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We show that a previously introduced key exchange based on a congruence-simple semiring action is not secure by providing an attack that reveals the shared key from the distributed public information for any of such semirings.

We present a metaheuristic-based attack against the traceability of an ultra-lightweight authentication protocol for RFID environments called SLMAP, and analyze its implications. The main interest of our approach is that it constitutes a complete black-box technique that does not make any assumptions on the components of the underlying protocol and can thus be easily generalized to analyze many other proposals.

Let $(n=pq,e=n^{\beta })$ be an RSA public key with private exponent $d=n^{\delta },$ where $p$ and $q$ are large primes of the same bit size. At Eurocrypt 96, Coppersmith presented a polynomial-time algorithm for finding small roots of univariate modular equations based on lattice reduction and then succussed to factorize the RSA modulus. Since then, a series of attacks on the key equation $ed-k\varphi (n)=1$ of RSA have been presented. In this paper, we show that many of such attacks can be unified in a single attack using a new notion called Coppersmith’s interval. We determine a Coppersmith’s interval for a given RSA public key $(n,e).$ The interval is valid for any variant of RSA, such as Multi-Prime RSA, that uses the key equation. Then we show that RSA is insecure if $\delta <\beta +\frac{1}{3}\alpha -\frac{1}{3}\sqrt{12\alpha \beta +4{\alpha }^2}$ provided that we have approximation $p_0\ge \sqrt{n}$ of $p$ with $\left|p-p_0\right|\le \frac{1}{2}{n}^{\alpha },$$\alpha \le \frac{1}{2}.$ The attack is an extension of Coppersmith’s result.

The Cramer-Shoup (CS) like cryptosystem based on index exchangeable family (IEF) construction is a novel scheme introduced in Asiaccs 2016 by Li et al. Its versatility was illustrated by building two public key encryption (PKE) schemes, a cramer-shoup encryption scheme based on IEFs, as well as an outsourcing technique based on non-abelian analog. However, the two schemes are not secure over the recommended linear group of Li et al. For them, we provide a new key-recovery attack by solving a linear equation respectively. Furthermore, we peel off complex encryption and decryption processes and propose more than three different attack methods. Finally, we give a corresponding example to illustrate the correctness of our attack methods. Our attack methods break an instance of claiming 80 bit security less than one minute under a personal computer.

This paper analyzes the security of a recent cryptosystem based on the ergodicity property of chaotic maps. It is shown how to obtain the secret key using a chosen-ciphertext attack. Some other design weaknesses are also shown.

This paper proposes a new symmetric key encryption algorithm based on one-dimensional chaotic map. This algorithm uses the random-like property and ergodicity of chaotic systems. In the process of encryption or decryption, this algorithm generates a chaotic pseudo-random sequence, changes the initial iterative times and the increment to encrypt the plaintext, and realizes fast encryption and decryption of all kinds of files. When analyzing the algorithm's performance and security, the result shows that, compared with the method of Baptista, the proposed method is safer, faster and more powerful.

Recently, a multiparty semiquantum secret sharing scheme based on rearranging orders of qubits was proposed by Gao et al. [Mod. Phys. Lett. B30 (2016) 1650130]. In this paper, we show that in their scheme the last agent and other agents can illegally get the sender’s secret keys without being detected. Furthermore, an improved scheme is proposed to resist such attack.

A recent paper proposed a semi-quantum secret sharing (SQSS) scheme based on Bell states [A. Yin et al., Mod. Phys. Lett. B. https://doi.org/10.1142/S0217984917501500]. This protocol was presumed that only the sender has the quantum power and all participants perform classical operations. However, we find this protocol is not that secure as it is expected. We can utilize the intercept-resend method to attack this scheme. Then, we give an improvement strategy based on semi-quantum key distribution, which ensures that the new scheme resists the attack we have proposed.

A semi-quantum secret sharing scheme using entangled states was proposed in a recent paper [Mod. Phys. Lett. B32 (2018) 1850256. https://doi.org/10.1142/S0217984918502561]. We find a loophole of this scheme. Based on the intercept-resend attack, we propose a deterministic attack strategy and a probabilistic attack strategy. The malicious participant can escape the detection and obtains the secret. We also suggest two improvements to help increase the security of the original scheme.

Recently, Shieh et al. have pointed out that Juang's password authenticated key agreement scheme and Chien et al.'s remote authentication scheme are vulnerable to some attacks. Therefore, they presented a modified protocol to avoid those attacks. However, the authors of this article shall show that Shieh et al.'s scheme and Juang's scheme have two weaknesses, respectively. Therefore, we shall improve the weaknesses of their schemes.

Fuzzy identity-based encryption (FIBE) scheme is a kind of identity-based encryption (IBE) scheme, in which any user's identity is composed by a set of attributes and any ciphertext encrypted under identity ID can be decrypted by using a private key corresponding to identity ID′ if ID′ is close to ID as measured by some metric. Due to the error-tolerance property, FIBE scheme is very useful in real-world applications. However, most FIBE schemes are provable secure only in a weaker security model. In order to eliminate this problem, Ren et al. recently proposed a new FIBE scheme and proved that it is fully chosen-ciphertext secure in the standard model. Unfortunately, in this paper, we will show that their FIBE scheme is even not chosen-plaintext secure.

