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An increasing demand of secure data transmission over internet leads to the challenge of implementing a consistent cryptosystem. In 2004, USA navy published the patent which highlights the importance of fractal as an encryption/decryption key in a cryptosystem [1]. Fractal possess butterfly effect i.e. sensitivity to initial condition, due to which small change in input produces a major change in output. This paper summarizes the various recent image encryption techniques in which fractal key is used to encrypt/decrypt followed by substitution, scrambling and diffusion techniques to provide strong cryptosystem. The algorithms covered both private key encryption as well as public key encryption technique in the paper. The analysed algorithms include a set of fractal function such as Mandelbrot set, Julia set, Hilbert curve, 3D fractal, multi-fractal, IFS and chaotic function to generate a complex key used in the encryption process. Corresponding performance of each algorithm is analysed by PSNR test, key space, sensitivity analysis and correlation coefficient value between the adjacent pixels of both images (Original image and encrypted image) which shows significant improvement in performance over the traditional encryption methods.

Recently, based on the Paillier cryptosystem [1] , Yi et al. outline a distributed ElGamal cryptosystem which allows for both a much simpler distributed key generation procedure and a more efficient distributed decryption of messages from a large plaintext domain [2] . In this paper, we analyze the security of their proposed variant of ElGamal encryption scheme and demonstrate that their proposed variant is not secure as claimed. Thus, whether an additively homomorphic cryptosytem satisfying the desired properties exists remains an open question.

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

This paper proposes a novel reversible data hiding scheme for encrypted images by using homomorphic and probabilistic properties of Paillier cryptosystem. In the proposed method, groups of adjacent pixels are randomly selected, and reversibly embedded into the rest of the image to make room for data embedding. In each group, there are a reference pixel and a few host pixels. Least significant bits (LSBs) of the reference pixels are reset before encryption and the encrypted host pixels are replaced with the encrypted reference pixel in the same group to form mirroring ciphertext groups (MCGs). In such a way, the modification on MCGs for data embedding will not cause any pixel oversaturation in plaintext domain and the embedded data can be directly extracted from the encrypted domain. In an MCG, the reference ciphertext pixel is kept unchanged as a reference while data hider embeds the encrypted additional data into the LSBs of the host ciphertext pixels by employing homomorphic multiplication. On the receiver side, the hidden ciphertext data can be retrieved by employing a modular multiplicative inverse operation between the marked host ciphertext pixels and their corresponding reference ciphertext pixels, respectively. After that, the hidden data are extracted promptly by looking for a one-to-one mapping table from ciphertext to plaintext. Data extraction and image restoration can be accomplished without any error after decryption. Compared with the existing works, the proposed scheme has lower computation complexity, higher security performance, and better embedding performance. The experiments on the standard image files also certify the effectiveness of the proposed scheme.

Bellare, Boldyreva, and O’Neill (CRYPTO ’07) initiated the study of deterministic public-key encryption as an alternative in scenarios where randomized encryption has inherent drawbacks. The resulting line of research has so far guaranteed security only for adversarially-chosen plaintext distributions that are independent of the public key used by the scheme. In most scenarios, however, it is typically not realistic to assume that adversaries do not take the public key into account when attacking a scheme.

Database encryption is essential for cloud database systems. For a large database, decryption could take a lot of computational time. Therefore, verifying an encryption that contains a correct plaintext without decryption becomes significant for a large database system. Plaintext-checkable encryption (PCE) is a potential tool for such database systems, which is first proposed by Canard et al. in CT-RSA 2012. Although the generic PCE in the random oracle model has been studied intensively, the generic PCE in the standard model and its efficient implementation are still challenging problems. This paper presents the first generic PCE in the standard model using smooth projective hash function (SPHF) and prove its s-priv1-cca security, which is independent of current unlink security. Based on the instantiated SPHF from DDH assumption, we obtain the most efficient PCE in the standard model, without any pairing operation. Finally, we improve two existing generic constructions in the random oracle model so that they are secure under chosen ciphertext attack.

To lower communication complexity, a Certificateless homomorphic encryption (CLHE) scheme based on the Learning with errors (LWE) problem is constructed by introducing a new technique called probabilistic encoding with weakly homomorphic property. This technique can conveniently convert an intended message into two elements in a ring, which will be respectively encrypted under both public keys of a user in certificateless cryptosystem. Upon knowing both elements simultaneously, the original message can be easily recovered. It is hidden perfectly by the probabilistic property of encoding. This CLHE removes evaluation keys by using the approximate eigenvector method given by Gentry et al., which makes it into a pure CLHE. It is proven to be semantic secure in the Random oracle model (ROM). The results indicate it is able to homomorphically evaluate any functions in a class functions with given multiplicative depth L.

