### Browsing by Author "Kaya, Kamer"

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Item Open Access Adapting iterative-improvement heuristics for scheduling file-sharing tasks on heterogeneous platforms(Springer, Berlin, Heidelberg, 2008) Kaya, Kamer; Uçar, B.; Aykanat, Cevdet; Xhafa, F.; Abraham, A.Show more We consider the problem of scheduling an application on a computing system consisting of heterogeneous processors and one or more file repositories. The application consists of a large number of file-sharing, otherwise independent tasks. The files initially reside on the repositories. The interconnection network is heterogeneous. We focus on two disjoint problem cases. In the first case, there is only one file repository which is called as the master processor. In the second case, there are two or more repositories, each holding a distinct set of files. The problem is to assign the tasks to the processors, to schedule the file transfers from the repositories, and to order the executions of tasks on each processor in such a way that the turnaround time is minimized. This chapter surveys several solution techniques; but the stress is on our two recent works [22,23]. At the first glance, iterative-improvement-based heuristics do not seem to be suitable for the aforementioned scheduling problems. This is because their immediate application suggests iteratively improving a complete schedule, and hence building and exploring a complex neighborhood around the current schedule. Such complex neighborhood structures usually render the heuristics time-consuming and make them stuck to a part of the search space. However, in both of the our recent works, we show that these issues can be solved by using a three-phase approach: initial task assignment, refinement, and execution ordering. The main thrust of these two works is that iterative-improve-based heuristics can efficiently deliver effective solutions, implying that iterative-improve-based heuristics can provide highly competitive solutions to the similar scheduling problems.Show more Item Open Access Capture resilient ElGamal signature protocols(Springer, 2006-11) Acan, Hüseyin; Kaya, Kamer; Selçuk, Ali AydınShow more One of the fundamental problems of public key cryptography is protecting the private key. Private keys are too long to be remembered by the user, and storing them in the device which performs the private key operation is insecure as long as the device is subject to capture. In this paper, we propose server-assisted protocols for the ElGamal signature scheme which make the system capture resilient in the sense that the security of the system is not compromised even if the signature device is captured. The protocols also have a key disabling feature which allows a user to disable the device's private key in case both the device and the password of the user are compromised simultaneously. © Springer-Verlag Berlin Heidelberg 2006.Show more Item Open Access Exact algorithms for a task assignment problem(World Scientific Publishing Company, 2009) Kaya, Kamer; Uçar, B.Show more We consider the following task assignment problem. Communicating tasks are to be assigned to heterogeneous processors interconnected with a heterogeneous network. The objective is to minimize the total sum of the execution and communication costs. The problem is NP-hard. We present an exact algorithm based on the well-known A* search. We report simulation results over a wide range of parameters where the largest solved instance contains about three hundred tasks to be assigned to eight processors. © World Scientific Publishing Company.Show more Item Open Access Foreword: 1st International Workshop on High Performance Computing for Big Data(IEEE, 2014-09) Kaya, Kamer; Gedik, Buğra; Çatalyürek, Ümit V.Show more The 1st International Workshop on High Performance Computing for Big Data (HPC4BD) is held on September 10, 2014 in concordance with 43rd International Conference on Parallel Processing (ICPP-2014). The workshop aimed to bring high performance computing (HPC) experts and experts from various application domains together to discuss their Big Data problems. There were four works accepted to be presented in this year's workshop. This foreword presents a summary of the them. © 2014 IEEE.Show more Item Open Access Generalized ID-based blind signatures from bilinear pairings(IEEE, 2008-10) Kalkan, Said; Kaya, Kamer; Selçuk, Ali AydınShow more Blind signature schemes provide the feature that a user is able to get a signature without giving the actual message to the signer. Recently a number of ID-based blind signatures have been proposed. In this paper, we introduce the concept of generalized ID-based blind signatures based on ElGamal signature variants. We obtain several new ID-based blind signatures from this generalized scheme which have not been explored before and some of them turn out to be more efficient than previously proposed schemes. © 2008 IEEE.Show more Item Open Access Generalized ID-based ElGamal signatures(IEEE, 2007-11) Kalkan, Said; Kaya, Kamer; Selçuk, Ali AydınShow more ID-based cryptography has been a very active area of research in cryptography since bilinear pairings were introduced as a cryptographic tool, and there have been many proposals for ID-based signatures recently. In this paper, we introduce the concept of generalized ID-based ElGamal signatures and show that most of the proposed ID-based signature schemes in the literature are special instances of this generalized scheme. We also obtain numerous new signatures from this generalized scheme which have not been proposed before. ©2007 IEEE.Show more Item Open Access Item Open Access Practical threshold signatures with linear secret sharing schemes(Springer, 2009-06) Bozkurt, İlker Nadi; Kaya, Kamer; Selçuk, Ali AydınShow more Function sharing deals with the problem of distribution of the computation of a function (such as decryption or signature) among several parties. The necessary values for the computation are distributed to the participating parties using a secret sharing scheme (SSS). Several function sharing schemes have been proposed in the literature, with most of them using Shamir secret sharing as the underlying SSS. In this paper, we investigate how threshold cryptography can be conducted with any linear secret sharing scheme and present a function sharing scheme for the RSA cryptosystem. The challenge is that constructing the secret in a linear SSS requires the solution of a linear system, which normally involves computing inverses, while computing an inverse modulo φ(N) cannot be tolerated in a threshold RSA system in any way. The threshold RSA scheme we propose is a generalization of Shoup's Shamir-based scheme. It is similarly robust and provably secure under the static adversary model. At the end of the paper, we show how this scheme can be extended to other public