Recently S. Papadimitriou et al. have proposed a new probabilistic encryption scheme based on chaotic systems. In this letter, we point out some problems with Papadimitriou et al.'s chaotic cryptosystem: (1) the size of the ciphertext and the plaintext cannot simultaneously ensure practical implementation and high security; (2) the estimated number of all possible virtual states is wrong; (3) the practical security to exhaustive attack is overestimated; (4) the fast encryption speed is dependent on the first defect; (5) problems about the dynamical degradation of digital chaotic systems; (6) no explicit indications are given to explain how to construct the virtual state space with the 2^d virtual attractors, the 2^e virtual states and the permutation matrix P. The detailed analyses and discussions on the above problems show that the proposed chaotic cipher is insecure and unpractical. Also, we give our suggestions on the design of general digital chaotic ciphers, and give some open topics in this area.

This paper investigates the weaknesses of cryptosystems that use observer based synchronized chaotic systems. It is shown that known plaintext and chosen plaintext attacks can successfully be launched against such cryptosystems to recover the system parameters and subsequently eavesdrop on the message transmission. The methods employed rely only on the basic mathematical relations that exist between the output sequence and the message sequence of the transmitter system and require very less computations.

As a powerful cryptanalysis tool, the method of return-map attacks can be used to extract secret messages masked by chaos in secure communication schemes. Recently, a simple defensive mechanism was presented to enhance the security of chaotic parameter modulation schemes against return-map attacks. Two techniques are combined in the proposed defensive mechanism: Multistep parameter modulation and alternative driving of two different transmitter variables. This paper restudies the security of this proposed defensive mechanism against return-map attacks, and points out that the security was much over-estimated in the original publication for both ciphertext-only attack and known/chosen-plaintext attacks. It is found that a deterministic relationship exists between the shape of the return map and the modulated parameter, and that such a relationship can be used to dramatically enhance return-map attacks thereby making them quite easy to break the defensive mechanism.

This paper studies the security of a chaotic cryptosystem based on Chua's circuit and implemented with State Controlled Cellular Neural Networks (SC-CNN). Here, we prove that the plaintext can be retrieved by bandpass filtering of the ciphertext or by using an imperfect decoder with wrong receiver parameters. In addition, we find that the key space of the system can be reduced notably, and the required resolution of the parameter values to recover a meaningful plaintext is as coarse as 5%, easing a brute-force attack. The system parameters can be determined with high precision through the analysis of the decoding error produced by the mismatch between the parameters of receiver and transmitter.

This paper addresses the cryptanalysis of three chaos-based secure communication schemes recently proposed by Yu et al. [2007]. Attacks with adaptive observers designed by the dynamical minimization algorithm are assumed. Considering Kerckhoff's principle, i.e. assuming that the basic structure of a cryptosystem is known but some user-specified parameters remain in secret, it is demonstrated that the covered messages in all these schemes can be estimated and hence their securities are challenged.

We cryptanalyze Fridrich's chaotic image encryption algorithm. We show that the algebraic weaknesses of the algorithm make it vulnerable against chosen-ciphertext attacks. We propose an attack that reveals the secret permutation that is used to shuffle the pixels of a round input. We demonstrate the effectiveness of our attack with examples and simulation results. We also show that our proposed attack can be generalized to other well-known chaotic image encryption algorithms.

Recently a chaotic cryptographic scheme based on composition maps was proposed. This paper studies the security of the scheme and reports the following problems: (1) the scheme can be broken by a differential attack with 6 + ⌈log_L(MN)⌉ chosen plaintexts, where MN is the size of the plaintext and L is the number of different elements in plaintext; (2)the two composition maps both do not work as a secure and efficient source of random numbers; (3)the scheme is not sensitive to the changes of the plaintext.

An essential issue for the validation of ciphers is cryptanalysis, that is, the study of attacks in order to reveal possible weaknesses. In this paper, we propose a systematic and unified methodology for cryptanalyzing known chaos-based cryptosystems borrowed from the open literature, namely shift keying, discrete parameter modulation, switched message-embedding, time-varying delay-based schemes. It is shown that all of them have a hybrid feature. Based on this consideration, the cryptanalysis leads to a specific parameter identification. The method is extended in straightforward way for hybrid cryptosystems defined over finite fields, involving in particular Boolean functions. The complexity of the cryptanalysis is derived regardless of the exhibited dynamics and provides a new quantitative measure for security assessment, thus allowing to show, by the way, that most of the chaos-based cryptosystems proposed so far in the literature are weak.

Since John von Neumann suggested utilizing Logistic map as a random number generator in 1947, a great number of encryption schemes based on Logistic map and/or its variants have been proposed. This paper re-evaluates the security of an image cipher based on transformed logistic maps and proves that the image cipher can be deciphered efficiently under two different conditions: (1) two pairs of known plain-images and the corresponding cipher-images with computational complexity of $O(2^{18}+L)$; (2) two pairs of chosen plain-images and the corresponding cipher-images with computational complexity of $O(L)$, where $L$ is the number of pixels in the plain-image. In contrast, the required condition in the previous deciphering method is 87 pairs of chosen plain-images and the corresponding cipher-images with computational complexity of $O(2^7+L)$. In addition, three other security flaws existing in most Logistic-map-based ciphers are also reported.