Cryptology ePrint Archive: Report 2005/198

Universally Composable Time-Stamping Schemes with Audit

Ahto Buldas and Peeter Laud and Märt Saarepera and Jan Willemson

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.

Category / Keywords: cryptographic protocols / Time-stamping, hash functions, Universal Composability

Publication Info: Accepted as a regular paper at the Information Security Conference -- ISC 2005.

Date: received 27 Jun 2005, last revised 27 Jun 2005

Contact author: Ahto Buldas at ut ee

Available format(s): Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation

Note: This is a full version of our ISC2005 paper

Version: 20050629:201516 (All versions of this report)

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