C# HMAC SHA512

HmacSha512.cs

using System;
using System.Text;
using System.Linq;

using Org.BouncyCastle.Crypto.Macs;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Parameters;

/**
 * Author:		Satyendra Singh
 * Created:		19-08-2022
 * Description:	Calculate HMACSHA512 based on pre-generated secret key.
 * 
 * Disclaimer:	This code is intended for demo purpose only, basis application need ensure implementation of error and exception handling.
*/ 
namespace HMAC.Class { 
    public class HMACUtility {
		
    public static string generateHmac(string text, string key) {
			var hmac = new HMac(new Sha512Digest());
			hmac.Init(new KeyParameter(hexStringToByteArray(key)));
			byte[] result = new byte[hmac.GetMacSize()];
			byte[] bytes = Encoding.UTF8.GetBytes(text);

			hmac.BlockUpdate(bytes, 0, bytes.Length);
			hmac.DoFinal(result, 0);

			return System.Convert.ToBase64String(result);
		}

		/// Convert HEX string into byte array.
		private static byte[] hexStringToByteArray(string hex) {
			return Enumerable.Range(0, hex.Length)
					   .Where(x => x % 2 == 0)
					   .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
					   .ToArray();
		}

		/// Demo code to call generateHmac method.
		public static void Main(string[] args) {
			 string value = generateHmac("message", "secret key in hex");
			 Console.WriteLine(value);
		}
	}
}