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Although many encryption methods are available, there is always an ongoing need for more to resist the adversaries’ ever-growing analytical skills and techniques. We propose in this paper an innovative method for text encryption. We devise a random number generation function that creates sequences of signed random numbers that depend on both plaintext and key. The random numbers support the functionality of four random operations: random mutation, random cyclic shifting, random permutation, and dirty symbol random insertion. These operations ensure the data security by steadily melting the statistical structure of plaintext and relationships to a key. The experiments with our prototype implementation showed that our method has high effectiveness (in terms of diffusion, confusion, avalanche) and high efficiency with respect to the computation demands. Keywords: Text encryption, Lookback text encryption, Random encryption operations, Security random generator

The study of sending and receiving secret messages is called cryptography. Generally, senders and receivers are unaware about the process of encryption and decryption. Hence, encryption plays an important role in data communication and data security. The meaning of encryption is not only to keep data confidential from unwanted access but also ensuring the data integrity through available way. As the capacity of breaking the security is increasing rapidly, so, the process that hides information is one of the most concerned topics. Advanced Encryption Standard is a popular, widely used and efficient encryption algorithm, which has been used since it was invented. This paper focuses on the AES key generation process and Substitution box. It modifies the conventional key generation technique and builds the dynamic 3-Dimensional S-box of Advance Encryption Standard. The proposed approach suggests 3-Dimensioanl Key Generation Matrix and S-box. As per shown this novel technique increases the amount of time it needs during encryption and decryption. The experimental result shows that it also enhances the strength of AES algorithm. The proposed approach illustrates the theoretical analysis and corresponding experimented results., 7 pages, 14 figures, 4 tables. Published in IJCSA in 2017

International audience; Functional encryption lies at the frontiers of the current research in cryptography; some variants have been shown sufficiently powerful to yield indistinguishability obfuscation (IO), while other variants have been constructed from standard assumptions such as LWE. Indeed, most variants have been classified as belonging to either the former or the latter category. However, one mystery that has remained is the case of secret-key functional encryption with an unbounded number of keys and ciphertexts. On the one hand, this primitive is not known to imply anything outside of minicrypt, the land of secret-key cryptography, but, on the other hand, we do no know how to construct it without the heavy hammers in obfustopia. In this work, we show that (subexponentially secure) secret-key functional encryption is powerful enough to construct indistinguishability obfuscation if we additionally assume the existence of (subexponentially secure) plain public-key encryption. In other words, secret-key functional encryption provides a bridge from cryptomania to obfustopia. On the technical side, our result relies on two main components. As our first contribution, we show how to use secret-key functional encryption to get “exponentially efficient indistinguishability obfuscation” (XIO), a notion recently introduced by Lin et al. (PKC’16) as a relaxation of IO. Lin et al. show how to use XIO and the LWE assumption to build IO. As our second contribution, we improve on this result by replacing its reliance on the LWE assumption with any plain public-key encryption scheme. Lastly, we ask whether secret-key functional encryption can be used to construct public-key encryption itself and therefore take us all the way from minicrypt to obfustopia. A result of Asharov and Segev (FOCS’15) shows that this is not the case under black-box constructions, even for exponentially secure functional encryption. We show, through a non-black-box construction, that subexponentially secure-key functional encryption indeed leads to public-key encryption. The resulting public-key encryption scheme, however, is at most quasi-polynomially secure, which is insufficient to take us to obfustopia.

Image encryption is rapidly increased recently by the increasing use of the internet and communication media. Sharing important images over unsecured channels is liable for attacking and stealing. Encryption techniques are the suitable methods to protect images from attacks. Hill cipher algorithm is one of the symmetric techniques, it has a simple structure and fast computations, but weak security because sender and receiver need to use and share the same private key within a non-secure channels. A new image encryption technique that combines Elliptic Curve Cryptosystem with Hill Cipher (ECCHC) has been proposed in this paper to convert Hill cipher from symmetric technique to asymmetric one and increase its security and efficiency and resist the hackers. Self-invertible key matrix is used to generate encryption and decryption secret key. So, no need to find the inverse key matrix in the decryption process. A secret key matrix with dimensions 4 × 4 will be used as an example in this study. Entropy, Peak Signal to Noise Ratio (PSNR), and Unified Average Changing Intensity (UACI) will be used to assess the grayscale image encryption efficiency and compare the encrypted image with the original image to evaluate the performance of the proposed encryption technique. Keywords: Elliptic Curve Cryptography, Hill cipher, Self-invertible, Entropy, Peak Signal to Noise Ratio, Unified Average Changing Intensity