Efficient searching on encrypted data outsourced to the cloud remains a research challenge. Identity-based encryption with equality test (IBEET) scheme has recently been identified as a viable solution, in which users can delegate a trapdoor to the server and the server then searches on user outsourced encrypted data to determine whether two different ciphertexts are encryptions of the same plaintext. Such schemes are, unfortunately, inefficient particularly for deployment on mobile devices (with limited power/battery life and computing capacity). In this paper, we propose an efficient IBEET scheme with bilinear pairing, which reduces the need for time-consuming HashToPoint function. We then prove the security of our scheme for one-way secure against chosen identity and chosen ciphertext attacks (OWIDCCA) in the random oracle model (ROM). The performance evaluation of our scheme demonstrates that in comparison to the scheme of Ma (2016), our scheme achieves a reduction of 36.7% and 39.24% in computation cost during the encryption phase and test phase, respectively, and that our scheme is suitable for (mobile) cloud deployment. We propose an identity-based encryption with equality test (IBEET) scheme using bilinear pairing for cloud storage.We show that our proposed concrete scheme is provably secure. It satisfies required security properties.Detailed performance analysis and experimental result are given.

Objectives: The principal objective of this paper is to develop an enhanced algorithm of cryptography through the hybridization of existing symmetric and asymmetric encryption. Methods/Analysis: The strength of several prevailing symmetric and asymmetric encryption were utilized in the proposed methodology. ElGamal’s key security based on difficulty of solving discrete logarithm, Chaos-based’s avalanche effect of using multiple keys, RSA’s security based on the difficulty of factorization of large numbers and AES’s S-Box mapping, which makes the encryption complex and unpredictable were adapted. Findings: The strength of security of the proposed hybrid algorithm is tested by the provided examples. It was found out that with the use of different keys in encryption, various ciphertexts were generated. The published public keys using such algorithm also make it infeasible to intrude because of the difficulty of solving discrete logarithm with large prime numbers. Furthermore, the value of the ciphertext of the proposed method is significantly different and, in some cases, larger than that of RSA’s. Applications: With this newly enhanced hybrid algorithm of data encryption, transferring and conveying of data will be much more secured.

We give a new black-box transformation from any semantically secure encryption scheme into a non-malleable one which has a better rate than the best previous work of Coretti et al. (in: Kushilevitz and Malkin (eds) TCC 2016-A, Part I, Springer, Heidelberg, 2016). We achieve a better rate by departing from the "matrix encoding" methodology used by previous constructions, and working directly with a single codeword. We also use a Shamir secret-share packing technique to improve the rate of the underlying error-correcting code.

Ye and Zhou [Appl. Soft. Comput. 22 (2014) 351–357] proposed an efficient chaotic based image encryption scheme which only employs diffusion, while usually both confusion and diffusion are used for encryption structures. We present both chosen-plaintext and chosen-ciphertext attacks against the scheme for any number of its rounds r by exploiting r -round differentials with probability 1. The result shows that the encryption structure proposed by Ye and Zhou does not fulfill basic requirements of a secure image encryption scheme.

