Abstract: The embodiments present a new class of content masking defenses against the Portable Document Format (PDF) standard. The defenses can identify attacks that cause documents to appear different than the underlying content extracted from the documents. A content masking defense method can include identifying a content masking attack by scanning a document file to extract a character code of a character appearing in the file. Next, the character is rendered based on a font that is embedded in the document file. Optical character recognition can be performed on the rendering, and a content masking attack can be identified based on a comparison of a result of the optical character recognition against the character code of the character.

Abstract: The embodiments present a new class of content masking attacks against the Portable Document Format (PDF) standard. The attacks cause documents to appear different than the underlying content extracted from the documents by information-based services. The first attack allows academic paper writers and reviewers to collude via subverting the automatic reviewer assignment systems in current use by academic conferences. The second attack renders plagiarism detection software ineffective, targeting specific small plagiarism similarity scores to appear natural and evade detection. The final attack places masked content into the indexes for various search engines, which renders as information entirely different from the keywords used to locate it. The final attack enables spam, profane, or possibly illegal content to go unnoticed by these search engines but still be returned in search results.