In this paper, we propose a key space enhanced chaos-based encryption scheme with no requirement of redundant sideband information in an orthogonal frequency division multiplexing passive optical network (OFDM-PON). For the first time, a simple 1-D chaotic logistic map is employed to scramble the chaotic subcarrier allocation both in time/frequency domain and logical operation, which provides a huge key space to enhance the physical layer confidentiality. Due to the dynamic chaotic permutations, the largest key space is achieved in comparison with the reported encryption schemes in OFDM-PON. In addition, a ∼10-Gb/s secure transmission with encrypted OFDM data is experimentally demonstrated over 25-km standard single-mode fiber. The proposed encryption scheme demonstrates the excellent security of data transmission in OFDM-PON and the robustness against exhaustive attacks.

The phase-shifting interferometry-based (PSI-based) encryption is one of most typical optical encryption systems. In this paper, we demonstrate a new approach to ciphertext-only attack (COA) on PSI-based encryption, revealing that there is serious security risk in PSI-based encryption. With the proposed COA approach, an opponent can crack the ciphertexts directly without use of the keys of the system. This demonstration, as far as our best knowledge, shows the PSI technique is vulnerable to COA for the first time. A series of attack results are shown to demonstrate the feasibility and robustness of the attack method. Our study reveals a critical security issue that should be taken in to account when designing an optical information security system.

In this paper, we introduce a new family of lattices, namely QC-MDPC lattices, which are a special case of LDPC lattices, and an improved bit flipping algorithm for decoding of these lattices. Encoding and decoding implementations of QC-MDPC lattices are practical in high dimensions. Indeed, to take advantage of practical decoding, we use “Construction-A”lattices which makes a tight connection between the structure of lattices and codes. Using these features, we design a lattice-based public key encryption scheme enjoying linear encryption and decryption complexities. The proposed scheme has a reasonable key size due to the sparseness of the parity-check matrix, and the quasi-cyclic structure of the parity-check and generator matrices. Besides, the message expansion of the proposed scheme is smaller than other lattice-based and code-based cryptosystems with comparative parameters. All these features provide a lattice-based public key encryption scheme with reasonable key size, linear encryption, and decryption algorithms and small message expansion. On the other hand, we show that the cryptosystem is resistant against all known attacks both on lattice-based and code-based cryptosystems for different levels of security.

The ultimate goal of private function evaluation is the complete outsourcing of processing tasks to distrusted platforms (such as clouds), so that arbitrary functions can be evaluated without any leakage of secret information. Several successful concepts have been proposed in the past, the most striking one having been fully homomorphic encryption besides the well-known garbled circuits and multiparty computation. In this paper, we look at an idealized model of outsourced computation, which we call a cryptocomputer . This is a (theoretical) machine that works exactly like a real-life computer in the sense of understanding a standard assembly language, but retaining all its internal signals, registers, and memory encrypted at all times. The encryption is assumed under a key that is unknown to the attacker, and taken as secure (in any cryptographically meaningful way), so that no leakage of information from any ciphertext can be expected from programs with reasonable (polynomial) time complexity. Unfortunately, such a cryptocomputer is necessarily insecure, irrespectively of how the encryption looks like. In particular, we explicitly do not assume any specific form of security (chosen-ciphertext or other) or (a)symmetry of encryption; our attack works only on ciphertexts and makes no assumptions whatsoever on the encryption. We prove insecurity of the cryptocomputer by taking the encryption as a black box, and show how to decipher every signal in the computer by pure virtue of submitting proper instructions for execution. Our attack falls into the general category of side-channel attacks, however unlike other related attacks, does neither exploit physical nor any logical characteristics of the underlying platform (besides the execution flow being observable). Somewhat surprisingly, it turns out that although the problem that we consider is cryptographic, it seemingly has no cryptographic solution and apparently calls for an interdisciplinary approach from new directions.

The need for fast and strong image cryptosystems motivates researchers to develop new techniques to apply traditional cryptographic primitives in order to exploit the intrinsic features of digital images. One of the most popular and mature technique is the use of complex ynamic phenomena, including chaotic orbits and quantum walks, to generate the required key stream. In this paper, under the assumption of plaintext attacks we investigate the security of a classic diffusion mechanism (and of its variants) used as the core cryptographic rimitive in some image cryptosystems based on the aforementioned complex dynamic phenomena. We have theoretically found that regardless of the key schedule process, the data complexity for recovering each element of the equivalent secret key from these diffusion mechanisms is only O(1). The proposed analysis is validated by means of numerical examples. Some additional cryptographic applications of our work are also discussed., Comment: 16 pages, 7 figures

