TCPDF SetProtection method is not working as expected

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I started writing here:

PHP PDF password protection (no open without password)

But I can't add comments due to my reputation here (I'm better on AskUbuntu but I can't take my rep points from there). I also started a bounty there, and if someone will answer here in two days with an acceptable solution, I will award there.

Now, the problem: SetProtection method is not working as expected.

Wanted behaviour: create a protected/encrypted PDF document with TCPDF library so that the document view is always granted to everyone without asking any password, but if one tries to edit, a password is requested.

I use the following syntax:

$pdf->SetProtection(array('modify', 'copy', 'annot-forms', 'fill-forms', 'extract', 'assemble'), null, 'mypwd', 1);

  1. I can open the file with a pdf viewer as expected.
  2. If I try to open the file with Libreoffice Draw, the password is requested (as expected), but I'm able to edit the document BOTH with mypwd (expected) AND giving a blank password (NOT expected).

What is the right syntax, if any, to have pdf readable by everyone BUT editable ONLY with "mypwd" provided?

EDIT:

here you are with a file with a blank user password and a strong master password. Ilovepdf.com finds it UNLOCKED, Libreoffice Draw can edit it. This is NOT the expected behaviour.

https://www.dropbox.com/s/864p8xjh1ue041z/tracking_12750_16.pdf?dl=0

tcpdf password-protection encryption pdf
1 Answers

As far as I can see your example PDF is encrypted just the way you wanted, with an empty user password and a non-empty owner password. Thus, TCPDF does just what it was asked to do.

Most likely the problem is that your expectation is too strong: If a program can open a PDF for reading, that program can do anything with the PDF, no matter how restricted it is configured to be. The permissions and different owner and user roles require the cooperation of the software in question, they are not technically enforced.

This already is clear from the specification:

Once the document has been opened and decrypted successfully, a PDF reader technically has access to the entire contents of the document. There is nothing inherent in PDF encryption that enforces the document permissions specified in the encryption dictionary. PDF readers shall respect the intent of the document creator by restricting user access to an encrypted PDF file according to the permissions contained in the file.

(ISO 32000-2, section 7.6.4 Standard security handler)

Apparently Libreoffice Draw simply does not behave as required by the PDF specification, i.e. it is not properly restricting user access to an encrypted PDF file according to the permissions contained in the file. Probably by design, probably just a programming glitch.

You should simply be aware that your expectation to

create a protected/encrypted PDF document with TCPDF library so that the document view is always granted to everyone without asking any password, but if one tries to edit, a password is requested.

cannot be implemented using standard PDF encryption facilities for arbitrary PDF processors, merely for those that follow the PDF specification requirement quoted above.

There are some providers of PDF DRM software solutions which are not so easy to circumvent, but I doubt any of them can withstand a determined hacker. (Unless the solution in question is not giving the PDF to the user at all but only images in a custom, webservice-based viewer; but this is not your use case.)

Depending on your actual requirements, you might want to investigate into using digital signatures instead of encryption; if your objective is to make sure that any recipient can be sure that he got your document contents and not what someone else edited into it, this appears more apropos.

user_17292650
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