• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.9
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• pp.3841-3857
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• 2020

RSA is one of the best well-known public key cryptosystems. This methodology is widely used at present because there is not any algorithm which can break this system that has all strong parameters within polynomial time. However, it may be easily broken when at least one parameter is weak. In fact, many weak parameters are already found and are solved by some algorithms. Some examples of weak parameters consist of a small private key, a large private key, a small prime factor and a small result of the difference between two prime factors. In this paper, the new weakness of RSA is proposed. Assuming Euler's totient value, Φ (n), can be rewritten as Φ (n) = ad + b, where d is the private key and a, b ∈ ℤ, if a divides both of Φ (n) and b and the new exponent for the decryption equation is a small integer, this condition is assigned as the new weakness for breaking RSA. Firstly, the specific algorithm which is created for this weakness directly is proposed. Secondly, two equations are presented to find a, b and d. In fact, one of two equations must be implemented to find a and b at first. After that, the other equation is chosen to find d. The experimental results show that if this weakness has happened and the new exponent is small, original plaintext, m, will be recovered very fast. Furthermore, number of steps to recover d are very small when a is large. However, if a is too large, d may not be recovered because m which must be always written as m = h^a is higher than modulus.

• The KIPS Transactions:PartC
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• v.18C no.6
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• pp.379-388
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• 2011

Ensuring the security of medical records is becoming an increasingly important problem as modern technology is integrated into existing medical services. As a consequence of the adoption of EMR(Electronic Medical Records) in the health care sector, it is becoming more and more common for a health professional to edit and view a patient's record. In order to protect the patient's privacy, a secure authentication model to access the electronic medical records system must be used. A traditional identity based digital certificate for the authenticity of EMR has private key management and key escrow of a user's private key. In order to protect the EMR, The traditional authentication system is based on the digital certificate. The identity based digital certificate has many disadvantages, for example, the private key can be forgotten or stolen, and can be easily escrow of the private key. Nowadays, authentication model using fingerprint recognition technology for EMR has become more prevalent because of the advantages over digital certificate -based authentication model. Because identity-based fingerprint recognition can eliminate disadvantages of identity-based digital certificate, the proposed authentication model provide high security for access control in EMR.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.5294-5302
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• 2014

The development of public-key-based technique that enables a variety of services(E-government, e-banking, e-payment, etc.) evaluated as having complete safety. On the other hand, vulnerabilities(e.g, heartbleed bug, etc.) are constantly being discovered. In this paper, a public key infrastructure to verify the safety and reliability, the collision rate using OpenSSL key pair was analyzed. the experiment was performed using the following procedure. Openssl was used to create five private certification agencies, and each of the private certificate authority certificates to create 2 million, generating a total of 10 million by the certificate of the key pair conflicts analysis. The results revealed 35,000 in 1 million, 0.35% chance of a public key, a private key conflict occurred. This is sufficient in various fields(E-payment, Security Server, etc.). A future public-key-based technique to remove the threat of a random number generator, large minority issues, in-depth study of selection will be needed.

• Journal of Internet Computing and Services
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• v.7 no.1
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• pp.59-64
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• 2006

Harn al proposed a GKRS(Global Key Recovery System) that combines the functions of the key recovery authorities and the public key certification authorities(CA), Among other features, user dominance(i.e, a user is allowed to select his own public-private key pair and especially a public element for verifying the validity of the public-private key pair)is proposed by [1] for wide acceptance of GKRS. In this paper, we attack the RSA version of GKRS by showing that its user-dominance feature and the corresponding key verification scheme employed by the CA allow for fraud by users against CA. We propose more secure GKPS than original GKPS, The proposed system makes the probability of user fraud negligible small.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.5
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• pp.781-793
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• 2020

