• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.12
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• pp.3261-3273
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• 2013

In the paper, we propose a novel adaptively secure hierarchical identity-based signature scheme from lattices. The size of signatures in our scheme is shortest among the existing hierarchical identity-based signature schemes from lattices. Our scheme is motivated by Gentry et al.'s signature scheme and Agrawal et al.'s hierarchical identity-based encryption scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.7
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• pp.2532-2553
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• 2014

In Asiacrypt 2003, Al-Riyami and Paterson proposed the notion of certificateless cryptography, a technique to remove key escrow from traditional identity-based cryptography as well as circumvent the certificate management problem of traditional public key cryptography. Subsequently much research has been done in the realm of certificateless encryption and signature schemes, but little to no work has been done for the identification primitive until 2013 when Chin et al. rigorously defined certificateless identification and proposed a concrete scheme. However Chin et al.'s scheme was proven in the random oracle model and Canetti et al. has shown that certain schemes provable secure in the random oracle model can be insecure when random oracles are replaced with actual hash functions. Therefore while having a proof in the random oracle model is better than having no proof at all, a scheme to be proven in the standard model would provide stronger security guarantees. In this paper, we propose the first certificateless identification scheme that is both efficient and show our proof of security in the standard model, that is without having to assume random oracles exist.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.10 no.1
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• pp.13-22
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• 2000

본 논문에서는 Skipjack의 변환규칙 A와 같은 반복적인 구조에 대한 차분 특성 및 선형 근사식의 확률의 상한 값을 제시하고 이를 증명한다. 즉 라운드 함수에 대한 확률의 최대 값이 p이면 15라운드 후에 p4이 됨을 보인다. 따라서 본 논문에서 고려한 구조는 현재까지 DC 및 LC에 대한 안전성을 증명할 수 있는 구조인 Feistel 구조 및 MISTY 구조와 더불어 블록 암호의 설계 방법에 대한 다양성을 제공한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.6
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• pp.2851-2873
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• 2016

Cloud storage as a service provides high scalability and availability as per need of user, without large investment on infrastructure. However, data security risks, such as confidentiality, privacy, and integrity of the outsourced data are associated with the cloud-computing model. Over the year's techniques such as, remote data checking (RDC), data integrity protection (DIP), provable data possession (PDP), proof of storage (POS), and proof of retrievability (POR) have been devised to frequently and securely check the integrity of outsourced data. In this paper, we improve the efficiency of PDP scheme, in terms of computation, storage, and communication cost for large data archives. By utilizing the capabilities of JAR and ZIP technology, the cost of searching the metadata in proof generation process is reduced from O(n) to O(1). Moreover, due to direct access to metadata, disk I/O cost is reduced and resulting in 50 to 60 time faster proof generation for large datasets. Furthermore, our proposed scheme achieved 50% reduction in storage size of data and respective metadata that result in providing storage and communication efficiency.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.9 no.3
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• pp.27-38
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• 1999

We study on the security for the block ciphers with 20block structure which have provable security against DC and LC on the view point of higher order DC, 2-block structures are classified three types according to the location of round function such as C(Center)-type R(Right)-type and L(Left)-type We prove that in the case of 4 rounds encryption function these three types provide the equal strength against higher order DC and that in the case of 5 or more rounds R-type is weaker than C-type and L-type.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.3
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• pp.607-625
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• 2011

Two-party key exchange protocol is a mechanism in which two parties communicate with each other over an insecure channel and output the same session key. A key exchange protocol that is secure against an active adversary who can control and modify the exchanged messages is called authenticated key exchange (AKE) protocol. LaMacchia, Lauter and Mityagin presented a strong security definition for public key infrastructure (PKI) based two-pass protocol, which we call the extended Canetti-Krawczyk (eCK) security model, and some researchers have provided eCK-secure AKE protocols in recent years. However, almost all protocols are provably secure in the random oracle model or rely on a special implementation technique so-called the NAXOS trick. In this paper, we present a PKI-based two-pass AKE protocol that is secure in the eCK security model. The security of the proposed protocol is proven without random oracles (under three assumptions), and does not rely on implementation techniques such as the NAXOS trick.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.2
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• pp.428-439
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• 2011

The main challenge in building efficient broadcast systems is to encrypt messages with short ciphertexts. In this paper, we present a new construction based on the identity. Our construction contains the desirable features, such as constant size ciphertexts and private keys, short public keys and not fixing the total number of possible users in the setup. In addition, the proposed scheme achieves the full security which is stronger than the selective-identity security. Furthermore we show that the proof of security does not rely on the random oracles. To the best our knowledge, it is the first efficient scheme that is full security and achieves constant size ciphertexts and private keys which solve the trade-off between the ciphertext size and the private key size.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2003.07a
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• pp.37-42
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• 2003

Threshold signature and blind signature are playing important roles in cryptography as well as practical applications such as e-cash and e-voting systems. In this paper, we present a new threshold blind digital signature based on pairings without a trusted third party. Our scheme operates on Gap Diffie-Hellman group, where Computational Diffie-Hellman problems are hard but Decision Diffie-Hellman problems are easy. For example, we use pairings that could be built from Weil pairing or Tate pairing. To the best of our knowledge, we claim that our scheme is the first threshold blind signature using pairings with provable security in the random oracle model.

• Journal of Information Processing Systems
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• v.7 no.1
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• pp.159-172
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• 2011

A designated verifier signature is a special type of digital signature, which convinces a designated verifier that she has signed a message in such a way that the designated verifier cannot transfer the signature to a third party. A strong designated verifier signature scheme enhances the privacy of the signer such that no one but the designated verifier can verify the signer's signatures. In this paper we present two generic frame works for constructing strong designated verifier signature schemes from any secure ring signature scheme and any deniable one-pass authenticated key exchange protocol, respectively. Compared with similar protocols, the instantiations of our construction achieve improved efficiency.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.1
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• pp.121-125
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• 2007

Differential cryptanalysis and linear cryptanalysis are the most powerful approaches known for attacking many block ciphers and used to evaluating the security of many block ciphers. So designers have designed secure block ciphers against these cryptanalyses. In this paper, we present new three block cipher structures. And for given r, we prove that differential(linear) probabilities for r-round blockcipher structures are upper bounded by $p^2(q^2),\;2p^2(2q^2)$ if the maximum differential(linear) probability is p(q) and the round function is a bijective function.