using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using System;

using System.Security.Cryptography;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var payload = @"{

    ""action"": ""Payment.Succeeded"",

    ""payload"": {

        ""sessionIdentifier"": ""02c7568b-95af-4e1d-8e5e-b2fabbce14f8"",

        ""amount"": ""50.00"",

        ""amountFormatted"": ""$50.00"",

        ""referenceNumber"": ""M24GZH-5ES3"",

        ""status"": ""Succeeded"",

        ""accountNumber"": ""25"",

        ""accountName"": ""Kristy Collins""

    }

}";

        var jsonPayload = JsonConvert.SerializeObject(JObject.Parse(payload));

        Console.WriteLine(jsonPayload);

        var secret = "a25aa7687a46f3b06f439877177d1987251d765a";

        var signature = DataSigning.HmacSha1HexDigest(secret, jsonPayload);

        var expectedSignature = "e0665b92e71a514ffdf7b387f7e3ae5c555d1cbf";

        Console.WriteLine(signature);

        Console.WriteLine(expectedSignature == signature);

    }

}

​

public static class DataSigning

{

    public static string HmacSha1HexDigest(string secret, string dataToSign)

    {

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

        var keyByte = encoding.GetBytes(secret);

        var hmacSha1 = new HMACSHA1(keyByte);

​

        var messageBytes = encoding.GetBytes(dataToSign);

        var hashMessage = hmacSha1.ComputeHash(messageBytes);

        return ByteToHexString(hashMessage).ToLower();

    }

​

    private static string ByteToHexString(byte[] buff)

    {

        return buff.Aggregate("", (current, t) => current + t.ToString("X2"));

    }

}