Revocation and key evolving paradigms are central issues in cryptography, and in PKI in particular. A novel concern related to these areas was raised in the recent work of Sahai, Seyalioglu, and Waters (CRYPTO 2012) who noticed that revoking past keys should at times (e.g., the scenario of cloud storage) be accompanied by revocation of past ciphertexts (to prevent unread ciphertexts from being read by revoked users). They introduced revocable-storage attribute-based encryption (RS-ABE) as a good access control mechanism for cloud storage. RS-ABE protects against the revoked users not only the future data by supporting key-revocation but also the past data by supporting ciphertext-update, through which a ciphertext at time T can be updated to a new ciphertext at time T + 1 using only the public key. Motivated by this pioneering work, we ask whether it is possible to have a modular approach, which includes a primitive for time managed ciphertext update as a primitive. We call encryption which supports this primitive a "self-updatable encryption" (SUE). We then suggest a modular cryptosystems design methodology based on three sub-components: a primary encryption scheme, a key-revocation mechanism, and a time-evolution mechanism which controls the ciphertext self-updating via an SUE method, coordinated with the revocation (when needed). Our goal in this is to allow the self-updating ciphertext component to take part in the design of new and improved cryptosystems and protocols in a flexible fashion. Specifically, we achieve the following results:We first introduce a new cryptographic primitive called self-updatable encryption (SUE), realizing a time-evolution mechanism. In SUE, a ciphertext and a private key are associated with time. A user can decrypt a ciphertext if its time is earlier than that of his private key. Additionally, anyone (e.g., a cloud server) can update the ciphertext to a ciphertext with a newer time. We also construct an SUE scheme and prove its full security under static assumptions. Following our modular approach, we present a new RS-ABE scheme with shorter ciphertexts than that of Sahai et al. and prove its security. The length efficiency is mainly due to our SUE scheme and the underlying modularity. We apply our approach to predicate encryption (PE) supporting attribute-hiding property, and obtain a revocable-storage PE (RS-PE) scheme that is selectively-secure. We further demonstrate that SUE is of independent interest, by showing it can be used for timed-release encryption (and its applications), and for augmenting key-insulated encryption with forward-secure storage. A new cryptographic primitive called self-updatable encryption is introduced to realize a time-evolution mechanism.A revocable-storage attribute-based encryption scheme with shorter ciphertexts was proposed by following our modular approach.A revocable-storage predicate encryption scheme that additionally supports attribute-hiding property is presented.

We propose two Key-Policy Attribute-Based Encryption (KP-ABE) schemes for Linear Secret-Sharing Scheme (LSSS)-realizable Monotone Access Structure (MAS). We show that the first construction is secure against Chosen Plaintext Attacks (CPAs) while the second scheme is secure against Chosen Ciphertext Attacks (CCAs), without introducing any random oracle heuristic. Both the schemes enjoy constant-size ciphertext, constant number of pairing operations, and constant computation cost during encryption and decryption. We further propose two non-monotone access structure variants, one is CPA secure and another is CCA secure, preserving the same functionality as that of MAS primitives. We thereafter present a large attribute universe KP-ABE for MAS, still utilizing low computation cost together with constant number of pairing operations and public parameters. Unlike the existing approaches, this does not impose a bound on the size of attribute sets used in encryption, however, the security is in random oracle model. Our final result is a dual-policy ABE supporting LSSS-realizable MAS with significantly low communication and computation cost. Furthermore, we extend our KP-ABE to efficient key-policy attribute-based broadcast encryption. While the secret key in all our constructions has quadratic-size in the number of attributes, the number of pairing evaluations is constant. The CPA and CCA security against selective-adversary of proposed schemes are achieved under the decisional Bilinear DiffieHellman Exponent assumption over prime order groups.

In this study, an encryption algorithm that uses chaos based S-BOX is developed for secure and speed image encryption. First of all, a new chaotic system is developed for creating S-Box and image encryption algorithm. Chaos based random number generator is designed with the help of the new chaotic system. Then, NIST tests are run on generated random numbers to verify randomness. A new S-Box design algorithm is developed to create the chaos based S-Box to be utilized in encryption algorithm and performance tests are made. As the next step, the new developed S-Box based image encryption algorithm is introduced in detail. Finally, image encryption application is carried out. To show the quality and strong of the encryption process, security analysis are performed. Proposed algorithm is compared with the AES and chaos algorithms. According to tests results, the proposed image encryption algorithm is secure and speed for image encryption application. (C) 2016 Elsevier Ltd. All rights reserved.

This paper introduces a secure speech communication approach, which is based on encryption and authentication. This system is based on Advanced Encryption Standard (AES) for encryption and private image database for enhancement of encryption and for authentication. The idea of this cryptosystem is based on XOR of one image from image database with the clear speech before encryption and embedding the index number of this image in the database as a least significant bit watermark into speech. A comparison study is held between the AES block cipher algorithm and the proposed algorithm. This proposed cryptosystem used to enhance the security of AES algorithm and increase its immunity to brute force attacks. It used also to provide authentication and enhance security by addition of extra key which don't need to be exchanged between parts depending on the embedded image. The extra proposed step remove residual intelligibility from clear speech and fill the silent periods within speech conversation and help in destroy format and pitch information. Security analyses are presented for the proposed cryptosystem from a strict cryptographic viewpoint. Experimental results verify and prove that the proposed cryptosystem is highly secure from the cryptographic viewpoint.

