Encryption Compatible Between Android and C#

Encryption compatible between Android and C#

Got some help from http://oogifu.blogspot.com/2009/01/aes-in-java-and-c.html.

Here is my Java class:

package com.neocodenetworks.smsfwd;

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import android.util.Log;

public class Crypto {
    public static final String TAG = "smsfwd";

    private static Cipher aesCipher;
    private static SecretKey secretKey;
    private static IvParameterSpec ivParameterSpec;

    private static String CIPHER_TRANSFORMATION = "AES/CBC/PKCS5Padding";
    private static String CIPHER_ALGORITHM = "AES";
    // Replace me with a 16-byte key, share between Java and C#
    private static byte[] rawSecretKey = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                                          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

    private static String MESSAGEDIGEST_ALGORITHM = "MD5";

    public Crypto(String passphrase) {
        byte[] passwordKey = encodeDigest(passphrase);

        try {
            aesCipher = Cipher.getInstance(CIPHER_TRANSFORMATION);
        } catch (NoSuchAlgorithmException e) {
            Log.e(TAG, "No such algorithm " + CIPHER_ALGORITHM, e);
        } catch (NoSuchPaddingException e) {
            Log.e(TAG, "No such padding PKCS5", e);
        }

        secretKey = new SecretKeySpec(passwordKey, CIPHER_ALGORITHM);
        ivParameterSpec = new IvParameterSpec(rawSecretKey);
    }

    public String encryptAsBase64(byte[] clearData) {
        byte[] encryptedData = encrypt(clearData);
        return net.iharder.base64.Base64.encodeBytes(encryptedData);
    }

    public byte[] encrypt(byte[] clearData) {
        try {
            aesCipher.init(Cipher.ENCRYPT_MODE, secretKey, ivParameterSpec);
        } catch (InvalidKeyException e) {
            Log.e(TAG, "Invalid key", e);
            return null;
        } catch (InvalidAlgorithmParameterException e) {
            Log.e(TAG, "Invalid algorithm " + CIPHER_ALGORITHM, e);
            return null;
        }

        byte[] encryptedData;
        try {
            encryptedData = aesCipher.doFinal(clearData);
        } catch (IllegalBlockSizeException e) {
            Log.e(TAG, "Illegal block size", e);
            return null;
        } catch (BadPaddingException e) {
            Log.e(TAG, "Bad padding", e);
            return null;
        }
        return encryptedData;
    }

    private byte[] encodeDigest(String text) {
        MessageDigest digest;
        try {
            digest = MessageDigest.getInstance(MESSAGEDIGEST_ALGORITHM);
            return digest.digest(text.getBytes());
        } catch (NoSuchAlgorithmException e) {
            Log.e(TAG, "No such algorithm " + MESSAGEDIGEST_ALGORITHM, e);
        }

        return null;
    }
}

I used http://iharder.sourceforge.net/current/java/base64/ for the base64 encoding.

Here's my C# class:

using System;
using System.Text;
using System.Security.Cryptography;

namespace smsfwdClient
{
    public class Crypto
    {
        private ICryptoTransform rijndaelDecryptor;
        // Replace me with a 16-byte key, share between Java and C#
        private static byte[] rawSecretKey = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                                              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

        public Crypto(string passphrase)
        {
            byte[] passwordKey = encodeDigest(passphrase);
            RijndaelManaged rijndael = new RijndaelManaged();
            rijndaelDecryptor = rijndael.CreateDecryptor(passwordKey, rawSecretKey);
        }

        public string Decrypt(byte[] encryptedData)
        {
            byte[] newClearData = rijndaelDecryptor.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
            return Encoding.ASCII.GetString(newClearData);
        }

        public string DecryptFromBase64(string encryptedBase64)
        {
            return Decrypt(Convert.FromBase64String(encryptedBase64));
        }

        private byte[] encodeDigest(string text)
        {
            MD5CryptoServiceProvider x = new System.Security.Cryptography.MD5CryptoServiceProvider();
            byte[] data = Encoding.ASCII.GetBytes(text);
            return x.ComputeHash(data);
        }
    }
}

I really hope this helps someone else!

How can I find an Android encryption library or class compatible with my C# code?

I wrote a crypto class that should work with your code, given correct configuration.

You can check it out here: https://github.com/Untouchab1e/yubinotes/blob/master/Android/src/com/connectutb/yubinotes/util/Crypto.java

You're using DES in your example, which is a flawed and obsolete algorithm (alternatively use 3DES), so I suggest moving to AES which provides better encryption.

What are the differences between C# and Java (Android) when encrypting using RSA with PKCS1 padding?

Both codes are right. You can encrypt data in same way with Java version and C# version. If one of them is working and another one is failing, probably you are using an incorrect public key (copy/paste error, some different bytes, etc...)

Need help converting c# encryption to java (android) encryption for cross compatibility

Here is the implementation I came up with for this code:

try (ByteArrayOutputStream plainTextStream = new ByteArrayOutputStream()) 
{
    // -- c# like CryptoStream
    try (CipherOutputStream decrypterStream = 
             new CipherOutputStream(plainTextStream, cipher)) 
    {
        // -- binaryWriter like c#
        try (DataOutputStream binaryWriter = new DataOutputStream(decrypterStream)) 
        {
            // -- Encrypt Data
            //Decrypt Cipher Text from Message
            binaryWriter.write(encryptedMessage,
                               nonSecretPayloadLength + iv.length,
                               encryptedMessage.length 
                                 - nonSecretPayloadLength 
                                 - iv.length 
                                 - sentTag.length);
        }

        //Return Plain Text
        //decrypterStream.flush();

    } finally {
        return plainTextStream.toByteArray();
    }

} catch (IOException e) {
    e.printStackTrace();
}

Decrypt AES data on android that comes from a C# MVC4 server

If you encrypt with PKCS#7 padding and then decrypt with no padding, it should work just fine, except that you get padding at the end. The padding is just x bytes containing the number x.

I stumbled upon the comment "c# byte goes from 0 to 255, whereas java byte goes from -128-127, so i just subtracted //128 from each c# byte, to get the java byte" and I think that might be your problem (or one problem anyway).

This isn't how two's complement works. Try to fix that first and see if it works.

---

Related Topics