Encrypt in java and Decrypt in C# For AES 256 bit

Question

1.I have java function which encrypt xml file and return encrypted String.

/// Java Class 
import java.security.Key;
import javax.crypto.Cipher;
import javax         


        

Answer 1

After I got very helpful suggestions from @deathismyfriend and other, I found out what I am missing in my C# Decrypt function.So I change my function as below.

/// C# Error Fixed Version - CipherMode.ECB
public static string keyStr = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

private static string Encrypt(string PlainText)
{
    RijndaelManaged aes = new RijndaelManaged();
    aes.BlockSize = 128;
    aes.KeySize = 256;

    /// In Java, Same with below code
    /// Cipher _Cipher = Cipher.getInstance("AES");  // Java Code
    aes.Mode = CipherMode.ECB; 

    byte[] keyArr = Convert.FromBase64String(keyStr);
    byte[] KeyArrBytes32Value = new byte[32];
    Array.Copy(keyArr, KeyArrBytes32Value, 32);

    aes.Key = KeyArrBytes32Value;

    ICryptoTransform encrypto = aes.CreateEncryptor();

    byte[] plainTextByte = ASCIIEncoding.UTF8.GetBytes(PlainText);
    byte[] CipherText = encrypto.TransformFinalBlock(plainTextByte, 0, plainTextByte.Length);
    return Convert.ToBase64String(CipherText);
}

private static string Decrypt(string CipherText)
{  
    RijndaelManaged aes = new RijndaelManaged();
    aes.BlockSize = 128;
    aes.KeySize = 256;

    /// In Java, Same with below code
    /// Cipher _Cipher = Cipher.getInstance("AES");  // Java Code
    aes.Mode = CipherMode.ECB;

    byte[] keyArr = Convert.FromBase64String(keyStr);
    byte[] KeyArrBytes32Value = new byte[32];
    Array.Copy(keyArr, KeyArrBytes32Value, 32);

    aes.Key = KeyArrBytes32Value;

    ICryptoTransform decrypto = aes.CreateDecryptor();

    byte[] encryptedBytes = Convert.FromBase64CharArray(CipherText.ToCharArray(), 0, CipherText.Length);
    byte[] decryptedData = decrypto.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length);
    return ASCIIEncoding.UTF8.GetString(decryptedData);
}

By using upper c# function , now I can decrypt and read cipher text.
Below is what I found out after I getting error again and again.

CryptographicException: Padding is invalid and cannot be removed.

 Solution:  
_RijndaelManaged.Padding = CipherMode.xxx;    ///should toggle here
_RijndaelManaged.Padding = PaddingMode.xxx;   ///should toggle here 


CryptographicException: Length of the data to decrypt is invalid. 
CryptographicException: Specified initialization vector (IV) does not match the block size for this algorithm.

Solution
1. _RijndaelManaged.BlockSize = 128; /// Must be
2. _RijndaelManaged.KeySize = 256; /// Must be
3. _RijndaelManaged.Key = Byte Array Size must be 32 in length ( more detail 32*8 = 256 KeySize )
4. _RijndaelManaged.IV = Byte Array Size must be 16 in length ( more detail 16*8 = 128 BlockSize)

But when it come to security reason, I think I should not use ECB mode.
According to

1. ECB mode is not secure
2. StackOverFlow link

So I Modify it again in Java and C#.

// Java code - Cipher mode CBC version.
// CBC version need Initialization vector IV.
// Reference from https://stackoverflow.com/questions/6669181/why-does-my-aes-encryption-throws-an-invalidkeyexception/6669812#6669812

import java.security.Key;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;

public class CryptoSecurity {

    public static String key = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
    public static byte[] key_Array = Base64.decodeBase64(key);

    public static String encrypt(String strToEncrypt)
    {       
        try
        {   
            //Cipher _Cipher = Cipher.getInstance("AES");
            //Cipher _Cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
            Cipher _Cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");        

            // Initialization vector.   
            // It could be any value or generated using a random number generator.
            byte[] iv = { 1, 2, 3, 4, 5, 6, 6, 5, 4, 3, 2, 1, 7, 7, 7, 7 };
            IvParameterSpec ivspec = new IvParameterSpec(iv);

