With the increasing integration of crowd computing, new vulnerabilities emerge in widely used cryptographic systems like the RSA cryptosystem, whose security is based on the factoring problem. It is strongly advised to avoid using the same modulus to produce two pairs of public-private keys, as the cryptosystem would be rendered vulnerable to common modulus attacks. Such attacks can take two forms: one that aims to factorize the common modulus based on one key pair and the other that aims to decrypt certain ciphertexts generated by two public keys if the keys are co-prime. This paper introduces a new type of common modulus attack on the RSA cryptosystem. In our proposed attack, given one public-private key pair, an attacker can obtain the private key corresponding to a given public key in RSA decryption. This allows the adversary to decrypt any ciphertext generated using this public key. It is worth noting that the proposed attack can be used in the CRT model of RSA. In addition, we propose a parallelizable factoring algorithm with an order equivalent to a cyclic attack in the worst-case scenario.

Abstract In this paper, using Mixed-Integer Linear Programming, a new automatic search tool for truncated differential characteristic is presented. Our method models the problem of finding a maximal probability truncated differential characteristic, being able to distinguish the cipher from a pseudo-random permutation. Using this method, we analyze Midori64, SKINNY64/X and CRAFT block ciphers, for all of which the existing results are improved. In all cases, the truncated differential characteristic is much more efficient than the (upper bound of) bit-wise differential characteristic proven by the designers, for any number of rounds. More specifically, the highest possible rounds, for which an efficient differential characteristic can exist for Midori64, SKINNY64/X and CRAFT are 6, 7 and 10 rounds, respectively, for which differential characteristics with maximum probabilities of $2^{-60}$, $2^{-52}$ and $2^{-62.61}$ (may) exist. Using our new method, we introduce new truncated differential characteristics for these ciphers with respective probabilities $2^{-54}$, $2^{-4}$ and $2^{-24}$ at the same number of rounds. Moreover, the longest truncated differential characteristics found for SKINNY64/X and CRAFT have 10 and 12 rounds, respectively. This method can be used as a new tool for differential analysis of SPN block ciphers.

The authors use the mixed‐integer linear programming (MILP) technique for the automatic search for differential characteristics of LEA and HIGHT ciphers. They show that the MILP model of the differential property of modular addition with one constant input can be represented with a much lesser number of linear inequalities compared to the general case. Benefiting from this model for HIGHT block cipher, they can achieve a reduction of 112 r out of 480 r in the total number of linear constraints for the MILP model of r ‐round of HIGHT. This saving accelerates the searching process of HIGHT about twice as fast. They enjoy the MILP model to investigate the differential effect of these ciphers and provide a more accurate estimation for the differential probability. Their observations show that despite HIGHT, LEA exhibits a strong differential effect. The results gained by this method improve/extend the previous results as follows. For LEA block cipher, they found more efficient 12‐ and 13‐round differentials whose probabilities are better than the best previous 12‐ and 13‐round differentials for a factor of about 2 6 and 2 7 , respectively. In the case of HIGHT block cipher, they found new 12‐ and 13‐round differentials, though with the same best‐reported probabilities.

Shamir's secret sharing is used as an important underlying primitive in many other cryptographic schemes, such as group authentication and group key agreement schemes. Although Shamir secret sharing has unconditional security, it is not necessarily the case for the protocols founded on that. A common imperfect assumption in such schemes is to be satisfied of only hiding the polynomials coefficients from the adversary. In this direction, we present a new method that can be potentially used for cryptanalysis of some Shamir's secret sharing-based schemes. This method is called the linear subspace cryptanalysis, in which the attack problem is made equivalent to the problem of studying the belongingness of a vector to a given linear subspace. Using the proposed method, we analyse the Harn's group authentication protocol, which is a remarkable scheme recently designed based on Shamir's scheme. This scheme has two main variants: one-time asynchronous and multiple-time asynchronous. In the one-time variant, it has been evaluated by the designer that the number of group members should be bounded to n <; kt + 1, in order to make the scheme resistant against outside attacks. This constraint has been relaxed in the multiple-time variant, backed by the hardness of the discrete logarithm problem. In this paper, we show that neither confining the number of group members nor using discrete logarithm have made the one-time and multiple-time variants of this scheme resistant against impersonation attack. We show that, in both cases, an outside attacker can impersonate an authorized group member in a polynomial time, when at least t + k-1 authorized members are participating in the group authentication session. The main observation, based on which the attack works, is that the dimension of the linear subspace spanned by the Lagrange components for any predefined set of users never exceeds t +k-1.

