using System;

using System.IO;

using System.Text;

using System.Security.Cryptography;

​

namespace Test

{

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Enter key:");

            var key = Console.ReadLine();

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

​

            if (keyAsBytes.Length * 8 != PayloadCrypto.KeySize)

            {

                Console.Error.WriteLine("Not a valid key");

                return;

            }

            Console.WriteLine("Enter json on one line:");

            var json = Console.ReadLine();

            Console.WriteLine(PayloadCrypto.Encrypt(keyAsBytes, json));

        }

        internal class PayloadCrypto

        {

            public static string Decrypt(byte[] key, byte[] bytesToDecrypt)

            {

                var iv = new byte[16];

                var text = new byte[bytesToDecrypt.Length - 16];

                Array.Copy(bytesToDecrypt, iv, 16);

                Array.Copy(bytesToDecrypt, 16, text, 0, text.Length);

​

                using var aes = Aes.Create();

                aes.Padding = PaddingMode.PKCS7;

                aes.IV = iv;

                aes.Key = key;

                aes.Mode = CipherMode.CBC;

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

                using var msDecrypt = new MemoryStream(text);

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

                using var srDecrypt = new StreamReader(csDecrypt);

                //Write all data to the stream.

                var plaintext = srDecrypt.ReadToEnd();

​

                return plaintext;

            }

​

            /// <summary>

            /// Encypts a string and returns the Base64 encoded result

            /// </summary>

            /// <param name="key">The key (32 bits)</param>

            /// <param name="stringToEncrypt">The string to encrypt</param>

            /// <returns>Base64 encoded encrypted string</returns>

            public static string Encrypt(byte[] key, string stringToEncrypt)

            {

                using var aes = Aes.Create();

                aes.Key = key;

                aes.GenerateIV();

                var iv = aes.IV;

                aes.Padding = PaddingMode.PKCS7;

                aes.Mode = CipherMode.CBC;

                var encryptor = aes.CreateEncryptor();

                using var msEncrypt = new MemoryStream();

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

                using (var swEncrypt = new StreamWriter(csEncrypt))

                {

                    //Write all data to the stream.

                    swEncrypt.Write(stringToEncrypt);

                }

                var encrypted = msEncrypt.ToArray();

                var final = new byte[iv.Length + encrypted.Length];

                iv.CopyTo(final, 0);

                encrypted.CopyTo(final, iv.Length);

                return Convert.ToBase64String(final);

            }

​

            public static string GetKeyFromUserSuppliedString(string userKey)

            {

                var rfcKey = new Rfc2898DeriveBytes(userKey, Encoding.UTF8.GetBytes("Some salt here"));

                var key = rfcKey.GetBytes(256 / 8);

                return Convert.ToBase64String(key);

            }

​

            public static int KeySize => Aes.Create().KeySize;

        }

    }

}