Attribute-based Encryption (ABE) is a new and promising public key encryption that allows fine-grained authorization on data based on user attributes. Such property is favorable for multiple applications that require encrypted storage or access control on data, in particular: eHealth applications. However, ABE schemes are known not to be efficient in the encryption phase because ciphertext size and the time required to encrypt grow with the complexity of the access policy. Such drawback is critical in the context of pervasive computing, for instance, in the Internet of Things, where data producers are usually resource-constrained devices, e.g. smart phones or sensing platforms. In this work, we propose OEABE standing for Outsourcing mechanism for the Encryption of Ciphertext-Policy ABE (CP-ABE). We show how a user can offload expensive operations of CP-ABE encryption to a semi-trusted party in a secure manner. Our proposed mechanism requires only one exponentiation on resource-constrained devices. We provide also an informal security analysis of possible attacks from a semi-honest adversary against the proposed solution. To demonstrate the performance gains of our mechanism, we first conducted a performance estimation on an emulated Wismote sensor platform. Then, we implemented our proposal and did comparison to an existing implementation of CP-ABE on a laptop.

Indistinguishability obfuscation (IO) is a tremendous notion, powerful enough to give rise to almost any known cryptographic object. Prior candidate IO constructions were based on specific assumptions on algebraic objects called multi-linear graded encodings. We present a generic construction of indistinguishability obfuscation from public-key functional encryption with succinct encryption circuits and subexponential security. This shows the equivalence of indistinguishability obfuscation and public-key functional encryption, a primitive that has previously seemed to be much weaker, lacking the power and the staggering range of applications of indistinguishability obfuscation. Our main construction can be based on functional encryption schemes that support a single functional key , and where the encryption circuit grows sub-linearly in the circuit-size of the function. We further show that sublinear succinctness in circuit-size for single-key schemes can be traded with sublinear succinctness in the number of keys (also known as the collusion-size ) for multi-key schemes. We also show that, under the Learning with Errors assumption, our techniques imply that any indistinguishability obfuscator can be converted into one where the size of obfuscated circuits is twice that of the original circuit plus an additive overhead that is polynomial in its depth, input length, and the security parameter.

International audience; We present two practically efficient functional encryption schemes for a large class of quadratic functionalities. Specifically, our constructions enable the computation of so-called bilinear maps on encrypted vectors. This represents a practically relevant class of functions that includes, for instance, multivariate quadratic polynomials (over the integers). Our realizations work over asymmetric bilinear groups and are surprisingly efficient and easy to implement. For instance, in our most efficient scheme the public key and each ciphertext consist of 2n+1 and 4n+2group elements respectively, where n is the dimension of the encrypted vectors, while secret keys are only two group elements. Our two schemes build on similar ideas, but develop them in a different way in order to achieve distinct goals. Our first scheme is proved (selectively) secure under standard assumptions, while our second construction is concretely more efficient and is proved (adaptively) secure in the generic group model.As a byproduct of our functional encryption schemes, we show new predicate encryption schemes for degree-two polynomial evaluation, where ciphertexts consist of only O(n) group elements. This significantly improves the O(n2)bound one would get from inner product encryption-based constructions.

International audience; In an inner-product functional encryption scheme, the plaintexts are vectors and the owner of the secret key can delegate the ability to compute weighted sums of the coefficients of the plaintext of any ciphertext. Recently, many inner-product functional encryption schemes were proposed. However, none of the known schemes are secure against chosen ciphertext attacks (IND-FE-CCA).We present a generic construction of IND-FE-CCA inner-product functional encryption from projective hash functions with homomorphic properties. We show concrete instantiations based on the DCR assumption, the DDH assumption, and more generally, any Matrix DDH assumption.

A distributed storage system (DSS) is a fundamental building block in many distributed applications. It applies linear network coding to achieve an optimal tradeoff between storage and repair bandwidth when node failures occur. Additively homomorphic encryption is compatible with linear network coding. The homomorphic property ensures that a linear combination of ciphertext messages decrypts to the same linear combination of the corresponding plaintext messages. In this paper, we construct a linearly homomorphic symmetric encryption scheme that is designed for a DSS. Our proposal provides simultaneous encryption and error correction by applying linear error correcting codes. We show its IND-CPA security for a limited number of messages based on binary Goppa codes and the following assumption: when dividing a scrambled generator matrix G^ into two parts G1^ and G2^, it is infeasible to distinguish G2^ from random and to find a statistical connection between G1^ and G2^. Our infeasibility assumptions are closely related to those underlying the McEliece public key cryptosystem but are considerably weaker. We believe that the proposed problem has independent cryptographic interest.

