Universally Composable Time-Stamping Schemes with Audit

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.

• Type: Conference
• Year: 2005
• Where: ISW
• Authors: Ahto Buldas, Peeter Laud, Märt Saarepera, Jan Willemson
• Keywords: Common Reference String Model, Composable Auditable Time-stamping, Composable Time-stamping Scheme, ISW 2005