Вы можете использовать метод Parse в System.Byte для анализа отдельных пар hax:
// Get the string from the user
string s=Console.ReadLine();
// Convert to a byte array
byte[] sBytes=s.Split(new char[] {' '})
.Select(hexChar => byte.Parse(hexChar,NumberStyles.HexNumber))
.ToArray();
// *** Test code follows ***
// Display the bytes (optional), to verify that the conversion worked
StringBuilder hexString=new StringBuilder(sBytes.Length*3);
foreach (byte b in sBytes)
{
// Separate hex pairs with a space
if (hexString.Length>0)
hexString.Append(' ');
// Append next hex pair (i.e., formatted byte)
hexString.AppendFormat("{0:x2}",b);
}
Console.WriteLine(hexString);