Abstract:

Digital signature schemes allow to exchange digital documents in a form that guarantees authenticity of the sender and full integrity of the data received. Any intentional or unintentional modification of the document is recognized, thus rendering the signature invalid. This paper describes a real-life case study in which the digital signature was corrupted merely by opening the file with the use of the macOS Preview app. Corruption may go unnoticed by the app user, leading to the submission of a digitally signed document with an invalid signature affixed thereto. In this paper, a method of reverting such changes is presented, along with recommendations for Apple software developers on how to prevent users from unintentional modification of signed documents.