using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

​

public class Program

{

    public static void Main()

    {

        Program program = new Program();

        var toEncryptReturn = program.EncryptString("5&&64&&41&&false&&&&dc&&", "mysmallkey123456");

        var toDecryptReturn = program.DecryptString(toEncryptReturn, "mysmallkey123456");

        Console.WriteLine(toDecryptReturn);

    }

    public string EncryptString(string text, string keyString)

    {

        var key = Encoding.UTF8.GetBytes(keyString);

​

        using (var aesAlg = Aes.Create())

        {

            using (var encryptor = aesAlg.CreateEncryptor(key, aesAlg.IV))

            {

                //aesAlg.Padding = PaddingMode.None;                        // Fix

                using (var msEncrypt = new MemoryStream())

                {

                    using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))

                    using (var swEncrypt = new StreamWriter(csEncrypt))

                    {

                        swEncrypt.Write(text);

                    }

​

                    var iv = aesAlg.IV;

​

                    var decryptedContent = msEncrypt.ToArray();

​

                    var result = new byte[iv.Length + decryptedContent.Length];

​

                    Buffer.BlockCopy(iv, 0, result, 0, iv.Length);

                    Buffer.BlockCopy(decryptedContent, 0, result, iv.Length, decryptedContent.Length);

​

                    return Convert.ToBase64String(result);

                }

            }

        }

    }

    public string DecryptString(string cipherText, string keyString)

    {

        var fullCipher = Convert.FromBase64String(cipherText);

​

        var iv = new byte[16];

        Buffer.BlockCopy(fullCipher, 0, iv, 0, iv.Length);

        //var cipher = new byte[16];                                        // Fix                                      

        //Buffer.BlockCopy(fullCipher, iv.Length, cipher, 0, iv.Length);

        var cipher = new byte[fullCipher.Length - iv.Length];

        Buffer.BlockCopy(fullCipher, iv.Length, cipher, 0, cipher.Length);

        var key = Encoding.UTF8.GetBytes(keyString);

​

        using (var aesAlg = Aes.Create())

        {

            //aesAlg.Padding = PaddingMode.None;                            // Fix

            using (var decryptor = aesAlg.CreateDecryptor(key, iv))

            {

                string result;

                using (var msDecrypt = new MemoryStream(cipher))

                {

                    using (var csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))

                    {

                        using (var srDecrypt = new StreamReader(csDecrypt))

                        {

                            result = srDecrypt.ReadToEnd();

                        }

                    }

                }

​

                return result;

            }

        }

    }

}