Fog computing is a paradigm that extends cloud computing to the edge of the network. It can provide computation and storage services to end devices in Internet of Things (IoT). Attribute-based cryptography is a well-known technology to guarantee data confidentiality and fine-grained data access control. However, its computational cost in encryption and decryption phase is linear with the complexity of policy. In this paper, we propose a secure and fine-grained data access control scheme with ciphertext update and computation outsourcing in fog computing for IoT. The sensitive data of data owner are first encrypted using attribute-based encryption with multiple policies and then outsourced to cloud storage. Hence, the user whose attributes satisfy the access policy can decrypt the ciphertext. Based on the attribute-based signature technique, authorized user whose attributes integrated in the signature satisfy the update policy can renew the ciphertext. Specifically, most of the encryption, decryption, and signing computations are outsourced from end devices to fog nodes, and thus, the computations for data owners to encrypt, end users to decrypt, re-encrypt, and sign are irrelevant to the number of attributes in the policies. The security analysis shows that the proposed scheme is secure against known attacks, and the experimental results show that the fog nodes perform most of the computation operations of encryption, decryption, and signing, and hence, the time of encryption for data owner, decryption, re-encryption, and signing for users is small and constant.

Cyber Security has become rising issue in recent years where encryption is one of solution and has an important role in data protection. Encryption algorithms that widely used in information security are asymmetric and symmetric. Advanced Encryption Standard (AES) is one of symmetric encryption that most used often and the most secure encryption today. However, AES encryption has slow computation. Our experiment show that both of algorithms combination needs 3.045 milliseconds for 1024 bytes of data and increase 3-4 milliseconds for 2048 bytes of data and so on. This paper proposes a novelty method to improve AES algorithm with Shift Row and S.Box modification for Mix Column transformation. The result show that our optimization has reduced 3 milliseconds and continue to increase as the number of bytes increases. Percentage average of the optimization is 86.143%.

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 paradigm of forward security provides a promising approach to deal with the key exposure problem as it can effectively minimize the damage caused by the key exposure. In this paper, we develop a new forward-secure identity-based encryption scheme without random oracles. We formally prove that the proposed scheme is secure against adaptive chosen-ciphertext attacks in the standard model. In the proposed scheme, the running time of the private key extraction and decryption algorithms and the sizes of the user's initial private key and the ciphertext are independent on the total number of time periods, and any other performance parameter has at most log-squared complexity in terms of the total number of time periods. Compared with the previous forward-secure identity-based encryption schemes, the proposed scheme enjoys obvious advantage in the overall performance. To the best of our knowledge, it is the first forward-secure identity-based encryption scheme that achieves direct chosen-ciphertext security in the standard model.

The notion of selective opening attacks (SOAs) was first introduced by Dwork et al. at FOCS'99. Informally, an encryption scheme is SOA secure if an adversary is given a vector of ciphertexts and can adaptively corrupt some fraction of them by obtaining not only their messages but also their randomness, the uncorrupted ciphertexts retain secure. Provably achieving security against SOA has been proven extremely challenging. In this paper, we propose a security model to capture simulation-based selective opening chosen-plaintext attacks (SIM-SO-CPA) for certificateless encryption. We provide a concrete construction and prove its security in our simulation-based selective opening chosen-plaintext attack security model, based on the real or random and computational Diffie–Hellman assumptions. Compared with previous SOA-secure public key encryption and identity-based encryption, our certificateless encryption scheme is more simple and efficient. Copyright © 2017 John Wiley & Sons, Ltd.

Dual receiver encryption (DRE) allows two independent receivers to decrypt a ciphertext into a same plaintext. Aiming at solving the dilemma of DRE in the traditional PKE settings, this paper gives an identity‐based variant version of DRE: identity‐based dual receiver encryption (ID‐DRE). Based on Waters' IBE, two concrete ID‐DRE constructions are given in the standard model. Moreover, adopting a random walk‐like methodology also results in better security tightness for Waters' IBE, which is consistent with Hofheinz and Kiltz's result (Crypto'08).

