That’s a bug in LO. It is fixed in 5.4 (master), but I cannot check atm if it is fixed in coming 5.3.1.
Actually, the file isn’t protected anymore. It just contains empty data that must not be there, and that makes both LO and Excel handle it as encrypted.
There is a method to restore the file. You need to edit the file with hex editor, though. Disclaimer: the following is only tested once with a test file sample, and may be inaccurate. I don’t take any responsibility wrt correctness of following recommendations.
I used two free tools in my test, both of them can be used without installation:
- Hex Edit: www.hexedit.com
- SS Viewer: MiTeC Homepage
First, you need to backup your file, and always have its safe copy.
- Open the file with with SS Viewer, and right-click on Workbook stream in left tree. Save stream to an external file.
- Then open the saved stream file with Hex Edit and go to offset 0x14 - it should start with
- Now select to offset 0x4E (not including the
E1 00 value) - the selection must be 58 bytes long, start with
2F 00, and end with
00 00 - and delete selection.
- Now close the Hex Edit and return to SS Viewer, right-click on the Workbook stream again, and choose to load stream from file. Accept default encoder, and choose the edited stream file.
After the procedure completed, the file should become readable again.