key cryptosystems and give an example on the Paillier cryptosystem. © 2009 Springer Berlin Heidelberg.Show more Item Open Access Robust threshold schemes based on the Chinese remainder theorem(Springer, 2008-06) Kaya, Kamer; Selçuk, Ali AydınShow more Recently, Chinese Remainder Theorem (CRT) based function sharing schemes are proposed in the literature. In this paper, we investigate how a CRT-based threshold scheme can be enhanced with the robustness property. To the best of our knowledge, these are the first robust threshold cryptosystems based on a CRT-based secret sharing. © 2008 Springer-Verlag Berlin Heidelberg.Show more Item Open Access Threshold broadcast encryption with reduced complexity(IEEE, 2007-11) Kaşkaloǧlu, K.; Kaya, Kamer; Selçuk, Ali AydınShow more Threshold Broadcast Encryption (TBE) is a promising extension of threshold cryptography with its advantages over traditional threshold cryptosystems, such as eliminating the need of a trusted party, the ability of setting up the system by individual users independently and the ability of choosing the threshold parameter and the group of privileged receivers at the time of encryption. An ElGamal-based solution for TBE was proposed by Ghodosi et al. In this paper, we propose an improved ElGamal-based TBE scheme with reduced transmission cost. ©2007 IEEE.Show more Item Open Access Threshold cryptography based on asmuth-bloom secret sharing(Springer, 2006-11) Kaya, Kamer; Selçuk, Ali Aydın; Tezcan, ZahirShow more In this paper, we investigate how threshold cryptography can be conducted with the Asmuth-Bloom secret sharing scheme and present two novel function sharing schemes, one for the RSA signature and the other for the ElGamal decryption functions, based on the Asmuth-Bloom scheme. To the best of our knowledge, these are the first threshold cryptosystems realized using the Asmuth-Bloom secret sharing. The proposed schemes compare favorably to the earlier function sharing schemes in performance as well as in certain theoretical aspects. © Springer-Verlag Berlin Heidelberg 2006.Show more Item Open Access Threshold cryptography with Chinese remainder theorem(2009) Kaya, KamerShow more Information security has become much more important since electronic communication is started to be used in our daily life. The content of the term information security varies according to the type and the requirements of the area. However, no matter which algorithms are used, security depends on the secrecy of a key which is supposed to be only known by the agents in the first place. The requirement of the key being secret brings several problems. Storing a secret key on only one person, server or database reduces the security of the system to the security and credibility of that agent. Besides, not having a backup of the key introduces the problem of losing the key if a software/hardware failure occurs. On the other hand, if the key is held by more than one agent an adversary with a desire for the key has more flexibility of choosing the target. Hence the security is reduced to the security of the least secure or least credible of these agents. Secret sharing schemes are introduced to solve the problems above. The main idea of these schemes is to share the secret among the agents such that only predefined coalitions can come together and reveal the secret, while no other coalition can obtain any information about the secret. Thus, the keys used in the areas requiring vital secrecy like large-scale finance applications and commandcontrol mechanisms of nuclear systems, can be stored by using secret sharing schemes. Threshold cryptography deals with a particular type of secret sharing schemes. In threshold cryptography related secret sharing schemes, if the size of a coalition exceeds a bound t, it can reveal the key. And, smaller coalitions can reveal no information about the key. Actually, the first secret sharing scheme in the literature is the threshold scheme of Shamir where he considered the secret as the constant of a polynomial of degree t − 1, and distributed the points on the polynomial to the group of users. Thus, a coalition of size t can recover the polynomial and reveal the key but a smaller coalition can not. This scheme is widely accepted by the researchers and used in several applications. Shamir’s secret sharing scheme is not the only one in the literature. For example, almost concurrently, Blakley proposed another secret sharing scheme depending on planar geometry and Asmuth and Bloom proposed a scheme depending on the Chinese Remainder Theorem. Although these schemes satisfy the necessary and sufficient conditions for the security, they have not been considered for the applications requiring a secret sharing scheme. Secret sharing schemes constituted a building block in several other applications other than the ones mentioned above. These applications simply contain a standard problem in the literature, the function sharing problem. In a function sharing scheme, each user has its own secret as an input to a function and the scheme computes the outcome of the function without revealing the secrets. In the literature, encryption or signature functions of the public key algorithms like RSA, ElGamal and Paillier can be given as an example to the functions shared by using a secret sharing scheme. Even new generation applications like electronic voting require a function sharing scheme. As mentioned before, Shamir’s secret sharing scheme has attracted much of the attention in the literature and other schemes are not considered much. However, as this thesis shows, secret sharing schemes depending on the Chinese Remainder Theorem can be practically used in these applications. Since each application has different needs, Shamir’s secret sharing scheme is used in applications with several extensions. Basically, this thesis investigates how to adapt Chinese Remainder Theorem based secret sharing schemes to the applications in the literature. We first propose some modifications on the Asmuth-Bloom secret sharing scheme and then by using this modified scheme we designed provably secure function sharing schemes and security extensions.Show more Item Open Access A verifiable secret sharing scheme based on the chinese remainder theorem(Springer, 2008-12) Kaya, Kamer; Selçuk, Ali AydınShow more In this paper, we investigate how to achieve verifiable secret sharing (VSS) schemes by using the Chinese Remainder Theorem (CRT). We first show that two schemes proposed earlier are not secure by an attack where the dealer is able to distribute inconsistent shares to the users. Then we propose a new VSS scheme based on the CRT and prove its security. Using the proposed VSS scheme, we develop a joint random secret sharing (JRSS) protocol, which, to the best of our knowledge, is the first JRSS protocol based on the CRT. © 2008 Springer Berlin Heidelberg.Show more