String型別轉成byte[]：

byte[] byteArray = System.Text.Encoding.UTF8.GetBytes ( strvalue );

byte[]轉成String：

String str = System.Text.Encoding.UTF8.GetString ( byteArray );

String型別轉成byte[]：

  private static byte[] HexStringToByteArray(string s)
        {
            s = s.Replace(" ", "");
            byte[] buffer = new byte[s.Length / 2];
            for (int i = 0; i < s.Length; i += 2)
                buffer[i / 2] = (byte)Convert.ToByte(s.Substring(i, 2), 16);
            return buffer;
        }

byte[]轉成String：
        private string ByteArrayToHexString(byte[] data)
        {
            System.Text.StringBuilder sb = new System.Text.StringBuilder(data.Length * 2);
            foreach (byte b in data)
                sb.Append(Convert.ToString(b, 16).PadLeft(2, '0').PadRight(2,' '));
            return sb.ToString().ToUpper();
        }