In this paper, we propose a new RLWE-based scheme named μ-Hope that exploits Error Correcting Code(ECC) on NewHope. The previous parameters of NewHope uses 12289 as a prime modulus, and the size of the public key, private key, and ciphertext is 928-byte, 1888-byte, and 1120-byte respectively, which can be said to be larger than other RLWE based algorithms. In this paper, we propose μ-Hope, which changes modulus 12289 to 769 to reduce the size of the public key, private key, and ciphertext. Also, we adopts XE1 as an Error Correcting Code(ECC) to solve the increased decryption failure rate caused by using a small prime modulus. As a result, the size of the public key, private key, and ciphertext decreased by 38%, 37%, and 37% respectively. As the computational efficiency caused by using a small prime modulus exceeds the performance degradation by exploiting ECC, this result in 25% performance improvement for a single key exchange.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.4
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• pp.635-641
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• 2010

In this paper, we propose an efficient public key broadcast encryption system which can also extend traitor trace and revoke system. Although the proposed system has limited collusion size, the ciphertext size in the system can be sublinear in the number of total users, the private key size is constant, the computational cost can be sublinear and it can support black-box tracing algorithm, therefore, our system can be an option to applications where reducing the ciphertext size, private key size is a top priority. Furthermore, we can also apply our system to military document broadcast system, because it has such an efficient measurement.

• Korean Security Journal
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• no.16
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• pp.357-371
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• 2008

Currently, the security operations in nation's key foundations in Korea are performed by private police and special security guard in accordance with the Private Police Act and Security Business Act, respectively. In 1960s, The Korean Government introduced the private police system in terms of the national security issues, but it was just a hurriedly-set plan on the basis of Japanese Sunsa system as by that time there was no such system revitalized. However, the special security guards could offer wider range of security services including those of the private police with the enactment and revision of the Security Business Act 1976 and April 2001, respectively. Moreover, the expectations and interests rose over the special security guards in nation's key foundations after 9.11Terror Event in the U. S. 2001. However, as we investigated the current education/training system for the special security guard, we found that such education/training which is not activating the specialty of special security guard will not respond to the social demands. Special security guard owns its own characteristics other than those of general security guard as they are in service in nation's key foundations. Thus, the effcient management and training for the special security guard is the most important matter for the safety and security of nation's key foundations. Therefore, the well-educated special security guard through the reorganized and specialized education/training for the protection of nation's key foundations is expected to offer qualitatively improved security services.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.1
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• pp.3-10
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• 2013

Several identity-based and authenticated key agreement protocols have been proposed. It remains at issue to design secure identity based and authenticated key agreement protocols. In this paper, we propose a one round authenticated group key agreement protocol which uses one more key pair as well as the public key and private key of typical IBE(Identity-Based Encryption) system. The proposed protocol modified Shi et al.'s protocol and He et al.'s protocol. The public and private keys and the signature process of our protocol are simpler than them of their protocols. Our protocol is secure and more efficient than their protocols in communication and computation costs.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.4
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• pp.67-76
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• 2002

Kerberos is designed to provide strong authentication between client and application servers which are working in distributed network environment by using symmetric-key cryptography, and supposed to trust other systems of the realm. In this paper, we design an efficient and strong authentication mechanism by introducing the public/private-key to Kerberos. In the mechanism to make a system more secure, the value of the session key is changed everytime using MAC(message authentication code) algorithm with the long-term key for user-authentication and a random number exchanged through the public key. Also, we employ a mutual authentication method, which is used on challenge-response mechanism based on digital signatures, to improve trust between realms, and present a way of reducing the number of keys by simplifying authentication steps.

• The Journal of the Korea Contents Association
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• v.17 no.6
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• pp.32-38
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• 2017

Despite the opinion that certificate is useless, half of the population in Korea (approx. 35 million) get an certificate, and use it for internet banking, internet shopping, stock trading, and so on. Most users store their certificates on a usb memory or smartphone, and certificates or passwords stored on such storage media can be easily attacked and used to disguise as legitimate users. Due to these security problem of certificate, a various authentication technologies has been proposed such as smartphone owner authentication using SMS, and a personal authentication using biometric authentication. However, a safe technique is not presented yet without user password, and certificate. In this paper, I proposed a method to secure certificate/private key without a user password using a combination of USIM card and smartphone's information. Even if a hacker gets the user password, the certificate, and the private key, he can not use the certificate. User do not need to remember complex password which is a combination of alphabetic / numeric / special characters, and use his certificate safely.