Chapter

Applied Algebra, Algebraic Algorithms and Error-Correcting Codes

Volume 3857 of the series Lecture Notes in Computer Science pp 183-192

Applying Fujisaki-Okamoto to Identity-Based Encryption

  • Peng YangAffiliated withInstitute of Industrial Science, University of Tokyo
  • , Takashi KitagawaAffiliated withResearch Centre for Information Security (RCIS), National Institute of Advanced Industrial Science and Technology (AIST)
  • , Goichiro HanaokaAffiliated withResearch Centre for Information Security (RCIS), National Institute of Advanced Industrial Science and Technology (AIST)
  • , Rui ZhangAffiliated withInstitute of Industrial Science, University of Tokyo
  • , Kanta MatsuuraAffiliated withInstitute of Industrial Science, University of Tokyo
  • , Hideki ImaiAffiliated withInstitute of Industrial Science, University of TokyoResearch Centre for Information Security (RCIS), National Institute of Advanced Industrial Science and Technology (AIST)

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Abstract

The Fujisaki-Okamoto (FO) conversion is widely known to be able to generically convert a weak public key encryption scheme, say one-way against chosen plaintext attacks (OW-CPA), to a strong one, namely, indistinguishable against adaptive chosen ciphertext attacks (IND-CCA). It is not known that if the same holds for identity-based encryption (IBE) schemes, though many IBE and variant schemes are in fact specifically using the FO conversion. In this paper, we investigate this issue and confirm that the FO conversion is generically effective also in the IBE case. However, straightforward application of the FO conversion only leads to an IBE scheme with a loose (but polynomial) reduction. We then propose a simple modification to the FO conversion, which results in considerably more efficient security reduction.