            Key SecretKey = new SecretKeySpec(key_Array, "AES");    
            _Cipher.init(Cipher.ENCRYPT_MODE, SecretKey, ivspec);       

            return Base64.encodeBase64String(_Cipher.doFinal(strToEncrypt.getBytes()));     
        }
        catch (Exception e)
        {
            System.out.println("[Exception]:"+e.getMessage());
        }
        return null;
    }

    public static String decrypt(String EncryptedMessage)
    {
        try
        {
            //Cipher _Cipher = Cipher.getInstance("AES");
            //Cipher _Cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING");
            Cipher _Cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");            

            // Initialization vector.   
            // It could be any value or generated using a random number generator.
            byte[] iv = { 1, 2, 3, 4, 5, 6, 6, 5, 4, 3, 2, 1, 7, 7, 7, 7 };
            IvParameterSpec ivspec = new IvParameterSpec(iv);

            Key SecretKey = new SecretKeySpec(key_Array, "AES");
            _Cipher.init(Cipher.DECRYPT_MODE, SecretKey, ivspec);           

            byte DecodedMessage[] = Base64.decodeBase64(EncryptedMessage);
            return new String(_Cipher.doFinal(DecodedMessage));

        }
        catch (Exception e)
        {
            System.out.println("[Exception]:"+e.getMessage());          

        }
        return null;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        StringBuilder sb = new StringBuilder();

        sb.append("xml file string ...");

        String outputOfEncrypt = encrypt(sb.toString());        
        System.out.println("[CryptoSecurity.outputOfEncrypt]:"+outputOfEncrypt);

        String outputOfDecrypt = decrypt(outputOfEncrypt);        
        //String outputOfDecrypt = decrypt(sb.toString());        
        System.out.println("[CryptoSecurity.outputOfDecrypt]:"+outputOfDecrypt);
    }

}

In C#, I modify it like below.

// C# Code, CipherMode.CBC
// CBC version need Initialization vector IV.

public static string keyStr = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
private static string Encrypt(string PlainText)
{
    RijndaelManaged aes = new RijndaelManaged();
    aes.BlockSize = 128;
    aes.KeySize = 256;

    // It is equal in java 
    /// Cipher _Cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");    
    aes.Mode = CipherMode.CBC;  
    aes.Padding = PaddingMode.PKCS7; 

    byte[] keyArr = Convert.FromBase64String(keyStr);
    byte[] KeyArrBytes32Value = new byte[32];
    Array.Copy(keyArr, KeyArrBytes32Value, 32);

    // Initialization vector.   
    // It could be any value or generated using a random number generator.
    byte[] ivArr = { 1, 2, 3, 4, 5, 6, 6, 5, 4, 3, 2, 1, 7, 7, 7, 7 };
    byte[] IVBytes16Value = new byte[16];
    Array.Copy(ivArr, IVBytes16Value, 16);

    aes.Key = KeyArrBytes32Value;
    aes.IV = IVBytes16Value;

    ICryptoTransform encrypto = aes.CreateEncryptor();

    byte[] plainTextByte = ASCIIEncoding.UTF8.GetBytes(PlainText);
    byte[] CipherText = encrypto.TransformFinalBlock(plainTextByte, 0, plainTextByte.Length);
    return Convert.ToBase64String(CipherText);

}

private static string Decrypt(string CipherText)
{
    RijndaelManaged aes = new RijndaelManaged();
    aes.BlockSize = 128;
    aes.KeySize = 256;

    aes.Mode = CipherMode.CBC;
    aes.Padding = PaddingMode.PKCS7;

    byte[] keyArr = Convert.FromBase64String(keyStr);
    byte[] KeyArrBytes32Value = new byte[32];
    Array.Copy(keyArr, KeyArrBytes32Value, 32);

    // Initialization vector.   
    // It could be any value or generated using a random number generator.
    byte[] ivArr = { 1, 2, 3, 4, 5, 6, 6, 5, 4, 3, 2, 1, 7, 7, 7, 7 };            
    byte[] IVBytes16Value = new byte[16];
    Array.Copy(ivArr, IVBytes16Value, 16);

    aes.Key = KeyArrBytes32Value;
    aes.IV = IVBytes16Value;

    ICryptoTransform decrypto = aes.CreateDecryptor();

    byte[] encryptedBytes = Convert.FromBase64CharArray(CipherText.ToCharArray(), 0, CipherText.Length);
    byte[] decryptedData = decrypto.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length);
    return ASCIIEncoding.UTF8.GetString(decryptedData);
}

Now it all work.
For more detail about AES, click this link which I was given by @deathismyfriend.
It is also very useful.