A two-level time-stamping system

Time-Stamping is a cryptographic technique which allows us to prove that an electronic document existed at a certain point in time and that it has not been modified since then. Different time-stamping schemes have already been proposed. Most of them use the concept of trusted Time-Stamping Authority (TSA). A TSA is in charge of time-stamping documents and delivering a time-stamping certificate for each time-stamped document. The purpose of this paper is to propose a new time-stamping scheme using a Local Time-stamping System (LTS). The main idea can be summarised as follows: digests of the documents to be time-stamped are sent to a Local Time-stamping System (LTS). The LTS accumulates the digests into a round value using a round-based protocol. The round value is then time-stamped by a trusted and official TSA, We show how this time-stamping scheme could be useful for an organisation such as a digital library or a company.