In the era of the Internet, image encryption plays an important role in information security. Chaotic systems and DNA operations have been proven to be powerful for image encryption. To further enhance the security of image, in this paper, we propose a novel algorithm that combines the fractional-order hyperchaotic Lorenz system and DNA computing (FOHCLDNA) for image encryption. Specifically, the algorithm consists of four parts: firstly, we use a fractional-order hyperchaotic Lorenz system to generate a pseudorandom sequence that will be utilized during the whole encryption process; secondly, a simple but effective diffusion scheme is performed to spread the little change in one pixel to all the other pixels; thirdly, the plain image is encoded by DNA rules and corresponding DNA operations are performed; finally, global permutation and 2D and 3D permutation are performed on pixels, bits, and acid bases. The extensive experimental results on eight publicly available testing images demonstrate that the encryption algorithm can achieve state-of-the-art performance in terms of security and robustness when compared with some existing methods, showing that the FOHCLDNA is promising for image encryption.

In the public-key setting, known constructions of function-private functional encryption (FPFE) were limited to very restricted classes of functionalities like inner-product [Agrawal et al. - PKC 2015]. Moreover, its power has not been well investigated. In this paper, we construct FPFE for general functions and explore its powerful applications, both for general and specific functionalities. As warmup, we construct from FPFE a natural generalization of a signature scheme endowed with functional properties, that we call functional anonymous signature (FAS) scheme. In a FAS, Alice can sign a circuit C chosen from some distribution D to get a signature s and can publish a verification key that allows anybody holding a message m to verify that (1) s is a valid signature of Alice for some (possibly unknown to him) circuit C and (2) C(m)=1. Beyond unforgeability the security of FAS guarantees that the signature s hide as much information as possible about C except what can be inferred from knowledge of D. Then, we show that FPFE can be used to construct in a black-box way functional encryption schemes for randomized functionalities (RFE). %Previous constructions of (public-key) RFE relied on iO [Goyal et al. - TCC 2015]. As further application, we show that specific instantiations of FPFE can be used to achieve adaptively-secure CNF/DNF encryption for bounded degree formulae (BoolEnc). Though it was known how to implement BoolEnc from inner-product encryption (IPE) [Katz et al. - EUROCRYPT 2008], as already observed by Katz et al. this reduction only works for selective security and completely breaks down for adaptive security; however, we show that the reduction works if the IPE scheme is function-private. Finally, we present a general picture of the relations among all these related primitives. One key observation is that Attribute-based Encryption with function privacy implies FE, a notable fact that sheds light on the importance of the function privacy property for FE.

This paper presents a comparative evaluation of possible encryption algorithms for use in a self-contained, ultra-secure router-to-router communication system, first proposed by El Rifai and Verma. The original proposal utilizes a discrete logarithm-based encryption solution, which will be compared in this paper to RSA, AES, and ECC encryption algorithms. RSA certificates are widely used within the industry but require a trusted key generation and distribution architecture. AES and ECC provide advantages in key length, processing requirements, and storage space, also maintaining an arbitrarily high level of security. This paper modifies each of the four algorithms for use within the self-contained router-to-router environment system and then compares them in terms of features offered, storage space and data transmission needed, encryption/decryption efficiency, and key generation requirements.

The number of attempts to break modern encryption methods increases day by day and therefore the need for the design of systems to ensure higher security has occurred. This study aims, an encryption algorithm that combines the strong of asymmetric encryption algorithm and the rich dynamic behaviors of chaotic systems is developed. In this study, firstly a new chaotic system design with high dynamic features is performed and then circuit realization and analyses are made. A chaos based RNG (random number generator) is designed with the help of the new developed chaotic system, NIST and FIPS tests are run. Chaos based hybrid RSA (CRSA) encryption algorithm design in which RNG and RSA algorithms are used together is performed. Text and image encryption is carried out with the algorithm and security analyses of these applications are made. Security analyses results are compared with classical RSA algorithm. It is observed that the developed CRSA algorithm provided better results than RSA algorithm in security tests. (C) 2017 Published by Elsevier Ltd.

