Non-interactive Timestamping in the Bounded Storage Model

摘要

A timestamping scheme is non-interactive if a stamper can stamp a document without communicating with any other player. The only communication done is at validation time. Non-Interactive timestamping has many advantages, such as information theoretic privacy and enhanced robustness. Unfortunately, no such scheme exists against polynomial time adversaries that have unbounded storage at their disposal. In this paper we show non-interactive timestamping is possible in the bounded storage model. In this model it is assumed that all parties participating in the protocol have small storage, and that in the beginning of the protocol a very long random string (which is too long to be stored by the players) is transmitted. To the best of our knowledge, this is the first example of a cryptographic task that is possible in the bounded storage model, but is impossible in the "standard cryptographic setting", even assuming cryptographic assumptions. We give an explicit construction that is secure against all bounded storage adversaries, and a significantly more efficient construction secure against all bounded storage adversaries that run in polynomial time.