4 ms·

I just remove the password with a command line tool without needing to know the password.

• lxgr 7y ago
  This tool likely only works for "passwordless" PDF encryption/protection, which restricts some aspect of using the document (printing, exporting single pages etc). This is the domain of DRM/whitebox cryptography, and leaving aside all discussions about the feasibility of such efforts, PDF's implementation of it can safely be assumed to be broken – the master key used can be found in several open source PDF tools' source code and on Stack Overflow, among other places. I assume the attacks presented in the paper are about the other type of PDF encryption, which requires a password to even display the protected content, which could definitely be done in a way not vulnerable to the attacks described.
  • poizan42 7y ago
    The "master key" is just the empty password which means that the effective key is all padding. This is documented in section 7.6.3.3 of ISO 32000-1:2008 (available for free from Adobe's website). There was never any real attempt to keep it secret.
• bonyt 7y ago
  The PDF format supports actual encryption, too. https://www.pdflib.com/pdf-knowledge-base/pdf-password-security/encryption/ https://www.pdflib.com/pdf-knowledge-base/pdf-password-secur...