3.1.9 Schneier 21 , et al. in their **attack** on IDEA exploited its **key** schedule since **key** schedule of IDEA is quite simple, sub keys are calculated by simply circularly shifting the original **key** 25 times in **key** scheduling algorithm. For 3-round IDEA, authors proposed a chosen **key** differential **attack**; it recovers 32 bits of **key** with 6 chosen plaintexts (PT). Out of these 6 PT, two are used with first **key** and the remaining four with the second **key**. In order to recover another 64 bits of **key** it needs 2 17 chosen PT under third **key**. Rest of the 32 bits is recovered **using** brute forcedly trying all 2 32 , choices. Schneier, et al. also proposed other variant of **attack** which is applicable on non reduced round IDEA with COA timing **attack** model. This **attack** enquires about 5x 2 17 , **related** keys and it encrypts 10, 48,576 (2 20 ) random chosen unknown PT blocks with these **related** keys. But, the difficult part of this **attack** is to accurately measure the timings of these encryptions.

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Generally, the performances of any evolutionary computation algorithm are closely **related** to the parameters values. Therefore, one of the main challenge is to find the optimal parameters setting allowing to improve efficiency of our algorithm. The values of parameters assumed in this paper such as α, β (weight of pheromone and heuristic value), N (Number of Ants), C (Number of Cycle), ‘Q’ and σ were fine-tuned by a combination of several experiments in order to optimize the cryptanalysis process. The default value of the parameters was α=1, β=1, Q=2, 𝜎=0.97 and 𝜏 0 = 5. We have implemented our algorithm with C++ language. 5.1. **Key** space analysis

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Impossible-differential attacks were introduced independently by Biham et al. [4] and Knudsen [6]. They are widely used as an important **cryptanalytic** technique. The **attack** starts with finding an input difference that can never result in an output difference, which makes up an impossible differential. By adding rounds before and/or after the impossible differential, one can collect pairs with certain plaintext and ciphertext differences. If there exists a pair that meets the input and output values of the impossible differential under some subkey, these subkeys must be wrong. In this way, we can filter as many wrong keys as possible and exhaustively search the rest of the keys.

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Multivariate quadratic (MQ) public **key** schemes are cryptosystems based on the NP-hard problem of solving polynomial systems of quadratic equations over finite fields, also known as the MQ-problem. Until the mid 2000’s, MQ cryptography was developing very rapidly, producing many interesting and versatile design ideas such as C ∗ [1], HFE [2], SFLASH [3], UOV [4], TTM [5], TTS [6]. However, many of them were soon successfully cryptanalysed, and the biggest surprise was probably the break of SFLASH in 2007 [7], shortly after it was chosen by the NESSIE European Consortium [8] as one of the three recommended public **key** signature schemes. As a consequence, the confidence in MQ cryptosystems declined, and as a result, did the research in this area as well.

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In a quantum optical implementation, the sender (Al- ice) encodes a random bit value “0” and “1” in the orthogonal polarization states of a single photon. She chooses at random either a linear or a circular polariza- tion basis. The receiver (Bob) uses a polarization bases chosen at random from these two bases. In the follow- ing classical communication, Alice and Bob identify those signals for which they used the same basis, and the cor- responding bit values form the sifted **key**. Either due to noise or due to eavesdropping, Alice’s and Bob’s version of the sifted **key** differ. As long as the error rate is be- low some threshold, they can correct these errors and perform privacy amplification [5] to obtain a secure **key**. The theoretical security analysis of this scheme has been a subject of intense research and only recently a full proof of security for the whole protocol has been given [6–9].

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Mobile ad hoc network is a self-governing system, where nodes or stations are connected with each other through wireless links. There is no limit on the nodes to join or depart the network, therefore the nodes join or left freely. Mobile ad hoc network has dynamic topology that can change promptly because the nodes move freely and can arrange themselves randomly. This property of the nodes makes the mobile ad hoc networks unpredictable from the point of view of scalability and topology decentralized wireless systems. MANET consists of mobile nodes that are free in moving in and out in the network. Nodes can be a device or host i.e. mobile phone, laptop, personal, MP3 player and personal computer that are participating in the network and are mobile. These nodes can act as host or router or both at same time. They can form illogical topologies depending on their connectivity with each other in the network. These nodes have the facility to configure themselves and because of their self configuration ability, they can be deployed urgently without the need of any infrastructure. Security in Mobile Ad Hoc Network is the most important concern for the basic functionality of network. Accessibility of network services, privacy and integrity of the data can be achieved by assuring that security issues have been met. MANET often endure from security attacks because of its nature like medium changing its topology dynamically, MANET work without any centralized medium there is no base station required. In MANET node can communicates with each other on the base of mutual trust. This characteristics makes the MANET more exposed to be exploited by an attacker from inside the network. Wireless links also makes the MANET more liable to attacks which make it easy for the attacker to go inside the network and can easily access to the ongoing communication Mobile nodes present within the range of wireless link can overhear and even participate in the network. MANET must have a secure way for transmission of data and communication and this is quite demanding and impetrative issue as there is increasing threats of **attack** on the Mobile Network. Security is the most important issue of the day. In order to provide secure communication and data transmission engineer must understand different types of attacks and their effects on the MANETs. Wormhole **attack**, Black hole **attack**, flooding **attack**, routing table overflow **attack**, Denial of Service selfish node, impersonation **attack** are kind of attacks that a MANET can suffer from. MANET is more open to these kinds of attacks because communication is based on mutual trust between the nodes, there is no central point for network management, any authorization facility, and vigorously changing topology

