Strong security notions for timed-release public-key encryption revisited

  • Authors:
  • Ryo Kikuchi;Atsushi Fujioka;Yoshiaki Okamoto;Taiichi Saito

  • Affiliations:
  • NTT Information Sharing Platform Laboratories, Japan;NTT Information Sharing Platform Laboratories, Japan;Tokyo Denki University, Japan;Tokyo Denki University, Japan

  • Venue:
  • ICISC'11 Proceedings of the 14th international conference on Information Security and Cryptology
  • Year:
  • 2011

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Abstract

Timed-release public-key encryption (TRPKE) provides a mechanism that a ciphertext cannot ordinarily be decrypted, even with its secret key, before a specific time. TRPKE with pre-open capability (TRPKE-PC) provides an additional mechanism where the sender can permit a receiver to decrypt the ciphertext before that specific time if necessary. A TRPKE(-PC) scheme should be secure in following aspects: against malicious receivers, a time-server, and, only in TRPKE-PC, against malicious senders. In this paper, we mention that previous security definitions are incomplete or insufficient, and propose new ones in all aspects of the above. We also present a generic construction of a TRPKE-PC scheme. Our construction provides the first TRPKE(-PC) scheme that is provably secure with respect to the above security definitions, especially against malicious key generations of the time-server.