조건 기반 프록시 재암호화에 대한 연구

DoctorIn a proxy re-encryption (PRE) scheme, a delegator gives a re-encryption key to a semi-trusted proxy who, by using the re-encryption key, can transform a ciphertext encrypted under the delegator's public key into one that can be decrypted using a private key of another user (called a delegatee). That is, the delegator can delegate his decryption rights through the proxy. Since PRE can be applied to many applications such as remote file storage, access control system, and digital right management, cryptographers have taken an interest in the study of PRE. However, there are applications where the delegator wants to delegate the decryption right for a subset of ciphertexts. For example, when Alice on vacation wants to delegate the decryption right for the encrypted e-mails with the keyword, urgent, to Bob, original PRE that only supports the all-or-nothing delegation is not enough. In this literature, the concept of conditional proxy re-encryption (C-PRE) was appeared to provide fine-grained delegation of decryption rights. C-PRE allows that a delegator delegates decryption rights from a delegator to a delegatee through a semi-trusted proxy within the ciphertexts computed under a specific condition. Such a C-PRE scheme can provide more fine-grained delegation in the applications of PRE. Tang proposed the first proxy-invisible C-PRE scheme, where proxy invisibility means that an adversary cannot distinguish between original ciphertexts and re-encrypted ciphertexts. However, Tang's scheme is only secure against chosen plaintext attacks (CPA-secure). Jia~et~al. proposed a proxy-invisible C-PRE scheme that is secure against chosen ciphertext attacks (CCA-secure) with random oracle heuristicwhereas the random oracle methodology that assumes public oracle access to a truly random function is a useful tool for designing a cryptosystem, the security of the cryptosystem proven in the random oracle model does not guarantee its security in the real world where random oracles do not exist. There is no CCA-secure and proxy-invisible C-PRE scheme in the standard model (i.e., without random oracles). This thesis studies the proxy-invisible C-PRE scheme that is CCA-secure in the standard model

인덱스 테이블을 이용한 효율적인 검색 가능 대칭키 암호 기법에 대한 연구

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ID기반 암호 기법들을 이용한 암호문 인증성을 제공하는 ID 기반 Signcryption 기법

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금융 거래 단말기의 성능에 따라 가변적으로 적용 가능한 해쉬 체인 운행 기법

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Single-Layer Fractal Hash Chain Traversal with Almost Optimal Complexity

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S/MIME과 SDES에 기반한 VoIP 보안 프로토콜의 취약점에 관한 연구

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서버에서 효율적인 메모리 사용량을 제공하는 공개키 기반 검색 암호 시스템

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