Hiding Malicious Content in PDF Documents
This exposes a critical security flaw in widely used e-government and e-business systems, posing risks for digital document integrity and trust.
The paper tackles a vulnerability in digital signatures by demonstrating how malicious content can be hidden in PDF documents, allowing attackers to deceive victims into signing files that appear as PDFs but contain hidden content like TIFF images, which remains valid after format changes without altering the signature.
This paper is a proof-of-concept demonstration for a specific digital signatures vulnerability that shows the ineffectiveness of the WYSIWYS (What You See Is What You Sign) concept. The algorithm is fairly simple: the attacker generates a polymorphic file that has two different types of content (text, as a PDF document for example, and image: TIFF - two of the most widely used file formats). When the victim signs the dual content file, he/ she only sees a PDF document and is unaware of the hidden content inside the file. After obtaining the legally signed document from the victim, the attacker simply has to change the extension to the other file format. This will not invalidate the digital signature, as no bits were altered. The destructive potential of the attack is considerable, as the Portable Document Format (PDF) is widely used in e-government and in e-business contexts.