Effort-Release Public-Key Encryption from Cryptographic Puzzles

  • Jothi Rangasamy
  • Douglas Stebila
  • Colin Boyd
  • Juan Manuel González-Nieto
  • Lakshmi Kuppusamy
Part of the Lecture Notes in Computer Science book series (LNCS, volume 7372)


Timed-release cryptography addresses the problem of “sending messages into the future”: a message is encrypted so that it can only be decrypted after a certain amount of time, either (a) with the help of a trusted third party time server, or (b) after a party performs the required number of sequential operations. We generalise the latter case to what we call effort-release public key encryption (ER-PKE), where only the party holding the private key corresponding to the public key can decrypt, and only after performing a certain amount of computation which may or may not be parallelisable. Effort-release PKE generalises both the sequential-operation-based timed-release encryption of Rivest, Shamir, and Wagner, and also the encapsulated key escrow techniques of Bellare and Goldwasser. We give a generic construction for ER-PKE based on the use of moderately hard computational problems called puzzles. Our approach extends the KEM/DEM framework for public key encryption by introducing a difficulty notion for KEMs which results in effort-release PKE. When the puzzle used in our generic construction is non-parallelisable, we recover timed-release cryptography, with the addition that only the designated receiver (in the PKE setting) can decrypt.


puzzles difficulty timed-release encryption key escrow 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  • Jothi Rangasamy
    • 1
  • Douglas Stebila
    • 1
  • Colin Boyd
    • 1
  • Juan Manuel González-Nieto
    • 1
  • Lakshmi Kuppusamy
    • 1
  1. 1.Information Security InstituteQueensland University of TechnologyBrisbaneAustralia

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