Convert Hex String to Byte Array and Vice-Versa

If you've dealt with legacy encryption schemes across multiple platforms, you know what a chore it can be to deal with the various encoding options, the character sets, etc. Sure, Microsoft provides various short-cuts for converting hex strings to/from byte arrays (BitConverter, Encoding.ASCII.GetBytes, etc) that seem to sometimes work depending on the details of what you're doing and the systems involved.. but time and again I wind up going back to an old tried-and-true method shown below.

       /// <summary>
       /// Convert string to byte_array
       /// </summary>
       /// <param name="strInput">
       private byte[] String_To_Bytes(string strInput)
       {
           // i variable used to hold position in string
           int i = 0;
           // x variable used to hold byte array element position
           int x = 0;
           // allocate byte array based on half of string length
           byte[] bytes = new byte[(strInput.Length) / 2];
           // loop through the string - 2 bytes at a time converting
           //  it to decimal equivalent and store in byte array
           while (strInput.Length > i + 1)
           {
               long lngDecimal = Convert.ToInt32(strInput.Substring(i, 2), 16);
               bytes[x] = Convert.ToByte(lngDecimal);
               i = i + 2;
               ++x;
           }
           // return the finished byte array of decimal values
           return bytes;
       }

       /// <summary>
       /// Convert byte_array to string
       /// </summary>
       /// <param name="bytes_Input">
       private string Bytes_To_String(byte[] bytes_Input)
       {
           // convert the byte array back to a true string
           string strTemp = "";
           for (int x = 0; x <= bytes_Input.GetUpperBound(0); x++)
           {
               int number = int.Parse(bytes_Input[x].ToString());
               strTemp += number.ToString("X").PadLeft(2, '0');
           }
           // return the finished string of hex values
           return strTemp;
       }

This allows you, for example, to go from a string value of say "A5B2FFD0" back and forth between the equivalent byte array { 0xA5, 0xB2, 0xFF, 0xD0 }.