Sunday, 1 October 2017

Common AES Encryption and Decryption between Java and .Net (C#)

In this article, I am going to provide you code for common AES encryption and decryption between java and .net (C#).

C# Implementation

Below is the C# implementation of encryption and decryption using rijndaelManaged.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Program p = new Program();
            string SecretKey = "$1234%&Key%"; // this is common key in java and .net
            string encryptedString = p.Encrypt("Data to encrypt", SecretKey);
            string decryptedString = p.Decrypt(encryptedString, SecretKey);
            Console.WriteLine("Encrypted String: " + encryptedString);
            Console.WriteLine("Decrypted string: " + decryptedString);
            Console.ReadKey();
        }

        // Encrypts plaintext using AES 128bit key and a Chain Block Cipher and returns a base64 encoded string
        public string Encrypt(String plainText, String key)
        {
            var plainBytes = Encoding.UTF8.GetBytes(plainText);
            return Convert.ToBase64String(Encrypt(plainBytes, GetRijndaelManaged(key)));
        }
        public string Decrypt(String encryptedText, String key)
        {
            var encryptedBytes = Convert.FromBase64String(encryptedText);
            return Encoding.UTF8.GetString(Decrypt(encryptedBytes, GetRijndaelManaged(key)));
        }
        public byte[] Encrypt(byte[] plainBytes, RijndaelManaged rijndaelManaged)
        {
            return rijndaelManaged.CreateEncryptor()
                .TransformFinalBlock(plainBytes, 0, plainBytes.Length);
        }
        public byte[] Decrypt(byte[] encryptedData, RijndaelManaged rijndaelManaged)
        {
            return rijndaelManaged.CreateDecryptor()
                .TransformFinalBlock(encryptedData, 0, encryptedData.Length);
        }
        public RijndaelManaged GetRijndaelManaged(String secretKey)
        {
            var keyBytes = new byte[16];
            var secretKeyBytes = Encoding.UTF8.GetBytes(secretKey);
            Array.Copy(secretKeyBytes, keyBytes, Math.Min(keyBytes.Length, secretKeyBytes.Length));
            return new RijndaelManaged
            {
                Mode = CipherMode.CBC,
                Padding = PaddingMode.PKCS7,
                KeySize = 128,
                BlockSize = 128,
                Key = keyBytes,
                IV = keyBytes
            };
        }
    }

}

Java Implementation

Below code is the Java implementation of encryption and decryption.

private final String characterEncoding = "UTF-8";
private final String cipherTransformation = "AES/CBC/PKCS5Padding";
private final String aesEncryptionAlgorithm = "AES";

public String encrypt(String plainText, String key) throws UnsupportedEncodingException, InvalidKeyException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException{
    byte[] plainTextbytes = plainText.getBytes(characterEncoding);
    byte[] keyBytes = getKeyBytes(key);
    return Base64.encodeToString(encrypt(plainTextbytes,keyBytes, keyBytes), Base64.DEFAULT);
}

public String decrypt(String encryptedText, String key) throws KeyException, GeneralSecurityException, GeneralSecurityException, InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException, IOException{
    byte[] cipheredBytes = Base64.decode(encryptedText, Base64.DEFAULT);
    byte[] keyBytes = getKeyBytes(key);
    return new String(decrypt(cipheredBytes, keyBytes, keyBytes), characterEncoding);
}

public  byte[] decrypt(byte[] cipherText, byte[] key, byte [] initialVector) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException
{
    Cipher cipher = Cipher.getInstance(cipherTransformation);
    SecretKeySpec secretKeySpecy = new SecretKeySpec(key, aesEncryptionAlgorithm);
    IvParameterSpec ivParameterSpec = new IvParameterSpec(initialVector);
    cipher.init(Cipher.DECRYPT_MODE, secretKeySpecy, ivParameterSpec);
    cipherText = cipher.doFinal(cipherText);
    return cipherText;
}

public byte[] encrypt(byte[] plainText, byte[] key, byte [] initialVector) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException
{
    Cipher cipher = Cipher.getInstance(cipherTransformation);
    SecretKeySpec secretKeySpec = new SecretKeySpec(key, aesEncryptionAlgorithm);
    IvParameterSpec ivParameterSpec = new IvParameterSpec(initialVector);
    cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivParameterSpec);
    plainText = cipher.doFinal(plainText);
    return plainText;
}

private byte[] getKeyBytes(String key) throws UnsupportedEncodingException{
    byte[] keyBytes= new byte[16];
    byte[] parameterKeyBytes= key.getBytes(characterEncoding);
    System.arraycopy(parameterKeyBytes, 0, keyBytes, 0, Math.min(parameterKeyBytes.length, keyBytes.length));
    return keyBytes;
}
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