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Re: CDF Security

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  • Subject: [mg128521] Re: CDF Security
  • From: Joseph Gwinn <joegwinn at>
  • Date: Sun, 28 Oct 2012 01:54:59 -0400 (EDT)
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  • References: <> <k6d0ki$282$>


One possible solution jumps to mind, a Hill Cipher:  

The answers could be stored in ciphertext form in the CDF notebook, and 
the key released a week later.  

I suppose that the absolute time (~date) could be woven in somehow, as 
an added limit.

Joe Gwinn

In article <k6d0ki$282$1 at>,
 Gregory Lypny <gregory.lypny at> wrote:

> Hi Juan,
> Thanks for the heads up.  Even when opened in a text editor the code is 
> sufficiently obscure that it wouldn't pose too much of a risk with my 
> first-year students.  But of course that is meaningless if just one savvy 
> student does what you describe.  I am going to tie the answer array to a 
> variable with the absolute time (somewhat obscure) so that the array contains 
> null in all its elements before the deadline and proper answers afterwards.  
> Still far from foolproof, but perhaps enough to buy time to think of 
> something better.  Ultimately, I don't that CDF will work for critical 
> coursework and large classes.  I will probably just set up a workflow to 
> generate PDFs instead.  Disappointing but a good learning experience.
> Thanks again for responding,
> Gregory
> On Thu, Oct 25, 2012, at 1:17 PM, "Miranda, Juan" <juan.miranda at> 
> wrote:
> > You can open any cdf file in Mathematica and use the ImputForm function to 
> > get its definition. You can do the same for any Mathematica palette. You 
> > can even right-click in the file ubication and select open with NotePad and 
> > all the definition of the CDF will be available, you can just paste the 
> > code in Mathematica and use it.
> > 
> > Best,
> > 
> > Juan
> > 
> > -----Original Message-----
> > From: Gregory Lypny [mailto:gregory.lypny at] 
> > Sent: Wednesday, October 24, 2012 10:42 PM
> > To: mathgroup at
> > Subject: CDF Security
> > 
> > Hello everyone,
> > 
> > I create CDF assignments for my students. They are pretty basic. A student 
> > selects their ID using a pull-down menu in a Manipulate, and the notebook 
> > is populated with randomized questions. The answers are buried in the 
> > document and are inaccessible until the deadline passes a week later, at 
> > which time I upload the same CDF but with a checkbox in the Manipulate that 
> > displays the answer under each question. So, at any given time, students 
> > have old CDF assignments for which the answers are accessible and new 
> > assignments in which they are not. I received a disturbing email today from 
> > a student who claims that he was able to see the answers for the new 
> > assignment by doing the following on his PC.
> > 
> > - Open new quiz (where answers are blocked) in Mathematica (not the CDF 
> > player), enable dynamics when prompted, select ID in the Manipulate 
> > pulldown menu
> > - Open old quiz (where answers are not blocked), enable dynamics, select ID
> > - Minimize both documents and Mathematica
> > - Reopen old quiz and then close it
> > - Reopen new quiz, and sadly, the answers are revealed
> > 
> > He sent me a screenshot showing the answers, but I was not able to 
> > reproduce this on my Mac. I'm trying to convince him to demonstrate this to 
> > me on my laptop. The only thing I can think of is that because the 
> > assignments use variables with the same name, Mathematica is loading answer 
> > variables from the old as globals and these are "unlocking" the same 
> > variables in the new. Any thoughts?
> > 
> > Gregory
> >

  • References:
    • CDF Security
      • From: Gregory Lypny <>
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