International audience; Private functional encryption guarantees that not only the information in ciphertexts is hidden but also the circuits in decryption tokens are protected. A notable use case of this notion is query privacy in searchable encryption. Prior privacy models in the literature were fine-tuned for specific functionalities (namely, identity-based encryption and inner-product encryption), did not model correlations between ciphertexts and decryption tokens, or fell under strong uninstantiability results. We develop a new indistinguishability-based privacy notion that overcomes these limitations and give constructions supporting different circuit classes and meeting varying degrees of security. Obfuscation is a common building block that these constructions share, albeit the obfuscators necessary for each construction are based on different assumptions. Our feasibility results go beyond previous constructions in a number of ways. In particular, a keyword search scheme that we base on point obfuscators tolerates arbitrary and possibly low-entropy correlations between encrypted data and queried keywords, even under (mildly restricted) adaptive token-extraction queries. Our more elaborate keyword search scheme achieves the strongest notion of privacy that we put forth (with no restrictions), but relies on stronger forms of obfuscation. We also develop a composable and distributionally secure hyperplane membership obfuscator and use it to build an inner-product encryption scheme that achieves an unprecedented level of privacy. This, in particular, positively answers a question left open by Boneh, Raghunathan and Segev (ASIACRYPT 2013) concerning the extension and realization of enhanced security for schemes supporting this functionality.

International audience; Authenticated encryption schemes which resist misuse of nonce at some desired level of privacy are two-pass or Macthen- Encrypt constructions (inherently inefficient but provide full privacy) and online constructions like McOE, sponge-type authenticated encryptions (such as duplex) and COPA. Only the last one is almost parallelizable except that for associated data processing, the final block-cipher call is sequential (it needs to wait for the encryption of all the previous ones). In this paper, we design a new online secure authenticated encryption, called ELmD or Encrypt-Linear mix-Decrypt, which is completely (two-stage) parallel (even in associated data) and fully pipeline implementable. It also provides full privacy when associated data is not repeated. Like COPA, our construction is based on EME, an Encrypt-Mix-Encrypt type SPRP construction (secure against chosen plaintext and ciphertext). But unlike EME, we have used an online computable efficient linear mixing instead of a non-linear mixing. We have also provided the hardware implementation of the construction and compare the performance with similar constructions like COPA and EME2.

International audience; We formally define the primitive of encryption switching protocol (ESP), allowing to switch between two encryption schemes. Intuitively, this two-party protocol converts given ciphertexts from one scheme into ciphertexts of the same messages under the other scheme, for any polynomial number of switches, in any direction. Although ESP is a special kind of two-party computation protocol, it turns out that ESP implies general two-party computation (2-PC) under natural conditions. In particular, our new paradigm is tailored to the evaluation of functions over rings. Indeed, assuming the compatibility of two additively and multiplicatively homomorphic encryption schemes, switching ciphertexts makes it possible to efficiently reconcile the two internal laws. Since no such pair of public-key encryption schemes appeared in the literature, except for the non-interactive case of fully homomorphic encryption which still remains prohibitive in practice, we build the first multiplicatively homomorphic ElGamal-like encryption scheme over $(\mathbb {Z}_n,\times )$ as a complement to the Paillier encryption scheme over $(\mathbb {Z}_n,+)$, where n is a strong RSA modulus. Eventually, we also instantiate secure ESPs between the two schemes, in front of malicious adversaries. This enhancement relies on a new technique called refreshable twin ciphertext pool, which we show being of independent interest. We additionally prove this is enough to argue the security of our general 2-PC protocol against malicious adversaries.

We introduce for the first time, to the best of our knowledge, a three-dimensional experimental joint transform correlator (JTC) cryptosystem allowing the encryption of information for any 3D object, and as an additional novel feature, a second 3D object plays the role of the encoding key. While the JTC architecture is normally used to process 2D data, in this work, we envisage a technique that allows the use of this architecture to protect 3D data. The encrypted object information is contained in the joint power spectrum. We register the key object as a digital off-axis Fourier hologram. The encryption procedure is done optically, while the decryption is carried out by means of a virtual optical system, allowing for flexible implementation of the proposal. We present experimental results to demonstrate the validity and feasibility of the method. Fil: Velez Zea, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; Argentina Fil: Barrera Ramírez, John Fredy. Universidad de Antioquia; Colombia Fil: Torroba, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; Argentina. Universidad Nacional de la Plata. Facultad de Ingeniería. Uidet Grupo de Ensayos Mecanicos Aplicados.; Argentina

Encryption of a digital image is very important especially in applications of body area networks (BANs) since the image may include a number of privacy. Past encryption methods have disadvantages of the small key space and low ability of resistance to attack. In this paper, we propose a new encryption algorithm based on discrete wavelet transform (DWT) and multichaos which has characteristics of the deterministic, pseudorandomness, and sensitivity of initial values. The image is first decomposed and spatial reconstructed by two-dimensional DWT and then is performed by multichaos matrices for space encryption. The experimental results indicate that the proposed algorithm has a large key space, high key sensitivity, and excellent ability of resistance to attack.