We give generic constructions of several fundamental cryptographic primitives based on a new encryption primitive that combines circular security for bit encryption with the so-called reproducibility property (Bellare et al. PKC 2003). At the heart of our constructions is a novel technique which gives a way of de-randomizing reproducible public-key bit-encryption schemes and also a way of reducing one-wayness conditions of a constructed trapdoor-function family (TDF) to circular security of the base scheme. The main primitives that we build from our encryption primitive include k-wise one-way TDFs (Rosen and Segev TCC 2009), CCA2-secure encryption and deterministic encryption. Our results demonstrate a new set of applications of circularly-secure encryption beyond fully-homomorphic encryption and symbolic soundness. Finally, we show the plausibility of our assumptions by showing that the DDH-based circularly-secure scheme of Boneh et al. (Crypto 2008) and the subgroup indistinguishability based scheme of Brakerski and Goldwasser (Crypto 2010) are both reproducible.

This article presents a novel cryptosystem for secure transmission of color images through a coordinate cryptosystem as well as a geometric cryptosystem with time domain and frequency domain. In this technique, we have designed image encryption and decryption by a proposed random matrix shift cipher (RMSC) associated with a discrete fractional Fourier transform (DFrFT). Our proposed random matrix shift cipher is a coordinate and geometric cryptosystem for security of color image data which is completely different from existing cryptosystems for security of any data. The combination of a random matrix shift cipher and discrete fractional Fourier transform provide a robust cryptosystem for color image data in the time domain as well as the frequency domain without loss of any information. Existing techniques provide single-layer protection of color image data, but the cryptosystem presented here gives multiple layers of protection. Computer simulation on a standard example (Lena and Barbara color im...

In CRYPTO'13, Gentry et al. proposed the first homomorphic encryption HE scheme for the attribute-based encryption ABE. However, Gentry's scheme requires the same index for encryption of each ciphertext and supports only the key-policy ABE. Indeed, in SECRYPT'13, Clear et al. left an open problem in the Gentry et al. scheme viz. a scheme that requires different sets of index in HE using ABE and supports the ciphertext-policy ABE CP-ABE, where the sender is assumed to be intelligent. In addition, in INDOCRYPT'12, Vaikuntanathan discussed an open problem viz. to work out the HE using cryptographic techniques other than lattice-based cryptography. With an aim to propose the CP-ABE scheme using HE, in this research attempt, we propose an approach that integrates the benefits of HE in CP-ABE and yet uses pairing-based cryptography. In our approach viz. attribute-based HE AB-HE, a user is able to successfully decrypt the ciphertext only if the attributes in the policy match those in the secret key. However, in addition, our approach also allows multiple invocations of multiplication operation on the ciphertext as in a typical partially HE, coupling the advantages of the partial HE in the CP-ABE. Further, we also propose an extension of the proposed scheme that serves as a pseudo-fully HE, but requires the help of a key authority. The security of the proposed scheme is based on the decisional bilinear Diffie-Hellman problem. To the best of our knowledge, ours is a unique attempt in integrating HE into the attribute-based cryptography with different indexes/policies. In addition, our AB-HE scheme is pairing-based, and by adding more ciphertexts, it does not blow the final ciphertext size because we use the constant length ciphertext approach for the encryption. Copyright © 2016 John Wiley & Sons, Ltd.

This paper describes the first constructions of identity-based broadcast encryption (IBBE) using Type-3 pairings, which can be proved secure against adaptive-identity attacks based on the Symmetric eXternal Diffie–Hellman assumption (which is a static, if not a standard, assumption) achieving a security degradation which is not exponential in the size of the target identity set. The constructions are obtained by extending the currently known most efficient identity-based encryption scheme proposed by Jutla and Roy in 2013. The new constructions fill both a practical and a theoretical gap in the literature on efficient IBBE schemes.

Predicate encryption is a public-key encryption that supports attribute-hiding as well as payload-hiding and achieves high flexibility in terms of access control. Since Katz, Sahai, and Waters first proposed the predicate encryption scheme in 2008, several predicate encryption schemes have been published. Unfortunately these are impractical as they require $O(n)$ pairing computations for decryption with considerably large sized public parameters, secret key, and ciphertext, where $n$ is the dimension of the attribute/predicate vectors. In this paper, we propose a very efficient predicate encryption scheme that requires only $n$ exponentiation plus three pairing computations for decryption with shorter sized public parameters, secret key, and ciphertext. The proposed scheme is proven selective attribute-secure against chosen-plaintext attacks in the standard model under the Asymmetric Decisional Bilinear Diffie-Hellman assumptions.

