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  • How to Enhance the Security of Public-Key Encryption at Minimum Cost

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本論文では、受動的攻撃に対し安全性が保証されているような確率暗号一般を、ランダムオラクルモデルのもとで、能動的攻撃に対しても安全性が保証されるものに変換する方式を提案する。この変換された暗号方式は、ランダムオラクルをSHA-1やMD5のような既存のハッシュ関数で代用させた場合、基となる方式に比べて、ハッシュ関数一回の手間を増やすだけで実現される。また、いわゆる「Exact Security」モデルにおいて、安全性の評価の上で、非常に効率の良い還元が存在する。本稿の最後には、既に受動的攻撃に対し安全性が保証されている確率暗号方式、ElGamal、Blum-Goldwasser、岡本-内山方式など[4, 7, 9]にこの変換を施した例を記載する。
This paper presents a simple and efficient conversion from a semantically secure public-key encryption scheme against passive adversaries to a non-malleable (or semantically secure) public-key encryption scheme against adaptive chosen-ciphertext attacks (active adversaries) in the random oracle model. Since our conversion requires only one random (hash) function operation, the converted scheme is almost as efficient as the original one, when the random function is replaced by a practical hash function such as SHA-1 and MD5. We also give a concrete analysis of the reduction for proving its security, and show that our security reduction is (almost) optimally efficient. Finally this paper gives some practical examples of applying this conversion to some practical and semantically secure encryption schemes such as the ElGamal, Blum-Goldwasser and Okamoto-Uchiyama schemes [4, 7, 9].


  • Technical report of IEICE. ISEC

    Technical report of IEICE. ISEC 98 (426), 75-86, 1998-11-20

    The Institute of Electronics, Information and Communication Engineers

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