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Can We Construct Unbounded Time-Stamping Schemes from Collision-Free Hash Functions?

  • Ahto Buldas
  • Margus Niitsoo
Part of the Lecture Notes in Computer Science book series (LNCS, volume 5324)

Abstract

It has been known for quite some time that collision-resistance of hash functions does not seem to give any actual security guarantees for unbounded hash-tree time-stamping, where the size of the hash-tree created by the time-stamping service is not explicitly restricted. We focus on the possibility of showing that there exist no black-box reductions of unbounded time-stamping schemes to collision-free hash functions. We propose an oracle that is probably suitable for such a separation and give strong evidence in support of that. However, the existence of a separation still remains open. We introduce the problem and give a construction of the oracle relative to which there seem to be no secure time-stamping schemes but there still exist collision-free hash function families. Although we rule out many useful collision-finding strategies (relative to the oracle) and the conjecture seems quite probable after that, there still remains a possibility that the oracle can be abused by some very smartly constructed wrappers. We also argue why it is probably very hard to give a correct proof for our conjecture.

Keywords

Hash Function Turing Machine Time Stamp Input Pair Polynomial Fraction 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2008

Authors and Affiliations

  • Ahto Buldas
    • 1
    • 2
    • 3
  • Margus Niitsoo
    • 1
    • 3
  1. 1.University of TartuTartuEstonia
  2. 2.Tallin University of TechnologyTallinnEstonia
  3. 3.Cybernetica ASTallinnEstonia

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