExit,btnDecrypt; Socket client; public ChatClient(String uname,String servername) throws Exception { super(uname); // set title for frame this.uname = uname; client = new Socket(servername,9999); br = new BufferedReader( new InputStreamReader( client.getInputStream()) ) ; pw = new PrintWriter(client.getOutputStream(),true); pw.println(uname); // send name to server buildInterface(); new MessagesThread().start(); // create thread for listening for messages } public void buildInterface() { btnSend = new JButton("Send"); btnExit = new JButton("Exit"); btnDecrypt=new JButton("Decrypt"); decryptText = new JTextArea(); taMessages = new JTextArea(); decryptText.setRows(10); decryptText.setColumns(50); decryptText.setEditable(false); taMessages.setRows(10); taMessages.setColumns(50); taMessages.setEditable(false); tfInput = new JTextField(50); JScrollPane sp = new JScrollPane(taMessages, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED); add(sp,"Center"); JPanel bp = new JPanel( new FlowLayout()); bp.add(tfInput); bp.add(btnSend); bp.add(btnDecrypt); bp.add(btnExit); bp.add(decryptText); add(bp,"South"); btnSend.addActionListener(this); btnDecrypt.addActionListener(new Eavesdropper(decryptText)); btnExit.addActionListener(this); setSize(500,300); setVisible(true); pack(); } public void actionPerformed(ActionEvent evt) { RSAEncryption rsa=new RSAEncryption(1024); String text1 = tfInput.getText(); // String ciphertext = rsa.encrypt(text1); BigInteger plaintext = new BigInteger(text1.getBytes()); BigInteger ciphertext = rsa.encrypt(plaintext); BigInteger plaintext1 = rsa.decrypt(ciphertext); String text2 = new String(plaintext1.toByteArray()); if ( evt.getSource() == btnExit ) { pw.println("end"); // send end to server so that server know about the termination System.exit(0); } /* else if(evt.getSource() == btnDecrypt) { decryptText.append(text2); } */ else { // send message to server pw.println("Encrypted Text:-"+ciphertext); } } public static void main(String ... args) { // take username from user String name = JOptionPane.showInputDialog(null,"Enter your name :", "Username", JOptionPane.PLAIN_MESSAGE); String servername = "localhost"; try { new ChatClient( name ,servername); } catch(Exception ex) { out.println( "Error --> " + ex.getMessage()); } } // end of main // inner class for Messages Thread class MessagesThread extends Thread { public void run() { String line; try { while(true) { line = br.readLine(); taMessages.append(line + "\n"); } // end of while } catch(Exception ex) {} } } public class RSAEncryption { private BigInteger n, d, e; private int bitlen = 1024; /** Create an instance that can encrypt using someone elses public key. */ public RSAEncryption(BigInteger newn, BigInteger newe) { n = newn; e = newe; } /** Create an instance that can both encrypt and decrypt. */ public RSAEncryption(int bits) { bitlen = bits; SecureRandom r = new SecureRandom(); BigInteger p = new BigInteger(bitlen / 2, 100, r); BigInteger q = new BigInteger(bitlen / 2, 100, r); n = p.multiply(q); BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q .subtract(BigInteger.ONE)); e = new BigInteger("3"); while (m.gcd(e).intValue() > 1) { e = e.add(new BigInteger("2")); } d = e.modInverse(m); } public RSAEncryption() { // TODO Auto-generated constructor stub } /** Encrypt the given plaintext message. */ public synchronized String encrypt(String message) { return (new BigInteger(message.getBytes())).modPow(e, n).toString(); } /** Encrypt the given plaintext message. */ public synchronized BigInteger encrypt(BigInteger message) { return message.modPow(e, n); } /** Decrypt the given ciphertext message. */ public synchronized String decrypt(String message) { return new String((new BigInteger(message)).modPow(d, n).toByteArray()); } /** Decrypt the given ciphertext message. */ public synchronized BigInteger decrypt(BigInteger message) { return message.modPow(d, n); } /** Generate a new public and private key set. */ public synchronized void generateKeys() { SecureRandom r = new SecureRandom(); BigInteger p = new BigInteger(bitlen / 2, 100, r); BigInteger q = new BigInteger(bitlen / 2, 100, r); n = p.multiply(q); BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE)); e = new BigInteger("3"); while (m.gcd(e).intValue() > 1) { e = e.add(new BigInteger("2")); } d = e.modInverse(m); } /** Return the modulus. */ public synchronized BigInteger getN() { return n; } /** Return the public key. */ public synchronized BigInteger getE() { return e; } } class Eavesdropper implements ActionListener { JTextArea myTextArea; public Eavesdropper(JTextArea ta) { myTextArea = ta; } public void actionPerformed(ActionEvent e) { String text1 = taMessages.getText(); String[] parts = text1.split("-"); String part1 = parts[1]; part1 = part1.replaceAll("(\n)", ""); RSAEncryption rsa=new RSAEncryption(1024); BigInteger plaintext = new BigInteger(part1.getBytes()); BigInteger plaintext1 = rsa.decrypt(plaintext); String text2 = new String(plaintext1.toByteArray()); // String plaintext1 = rsa.decrypt(part1); myTextArea.append(text2); } } } // end of client




Code - which runs decrypt button is clicked
String text1 = taMessages.getText(); String[] parts = text1.split("-"); String part1 = parts[1]; part1 = part1.replaceAll("(\n)", ""); RSAEncryption rsa=new RSAEncryption(1024); BigInteger plaintext = new BigInteger(part1.getBytes()); BigInteger plaintext1 = rsa.decrypt(plaintext); String text2 = new String(plaintext1.toByteArray()); // String plaintext1 = rsa.decrypt(part1); myTextArea.append(text2);