User-side Forward-dating Attack on Time-stamping Protocols

Abstract

In many situations of the Internet, digital documents are widely exchanged. Time-stamping protocol, which can certify by the third party that a specified digital document was exist at a certain time, is widely researched and many actual time-stamping services are conducted over the Internet. Most time-stamp services address an application such that the earliest document takes precedence among the same contents. Protecting intellectual property is good example. Back-dating attack, that is obtaining a time-stamp token of earlier time, is major at- tack on this type of application. Hence, many researches are conducted on this attack. In this paper, we define user-side forward-dating attack, that is obtaining a time-stamp token of later time by a participant. Then we also define its adversary model in applications such that the latest document takes precedence. Next, we propose countermeasures to prevent this attack. Especially, we propose an protocol using hash-chain based commitment to prevent forward-dating attack by an adversary who colludes with timestamp authority.