Stamp and Extend – Instant But Undeniable Timestamping Based on Lazy Trees

  • Łukasz Krzywiecki
  • Przemysław Kubiak
  • Mirosław Kutyłowski
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 7711)

Abstract

We present a Stamp&Extend time-stamping scheme based on linking via modified creation of Schnorr signatures. The scheme is based on lazy construction of a tree of signatures.

Stamp&Extend returns a timestamp immediately after the request, unlike the schemes based on the concept of timestamping rounds. Despite the fact that all timestamps are linearly linked, verification of a timestamp requires a logarithmic number of steps with respect to the chain length. An extra feature of the scheme is that any attempt to forge a timestamp by the Time Stamping Authority (TSA) results in revealing its secret key, providing an undeniable cryptographic evidence of misbehavior of TSA.

Breaking Stamp&Extend requires not only breaking Schnorr signatures, but to some extend also breaking Pedersen commitments.

Keywords

timestamping undeniability forgery evidence Schnorr signature 

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Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  • Łukasz Krzywiecki
    • 1
  • Przemysław Kubiak
    • 1
  • Mirosław Kutyłowski
    • 1
  1. 1.Faculty of Fundamental Problems of TechnologyWrocław University of TechnologyPoland

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