using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

​

namespace TestAes256Encryption

{

    internal class Program

    {

        static void Main(string[] args)

        {

            string hexKey = "5468576D597133743677397A24432646294A404E635266556A586E3272347537";

            string valueToEncrypt = "100121";

            string encryptString = Aes256Encrypt(valueToEncrypt, hexKey);

            string encryptString2 = "S08KMR5zehPSfypSX1ON1A==";

            string encryptString3 = "EjvIjnaxNSzKtEXfE8h1YZ2MRg5+K130Jv8G+efaaFw="; 

            Console.WriteLine(valueToEncrypt);

            Console.WriteLine(encryptString);

            Console.WriteLine(AES256Decrypt(encryptString, hexKey));

            Console.WriteLine(AES256Decrypt(encryptString2, hexKey));

            Console.WriteLine(AES256Decrypt(encryptString3, hexKey));

            Console.ReadLine();

        }

​

        public static string AES256Decrypt(string base64StringToDecrypt, string hexEncryptionKey)

        {

            string response = string.Empty;

​

            if (String.IsNullOrEmpty(base64StringToDecrypt) || String.IsNullOrEmpty(hexEncryptionKey))

            {

                return null;

            }

​

            var base64EncodedBytes = Convert.FromBase64String(base64StringToDecrypt);

​

            using (Aes aesAlg = Aes.Create())

            {

                aesAlg.Key = HexToByteArray(hexEncryptionKey);

                byte[] IV = new byte[aesAlg.BlockSize / 8];

                byte[] toDecrypt = new byte[base64EncodedBytes.Length - IV.Length];

​

                Array.Copy(base64EncodedBytes, IV, IV.Length);

                Array.Copy(base64EncodedBytes, IV.Length, toDecrypt, 0, toDecrypt.Length);

​

                aesAlg.IV = IV;

                aesAlg.Mode = CipherMode.CBC;

​

                ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);

​

                using (var msDecrypt = new MemoryStream(toDecrypt))

                {

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

                    {

                        using (var srDecrypt = new StreamReader(csDecrypt))

                        {

                            response = srDecrypt.ReadToEnd();

                        }

                    }

                }

            }

​

            return response;

        }

​

        public static string Aes256Encrypt(string stringToEncrypt, string hexEncryptionKey)

        {

            byte[] encrypted;

            byte[] IV;

​

            if (String.IsNullOrEmpty(stringToEncrypt) || String.IsNullOrEmpty(hexEncryptionKey))

            {

                return null;

            }

​

            using (Aes aesAlg = Aes.Create())

            {

                aesAlg.Key = HexToByteArray(hexEncryptionKey);

                aesAlg.GenerateIV();

                IV = aesAlg.IV;

                aesAlg.Mode = CipherMode.CBC;

                aesAlg.Padding = PaddingMode.PKCS7;

​

                var encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

​

                using (var msEncrypt = new MemoryStream())

                {

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

                    {

                        using (var swEncrypt = new StreamWriter(csEncrypt))

                        {

                            swEncrypt.Write(stringToEncrypt);

                        }

                        encrypted = msEncrypt.ToArray();

                    }

                }

            }

​

            var combinedIvWithEncrypted = new byte[IV.Length + encrypted.Length];

            Array.Copy(IV, 0, combinedIvWithEncrypted, 0, IV.Length);

            Array.Copy(encrypted, 0, combinedIvWithEncrypted, IV.Length, encrypted.Length);

​

            return Convert.ToBase64String(combinedIvWithEncrypted);

        }

​

​

        public static byte[] HexToByteArray(string value)

        {

            value = ComputeMd5Hash(value);

            return Convert.FromBase64String(value);

        }

​

​

        public static string ComputeMd5Hash(string message)

        {

            using (MD5 md5 = MD5.Create())

            {

                byte[] input = Encoding.ASCII.GetBytes(message);

                byte[] hash = md5.ComputeHash(input);

​

                StringBuilder sb = new StringBuilder();

                for (int i = 0; i < hash.Length; i++)

                {

                    sb.Append(hash[i].ToString("X2"));

                }

​

                return sb.ToString();

            }

        }

    }

}

​