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This paper uses the detection method of the **key** node oriented black hole **attack** based on neighbor node behaviors. That is recognize the **key** node at first, then let **key** node maintain a continuous counter of the number of continual packet loss for each neighbor nodes, and monitoring how its neighbor nodes process those received package. If a node was monitored that it dropped a data packet, the relevant counter of the node will plus one. If a counter relevant one node reached the threshold, the node will be reported as black hole. If a node transmitted a packet as usual before its counter reached threshold, reset the counter. The procedure of the detection of **key** node oriented black hole **attack** is as follows.

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There is a lot of research going on the cryptanalysis techniques. Many authors have suggested different **cryptanalytic** techniques for Symmetric and Asymmetric Encryptions but this paper discusses the **Cryptanalytic** techniques of Block Ciphers for Symmetric Encryption. This research work is being carried out after a thorough review on primary **cryptanalytic** techniques that are done on Block Ciphers such as Differential Cryptanalysis, Linear Cryptanalysis, the exploitation of weak keys and Algebraic attacks. A Smart card can be viewed as an intelligent data carrier which can store data like PINS, sensitive personal data and private keys in a secured manner and ensure data security during transactions but smart card industry is facing a lot many problems which is addressed in this work. The security issues are one major area of hindrance in smart card development and the level of threat imposed by malicious attacks on the integrated software is of high concern today. So SAFER++ proposed in this research work will be a very good solution for the problems faced by the smart cards industry.

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Remark. If the padding of the nonce in Prøst-OTR were done on the most significant bits, no **attack** similar to Step 2 could recover the corresponding **key** bits: the modular addition is a triangular function (meaning that the result of a + b on a bit i only depends on the value of bits of position less than i in a and b), and therefore no XOR in the nonce in the less significant bits could control modular differences introduced in the padding in the more significant bits. An **attack** in that case would thus most likely be applicable to general ciphers when **using** only the φ + class, and it is proven that no such **attack** is efficient. However, one could always imagine **using** a **related**-**key** class **using** an addition operation reading the bits in reverse. While admittedly unorthodox, this would not result in a stronger model than **using** φ + , strictly speaking.

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In this study, we considered the first quantum **key**-recovery **attack** against Feistel structures. Inspired by Leander and May’s works, we combined Grover’s and Simon’s algorithms to construct the **attack**. Our attacks required 2 nr/4−3n/4 quantum queries. When compared with the quantum brute-force search, the time complexity is reduced by a factor of 2 0.75n . When compared with the best classical attacks, the time

Most symmetric cryptographic primitives can be described by boolean functions over secret variables and public variables. The secret variables are often **key** bits, the public variables are often plaintext bits for block ciphers and IV bits for stream ciphers. The ANF (algebraic normal form) representation of the output is usually very complex by repeatedly executing a simple iterative function, where the iterative function is a round function for block ciphers or a feedback function for stream ciphers based on nonlinear feedback shift registers. For stream ciphers, obtaining the exact output boolean functions is usually impossible. But if its degree is low, the cipher can not resist on many known attacks, such as higher order differential attacks [15,13], cube attacks [1,4], and integral attacks [14]. Hence, it is important to reduce the degree of polynomials for cryptanalysis of stream ciphers.

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Let us mention one more issue that is not necessarily specific to the perfect rainbow tradeoff, but is closely **related** to this work. The work [2] claimed that each entry in the pre-computation table for the DP tradeoff can be represented by half the number of bits required for the rainbow tradeoff, but their explanation was rather brief. They followed this claim with a short argument stating that, if the effects of false alarms were to be ignored, one must conclude that the DP tradeoff is twice as efficient as the rainbow tradeoff. An attempt to refute this was made by [1], which maintained that the claim of [2] concerning the required storage bits per table entry was incorrect. With neither [2] nor [1] providing any detail, the work [11] clarified that, in the case of non-perfect tradeoffs, the storage requirement comparison of [2] was correct, but that the rainbow tradeoff may still be seen as being advantageous over the DP tradeoff in typical environments. However, the case of the perfect tradeoffs was left untreated.

