فصلنامه پدافند الکترونیکی و سایبری
سال چهارم شماره 1 (پیاپی 13، بهار 1395)

In this article, polar codes that have recently been presented by Arikan, to integrate channel coding and encryption is used. Polar coded bits are divided into two categories. The first batch are the bits that virtual high-capacity channels of the passage that briefly bits of high-capacity are called and the information on it. The second group are bits that are virtual channels with capacity for short passes that "constant bits" are called. In the first proposal of fixed bits as we use encryption key, and on all bits of the plan (data bits and fixed bits) are key. In fact, the plan proposed 8-bit Arikan, we use the 8 key. Then, the proposed method is that it can be applied to the number of key bits can be reduced. The encryption system is effective and desirable that, in addition to the high complexity and lack of correlation between bits, the least it used to be key.

Distributed communication networks provide proper connection with ooptimum cost between different domains of smart gride such as: home area network, neighbor area network and substation area network. With respect to handshake and key distribution are security challenges in smart grid, this paper proposed novel distribution and dynamic key procedures to enhance network resilience against malicious DoS attack. Proposed procedures using two famous security protocols: SAE and EMSA. These procedures are based on hash function and protocol stage dependency to improve network resilience against DoS attacks, because SAE and EMSA use 4-way handshake. Proposed procedures have optimum overhead. Finally, AVISPA is applied to prove the security of the enhanced protocol in smart grid. With extremely simulations and extended DoS attack model securities of proposed procedures are proved.

Trust brings a novel means to improve the security and enable interoperability of current heterogeneous independent cloud platforms. In fact, trust is the most complex relationship among entities, because it is extremely subjective, context-dependant, non-symmetric, uncertain, partially transitive, and difficult to evaluate and establish. In the cloud environment, however, entities potentiallyinitiate transactions with each other without having had prior contacts. However, there is no special trust evaluation model for a cloud computing environment. This paper, presents a trust model based on fuzzy logic and fuzzy mathematics in cloud computing environment according to success and failure interaction between cloud entities based on the properties and semantics of trust. To compute trust in cloud systems, an algorithm based on proposed model is given and also, we designed the proposed moded with petri net. Simulation results show that the proposed model has some identification and containment capability in synergies cheating, malicious entities identification, promotes interaction between entities, and improves the performance of the entire cloud environment.

Existence of a vulnerability for hackers don’t be exploitable only and whatever give credit to vulnerability is Exploit. Automated Exploit Generation (AEG) confront problems because of various protections ,behavior and vulnerability conditions but nonetheless had did researches in subject. Whatever I had peruse in this thesis is possibility of automated exploit generation for vulnerabilities of Internet Explorer (IE) 7 & 8 in Win XP and Win 7. Generated exploits are for two vulnerability type: Stack Buffer Overflow and Function Pointer Overwrite. In my savory method that use from instrumentation tools, would hoarded necessary information from program through dynamic analysis. In this method has detected vulnerability type and has bypassed methods of protections and has showing proper patterns for exploit. Must I Reminisce you that in the project don’t discovery vulnerability and there are vulnerability.

The execution time of a cryptographic algorithm, can act as a useful source of information for an attacker and provide him a large amount of valuable data. In timing analysis attack where is a kind of side channel attacks, the algorithm is applied on different inputs and its execution times is measured. These measurements are fed into a statistical model. This model is able to predict some bits of cryptographic key through calculating correlation and variance of different measurements. In this paper a stream cipher based on words and its vulnerabilities against timing analysis attack are studied. A special function used in controlling LFSRs clock signal has made the attack possible. This function not only leaks information about number of clock periods, but also reveals some bits of LFSRs in each clock period. As a counter measure against timing analysis attack, we modified the aforementioned function. The modified algorithm is more than 26% faster in key generation.

The stream ciphers are one of the most important cryptosystem in cryptography and their applications are very diverse, particularly in defense industries and telecommunications. This crypto system is designed based on a key stream and also the key stream is created using a pseudo random number generator. In this paper, first, a new pseudorandom number generator is designed based on discrete logistic map and independency, uniformity and randomness of the generated numbers by proposed pseudo random number generator are tested by correlation test, goodness of fit test and NIST tests. The tests results illustrate suitable quality of proposed generator for cryptographic applications properly. Next, a new synchronous stream cipher algorithm using the proposed pseudo random number generator is designed and simulated. Finally, the algorithm has been tested using three different methods and is compared with some other cryptography algorithms.

Jamming cancellation is an important issue for global positioning system (GPS) receivers. As continuous wave (CW) jamming is the most widely used type of the jamming, this paper proposes a new anti-jamming system for mitigation CW jamming in GPS receivers. The proposed method employs infinite impulse response notch filters and wavelet transform for jamming mitigation. The proposed system can be implemented in the digital signal processor of the receiver. The computational complexity of the proposed method is low and it leads to an accurate positioning. Simulation results show that the proposed method has an average progress of 82.5% in term of positioning accuracy compared with standard method.

Despite several studies and attempts, in time-memory trade-off attacks on cryptographic algorithms, the coverage of Hellman tables and similar methods are practically much less than half and their probability of success is low. In fact, Hellman chains are paths with given starting and end vertices on a functional graph. In this paper, behavior of these chains is investigated with this approach. In the beginning of the paper, parameters of the functional graph for a random mapping are defined and based on these parameters, Hellman chains are analyzed. Our results show that the coverage of such tables can’t be high, for the following reasons: First, there exist some remarkable terminal vertices (37%) on the functional graph such that the possible occurrence of these vertices on chains (except in the starting vertices) is zero. Secondly, appropriate parameters for constructing chains exist in graph for about half of all hidden states of cipher function. Thirdly, for construction of noncyclic chains and collision of chains, we must pay attention to the obtained probabilities in this note.Practically, above reasons show that after some point the coverage of a Hellman table tends to zero quickly, and so construction of them will be ineffective. Our results are implemented on mAES algorithm where validate our theatrical results .