Some Timestamping Protocol Failures

Protocol failures are presented for two timestamping schemes. These failures emphasize the importance and di culty of implementing a secure protocol even though there exist secure underlying algorithms. As well, they indicate the importance of clearly de ning the goals for a protocol. For the scheme of Benaloh and de Mare Eurocrypt '93, it is shown that although an indication of time can be included during the computation of the timestamp, the veri ation of the timestamp does not allow for the recovery of this temporal measure. For the scheme of Haber and Stornetta Journal of Cryptology '91, we demonstrate how a collusion attack between a single user and a timestamping service allows for the backdating of timestamps. This attack is successful despite the claim that the timestamping service need not be trusted. For each of these schemes we discuss methods for improvement.

• Type: Conference
• Year: 1998
• Where: NDSS
• Authors: Mike Just
• Keywords: Computer Networks, NDSS 1998, Secure Underlying Algorithms, Timestamping Schemes, Timestamping Service