using System;

using System.Text;

using System.Security.Cryptography;

​

public class Program

{

    public static void Main()

    {

        var signature = "{\"a\": 1, \"b\": \"c\", \"d\": \"efg\", \"h\": 12.45}";

        var key = "abcde";

​

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

        using (var shaAlgorithm = new HMACSHA256(shaKeyBytes))

        {

            var signatureBytes = Encoding.UTF8.GetBytes(signature);

            var signatureHashBytes = shaAlgorithm.ComputeHash(signatureBytes);

            var signatureHashHex = string.Concat(Array.ConvertAll(signatureHashBytes, b => b.ToString("X2"))).ToLower();

            var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(signatureHashHex);

            var signatureBase64 = System.Convert.ToBase64String(plainTextBytes);

​

            Console.WriteLine(signatureHashHex);

            Console.WriteLine(signatureBase64);

        }

    }

}