Paper 2013/730

Stamp \& Extend -- Instant but Undeniable Timestamping based on Lazy Trees

Łukasz Krzywiecki, Przemys{\l}aw Kubiak, and Miros{\l}aw Kuty{\l}owski


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.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Chris J. Mitchell and Allan Tomlinson, editors, INTRUST, volume 7711 of Lecture Notes in Computer Science, pages 5–24. Springer, 2012.
timestampingundeniabilityforgery evidenceSchnorr signature
Contact author(s)
przemyslaw kubiak @ pwr wroc pl
2013-11-13: received
Short URL
Creative Commons Attribution


      author = {Łukasz Krzywiecki and Przemys{\l}aw Kubiak and Miros{\l}aw Kuty{\l}owski},
      title = {Stamp \& Extend -- Instant but Undeniable Timestamping based on Lazy Trees},
      howpublished = {Cryptology ePrint Archive, Paper 2013/730},
      year = {2013},
      doi = {10.1007/978-3-642-35371-0_2},
      note = {\url{}},
      url = {}
Note: In order to protect the privacy of readers, does not use cookies or embedded third party content.