How to password protect an Excel document with Open XML

Question

At the moment, I am creating a new Excel document with Open XML's SpreadsheetDocument class by passing a MemoryStream parameter. I now need to set a password on this SpreadsheetDocument object, but what I have attempted does not seem to work. The Excel document open's up without asking for a password. Below is what I have tried so far (mem being the MemoryStream parameter):

using (SpreadsheetDocument spreadsheet = SpreadsheetDocument.Open(mem, true))
{
    foreach (var sheet in spreadsheet.WorkbookPart.WorksheetParts)
    {
        sheet.Worksheet.Append(new SheetProtection() { Password = "test" });
    }
}

I have also attempted the following with no success:

using (SpreadsheetDocument spreadsheet = SpreadsheetDocument.Open(mem, true))
{
    spreadsheet.WorkbookPart.Workbook.WorkbookProtection = new WorkbookProtection
    {
        LockStructure = true,
        LockWindows = true,
        WorkbookPassword = "test"
    }
}

What am I missing please?

Answer 1

Openxml sheet protect Password has input Data type of "HexBinaryValue". so the input password as to be converted from string to hexa binary.

foreach (var worksheetPart in spreadsheet.WorkbookPart.WorksheetParts)
     {
         //Call the method to convert the Password string "MyPasswordfor sheet" to hexbinary type
         string hexConvertedPassword =  HexPasswordConversion("MyPasswordfor sheet");
//passing the Converted password to sheet protection
          SheetProtection sheetProt = new SheetProtection() { Sheet = true, Objects = true, Scenarios = true, Password = hexConvertedPassword };
          worksheetPart.Worksheet.InsertAfter(sheetProt,worksheetPart.Worksheet.Descendants<SheetData>().LastOrDefault());
worksheetPart.Worksheet.Save();
     }


/* This method will convert the string password to hexabinary value */
 protected string HexPasswordConversion(string password)
        {
            byte[] passwordCharacters = System.Text.Encoding.ASCII.GetBytes(password);
            int hash = 0;
            if (passwordCharacters.Length > 0)
            {
                int charIndex = passwordCharacters.Length;

                while (charIndex-- > 0)
                {
                    hash = ((hash >> 14) & 0x01) | ((hash << 1) & 0x7fff);
                    hash ^= passwordCharacters[charIndex];
                }
                // Main difference from spec, also hash with charcount
                hash = ((hash >> 14) & 0x01) | ((hash << 1) & 0x7fff);
                hash ^= passwordCharacters.Length;
                hash ^= (0x8000 | ('N' << 8) | 'K');
            }

            return Convert.ToString(hash, 16).ToUpperInvariant();
        }