An encryption/decryption approach is proposed dedicated to one-way communication between a transmitter which is a computationally powerful party and a receiver with limited computational capabilities. The proposed encryption technique combines traditional stream ciphering and simulation of a binary channel which degrades channel input by inserting random bits. A statistical model of the proposed encryption is analyzed from the information-theoretic point of view. In the addressed model an attacker faces the problem implied by observing the messages through a channel with random bits insertion. The paper points out a number of security related implications of the considered channel. These implications have been addressed by estimation of the mutual information between the channel input and output and estimation of the number of candidate channel inputs for a given channel output. It is shown that deliberate and secret key controlled insertion of random bits into the basic ciphertext provides security enhancement of the resulting encryption scheme.

Hacking is one of the greatest problems in the wireless local area networks. Many algorithms have been used to prevent the outside attacks to eavesdrop or prevent the data to be transferred to the end-user safely and correctly. In this paper, a new symmetrical encryption algorithm is proposed that prevents the outside attacks. The new algorithm avoids key exchange between users and reduces the time taken for the encryption and decryption. It operates at high data rate in comparison with The Data Encryption Standard (DES), Triple DES (TDES), Advanced Encryption Standard (AES-256), and RC6 algorithms. The new algorithm is applied successfully on both text file and voice message.

In Ciphertext-Policy Attribute-Based Encryption (CP-ABE), a user secret key is associated with a set of attributes, and the ciphertext is associated with an access policy over attributes. The user can decrypt the ciphertext if and only if the attribute set of his secret key satisfies the access policy specified in the ciphertext. Several CP-ABE schemes have been proposed, however, some practical problems, such as attribute revocation, still needs to be addressed. In this paper, we propose a mediated Ciphertext-Policy Attribute-Based Encryption (mCP-ABE) which extends CP-ABE with instantaneous attribute revocation. Furthermore, we demonstrate how to apply the proposed mCP-ABE scheme to securely manage Personal Health Records (PHRs).

An Attribute-Based Encryption (ABE) is an encryption scheme, where users with some attributes can decrypt ciphertexts associated with these attributes. However, the length of the ciphertext depends on the number of attributes in previous ABE schemes. In this paper, we propose a new Ciphertext-Policy Attribute-Based Encryption(CP-ABE) with constant ciphertext length. Moreover, the number of pairing computations is also constant., Proceedings of the 5th International Conference, ISPEC 2009 Xi’an, China, April 13-15, 2009.

In this paper, we first present the notion of stateful identity-based encryption (IBE) and then extend standard security definitions for IBE to the stateful setting. After that, we demonstrate a concrete stateful IBE scheme, whose security meets the strongest definition in the setting in random oracle model, and whose encryption and decryption are very efficient, compared to existing IBEs: one pairing each for encryption and decryption.

International audience; This paper presents a novel and robust chaos-based cryptosystem for secure transmitted images and four other versions. In the proposed block encryption/decryption algorithm, a 2D chaotic map is used to shuffle the image pixel positions. Then, substitution (confusion) and permutation (diffusion) operations on every block, with multiple rounds, are combined using two perturbed chaotic PWLCM maps. The perturbing orbit technique improves the statistical properties of encrypted images. The obtained error propagation in various standard cipher block modes demonstrates that the proposed cryptosystem is suitable to transmit cipher data over a corrupted digital channel. Finally, to quantify the security level of the proposed cryptosystem, many tests are performed and experimental results show that the suggested cryptosystem has a high security level.

The secure destruction of expired data is one of the important contents in the research of cloud storage security. Applying the attribute-based encryption (ABE) and the distributed hash table (DHT) technology to the process of data destruction, we propose a secure ciphertext self-destruction scheme with attribute-based encryption called SCSD. In SCSD scheme, the sensitive data is first encrypted under an access key and then the ciphertext shares are stored in the DHT network along with the attribute shares. Meanwhile, the rest of the sensitive data ciphertext and the shares of access key ciphertext constitute the encapsulated self-destruction object (EDO), which is stored in the cloud. When the sensitive data is expired, the nodes in DHT networks can automatically discard the ciphertext shares and the attribute shares, which can make the ciphertext and the access key unrecoverable. Thus, we realize secure ciphertext self-destruction. Compared with the current schemes, our SCSD scheme not only can support efficient data encryption and fine-grained access control in lifetime and secure self-destruction after expiry, but also can resist the traditional cryptanalysis attack as well as the Sybil attack in the DHT network.

