using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

​

using System.Security.Cryptography;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/53352441/c-sharp-problem-with-aes-decryption-always-get-null

​

    class Encryptor 

    {

        //text to encrypt or already decrypted

        private String decryptedText = "";

        //text to decrypt or already encrypted

        private String encryptedText = "";

        private String key = "";

​

        public Encryptor setDecryptedText(String text)

        {

            decryptedText = text;

​

            return this;

        }

​

        public Encryptor setEncryptedText(String text)

        {

            encryptedText = text;

​

            return this;

        }

        public Encryptor setKey(String text)

        {

            key = text;

​

            return this;

        }

​

        Byte[] getHash(Byte[] hash)

        {

            Byte[] newHash = new Byte[32];

            for (int i = 0; i < 32; i++)

            {

                newHash[i] = hash[i];

            }

​

            return newHash;

        }

​

        Byte[] getIV(Byte[] hash)

        {

            Byte[] newHash = new Byte[16];

            int j = 0;

            for (int i = 32; i < 48; i++)

            {

                newHash[j++] = hash[i];

            }

​

            return newHash;

        }

​

        String EncryptAesManaged()

        {

            SHA512 shaM = new SHA512Managed();

​

            Byte[] data = Encoding.UTF8.GetBytes(key);

            Byte[] hash = shaM.ComputeHash(data);

​

            try

            {

                return Encrypt(decryptedText, getHash(hash), getIV(hash));

            }

            catch (Exception ex)

            {

                Console.WriteLine(ex.Message);

            }

​

            return null;

        }

​

        String DecryptAesManaged()

        {

            SHA512 shaM = new SHA512Managed();

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

            Byte[] hash = shaM.ComputeHash(data);

            try

            {

                return Decrypt(Convert.FromBase64String(encryptedText), getHash(hash), getIV(hash));

            }

            catch (Exception ex)

            {

                Console.WriteLine(ex.Message);

            }

            return "";

        }

​

        static String Encrypt(string plainText, byte[] Key, byte[] IV)

        {

            string encrypted;

            using (var aes = new RijndaelManaged())

            {

                aes.Mode = CipherMode.CBC;

                aes.BlockSize = 128;

                aes.KeySize = 256;

                ICryptoTransform encryptor = aes.CreateEncryptor(Key, IV);

                using (var ms = new MemoryStream())

                {

                    using (var cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write, true))

                    {

                        using (var sw = new StreamWriter(cs)) 

                        { 

                            sw.Write(plainText);

                        }

                    }

                    // Calling GetBuffer() avoids the extra allocation of ToArray().

                    encrypted = Convert.ToBase64String(ms.GetBuffer(), 0, checked((int)ms.Length)); 

                }

                aes.Clear();

            }

            return encrypted;

        }

​

        static string Decrypt(byte[] cipherText, byte[] Key, byte[] IV)

        {

            string plaintext = null;

            using (RijndaelManaged aes = new RijndaelManaged())

            {

                aes.Mode = CipherMode.CBC;

                aes.BlockSize = 128;

                aes.KeySize = 256;

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

                try

                {

                    using (MemoryStream ms = new MemoryStream(cipherText))

                        using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))

                        using (StreamReader reader = new StreamReader(cs))

                    {

                        plaintext = reader.ReadToEnd(); //Here get null

                    }

​

                    aes.Clear();

                }

                catch (Exception ex)

                {

                    Console.WriteLine(ex.Message);

                }

            }

​

            return plaintext;

        }

​

        public String getEncrypted()

        {

            return EncryptAesManaged();

        }

​

        public String getDecrypted()

        {

            return DecryptAesManaged();

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var key = "my key";

            var plainText = "hello";

            var encryptor = new Encryptor();

            encryptor.setDecryptedText(plainText);

            encryptor.setKey(key);

            var encrypted = encryptor.getEncrypted();

            Console.WriteLine(encrypted);

            var deecryptor = new Encryptor();

            deecryptor.setEncryptedText(encrypted);

            deecryptor.setKey(key);

            var decrypted = deecryptor.getDecrypted();

            Console.WriteLine(decrypted);

            Assert.IsTrue(plainText == decrypted);

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​