Knowledge-Binding Commitments with Applications in Time-Stamping

  • Ahto Buldas
  • Sven Laur
Conference paper

DOI: 10.1007/978-3-540-71677-8_11

Part of the Lecture Notes in Computer Science book series (LNCS, volume 4450)
Cite this paper as:
Buldas A., Laur S. (2007) Knowledge-Binding Commitments with Applications in Time-Stamping. In: Okamoto T., Wang X. (eds) Public Key Cryptography – PKC 2007. PKC 2007. Lecture Notes in Computer Science, vol 4450. Springer, Berlin, Heidelberg


We prove in a non-black-box way that every bounded list and set commitment scheme is knowledge-binding. This is a new and rather strong security condition, which makes the security definitions for time-stamping much more natural compared to the previous definitions, which assume unpredictability of adversaries. As a direct consequence, list and set commitment schemes with partial opening property are sufficient for secure time-stamping if the number of elements has an explicit upper bound N. On the other hand, white-box reductions are in a sense strictly weaker than black-box reductions. Therefore, we also extend and generalize the previously known reductions. The corresponding new reductions are \(\Theta(\sqrt{N})\) times more efficient, which is important for global-scale time-stamping schemes where N is very large.

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Copyright information

© Springer Berlin Heidelberg 2007

Authors and Affiliations

  • Ahto Buldas
    • 1
    • 2
    • 3
  • Sven Laur
    • 4
  1. 1.Cybernetica AS, Akadeemia tee 21, 12618 TallinnEstonia
  2. 2.Tallinn University of Technology, Raja 15, 12618 TallinnEstonia
  3. 3.University of Tartu, Liivi 2, 50409 TartuEstonia
  4. 4.Helsinki University of Technology, Laboratory for Theoretical Computer Science, P.O.Box 5400, FI-02015 TKKFinland

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