In order to solve the security problem of transmission image across public networks, a new image encryption algorithm based on TD-ERCS system and wavelet neural network is proposed in this paper. According to the permutation process and the binary XOR operation from the chaotic series by producing TD-ERCS system and wavelet neural network, it can achieve image encryption. This encryption algorithm is a reversible algorithm, and it can achieve original image in the rule inverse process of encryption algorithm. Finally, through computer simulation, the experiment results show that the new chaotic encryption algorithm based on TD-ERCS system and wavelet neural network is valid and has higher security.

Providing a way to achieve the privacy and authenticity of information transmitted over or stored in an unreliable medium is a prime necessity in the world of computing and communication. In this paper, we propose a new deduction system called judgment deduction system (or JD-System), which can be used to formalize an idealized asymmetric (and symmetric) encryption scheme. In our system, deductive reasoning is used to identify the security properties of asymmetric and symmetric encryption. New notions are introduced for describing several security properties. For example, we use the notion of “judgment” in our system. Conversely, we also introduce the notion of “unjudgment” as a property of JD-system. By using these notions, we can express and prove the security properties content-indistinguishability, key-indistinguishability, content-non-malleability, content-length-indistinguishability, key-length-indistinguishability, content-length-non-malleability, and key-length-non-malleability of asymmetric (and symmetric) encryption schemes and the security property key-non-malleability of asymmetric encryption. Formal proofs are given showing the sufficient conditions for these security properties and showing formally the difference between asymmetric encryption and symmetric encryption scheme. Some security properties can be achieved in case of asymmetric encryption and cannot be achieved in case of symmetric encryption.

Functional encryption is a novel paradigm for public-key encryption that enables both fine-grained access control and selective computation on encrypted data, as is necessary to protect big, complex data in the cloud. In this article, we provide a brief introduction to functional encryption, and an overview of its overarching impact on the field of cryptography.

International audience; Indistinguishability under adaptive chosen-ciphertext attack (IND-CCA) is now considered the de facto security notion for public-key encryption. However, the security guarantee that it offers is sometimes stronger than what is needed by certain applications. In this paper, we consider a weaker notion of security for public-key encryption, termed indistinguishability under plaintext-checking attacks (IND-PCA), in which the adversary is only given access to an oracle which says whether or not a given ciphertext encrypts a given message. After formaliz- ing the IND-PCA notion, we then design a new public-key encryption scheme satisfying it. The new scheme is a more efficient variant of the Cramer-Shoup encryption scheme with shorter ciphertexts and its secu- rity is also based on the plain Decisional Diffie-Hellman (DDH) assump- tion. Additionally, the algebraic properties of the new scheme also allow for proving plaintext knowledge using Groth-Sahai non-interactive zero- knowledge proofs or smooth projective hash functions. Finally, in order to illustrate the usefulness of the new scheme, we further show that, for many password-based authenticated key exchange (PAKE) schemes in the Bellare-Pointcheval-Rogaway security model, one can safely replace the underlying IND-CCA encryption schemes with our new IND-PCA one. By doing so, we were able to reduce the overall communication complex- ity of these protocols and obtain the most efficient PAKE schemes to date based on the plain DDH assumption.

International audience; In this paper we present an efficient encryption system based on Compressive Sensing, without the additional computational cost of a separate encryption protocol, when applied to indoor location estimation problems. The breakthrough of the method is the use of the weakly encrypted measurement matrices which are generated when solving the optimization problem to localize the source. It must be noted that in this method an alternative key is required to secure the system.

In the field of chaotic image encryption, the algorithm based on correlating key with plaintext has become a new developing direction. However, for this kind of algorithm, some shortcomings in resistance to reconstruction attack, efficient utilization of chaotic resource, and reducing dynamical degradation of digital chaos are found. In order to solve these problems and further enhance the security of encryption algorithm, based on disturbance and feedback mechanism, we present a new image encryption scheme. In the running-key generation stage, by successively disturbing chaotic stream with cipher-text, the relation of running-key to plaintext is established, reconstruction attack is avoided, effective use of chaotic resource is guaranteed, and dynamical degradation of digital chaos is minimized. In the image encryption stage, by introducing random-feedback mechanism, the difficulty of breaking this scheme is increased. Comparing with the-state-of-the-art algorithms, our scheme exhibits good properties such as large key space, long key period, and extreme sensitivity to the initial key and plaintext. Therefore, it can resist brute-force, reconstruction attack, and differential attack.

