1,283 research outputs found
Turbo-coded CDMA-based two-way relaying
No full textIn this contribution, we have studied the performance of a Turbo-Coded (TC) Code Division Multiple Access (CDMA) based two-way relaying scheme. More explicitly, we employ a seven-user CDMA model, where two of the CDMA users are communicating with each other with the aid of an additional relay node, while the other five CDMA users are interferers. More explicitly, two CDMA users exchange their information frames within two timeslots. Note that the conventional one-way relaying system can only transmit one information frame within two timeslots because the relay node is half-duplex, where it cannot listen and transmit simultaneously. We found that our proposed TC-CDMA two-way relaying scheme is capable of attaining over 4 dB of SNR gain at a Bit Error Rate (BER) of 10-6 when compared to a conventional non-cooperative TC-CDMA system. We also found that there is about two dB of SNR loss at a BER of 10-6, due to the error propagation from the relay node. The proposed scheme exploits the benefits of TC and CDMA schemes in order to assist the two-way relaying system to operate with a reduced transmit power. The reduction of the transmit power can also be exploited for increasing the coverage area of a cellular cell. Hence, the TC-CDMA two-way relaying scheme is a good candidate for future generation mobile system
Performance Analysis of Modified SHA-3
No full textAbstractSecurity services have become an inseparable feature of almost all digital transactions. A crucial module of these scheme isintegrity, which is performed using a cryptographic hash function. Secure Hash Algorithm can be an efficient hashing technique.SHA-3 is the most recent and efficient Secure Hash Algorithm. Keccak has been chosen as the official algorithm for SHA-3 in2012. In this paper we propose a modification on the design of Secure Hash Algorithm (SHA-3) on Xilinx Field ProgrammableGate Array (FPGA) device. In order to provide reliable architecture for this algorithm, a concurrent error tolerant scheme forSHA-3 is used. A system based on the combination of SHA-3 and error tolerant scheme is also described. Simulation resultsshows, an efficiency in area and delay of SHA-3 designs
Security and usability of standard has hfunctions, in particular MD-5, SHA-1 and SHA-2
No full textTitle: Security and usability of standard hash functions, in particular MD-5, SHA-1 and SHA-2 Author: Galaczová Barbora Department: Department of Algebra Supervisor: Doc. RNDr. Tůma Jiří, DrSc., Department of Algebra Consultant: Ing. Budiš Petr, Ph.D. Abstract: In the present work we try to digestedly describe standard hash functions, in particular MD-5, SHA-1 and SHA-2. We describe resume of existing attacks on these hash functions. We closely focused on MD-5 collision attacks, because the other hash function collision attacks result from these. Next we describe posibilities of practical usage of hash function collisions, in particular into the qualified certificates area and possible threats. At the end to the present work we describe new hash functions, which could replace current hash functions. This work also contains software to calculate MD-5 hash and search it`s collisions. The software is based on method invented by Czech cryptoanalytist Vlastimil Klíma. Keywords: hash function, collision, qualified certificate, security
Cryptanalysis of Dynamic SHA(2)
No full textIn this paper, we analyze the hash functions Dynamic SHA and Dynamic SHA2, which have been selected as first round candidates in the NIST hash function competition. These hash functions rely heavily on data-dependent rotations, similar to certain block ciphers, e.g., RC5. Our analysis suggests that in the case of hash functions, where the attacker has more control over the rotations, this approach is less favorable than in block ciphers. We present practical, or close to practical, collision attacks on both Dynamic SHA and Dynamic SHA2. Moreover, we present a preimage attack on Dynamic SHA that is faster than exhaustive search. © 2009 Springer-Verlag Berlin Heidelberg.sponsorship: Supported by the Swiss National Science Foundation, project no. 113329. This author was supported by the France Telecom chaire. F.W.O. Research Assistant, Fund for Scientific Research Flander s (Belgium) (Swiss National Science Foundation|113329, France Telecom chaire, Scientific Research)status: Publishe
Design & Characterization of SHA 3- 256 Bit IP Core
No full textAbstractIn the era of internet and computer networking the need for security have increased rapidly. Various crypto algorithms are used for secured data transmission and reception through the network, of which hash function possess a key role in various cryptographic protocols. Keccak algorithm is the winner of SHA-3 competition conducted by NIST. SHA-3 consists of different variant such as 224, 256, 384 and 512 bit. This paper discuss the design and implementation of SHA-3 256- bit core. The core is designed using Verilog HDL and prototyped using Xilinx® Virtex®-6FPGA
