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I got this Client-Server app : Encrypting a message in side and decrypting it in the other Side
but in decrypting i get this Error " Input length must be multiple of 8 when decrypting with padded cipher "
the Server Class

public class ServerApp 

 public static byte encrypt(String input, Key k) 
 try 

 Cipher cipher = Cipher.getInstance("DES");
 cipher.init(Cipher.ENCRYPT_MODE, k);
 byte data = input.getBytes();
 byte result = cipher.doFinal(data);

 return result;
 catch (Exception ex) 
 return null;
 
 

 public static String decrypt(byte cipher, Key k) 
 try 

 Cipher cipher1 = Cipher.getInstance("DES");
 cipher1.init(Cipher.DECRYPT_MODE, k);
 byte original = cipher1.doFinal(cipher);
 return new String(original);

 catch (Exception ex) 
 return null;
 //Logger.getLogger(DES.class.getName()).log(Level.SEVERE, null, ex);
 
 

 public static void main(String args) throws NoSuchAlgorithmException 
 try 

 Key key=KeyGen.getSecretKey();
 ServerSocket ser = new ServerSocket(3333);
 System.out.println("Server Started");
 Socket client = ser.accept();
 DataInputStream in = new DataInputStream(client.getInputStream());
 DataOutputStream out = new DataOutputStream(client.getOutputStream());
 Scanner scan = new Scanner(System.in);
 // SecretSocket sc = new SecretSocket(client, KeyGen.getSecretKey());
 String serMsg, cliMsg, plain;
 // OutputStream sout = sc.getOutputStream();
 // InputStream sin = sc.getInputStream();
 do 
 System.out.print("You say: ");
 serMsg = scan.nextLine();

 // sout.write(serMsg.getBytes());
 // System.out.println("cli server "+sin.read());

 byte ci = encrypt(serMsg, KeyGen.getSecretKey());
 System.out.println("encrypt " +ci.toString());
 out.writeUTF(ci.toString());
 plain = decrypt(ci, KeyGen.getSecretKey() );
 System.out.println("decrypt " + plain);
 while (!serMsg.equals("end"));
 client.close();
 ser.close();
 catch (IOException ex) 
 Logger.getLogger(ServerApp.class.getName()).log(Level.SEVERE, null, ex);
 
 

and here is the Client Code

public class ClientApp {

 public static byte encrypt(String input, Key k) 
 try 

 Cipher cipher = Cipher.getInstance("DES");
 cipher.init(Cipher.ENCRYPT_MODE, k);
 byte data = input.getBytes();
 byte result = cipher.doFinal(data);

 return result;
 catch (Exception ex) 
 return null;
 
 

 public static String decrypt(byte cipher, Key k) 
 try 

 Cipher cipher1 = Cipher.getInstance("DES/CBC/PKCS5Padding");
 cipher1.init(Cipher.DECRYPT_MODE, k);
 byte original = cipher1.doFinal(cipher);
 return new String(original);

 catch (Exception ex) 
 return null;
 //Logger.getLogger(DES.class.getName()).log(Level.SEVERE, null, ex);
 
 

 public static void main(String args) throws NoSuchAlgorithmException, InvalidKeyException, NoSuchPaddingException, IllegalBlockSizeException, BadPaddingException 
 try 
 Socket s = new Socket("localhost", 3333);
 DataInputStream in = new DataInputStream(s.getInputStream());
 DataOutputStream out = new DataOutputStream(s.getOutputStream());
 Scanner scan = new Scanner(System.in);
 String serMsg, cliMsg, plain;

 do 

 System.out.println("server server "+in.readUTF());

 serMsg = in.readUTF();
 System.out.println("enc: " + serMsg);
 plain = decrypt(serMsg.getBytes("UTF-8"), KeyGen.getSecretKey());
 System.out.println("Server says: " + plain);

 while (!serMsg.equals("end"));
 s.close();
 catch (IOException ex) 
 Logger.getLogger(ClientApp.class.getName()).log(Level.SEVERE, null, ex);
 
 

the thing is i tried ("DES/CBC/PKCS5Padding") and ("UTF-8")
but still the Same Problem
Any help ??

 Cipher cipher = Cipher.getInstance("DES");
 cipher.init(Cipher.ENCRYPT_MODE, k);
 byte data = input.getBytes();
 byte result = cipher.doFinal(data);

1. Using DES without IV you are implicitly using DES/ECB/PKCS5Padding.




2. do not print a byte array directly. Java will output only printable characters. Always encode and decode a byte array when printing (Hex or Base64 are the most common encodings)

Here is an example project

Base64.getEncoder().encodeToString(byteArray) 

3. I hope you are aware DES is considered a weak cipher today and should be used only for backward compatibility.