Large-scale cloud storage systems often attempt to achieve two seemingly conflicting goals: (1) the systems need to reduce the copies of redundant data to save space, a process called deduplication; and (2) users demand encryption of their data to ensure privacy. Conventional encryption makes deduplication on ciphertexts ineffective, as it destroys data redundancy. A line of work, originated from Convergent Encryption [27], and evolved into Message Locked Encryption [13] and the latest DupLESS architecture [12], strives to solve this problem. DupLESS relies on a key server to help the clients generate encryption keys that result in convergent ciphertexts. In this paper, we first introduce a new security notion appropriate for the setting of deduplication and show that it is strictly stronger than all relevant notions. We then provide a rigorous proof of security against this notion, in the random oracle model, for the DupLESS architecture which is lacking in the original paper. Our proof shows that using additional secret, other than the data itself, for generating encryption keys achieves the best possible security under current deduplication paradigm. We also introduce a distributed protocol that eliminates the need for the key server. This not only provides better protection but also allows less managed systems such as P2P systems to enjoy the high security level. Implementation and evaluation show that the scheme is both robust and practical.

Comunicació presentada a: PKC 2014 17th International Conference on Practice and Theory in Public-Key Cryptography, celebrada a Buenos Aires, Argentina, del 26 al 28 de març de 2014 Lossy trapdoor functions, introduced by Peikert and Waters (STOC’08), have received a lot of attention in the last years, because of their wide range of applications. The notion has been recently extended to the identity-based setting by Bellare et al. (Eurocrypt’12). An identity-based trapdoor function (IB-TDF) satisfying the lossy property introduced by Bellare et al. can be used to construct other cryptographic primitives in the identity-based setting: encryption schemes with semantic security under chosen-plaintext attacks, deterministic encryption schemes, and hedged encryption schemes that maintain some security when messages are encrypted using randomness of poor quality. However, the constructed primitives can be proved secure only against selective adversaries who select the target identity upfront. Our first contribution is an alternative definition for the lossiness of an identity-based trapdoor function. We prove that an IB-TDF satisfying the new property can be used to construct all the aforementioned primitives, in the identity-based setting, with security against adaptive adversaries. We further consider the new definition and its implications in the more general scenario of hierarchical identity-based cryptography, which has proved very useful both for practical applications and to establish theoretical relations with other cryptographic primitives (including encryption with chosen-ciphertext security or with forward-security). As a second contribution, we describe a pairing-based hierarchical IB-TDF satisfying the new definition of lossiness against either selective or, for hierarchies of constant depth, adaptive adversaries. This is also the first example of hierarchical trapdoor functions based on traditional (i.e., non-lattice-related) number theoretic assumptions. As a direct consequence of our two contributions, we obtain a hierarchical identity-based (HIB) encryption scheme with chosen-plaintext security, a HIB deterministic encryption scheme and a HIB hedged encryption scheme, all of them with security against adaptive adversaries.

International audience; In the paper, we study whether it is possible to construct an efficient leakage-resilient symmetric scheme using the AES block cipher. We aim at bridging the gap between the theoretical leakage-resilient symmetric primitives used to build encryption schemes and the prac-tical schemes that do not have any security proof against side-channel adversaries. Our goal is to construct an as efficient as possible leakage-resilient encryption scheme, but we do not want to change the crypto-graphic schemes already implemented. The basic idea consists in adding a leakage-resilient re-keying scheme on top of the encryption scheme and has been already suggested by Kocher to thwart differential power analy-sis techniques. Indeed, in such analysis, the adversary queries the encryp-tion box and from the knowledge of the plaintext/ciphertext, she can per-form a divide-and-conquer key recovery attack. The method consisting in changing the key for each or after a small number of encryption with the same key is known as re-keying. It prevents DPA adversaries but not SPA attacks which uses one single leakage trace. Here, we prove that using a leakage-resilient re-keying scheme on top of a secure encryption scheme in the standard model, leads to a leakage-resilient encryption scheme. The main advantage of the AES block cipher is that its implementations are generally heuristically-secure against SPA adversaries. This assump-tion is used in many concrete instantiations of leakage-resilient symmet-ric primitives. Consequently, if we use it and change the key for each new message block, the adversary will not be able to recover any key if the re-keying scheme is leakage-resilient. There is mainly two different techniques for re-keying scheme, either parallel or sequential, but if we want to avoid the adversary having access to many inputs/outputs, only the sequential method is possible. However, the main drawback of the latter technique is that in case of de-synchronization, many useless com-putations are required. In our re-keying scheme, we use ideas from the skip-list data structure to efficiently recover a specific key. Full version of the paper published in the proceedings of CHES 2013.