Binary helper C#

BinaryHelper.cs

using System;
using System.Text;
using System.Text.RegularExpressions;

namespace CryptoLib
{
    public class BinaryHelper
    {
        public static string ToBase64UrlString(byte[] payload)
        {
            char[] padding = { '=' };
            string returnValue = Convert.ToBase64String(payload)
                                //.TrimEnd(padding)
                                .Replace('+', '-')
                                .Replace('/', '_');

            return returnValue;
        }

        public static byte[] FromBase64UrlString(string b64Payload)
        {
            string incoming = b64Payload
                .Replace('_', '/').Replace('-', '+');
            switch (b64Payload.Length % 4)
            {
                case 2: incoming += "=="; break;
                case 3: incoming += "="; break;
            }
            byte[] bytes = Convert.FromBase64String(incoming);

            return bytes;
        }        

        public static string HexStringToAsciiString(String hex)
        {
            return Encoding.ASCII.GetString(HexStringToByteArray(hex));
        }

        public static byte[] HexStringToByteArray(String hex)
        {
            hex = Regex.Replace(hex, " ", "");
            int numberChars = hex.Length;
            if(numberChars%2!=0)
                throw new InvalidOperationException("must have even number of hexadecimal characters");

            byte[] bytes = new byte[numberChars / 2];
            for (int i = 0; i < numberChars; i += 2)
                bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
            return bytes;
        }

        public static string ByteArrayToHexString(byte[] ba, bool useUppercase=false)
        {
            var format=useUppercase? "{0:X2}": "{0:x2}";
            StringBuilder hex = new StringBuilder(ba.Length * 2);
            foreach (byte b in ba)
                hex.AppendFormat(format, b);
            return hex.ToString();
        }

        public static string AsciiStringToHexString(String ascii)
        {
            return ByteArrayToHexString(Encoding.ASCII.GetBytes(ascii));
        }
    }
}