Chapter

Information Security and Privacy

Volume 7372 of the series Lecture Notes in Computer Science pp 194-207

Effort-Release Public-Key Encryption from Cryptographic Puzzles

  • Jothi RangasamyAffiliated withInformation Security Institute, Queensland University of Technology
  • , Douglas StebilaAffiliated withInformation Security Institute, Queensland University of Technology
  • , Colin BoydAffiliated withInformation Security Institute, Queensland University of Technology
  • , Juan Manuel González-NietoAffiliated withInformation Security Institute, Queensland University of Technology
  • , Lakshmi KuppusamyAffiliated withInformation Security Institute, Queensland University of Technology

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Abstract

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.

Keywords

puzzles difficulty timed-release encryption key escrow