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Old 04-19-2010, 10:53 PM
Gunnar Wolf
 
Default PDF is blocked for printing, etc. OK for acroread (it behaves as expected), but KPDF allows me to print it, even if it is protected! Why?

Merciadri Luca dijo [Mon, Apr 19, 2010 at 05:32:51PM +0200]:
> > Pdf "anti-features" are fake security. Don't trust on them, never.
> And what do you suggest if one wants some real protection _and_ the
> benefits of a format like PDF? Thanks.

Thing is, PDF is a printing-oriented format. It is a close descendent
of PostScript, a full-fledged programming language, but geared towards
printers. The main point that makes PDF a more convenient format is
that Acrobat made a big campaign to distribute its PDF reader program.

As you quote, others have told you the PDF-provided security is
fake. It is just a flag flipped to tell the reader program to pretty
please make life miserable for the user.

What do you want to achieve with this _real_ protection you say?
Whatever can be displayed on screen can be captured (i.e. with the
common "PrtScr" keybinding in many environments). If you want to
distribute material and make it hellish to your users to print it,
copy from it or use it in any useful way, why don't you send the
document as a .jpg file?

Greetings,

--
Gunnar Wolf • gwolf@gwolf.org • (+52-55)5623-0154 / 1451-2244


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Old 04-19-2010, 10:53 PM
Gunnar Wolf
 
Default PDF is blocked for printing, etc. OK for acroread (it behaves as expected), but KPDF allows me to print it, even if it is protected! Why?

Merciadri Luca dijo [Mon, Apr 19, 2010 at 05:32:51PM +0200]:
> > Pdf "anti-features" are fake security. Don't trust on them, never.
> And what do you suggest if one wants some real protection _and_ the
> benefits of a format like PDF? Thanks.

Thing is, PDF is a printing-oriented format. It is a close descendent
of PostScript, a full-fledged programming language, but geared towards
printers. The main point that makes PDF a more convenient format is
that Acrobat made a big campaign to distribute its PDF reader program.

As you quote, others have told you the PDF-provided security is
fake. It is just a flag flipped to tell the reader program to pretty
please make life miserable for the user.

What do you want to achieve with this _real_ protection you say?
Whatever can be displayed on screen can be captured (i.e. with the
common "PrtScr" keybinding in many environments). If you want to
distribute material and make it hellish to your users to print it,
copy from it or use it in any useful way, why don't you send the
document as a .jpg file?

Greetings,

--
Gunnar Wolf • gwolf@gwolf.org • (+52-55)5623-0154 / 1451-2244


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Old 04-19-2010, 11:05 PM
Gunnar Wolf
 
Default PDF is blocked for printing, etc. OK for acroread (it behaves as expected), but KPDF allows me to print it, even if it is protected! Why?

Russ Allbery dijo [Mon, Apr 19, 2010 at 02:14:21PM -0700]:
> I think people are not understanding why users use this feature in some
> environments.
>
> Yes, sometimes it's a misguided attempt at DRM, but I've more often seen
> it inside a workplace as defense in depth against *mistakes*. One might,
> for instance, mark a document as not printable because it contains social
> security numbers and salary information and it's corporate policy not to
> create hard copies of the document beause of the risk of exposure of
> personal information that might put the company at legal risk.
>
> That's not to say that Debian PDF viewers should support this the way that
> Acrobat does, but for that use case, the desired UI is probably something
> like a dialog box that pops up and says that the document author has
> marked this PDF as not printable and asking the user if they're sure they
> want to override. For this use case, such a warning would probably serve
> the same purpose.

The reasons not to want a document printed are quite easy to
understand, but the mechanism is flawed. Given the setting you
mention, you can just slap a red banner stating "Confidential, do not
print". If it is on a corporate setting, just state it as a policy -
and if somebody fails to comply with the policy, there should be
sanctions.

Of course, somebody interested in printing the file will do it. Either
by his own means or, like my users, by mailing the "techie" the
document asking him to unprotect it. Or by sticking it on a USB key
and taking it off-site to a location they can freely tinker with.

As I said on my previous mail: If you don't want it to be printed,
distribute in a way that makes it hard to be useful when
printed. Don't you trust somebody with social security numbers and
salary information? Don't give it to them.

--
Gunnar Wolf • gwolf@gwolf.org • (+52-55)5623-0154 / 1451-2244


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Old 04-20-2010, 01:54 PM
Gunnar Wolf
 
Default PDF is blocked for printing, etc. OK for acroread (it behaves as expected), but KPDF allows me to print it, even if it is protected! Why?

Merciadri Luca dijo [Tue, Apr 20, 2010 at 02:00:13PM +0200]:
> > As you quote, others have told you the PDF-provided security is
> > fake. It is just a flag flipped to tell the reader program to pretty
> > please make life miserable for the user.
> >
> Yes, but it is often sufficient to prevent _beginners_ from hacking the
> whole stuff.

Yet, you say in your previous reply they would be able to remove the
watermark from the document. That is clearly more complicated.

> > Whatever can be displayed on screen can be captured (i.e. with the
> > common "PrtScr" keybinding in many environments). If you want to
> > distribute material and make it hellish to your users to print it,
> > copy from it or use it in any useful way, why don't you send the
> > document as a .jpg file?
> >
> With such files (.jpg ones) they can print it directly, can't they?

If you distribute an image file in such a fashion it can be read on
screen but lacks enough resolution to be good for printing, fewer
people will print it. Of course, depends on what you want to achieve,
on the nature of the document.

--
Gunnar Wolf • gwolf@gwolf.org • (+52-55)5623-0154 / 1451-2244


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