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Abstract. In this paper we show that a large class of diverse prob- lems have a bicomposite structure which makes it possible to solve them with a new type of algorithm called dissection, which has much better time/memory tradeoffs than previously known algorithms. A typical ex- ample is the problem of finding the **key** of multiple encryption schemes with r independent n-bit keys. All the previous error-free attacks re- quired time T and memory M satisfying T M = 2 rn , and even if “false negatives” are allowed, no **attack** could achieve T M < 2 3rn/4 . Our new technique yields the first algorithm which never errs and finds all the possible keys with a smaller product of T M, such as T = 2 4n time and M = 2 n memory for breaking the sequential execution of r=7 block ci- phers. The improvement ratio we obtain increases in an unbounded way as r increases, and if we allow algorithms which can sometimes miss solutions, we can get even better tradeoffs by combining our dissection technique with parallel collision search. To demonstrate the generality of the new dissection technique, we show how to use it in a generic way in order to improve rebound attacks on hash functions and to solve with better time complexities (for small memory complexities) hard combina- torial search problems, such as the well known knapsack problem.

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Among the different hash function designs, Merkle-Damg˚ ard [34, 16] or MD hash function has been the most popular and widely used design. Naturally, it is the most studied design as well. The cryptanalysis of MD hash has revealed several weaknesses in the design. Dean [17] first showed that the fixed points (i.e., f (h, m) = h) in the underlying compression function can be used for a long message second preimage **attack** in O(2 n/2 ) complexity. Later, the seminal work by Joux [25] suggested a new efficient way to construct multicollision 1 on the MD hash. Immediately after his work, Kelsey and Schneier [28] applied the ideas of Joux **attack** to Deans **attack**, and eliminated the requirement of fixed points in the compression function by building a new structure called [a, b]-expandable message. 2

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In this paper, a security flaw of Haiyan Sun's protocol has been identified and then a modification has been proposed to design a new paring-free **key** agreement protocol based on elliptic curve cryptography. A certificateless **key** agreement protocol without bilinear pairings is proposed which is an extension to the first proposed one. The security analysis of the proposed paring free this **key** agreement protocol has been discussed. It is found that the proposed protocol achieves all security requirements and avoids the **key**-off set **attack**. The performance of the proposed protocol is compared with other protocols and it is found that the proposed protocol is requires computations with improved security properties. The proposed protocol has been implemented **using** the Mathematica(7) program.

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Fig. 1. Asymmetric **Key** Cryptography Process [16] Public **key** algorithms are created dependent on some number theoretic idea which includes number-crunching tasks. Longer the keys and operands increasingly secure the algorithms is. RSA is considered as more secured, efficient and well-known Public **Key** Cryptosystem (PKC) which ruled public **key** cryptosystem from most recent 4 decades. RSA algorithm remains on the numerical capacities, for example, factorization, Euler totient work and modular exponent. During development of PKC discrete logarithms and integer factorization’s are the

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Our **attack** is generic and exploits the combination of the OTR mode of oper- ation with an Even-Mansour block cipher construction. It is independent of the used permutation, and thus does not use any particular properties or weaknesses of the Prøst permutation. Consequently, the other members of the Prøst fam- ily, Prøst-COPA and Prøst-APE, are not affected or endangered by the **attack**. However, the **attack** demonstrates the possible complications of **using** an Even- Mansour construction as a block cipher in otherwise secure modes of operation. The Even-Mansour approach of creating a block cipher from a pseudorandom permutation by xoring a secret **key** before and after applying the permutation to the plaintext has been studied extensively [6,7,8,9,13,18]. It has been proven secure under different notions of security, with detailed bounds relating the secu- rity level with the **key** length. However, it is inherently susceptible to **related**-**key** attacks. The OTR mode of operation allows to “lift” this property to the full en- cryption and authentication scheme. This unfortunate combination of otherwise secure building blocks shows two things: that the Even-Mansour construction should only be used very cautiously, and that **related**-**key** properties are not well covered by the classical security notions, although they can lead to powerful forgery attacks.

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The second and more important reason that **using** the relative speed doesn’t work in this scenario is that the conditions on the nodes doing work are subject to change and are outside of the control of the parallel application. As noted in section 4.5, system memory was not considered a significant enough factor in determining the differences between processor types, but it was measured at 10%, which is statistically significant for this scenario. In the case of this testing, the process **using** the additional memory was a database server. Over the course of 72 hours, this becomes 7.2 hours of additional processing that must take place on that processor, which creates a significant amount of idle time on the other processors. In a 10 node system, this alone reduces the efficiency from 100% to 90%, as per the following equation.

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The research community has proposed new PKI archi- tectures to address these issues. Recent proposals include Certificate Transparency (CT) [5] and Sovereign Keys [6], which add accountability by **using** log servers to make compromises visible, and the Accountable **Key** Infrastructure (AKI) [7] that prevents attacks by **using** checks-and-balances to prevent a compromised CA from impersonating domains. Although such proposals provide good starting points and building blocks, they require many interacting entities and thus are inherently highly complex. History has shown that humans will miss cases when considering the security of such complex systems. Moreover, a PKI architecture must satisfy efficiency requirements and fit with existing business models, as well as offer improved security. Finally, even advanced proposals such as CT and AKI are still incomplete (as they do not handle all corner cases in the certificate life cycle) and have been designed in an ad-hoc fashion, without a formal proof of correctness. We will discuss the limitations of the existing state-of-the-art further in Section 3.

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