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Published in:
2007 | OriginalPaper | Chapter
Knowledge-Binding Commitments with Applications in Time-Stamping
Authors : Ahto Buldas, Sven Laur
Published in: Public Key Cryptography – PKC 2007
Publisher: Springer Berlin Heidelberg
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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.