In this study, the authors evaluate the security of the lightweight block cipher KLEIN‐64 using biclique cryptanalysis. They first point out some new weaknesses of the diffusion layer and key schedule of this algorithm. Then they exploit them to cryptanalyst the full round version of KLEIN‐64 using an asymmetric biclique. The (worst case) computations and data complexity of this cryptanalysis are 2 62.84 and 2 39 , respectively. A modified version of this cryptanalysis is also presented which is slightly faster at the expense of the data required.

In this paper, a multiuser two-way filter-and- forward relaying scheme for wireless communication over wideband channels is considered. We propose pre/post-rake processing in conjunction with optimized filtering at the relay to reduce the signal processing burden at the source and destination nodes. Two relay filter design problem formulations are introduced, namely (a) a convex optimization problem formulation with closed-form solutions and (b) the more general case, which is a non-convex problem solvable via an alternating optimization algorithm. For both design alternatives widely linear formulations are devised. The presented numerical results demonstrate the capability of the proposed designs to establish reliable two-way communication links between nodes with limited signal processing power and in the absence of a direct link.

In this paper, we present a framework for biclique cryptanalysis of block ciphers which extremely requires a low amount of data. To that end, we enjoy a new representation of biclique attack based on a new concept of cutset that describes our attack more clearly. Then, an algorithm for choosing two differential characteristics is presented to simultaneously minimize the data complexity and control the computational complexity. Then, we characterize those block ciphers that are vulnerable to this technique and among them, we apply this attack on lightweight block ciphers Piccolo-80, Piccolo-128, and HIGHT. The data complexity of these attacks is only 16-plaintext-ciphertext pairs, which is considerably less than the existing cryptanalytic results. In all the attacks, the computational complexity remains the same as the previous ones or even it is slightly improved.

In this paper, we propose multiuser two-way relaying strategies for pairwise internode communication in a network consisting of ultrawideband transceivers with limited signal processing capability, via a central relay unit. We propose reducing the complexity associated with the design of filters at the relay by using pre/post-rake processing in conjunction with optimized filtering at the relay. Two relaying strategies relevant to multipath fading channels, namely, detect-and-forward and filter-and-forward with self-interference cancelation, are considered. For both methods, we start with a convex optimization problem formulation with closed-form solutions, then extend the design to the more general case, which is a nonconvex problem, and use an alternating optimization algorithm to solve the design problems. Furthermore, for both design schemes, widely linear design formulations are devised. The presented numerical results demonstrate the capability of the proposed design schemes in establishing a reliable communication link between nodes with limited signal processing power and in the absence of a direct link.

Pre-rake ultra-wideband (UWB) systems are appealing for UWB communications applications which include devices with different processing capabilities so that signal processing complexity need to be shifted from the receiver of one or more devices to the transmitter of another. Recently, basic pre-rake schemes have been extended to include full pre-equalization, multiple-antenna, and multi-user interference processing. All these design approaches for pre-rake UWB systems have relied on the availability of accurate channel state information (CSI) at the transmitter. However, uncertainties in the acquisition of CSI can drastically affect the overall system performance. Therefore, in this paper, we present robust design methods for pre-equalization filters (PEFs) for pre-rake UWB systems that take CSI uncertainties into account. We treat the general case of a broadcast (i.e., multiuser) pre-rake UWB system, which includes single-user communication often considered in literature as a special case. For this general setting, we derive new PEF designs that improve system performance with imperfect CSI. Similar to the literature on robust filter designs for multiple-input multiple output (MIMO) systems, we consider two uncertainty models, namely stochastic and bounded uncertainty, which correspond to different performance optimization paradigms, and we adjust these according to channel estimation of UWB channels. As most of previous work on (pre-rake) UWB, we focus on binary transmission. We argue that widely linear filter design should be applied in this case and thus extend the robust filter design methodology accordingly. Our numerical results for typically UWB test channels demonstrate the efficacy of the proposed design procedures to achieve reliable communication in multiuser pre-rake UWB systems.

Privacy is faced with serious challenges in the ubiquitous computing world. In order to handle this problem, some researchers in recent years have focused on design and analysis of privacy-friendly ultralightweight authentication protocols. Although the majority of these schemes have been broken to a greater or lesser extent, most of these attacks are based on ad-hoc methods that are not extensible to a large class of ultralightweight protocols. So this research area still suffers from the lack of structured cryptanalysis and evaluation methods. In this paper, we introduce new frameworks for full disclosure attacks on ultralightweight authentication protocols based on new concepts of recursive linear and recursive differential cryptanalysis. The recursive linear attack is passive, deterministic, and requires only a single authentication session, if it can be applied successfully. The recursive differential attack is more powerful and can be applied to the protocols on which the linear attack may not work. This attack is probabilistic, active in the sense that the attacker suffices only to block some specific messages, and requires a few authentication sessions. Having introduced these frameworks in a general view, we apply them on some well-known ultralightweight protocols. The first attack can retrieve all the secret data of Yeh and SLMAP authentication protocols and the second one can retrieve all the secret data of LMAP++, SASI, and David-Prasad authentication protocols.

