International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Universally Composable Time-Stamping Schemes with Audit

Ahto Buldas
Peeter Laud
M?rt Saarepera
Jan Willemson
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Abstract: We present a universally composable time-stamping scheme based on universal one-way hash functions. The model we use contains an ideal auditing functionality (implementable in the Common Reference String model), the task of which is to check that the rounds' digests are correctly computed. Our scheme uses hash-trees and is just a slight modification of the known schemes of Haber-Stornetta and Benaloh-de Mare, but both the modifications and the audit functionality are crucial for provable security. The scheme turns out to be nearly optimal -- we prove that in every universally composable auditable time-stamping scheme, almost all time stamp requests must be communicated to the auditor.
  title={Universally Composable Time-Stamping Schemes with Audit},
  booktitle={IACR Eprint archive},
  keywords={cryptographic protocols / Time-stamping, hash functions, Universal Composability},
  note={Accepted as a regular paper at the Information Security Conference -- ISC 2005. 12961 received 27 Jun 2005, last revised 27 Jun 2005},
  author={Ahto Buldas and Peeter Laud and M?rt Saarepera and Jan Willemson},