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I've googled the internet for answers regarding secured pdf/cracking them and found huge amount of stuff. But most of it is quite old. So could someone confirm the following is still valid in modern days.
pdf can have two password: the master one which prevents people from doing certain operation like printing,editing. This one is 'easily' hackable because it is based on the document reader software (hence if I wrote my own reader, I could bypass all the security checks in the document).
The second password is the user password (or open password) which is used to encrypt the document itself and enables you to open and read it. Without it you have no access at all. It's fairly hard to crack (need big amount of cpu).
I am correct?
LINKS: Following are some of the links that I found intersting
The following White paper “How Secure Is PDF ?” by Bryan Guignard http://www.cs.cmu.edu/~dst/Adobe/Gallery/PDFsecurity.pdf sums it up the best. However it’s states pdf v1.3 which dates back to 2000.
The issue were still alive in 2008 with Adobe Acrobat 9
LockLizard also has a link to this paper in its general issues section http://www.locklizard.com/pdf_security_news/ and they seem to keep the page up to date.
Finally this paper http://www.besthackingtricks.com/how-to-open-password-protected-pdf-documents-pdf-password-remover/ says roughly the same thing but only dates back to august 2015.