using System;

using System.Security.Cryptography;

public class Program

{

    public static void Main()

    {

        var message =

            "TransactionId=439476165&Amount=57980.00&Currency=RUB&PaymentAmount=57980.00&PaymentCurrency=RUB&OperationType=Payment&InvoiceId=01ee87qh89x46xh6x8ezjcwfcn&AccountId=1212dwqw@dqwd.qw&SubscriptionId=&Name=TEST&Email=1212dwqw@dqwd.qw&DateTime=2020-07-27 13:35:14&IpAddress=95.220.194.216&IpCountry=RU&IpCity=Москва&IpRegion=Москва&IpDistrict=Центральный федеральный округ&IpLatitude=55.755787&IpLongitude=37.617634&CardFirstSix=424242&CardLastFour=4242&CardType=Visa&CardExpDate=11/22&Issuer=CloudPayments&IssuerBankCountry=RU&Description=Оплата заказа №983373&AuthCode=A1B2C3&Token=477BBA133C182267FE5F086924ABDC5DB71F77BFC27F01F2843F2CDC69D89F05&TestMode=1&Status=Completed&GatewayName=Test&Data={\"cloudPayments\":{\"CustomerReceipt\":{\"Items\":[{\"label\":\"Информатика Олимпиады. 7–11 классы. 20 занятий с репетитором\",\"price\":57980,\"quantity\":1,\"amount\":57980,\"vat\":0},{\"label\":\"Математика Олимпиады. 5–11 классы. 20 занятий с репетитором\",\"price\":57980,\"quantity\":1,\"amount\":57980,\"vat\":0}],\"email\":\"1212dwqw@dqwd.qw\"}}}&TotalFee=0.00&CardProduct=I&PaymentMethod=";

​

        var generatedHmac = message.GenerateHmac("54e83824872b9e70dca3f65d0433c4b1");

        Console.WriteLine(generatedHmac);

    }

}

    public static class Helper

    {

        public static string GenerateHmac(this string message, string secret)

        {

            var encoding = new System.Text.ASCIIEncoding();

            var keyByte = encoding.GetBytes(secret);

            var messageBytes = encoding.GetBytes(message);

            var hmacsha256 = new HMACSHA256(keyByte);

            var hashmessage = hmacsha256.ComputeHash(messageBytes);

            return Convert.ToBase64String(hashmessage);

        }

    }