Proxy re-encryption (PRE) enables an authorized proxy to convert a ciphertext under Alice's public key into a ciphertext under Bob's public key without exposing the encrypted message. In existing PRE systems, the original ciphertexts and the re-encrypted ones are both required to be in the same cryptosystem, which limits their applications in cloud computing systems. In this paper, we propose a new proxy re-encryption pattern, referred to as an identity-based proxy re-encryption version 2 (IBPRE2). It allows an authorized proxy to convert a ciphertext of an identity-based broadcast encryption (IBBE) scheme into a ciphertext of an identity-based encryption (IBE) scheme. With IBPRE2, one can take advantage of IBBE to securely share data with a set of recipients, and then incorporate an additional one into the authorized set through the re-encryption mechanism, without decrypting the IBBE ciphertext nor leaking any sensitive information. We formalize the security requirements in IBPRE2 and propose a provably CCA-secure scheme. The unique feature of ciphertext transformation from a complicated cryptosystem to a simple one makes our IBPRE2 a versatile cryptographic tool to secure outsourced data in cloud computing. We propose a framework of identity-based proxy re-encryption (IBPRE2) system for cloud computing.We formally define the CCA (chosen-ciphertext attack) security of the IBPRE2.We construct an IBPRE2 scheme and prove its CCA-security assuming that the underlying cryptographic primitives are secure.

One of the approaches to modify the McEliece cryptosystem to overcome its large key size is replacing binary Goppa codes with a new structured code. However, this modification makes such cryptosystems encounter some new attacks. There are a few modified McEliece cryptosystem variants which are known to be secure. One of them is the cryptosystem introduced by Baldi et al. which uses quasi-cyclic low-density parity check (QC-LDPC) codes. This cryptosystem is still unbroken as no efficient attack has been reported against it since 2008. In this study, an attack has been applied to this cryptosystem which is feasible when the code length is a multiple of a power of 2. Also an important weakness of this kind of cryptosystem has been pointed out, namely utilising a too low-weight intentional error vector. The authors have established a new security level for this cryptosystem which is applicable to other McEliece-like cryptosystems using QC-LDPC codes. This security level for instance is 29.18 times lower than previous ones in the case of n = 4 x 4096 when only one ciphertext is available. The gain of the attack in this study can be increased if more than one ciphertext is available.

Goldwasser and Micali (J Comput Syst Sci 28(2):270---299, 1984) highlighted the importance of randomizing the plaintext for public-key encryption and introduced the notion of semantic security. They also realized a cryptosystem meeting this security notion under the standard complexity assumption of deciding quadratic residuosity modulo a composite number. The Goldwasser---Micali cryptosystem is simple and elegant but is quite wasteful in bandwidth when encrypting large messages. A number of works followed to address this issue and proposed various modifications. This paper revisits the original Goldwasser---Micali cryptosystem using $$2^k$$2k-th power residue symbols. The so-obtained cryptosystems appear as a very natural generalization for $$k \ge 2$$kź2 (the case $$k=1$$k=1 corresponds exactly to the Goldwasser---Micali cryptosystem). Advantageously, they are efficient in both bandwidth and speed; in particular, they allow for fast decryption. Further, the cryptosystems described in this paper inherit the useful features of the original cryptosystem (like its homomorphic property) and are shown to be secure under a similar complexity assumption. As a prominent application, this paper describes an efficient lossy trapdoor function-based thereon.

In classical cryptography, the Hill cipher is a polygraphic substitution cipher based on linear algebra. In this work, we proposed a new problem applicable to the public key cryptography, based on the Matrices, called “Matrix discrete logarithm problem”, it uses certain elements formed by matrices whose coefficients are elements in a finite field. We have constructed an abelian group and, for the cryptographic part in this unreliable group, we then perform the computation corresponding to the algebraic equations, Returning the encrypted result to a receiver. Upon receipt of the result, the receiver can retrieve the sender’s clear message by performing the inverse calculation.

A public key cryptosystem consists of a public key, which is used for encryption, and a private key, used for decryption. Therefore, anybody can encrypt plain-text since the encryption key is available to everyone, but only the holders of the private key corresponding to the public key used for encryption can decrypt the cipher -text. RSA is the most popular Asymmetric cryptosystem as it uses pair of keys, one of which is used to encrypt the data in such a way that it can only be decrypted with the other key. The keys are generated by a common process, but they cannot be feasibly generated from each other. The security of the RSA system is based on the assumption that factoring of large number is difficult. But if one could factor a large number into its prime factors then he could break the security. So a new algorithm is developed to increase the security of RSA called Dual Modulus RSA based on Jordan-Totient function (DMRJT). DMRJT algorithm is more secure as compared to RSA algorithm as it uses dual modulus based double encryption and decryption with the use of Jordan function. It is shown here that dual modules play an important role in increasing the complexity of decomposing them into its factors and Jordan function increase the size of the private key hence increases the security. DMRJT algorithm uses double encryption and decryption using double private and public keys to provide security against Brute-force attacks.

