Abstract: 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 ebusiness contexts.
In 2012, Popescu et al. presented a proof-of-concept for bypassing a specific digital signature REF based on a polymorphic file that contained two different file types -PDF and TIFF -and lead to a different display of the same signed content.
Hiding Malicious Content in PDF Documents
Popescu, D. (2011). Hiding Malicious Content in PDF Documents. Journal Of Mobile, Embedded And Distributed Systems, 3(3), 120-127. Retrieved from http://www.jmeds.eu/index.php/jmeds/article/view/Hiding-Malicious-Content-in-PDF-Documents
Computer Science