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RISS 인기검색어
- 검색키워드
- 주제어 : tight security (검색결과 3 건)
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Tight security for cryptographic schemes in the multi-instance settings
이영경 Graduate School of Cybersecurity, Korea University 2021 국내박사
This thesis presents tight security results in independent cryptographic schemes public-key encryption (PKE) and identity-based signature (IBS). The security of PKE schemes in multi-user settings is aimed at capturing real-world scenarios in which an adversary could attack multiple users and multiple ciphertexts of its choice. However, the fact that a real-world adversary can also mount key-exposure attacks requires us to consider a more realistic notion of security in multi-user settings. An IBS scheme can be generically constructed from an ordinary signature scheme. But it was unclear that a generic construction leads to a tightly secure IBS scheme, no matter what tightly secure signature scheme be used as a building block. The summary of tight security results of this thesis is presented as follows: • This thesis defines the security notion of PKE in a multi-user setting with corruptions, where an adversary is able to issue corruption (i.e., private key) queries. Then, this thesis proposes the first practical and tightly secure PKE scheme in the multi-user setting with corruptions. • This thesis shows that the recent work by Seo, Abdalla, Lee, and Park (Information Sciences, July 2019) has a flaw in the security analysis of CCA conversion methods and presents revised security proofs. • This thesis demonstrates that the generic construction of IBS can achieve tightness if the underlying signature scheme is tightly secure in the multiuser setting with corruption. In addition, this thesis extends the tightness result of IBS to the multi-instance setting, where an adversary can corrupt multiple key generation centers and obtain related master secret keys.
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RSA 문제와 동등한 안전성을 갖는 온라인/오프라인 서명 기법
최경용 상명대학교 일반대학원 2018 국내석사
온라인/오프라인(On-line/off-line) 서명은 오프라인 단계에서 서명생성에 필요한 무거운 연산을 수행하고, 온라인 단계에서 간단한 연산만으로 최종 서명을 완성하는 기법이다. 이는 다수의 사용자에게 즉각적인 서명 응답을 해야 하는 응용환경에 적합하다. 본 논문에서는 RSA 문제에 기반한 새로운 온라인/오프라인 서명기법을 두 가지로 제안한다. 첫 번째 기법은 온라인 서명 시 고정된 밑수에서의 지수 승이면 되고, 두 번째 기법은 해쉬 연산과 같은 매우 간단한 계산만으로 온라인 서명을 완성할 수 있다. 두 서명의 안전성은 모두 RSA 문제로 환원되는데, 랜덤오라클 모델에서 안전성 손실 없이 증명이 된다. 주제어: 온라인/오프라인 전자서명, RSA 문제, Reduction 안전성 On-line/off-line signature is a technique for performing heavy computations required for signature generation in the off-line stage and completing the final signature by a simple operation in the online stage. This is suitable for application environments that require immediate signing responses to multiple users. In this paper, we propose two new on-line/off-line signature schemes based on RSA problem. The first technique can generate a signature with a fixed base exponentiation when signing online, and the second technique can complete an online signature with a very simple calculation such as a hash operation. The security of both signatures is based on the RSA problem, which is proven to be tightly secure without security loss in the random oracle model. key words: On-line/off-line signature, RSA problem, tight security reduction
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Ghoshal, Ashrujit University of Washington ProQuest Dissertations & 2023 해외박사(DDOD)
The primary objective of provable security is to characterize, as precisely as possible, the resources an attacker needs to compromise the security of a cryptographic system. While the time complexity of an attacker has traditionally been the key factor considered, actual attackers choose to invest in various other resources such as memory, preprocessing, parallelism etc. Moreover, an attacker may also exploit tradeoffs between these various resources in order to compromise security. This thesis develops new theory that characterizes the tradeoffs between various resources required to compromise the security of a cryptographic system. It makes progress in the two following directions:1. Memory-tightness: Firstly, this thesis develops a toolbox of new techniques for giving memory-tight reductions. Earlier works on memory-tightness gave some generic elementary techniques to make reductions memory-tight, but they were somewhat limited in their applicability. The work here addresses this issue and invents more involved techniques to make certain types of reductions memory-tight. Secondly, this thesis gives new results on the impossibility of making certain reductions memory-tight. While prior impossibility results in other settings were known, this thesis proves a memory-tightness impossibility for a scheme with algebraic structure for the first time.2. Time-space tradeoffs: This thesis continues the recent line of work on time-space tradeoffs in cryptography. Firstly, it proves new results that characterize time-space tradeoffs for mechanisms underlying the most popular cryptographic hash functions. Secondly, it gives a new hashing mechanism that provides optimal security against these time-space tradeoff attacks. Finally, it addresses the question of how much time is needed to produce the advice for preprocessing attacks.
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