Recently, a number of extended Proxy Re-Encryptions (PRE), e.g. Conditional (CPRE), identity-based PRE (IPRE) and broadcast PRE (BPRE), have been proposed for flexible applications. By incorporating CPRE, IPRE and BPRE, this paper proposes a versatile primitive referred to as conditional identity-based broadcast PRE (CIBPRE) and formalizes its semantic security. CIBPRE allows a sender to encrypt a message to multiple receivers by specifying these receivers’ identities, and the sender can delegate a re-encryption key to a proxy so that he can convert the initial ciphertext into a new one to a new set of intended receivers. Moreover, the re-encryption key can be associated with a condition such that only the matching ciphertexts can be re-encrypted, which allows the original sender to enforce access control over his remote ciphertexts in a fine-grained manner. We propose an efficient CIBPRE scheme with provable security. In the instantiated scheme, the initial ciphertext, the re-encrypted ciphertext and the re-encryption key are all in constant size, and the parameters to generate a re-encryption key are independent of the original receivers of any initial ciphertext. Finally, we show an application of our CIBPRE to secure cloud email system advantageous over existing secure email systems based on Pretty Good Privacy protocol or identity-based encryption.

Attribute Based Encryption (ABE) is a type of public encryption in decryptor can only decrypt the ciphertext if its attributes of secret key matches the attributes of ciphertext but functionality comes at higher cost. The main idea of this paper is to provide multi authority in attribute based encryption which also allows fast decryption. Multi authority concept allows any polynomial number of independent authorities to monitor attributes, distribute secret keys and decrypt the message. In this paper, a secure multi authority attribute based encryption with fast decryption scheme is design.

In this fast world of networking, secure image transmission of data whether the image having some information or some text, is one of the area focus for security. Here we had tried to implement the proposed technique fuzzy logic based image encryption for confidential data transfer using (2, 2) secret sharing scheme. Using fuzzy logic makes encryption and decryption complex. The (2, 2) secret sharing scheme provides secured and confidential authentication. For image encryption AES algorithm is used for encryption and decryption. The implementation of encryption algorithms can be very complex when we are focusing on rule based share generation.

This paper revisits the notion of dynamic threshold identity-based encryption, due to the recent practical interest. In this notion, an encryptor selects n recipients and a threshold value t for the creation of the ciphertext. The plaintext can only be recovered if at least t receivers cooperate. The key issue in this notion is its dynamicity, where after the users enroll to the system, the sender can dynamically select the set of recipients as well as dynamically set the threshold t upon the creation of the ciphertext. Another essential feature of this notion is the need for a constant-size ciphertext. Interestingly, the work by Delerablee and Pointcheval in Crypto 2008 is the only work that achieves this essential feature. In this work, we propose a new scheme achieving all of these nice properties with significant improvements in terms of the computational efficiency (both the encryption and decryption). In our scheme, there is no need to conduct any encryption and decryption using additional dummy users, which are not part of the recipient group, which is in contrast to Delerablee and Pointcheval's work. This improvement has significantly reduced the amount of computations required in both encryption and decryption algorithms.

In this study, we consider the problem of constructing a homomorphic encryption scheme that is secure against adaptive chosen ciphertext attack (CCA2). This type of scheme has many applications in secure multi-party computation, electronic voting, and cloud storage and computation. We present an encryption scheme, based on the composite degree residuosity classes, which can block CCA2 while maintaining homomorphism. Our cryptosystem, which is based on standard modular arithmetic, is provable with indistinguishable security under CCA2. An additional contribution of this study is a new definition of preventing CCA2 (or blocking CCA2). We construct a homomorphic encryption scheme with CCA2 security but without random oracle.We present a novel concept of preventing or blocking adaptive chosen ciphertext attacks.We examine how to deal with CCA2 over homomorphic encryption scheme, while keeping homomorphism.