In this paper we study the effect of channel uncertainty on the performance of pre-equalized pre-rake UWB systems. We consider a bounded uncertainty model and propose a pre-rake design that enables the system to satisfy the required performance in absence of ideal channel state information. Furthermore, we integrate spectral mask constraints into the proposed robust design and investigate the performance of the resulting robust pre-equalized pre-rake UWB system. Our numerical results show the efficacy of the proposed robust design in retaining the required quality of service also in the presence of channel estimation errors while satisfying the spectral mask constraints.

We consider the design of ultra-wideband (UWB) systems that enable high data rate communications for short-range wireless applications. In particular, we consider the downlink of a direct sequence UWB (DS-UWB) system in which the base station is equipped with multiple antennas and employs pre-rake combining, while each user employs a simple single antenna receiver. We propose the use of multiuser filters for the purpose of pre-equalization at the transmitter in order to mitigate the combined effects of intersymbol interference (ISI) and multiuser interference (MUI) that are generated at the receivers as a result of the wideband nature of the users' channels. For this system, we study the joint design of the transmitter's pre-equalization filters and each receiver's scalar gain under two design criteria. The first design minimizes the total transmitted power from the base station subject to achieving physical layer quality of service requirements of different users. For this design, we show that the calculation of the pre-equalization filters and the receiver gains can be formulated as an efficiently solvable convex optimization problem. In the second design, we consider the minimization of a weighted sum of each user's mean-square error. In order to obtain a computationally tractable solution for this design criterion, we exploit the dual DS-UWB uplink that employs rake combining and post-equalization filters at a central receiver. The numerical studies for each design criterion under realistic models of UWB channel propagation demonstrate the effectiveness of the proposed multiuser pre-equalization filter designs in mitigating ISI and MUI, and thus their ability to enable reliable pre-rake DS-UWB downlink transmission.

We consider the design of ultra-wideband (UWB) systems that provide high capacity communication for short-range wireless applications. The design configuration is a multiuser pre-rake UWB broadcast communication system in which the base station is equipped with multiple antennas to achieve high data rates while each user is equipped with a simple and cost-efficient single antenna receiver. We assume the use of multiuser pre-equalization filters at the base station to mitigate the effect of inter-symbol interference (ISI) and multiuser interference (MUI) at the receivers. For the optimization of these filters we develop an analytical framework that minimizes the total transmission power while satisfying (physical layer) users' quality of service for reliable communications. In particular, the quality of service constraints are expressed in terms of the mean square error (MSE) for each user. We show that the design problem is equivalent to a convex optimization problem that can be solved efficiently. The numerical studies confirm that the proposed design strategy for multiuser pre-equalization filters enables the reduction of the total transmission power to achieve a given set of requested MSE targets.

The recently approved IEEE 802.15.4a standard defines an ultra-wideband (UWB) based physical layer using concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM) and direct-sequence spreading with time hopping. The concatenated code consists of an outer Reed-Solomon (RS) and an inner convolutional code, and the coding and modulation are combined such that both coherent and noncoherent receiver architectures are supported. In this paper, the error-rate performance of IEEE 802.15.4a compliant UWB radios is investigated. To this end, semi-analytical expressions for the bit-error rate (BER) and frame-error rate (FER) of the coded UWB system are derived. The presented framework is comprehensive in that (i) different methods for generating reliability information (i.e., decoding metrics), (ii) the effects of suboptimal multipath combining, and (iii) coherent and noncoherent reception methods are included. Furthermore, a particularly suited errors-and-erasures RS decoding scheme is devised. The evaluation of the error-rate expressions together with simulation results for realistic UWB channels show that (i) the error-rate approximations are tight over wide ranges of BER and FER, (ii) symbol-wise metrics are clearly advantageous over bit-wise metrics for decoding of the convolutional code, (iii) combining the 5 to 10 strongest multipath components approaches the performance of full combining within 1-2 dB for residential and 3-5 dB for outdoor UWB environments, and (iv) the simplicity of noncoherent detection comes at loss of more than 10 dB in signal-to-noise ratio compared to coherent detection.