An IND-CCA2 public-key cryptosystem with fast decryption

Johannes Buchmann, Kouichi Sakurai, Tsuyoshi Takagi

Research output: Chapter in Book/Report/Conference proceedingConference contribution

5 Citations (Scopus)


We propose an IND-CCA2 public-key cryptosystem with fast decryption, called the NICE-X cryptosystem. Its decryption time is the polynomial time of degree 2 by the bit-length of a public-key D, i.e., O((log |D|)2), and the cost of two hash functions. The NICE-X is an enhancement of the NICE cryptosystem, which is constructed over the quadratic class group Cl(D). We first show that the one-wayness of the encryption of the NICE cryptosystem is as intractable as the Smallest Kernel Equivalent Problem (SKEP). We also prove that the NICE cryptosystem is IND-CPA under the Decisional Kernel Problem (DKP). Then we prove that the NICE-X cryptosystem is IND-CCA2 under the SKEP in the random oracle model. Indeed, the overhead of the decryption of the NICE-X from the NICE is only the cost of one ideal multiplication and two hash functions. Our conversion technique from the NICE to the NICE-X is based on the REACT. However we modify it to be suitable for the NICE. A message of the NICE-X is encrypted with the random mask of the encryption function of the NICE, instead of the encrypted key. Then the reduced security problem of the NICE-X is enhanced from the Gap-SKEP to the SKEP.

Original languageEnglish
Title of host publicationInformation Security and Cryptology - ICISC 2001 - 4th International Conference, Proceedings
EditorsKwangjo Kim
PublisherSpringer Verlag
Number of pages21
ISBN (Print)3540433198, 9783540433194
Publication statusPublished - 2002
Event4th International Conference on Information Security and Cryptology, ICISC 2001 - Seoul, Korea, Republic of
Duration: Dec 6 2001Dec 7 2001

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Other4th International Conference on Information Security and Cryptology, ICISC 2001
Country/TerritoryKorea, Republic of

All Science Journal Classification (ASJC) codes

  • Theoretical Computer Science
  • General Computer Science


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