• Journal of Information Processing Systems
• /
• v.6 no.3
• /
• pp.335-346
• /
• 2010

The present study investigates the difficulty of solving the mathematical problem, namely the DLP (Discrete Logarithm Problem) for ephemeral keys. The DLP is the basis for many public key cryptosystems. The ephemeral keys are used in such systems to ensure security. The DLP defined on a prime field $Z^*_p of random prime is considered in the present study. The most effective method to solve the DLP is the ICM (Index Calculus Method). In the present study, an efficient way of computing the DLP for ephemeral keys by using a new variant of the ICM when the factors of p-1 are known and small is proposed. The ICM has two steps, a pre-computation and an individual logarithm computation. The pre-computation step is to compute the logarithms of a subset of a group and the individual logarithm step is to find the DLP using the precomputed logarithms. Since the ephemeral keys are dynamic and change for every session, once the logarithms of a subset of a group are known, the DLP for the ephemeral key can be obtained using the individual logarithm step. Therefore, an efficient way of solving the individual logarithm step based on the newly proposed precomputation method is presented and the performance is analyzed using a comprehensive set of experiments. The ephemeral keys are also solved by using other methods, which are efficient on random primes, such as the Pohlig-Hellman method, the Van Oorschot method and the traditional individual logarithm step. The results are compared with the newly proposed individual logarithm step of the ICM. Also, the DLP of ephemeral keys used in a popular password key exchange protocol known as Chang and Chang are computed and reported to launch key recovery attack.

• The KIPS Transactions:PartC
• /
• v.18C no.6
• /
• pp.369-378
• /
• 2011

To ensure data confidentiality and fine-grained access control in business environment, system model using KP-ABE(Key Policy-Attribute Based Encryption) and PRE(Proxy Re-Encryption) has been proposed recently. However, in previous study, data confidentiality has been effected by decryption right concentrated on cloud server. Also, Yu's work does not consider a access privilege management, so existing work become dangerous to collusion attack between malicious user and cloud server. To resolve this problem, we propose secure system model against collusion attack through dividing data file into header which is sent to privilege manager group and body which is sent to cloud server. And we construct the model of access privilege management using AONT based XOR threshold Secret Sharing, In addition, our scheme enable to grant weight for access privilege using XOR Share. In chapter 4, we differentiate existing scheme and proposed scheme.

• Annals of Clinical Neurophysiology
• /
• v.9 no.1
• /
• pp.1-4
• /
• 2007

Vertigo is an illusion of rotation, which results from an imbalance within the vestibular system. This review focuses on two common presentations of spontaneous vertigo: acute prolonged spontaneous vertigo and recurrent spontaneous vertigo. Common causes of acute prolonged spontaneous vertigo include vestibular neuritis, labyrinthitis, and brainstem or cerebellar stroke. The history and detailed neurological/neurotological examinations usually provide the key information for distinguishing between peripheral and central causes of vertigo. Brain MRI is indicated in any patient with acute vertigo accompanied by abnormal neurological signs, profound imbalance, severe headache, and central patterns of nystagmus. Recurrent spontaneous vertigo occurs when there is a sudden, temporary, and largely reversible impairment of resting neural activity of one labyrinth or its central connections, with subsequent recovery to normal or near-normal function. Meniere's disease, migrainous vertigo, and vertebrobasilar insufficiency (VBI) are common causes. The duration of the vertigo attack is a key piece of information in recurrent spontaneous vertigo. Vertigo of vascular origin, such as VBI, typically lasts for several minutes, whereas recurrent vertigo due to peripheral inner-ear abnormalities lasts for hours. Screening neurotological evaluations, and blood tests for autoimmune and otosyphilis are useful in assessment of recurrent spontaneous vertigo that are likely to be peripheral in origin.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.15 no.1
• /
• pp.29-40
• /
• 2005

In this paper we consider the security of recently proposed software-orienred stram cipher HELIX, SCREAM, MUGI, and PANAMA against algebraic attacks. Algebraic attack is a key recovery attack by solving an over-defined system of multi-variate equations with input-output pairs of an algorithm. The attack was firstly applied to block ciphers with some algebraic properties and then it has been mon usefully applied to stream ciphers. However it is difficult to obtain over-defined algebraic equations for a given cryptosystem in general. Here we analyze recently proposed software-oriented stream ciphers by constructing a system of equations for each cipher. furthermore we propose three design considerations of software-oriented stream ciphers.

• Convergence Security Journal
• /
• v.19 no.3
• /
• pp.43-50
• /
• 2019

In a hyper-connected society, electric power infrastructures and information and communication infrastructures are the core of critical national infrastructures. However, electric power infrastructure is very deadly to high-frequency nuclear electromagnetic pulse (HEMP) threats recently issued by North Korea, so the resilience through rapid recovery after attack is directly related to the survivability of our country. Therefore, electric power infrastructure should take precedence over any other key infrastructure, with preemptive protection measures and fast recovery plans. In this paper, the characteristics of the HEMP threats was examined, and the risks and effective major protection measures of the electric power infrastructures are discussed. In the future, it is expected that it will be able to help establish the direction of enactment and revision of legal schems related to the 'high power EMP infringement prevention' for Korea's electric power infrastructures.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.33 no.2
• /
• pp.243-252
• /
• 2023

As an efficient key recovery attack on SIDH/SIKE was proposed, CSIDH is drawing attention again. CSIDH is an isogeny-based key exchange algorithm that is safe against known attacks to date, and provide efficient NIKE by modernizing CRS scheme. In this paper, we firstly present the optimized implementation of CSIDH-512 on ARM Cortex-M7. We use three-level hybrid Montgomery reduction and present the results of our implementation, limitations, and future research directions. This is a CSIDH implementation in 32-bit embedded devices that has not been previously presented, and it is expected that the results of this paper will be available to implement CSIDH and derived cryptographic algorithms in various embedded environments in the future.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.27 no.3
• /
• pp.427-437
• /
• 2017

Impossible differential characteristics distinguish the corresponding block cipher from random substitution and can also be used for key recovery attack. Recently Cui et al. proposed an automatic method for searching impossible differential characteristics of several ARX - based block ciphers using Mixed Integer Linear Programming(MILP). By optimizing the method proposed by Cui et al., It was possible to find new impossible differential characteristics which could not be founded by the method by using less linear constraint expression than the existing method. It was applied to the SPECK family and LEA using the modified method. We found 7-rounds for SPECK32, SPECK48, SPECK64, SPECK96 and 8-rounds impossible differential characteristics of SPECK128. These impossible differential characteristics are all newly found. We also found existing 10-rounds of impossible differential characteristic and new 10-rounds of impossible differential characteristics of LEA.