## Cryptology ePrint Archive: Report 2006/408

**A Generic Construction of CCA-Secure Cryptosystems without NIZKP for a Bounded Number of Decryption Queries**

*Goichiro Hanaoka and Hideki Imai*

**Abstract: **In this paper, we propose a generic construction of chosen-ciphertext secure cryptosystems against adversaries with a bounded number of decrytion queries from arbitrary semantically secure encryption in a black box manner. Our construction is not only an alternative to the previously known technique, i.e. the Naor-Yung paradigm, but also has some interesting properties. Especially, (1) it does not require non-interactive zero-knowledge proof, and (2) its component ciphertexts can be compressed into only one if the underlying encryption has a certain homomorphic property. Consequently, when applying our construction to the ElGamal encryption, ciphertext overhead of the resulting scheme will be only one group element which is considered optimal since it is the same as the original ElGamal. Disadvantages to previous schemes are that the upper bound of the number of decryption queries (e.g. 2^{30}) has to be known before set-up phase, and the size of public key is large.

**Category / Keywords: **public-key cryptography / public key encryption, chosen-ciphertext security, short ciphertext length

**Date: **received 13 Nov 2006

**Contact author: **hanaoka-goichiro at aist go jp

**Available format(s): **Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation

**Version: **20061113:110215 (All versions of this report)

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