Data security has a major role in the development of communication system, where more randomization in the secret keys increases the security as well as the complexity of the cryptography algorithms. In the recent years network security has become an important concern. Cryptography plays a vital role in the information security system against various attacks. Efficient and newer versions of cryptography techniques can help to reduce this security threat. The Advanced Encryption Standard is a strong symmetric key cryptographic algorithm which uses a number of table look ups to increase its performance. The Cache Timing Attack correlates the timing details for encryption under a known key with an unknown key to infer the unknown key. This paper proposes an extension of a public-key cryptosystem to support a private key cryptosystem which is a combination of Advanced Encryption Standard and ECC. The past results have been computed on the basis of AES key length as 128 bit and no. of iterations as 10.To increase competency and to minimize drawbacks this paper proposes a hybrid encryption scheme. The parameters to be studied will primarily focus on the key length, no. of iterations and the type of side channel attack to be implemented. The key length for this work has been increased to 192 bit and the no. of iterations taken will be 12.

Networked control systems with encrypted sensors measurements is considered. Semi-homomorphic encryption is used so that the controller can perform the required computation on the encrypted data. Specifically, in this paper, the Paillier encryption technique is utilized that allows summation of decrypted data to be performed by multiplication of the encrypted data. Conditions on the parameters of the encryption technique are provided that guarantee the stability of the closed-loop system and ensure certain bounds on the closed-loop performance.

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.

In this paper, an optical implementation of a novel asymmetrical cryptosystem combined with D-H secret key sharing and triple DES is proposed. The proposed optical cryptosystem is realized by performing free-space interconnected optical logic operations such as AND, OR and XOR which are implemented in Mach-Zehnder type interferometer architecture. The advantage of the proposed optical architecture provides dual outputs simultaneously, and the encryption optical setup can be used as decryption optical setup only by changing the inputs of SLMs. The proposed cryptosystem can provide higher security strength than the conventional electronic algorithm, because the proposed method uses 2-D array data, which can increase the key length surprisingly and uses 3DES algorithm, which protects against “meet in the middle” attacks. Another advantage of the proposed asymmetrical cryptosystem is that it is free to change the user’s two private random numbers in generating the public keys at any time. Numerical simulation and performance analysis verify that the proposed asymmetric cryptosystem is effective and robust against attacks for the asymmetrical cipher system.

In an attribute-based encryption (ABE) scheme, a ciphertext is associated with an ℓ-bit public index ind and a message m, and a secret key is associated with a Boolean predicate P. The secret key allows decrypting the ciphertext and learning m if and only if P(ind) = 1. Moreover, the scheme should be secure against collusions of users, namely, given secret keys for polynomially many predicates, an adversary learns nothing about the message if none of the secret keys can individually decrypt the ciphertext. We present attribute-based encryption schemes for circuits of any arbitrary polynomial size, where the public parameters and the ciphertext grow linearly with the depth of the circuit. Our construction is secure under the standard learning with errors (LWE) assumption. Previous constructions of attribute-based encryption were for Boolean formulas, captured by the complexity class NC1. In the course of our construction, we present a new framework for constructing ABE schemes. As a by-product of our framework, we obtain ABE schemes for polynomial-size branching programs, corresponding to the complexity class LOGSPACE, under quantitatively better assumptions., United States. Defense Advanced Research Projects Agency (FA8750-11-2-0225)

The existing homomorphic encryption schemes are mostly in the form of “one-to-one” deployment models, where one party usually encrypts the plaintext and another party decrypts the ciphertext in public key cryptosystem. This form of cryptography loses efficiency under the demands of “one-to-many”, “many-to-one”, and “many-to-many” scenarios. In practice, there are many “many-to-one” scenarios, where the number of the receivers is usually very small compared with the number of the senders, and a receiver may serve millions of senders. The traditional “one-to-one” homomorphic encryption schemes are inefficient in such “many-to-one” scenarios. In this paper, we combine the homomorphic encryption concept with the cryptography form of “multi-party encryption, one-party decryption” to propose the “many-to-one” homomorphic encryption scheme. Firstly, the model of “many-to-one” homomorphic encryption scheme is built. Secondly, a “many-to-one” homomorphic encryption scheme is constructed based on the “somewhat” scheme, following by which, proving the correctness, homomorphism and security of our proposed scheme. Furthermore, an application example of our scheme is illustrated, and the complexity analysis of our scheme is presented. The complexity analysis along with a comparative study of our scheme with the existing schemes indicates that our proposed scheme is more efficient than the existing schemes. Finally, based on the construction of our proposed many-to-one scheme, a multi-level “many-to-one” homomorphic encryption scheme is also proposed. Copyright © 2015 John Wiley & Sons, Ltd.