using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

using System.Linq;

using Newtonsoft.Json;

​

public class Program

{

    public static void Main()

    {

        var secret = "Segredo";

        var serializedRequest = @"{""encryptedData"":""UXGtgNgbJmQDr3Jd0wrSSwk95X8DBfeKN/W7xy3sz1YDDPBhJw2AXIfG5SdCFmEAHvaTk0SaIPFi2deJTgawtUTyW6chIApxhCYNCVIx7XU="",""iv"":""rrwHcs5cS8z9cElBzZRSnw=="",""hash"":""DijdTPCTwrrDKvO8Tiy7QMeYbc69Tz63M4neMNRUVto=""}";

        var request = JsonConvert.DeserializeObject<EncryptedMessage>(serializedRequest);

        var encryptedData = request.EncryptedData.FromBase64();

        var iV = request.IV.FromBase64();

        var hash = request.Hash.FromBase64();

        var key = secret.ToUTF8().ToSHA256();

        var decryptedData = encryptedData.DecryptAES(key, iV);

        var decryptedHash = decryptedData.ToSHA256();

        var hashMatches = decryptedHash.SequenceEqual(hash);

        if(hashMatches is false) {

            Console.WriteLine("Secret is invalid");

        }

        var serializedData = decryptedData.FromUTF8();

        Console.WriteLine(serializedData);

    }

}

​

public record EncryptedMessage(string EncryptedData, string IV, string Hash);

public static class ExtensionMethods

{

    public static byte[] FromBase64(this string value) {

      return Convert.FromBase64String(value);

    }

    public static string FromUTF8(this byte[] value) {

      return Encoding.UTF8.GetString(value);

    }

    public static byte[] ToUTF8(this string value)

    {

        return Encoding.UTF8.GetBytes(value);

    }

​

    public static byte[] ToSHA256(this byte[] value)

    {

        using var sha256 = SHA256.Create();

        return sha256.ComputeHash(value);

    }

​

    public static byte[] DecryptAES(this byte[] value, byte[] key, byte[] iv) {

      using var aes = Aes.Create();

      using var cryptoTransform = aes.CreateDecryptor(key, iv);

      using var memoryStream = new MemoryStream();

      using var cryptoStream = new CryptoStream(memoryStream, cryptoTransform, CryptoStreamMode.Write);

      cryptoStream.Write(value);

      cryptoStream.FlushFinalBlock();

​

      return memoryStream.ToArray();

    }

}