Paper 2005/198

Universally Composable Time-Stamping Schemes with Audit

Ahto Buldas, Peeter Laud, Märt Saarepera, and Jan Willemson


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.

Note: This is a full version of our ISC2005 paper

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Accepted as a regular paper at the Information Security Conference -- ISC 2005.
Time-stampinghash functionsUniversal Composability
Contact author(s)
Ahto Buldas @ ut ee
2005-06-29: received
Short URL
Creative Commons Attribution


      author = {Ahto Buldas and Peeter Laud and Märt Saarepera and Jan Willemson},
      title = {Universally Composable Time-Stamping Schemes with Audit},
      howpublished = {Cryptology ePrint Archive, Paper 2005/198},
      year = {2005},
      note = {\url{}},
      url = {}
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