Incorrect decryption operation in client-server

Question

Hi all, sorry for my English, I don't know where is the problem and I don't see examples for internet.
I have a cliente-server aplication, where client read a file, encrypt it and send it to server. The server doesn't decrypt de text correcty. For example if the file contents:
"Hola, probando el cifrado y descifrado.", the server shows "Hola, probando eifrado."
I think that the problem is in the form for send and receive the cipher text.
I put the code for client:
import java.net.*;
import java.io.*;
import java.security.*;
import javax.crypto.*;
class ClientAES {
  public static void main(String argv[]) {
    try {
      System.out.print("Introduce the key : ");
      String cadena = Teclado.readString();
      SecureRandom rand = new SecureRandom(cadena.getBytes());
      System.out.println("Generating key...");
      KeyGenerator keyGen = KeyGenerator.getInstance("AES");
      keyGen.init(rand);
      SecretKey desKey = keyGen.generateKey();
      System.out.println("Key generated");
      Socket s=new Socket(argv[0],4096);
      FileInputStream fis = new FileInputStream(argv[1]);
      byte[] b=new byte[fis.available()];
      System.out.println("Bytes that can be read of file: "+fis.available());
      fis.read(b);
      System.out.println(Text send: "+new String(b));
      Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
      cipher.init(cipher.ENCRYPT_MODE,desKey);
      CipherOutputStream cos = new CipherOutputStream(s.getOutputStream(), cipher);
      cos.write(b, 0, b.length);
      fis.close();
      cos.close();
      s.close();
    } catch (Exception e) { e.printStackTrace(); }
}and server:
import java.net.*;
import java.io.*;
import java.security.*;
import javax.crypto.*;
class ServerAES {
  public static void main(String argv[]) {
    try {
      System.out.print("Introduce the key: ");
      String cadena = Teclado.readString();
      SecureRandom rand = new SecureRandom(cadena.getBytes());
      System.out.println("Generating key...");
      KeyGenerator keyGen = KeyGenerator.getInstance("AES");
      keyGen.init(rand);
      SecretKey desKey = keyGen.generateKey();
      System.out.println("Key generated");
      ServerSocket servidor=new ServerSocket(4096);
      System.out.println("Waiting a client...");
      Socket s=servidor.accept();
      System.out.println("Recieve a client connection");
      Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
      cipher.init(cipher.DECRYPT_MODE,desKey);
      CipherInputStream cis = new CipherInputStream(s.getInputStream(), cipher);
      byte[] in = new byte[cipher.getBlockSize()];
      int length;   
      System.out.println(cipher.getBlockSize());
       length = cis.read(in,  0, in.length);
      System.out.println(new String(in)+new String(cipher.doFinal()));
      cis.close();
      s.close();
    } catch (Exception e) { e.printStackTrace(); }
}

Answer 1

eeeh, if I understand your code correctly, then you are creating keys in each process. That means, you'll have two different keys. But you are using AES, which is a symmetric encryption algorithm. Hence you'll need to have the same key on both sides. Otherwise you'll not decrypting the stuff you where encrypting before.
stephan