Excel protection

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Branko - 05 Apr 2005 17:29 GMT

Is there any way to safely protect your Excel files (file, sheets and VBA
project) against comercial password crackers?
Someone has a solution?

Thanks!

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JE McGimpsey - 06 Apr 2005 00:23 GMT

File, workbook, worksheet, and VBA protection can all be hacked within a
few minutes.

If you use Office 2003 with Windows Server 2003, IRM is supposed to be
more secure.

The only other way I know of is to compile them into COM add-ins. I
don't know of any commercial decompilers.

> Is there any way to safely protect your Excel files (file, sheets and VBA
> project) against comercial password crackers?
> Someone has a solution?

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Branko - 06 Apr 2005 03:29 GMT

OK.
But if I have in

sub Workbook_Open()
Application.EnableCancelKey = xlDisabled: Application.DisplayAlerts
= False
...
etc.

a password that is a function of current date and time (minutes, hours,
etc.) and that function is, e.g.,
password=3*min+5*month+...
known to me is it still possible to crack it?

Thanks!
Branko

> File, workbook, worksheet, and VBA protection can all be hacked within a
> few minutes.
[quoted text clipped - 8 lines]
> > project) against comercial password crackers?
> > Someone has a solution?

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JE McGimpsey - 06 Apr 2005 06:24 GMT

In about a heartbeat. The first step is to open the file with the Shift
key down so that your Workbook_Open macro doesn't run.

Breaking the passwords doesn't depend on what they are or how you
generated it.

Take a look at

http://www.mcgimpsey.com/excel/removepwords.html

> OK.
> But if I have in
[quoted text clipped - 9 lines]
> password=3*min+5*month+...
> known to me is it still possible to crack it?

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Branko - 07 Apr 2005 16:43 GMT

Is there any way to run any macro when file is loaded?
Idea is to have a timer which would again ask for a password after a couple
of seconds if Shift is pressed at start-up (it would be detected since no
password is entered and stored in Module).

Even it could ask for a dynamic (time dependent) password from another
workbook.

As much as I understand the cracking it checks for a certain number of
combinations so it could happen that it has already checked at the beggining
for the current password that changes with time and will not repeat it again.

> In about a heartbeat. The first step is to open the file with the Shift
> key down so that your Workbook_Open macro doesn't run.
[quoted text clipped - 19 lines]
> > password=3*min+5*month+...
> > known to me is it still possible to crack it?

Reply to this Message

JE McGimpsey - 07 Apr 2005 17:43 GMT

No, if the shift key is held down, macros won't run, period.

You could hide all your sheets except for one, which you can use as a
splash screen to tell the user that macros must be enabled. If you use
code to make the sheets' .Visible property xlVeryHidden, they won't show
up on the Unhide menu.

You'd then need to unhide the sheets when the correct password was
given, and rehide them before the workbook is saved.

That protection is pretty weak, however.

> Is there any way to run any macro when file is loaded?
> Idea is to have a timer which would again ask for a password after a couple
[quoted text clipped - 7 lines]
> combinations so it could happen that it has already checked at the beggining
> for the current password that changes with time and will not repeat it again.

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