A Time Authentication Scheme Based on PKI Framework

In many situations there is a need to certify the time a digital document was created or modified. Time authentication shows its importance in E-commerce and intellectual property protection. At present the main technique widely used is to time-stamp an electronic document. This paper introduces the up-to-date time-stamp protocols: linking protocol, distributed trust protocol and binary tree protocol. Linking Protocol observes the sequence of clients requesting time-stamps and is based on the fact that the hashes they submit cannot be known in advance. Distributed trust protocol selects witnesses randomly in a given group, and constitutes a believable time-stamp via their signature lists. Binary tree protocol combines hashes into one via a binary tree, and publishes the resulting single hash in newspaper advertisement. A time authentication scheme based on the PKI technology is presented. A TSA with its certificate is involved as a trusted third-party witness. Trusted time can be required, and one side or multi-side time authentication request can be responded by TSA. How to extend the lifetime of a time-stamp is also discussed. This paper evaluates the protocols above in terms of the calculation complexity, storage capacity and practicability. Since certificate technique is adopted in digital signature and authentication, the proposed scheme has advantages over other schemes in efficiency and other aspects.