Uma solução de autenticação fim a fim para o LDP (Label Distribution Protocol)
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência da Computação.Este trabalho propõe uma solução de autenticação para o protocolo LDP (Label Distribution Protocol) que tem por objetivo autenticar, em um escopo fim a fim, o estabelecimento de um LSP (Label Switching Path) entre um LSR (Label Switching Router) de Ingresso e o seu respectivo LSR de Egresso. Objetiva-se suprir a deficiência do protocolo LDP de não possuir um mecanismo de autenticação fim a fim definido, aplicável entre LSRs não-adjacentes. Conforme foi verificado pelo levantamento de trabalhos correlatos, atualmente é desconhecida uma solução de autenticação semelhante, que efetivamente atenda o propósito de autenticar num escopo fim a fim, o estabelecimento de LSPs no protocolo LDP. Dessa forma a solução deste trabalho é inédita no seu escopo de aplicação. A solução foi planejada para ambientes onde LSPs atravessam múltiplos domínios externos, não confiáveis entre si, e que por isso necessitam de um mecanismo de autenticação durante o estabelecimento dos LSPs. A solução faz uso de um mecanismo de autenticação, baseado em criptografia assimétrica (chave pública e privada), anexado a cada mensagem LDP. Este mecanismo possibilita ao LSR receptor verificar e autenticar o originador da mensagem LDP. Adicionalmente a solução provê integridade de dados através de um mecanismo de resumo de mensagens (hash) e também protege contra ataques de repetição através da inserção de um nonce às mensagens LDP
Influence of equal-channel angular pressing on pPrecipitation kinetics in an Al-Zn-Mg-Cu alloy
No full textProcessing by equal-channel angular pressing (ECAP) affects the morphology of ? precipitates in an Al–Zn–Mg–Cu (Al-7136) alloy. It is shown by transmission electron microscopy that ECAP changes the orientation of precipitates and this influences the atomic configuration and the interfacial energy at the ?/?-Al interfaces. Consequently, ? precipitates adopt an isotropic growth mode and evolve into equiaxed particles. A three-dimensional atom probe analysis demonstrates that large ? precipitates formed in different numbers of ECAP passes are of similar composition. The coalescence of smaller precipitates, rather than the fragmentation of larger precipitates, dominates the precipitate evolution
Practical collision attacks against round-reduced SHA-3
No full textThe Keccak hash function is the winner of the SHA-3 competition (2008–2012) and became the SHA-3 standard of NIST in 2015. In this paper, we focus on practical collision attacks against round-reduced SHA-3 and some Keccak variants. Following the framework developed by Dinur et al. at FSE 2012 where 4-round collisions were found by combining 3-round differential trails and 1-round connectors, we extend the connectors to up to three rounds and hence achieve collision attacks for up to 6 rounds. The extension is possible thanks to the large degree of freedom of the wide internal state. By linearizing S-boxes of the first round, the problem of finding solutions of 2-round connectors is converted to that of solving a system of linear equations. When linearization is applied to the first two rounds, 3-round connectors become possible. However, due to the quick reduction in the degree of freedom caused by linearization, the connector succeeds only when the 3-round differential trails satisfy some additional conditions. We develop dedicated strategies for searching differential trails and find that such special differential trails indeed exist. To summarize, we obtain the first real collisions on six instances, including three round-reduced instances of SHA-3, namely 5-round SHAKE128, SHA3-224 and SHA3-256, and three instances of Keccak contest, namely Keccak[1440, 160, 5, 160], Keccak[640, 160, 5, 160] and Keccak[1440, 160, 6, 160], improving the number of practically attacked rounds by two. It is remarked that the work here is still far from threatening the security of the full 24-round SHA-3 family.NRF (Natl Research Foundation, S’pore
Microstructural evolution of Fe-rich particles in an Al-Zn-Mg-Cu Alloy during equal-channel angular pressing
No full textThe microstructures of a severely deformed Al–Zn–Mg–Cu (AA7136) alloy have been characterized carefully using transmission electron microscopy and three-dimensional atom probe analysis. The Fe-rich intermetallic particles are predominantly Al13Fe4 type in the as-extruded alloy. Significantly, equal-channel angular pressing (ECAP) at 200 °C refines Fe-rich particles from 1 to 2 ?m to as small as 50 nm after 4 passes processing, and effectively narrow down their size distribution with the increase of number of ECAP passes. In addition, small Fe-rich particles evolve into spherical morphology and are in a more uniform distribution. The formations of Fe-rich phases in AA7136, the kinetic and thermodynamic effects in relation to the refinement of Fe-rich particles and their morphology evolution during ECAP processing are discussed.<br/
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