Chosen-Ciphertext Secure Key-Encapsulation Based on Gap Hashed Diffie-Hellman

In this paper, we propose a new “full public verifiability” concept for hybrid public-key encryption schemes. We also present a new hybrid public-key encryption scheme that has this feature, which is based on the decisional bilinear Diffie-Hellman assumption. We have proven that the new hybrid public-key encryption scheme is secure against adaptive chosen ciphertext attack in the standard model. The “full public verifiability” feature means that the new scheme has a shorter ciphertext and reduces the security requirements of the symmetric encryption scheme. Therefore, our new scheme does not need any message authentication code, even when the one-time symmetric encryption scheme is passive attacks secure. Compared with all existing publickey encryption schemes that are secure to the adaptive chosen ciphertext attack, our new scheme has a shorter ciphertext, efficient tight security reduction, and fewer requirements (if the symmetric encryption scheme can resist passive attacks).

Indistinguishability under chosen-ciphertext attack (IND-CCA) is now considered the de facto security notion for public-key encryption. However, this sometimes offers a stronger security guarantee than what is needed. In this study, the authors consider a weaker security notion, termed as indistinguishability under plaintext-checking attacks (IND-PCA), in which the adversary has only access to an oracle indicating whether or not a given ciphertext encrypts a given message. After formalising this notion, the authors design a new public-key encryption scheme satisfying it. The new scheme is a variant of the Cramer–Shoup encryption scheme with shorter ciphertexts. Its security is also based on the plain decisional Diffie–Hellman (DDH) assumption. Additionally, the algebraic properties of the new scheme allow proving plaintext knowledge using Groth–Sahai non-interactive zero-knowledge proofs or smooth projective hash functions. Finally, as a concrete application, the authors show that, for many password-based authenticated key exchange (PAKE) schemes in the Bellare–Pointcheval–Rogaway security model, they can safely replace the underlying IND-CCA encryption schemes with their new IND-PCA one. By doing so, they reduce the overall communication complexity of these protocols and obtain the most efficient PAKE schemes to date based on plain DDH.

The concept of policy-based cryptography is a promising paradigm for trust establishment and authorization in largescale open environments like the Internet and Mobile Networks. It aims at providing a framework for performing cryptographic operations with respect to policies formalized as monotone Boolean expressions written in standard normal forms. A policy involves conjunctions and disjunctions of conditions where each condition is fulfilled by a digital credential representing the signature of a specific credential issuer on a set of statements about a certain entity. Therefore, an entity fulfills a policy if any only if it has been issued a set of credentials fulfilling the combination of conditions specified by the policy.In this work, we focus on policy-based encryption schemes which allow to encrypt a message according to a policy so that only entities fulfilling the policy are able to decrypt the message. More generally, policy-based encryption belongs to an emerging family of encryption schemes sharing the ability to integrate encryption with access control structures. This ability is mainly enabled by bilinear pairings over elliptic curves and allows for several interesting applications in different contexts.A policy-based encryption scheme has to fulfill two primary requirements: on one hand, provable security under well defined attack models. On the other hand, efficiency, especially when dealing with the conjunctions and disjunctions of credential-based conditions.The contributions of our research work are twofold:1. The standard acceptable notion of security for public-key encryption schemes is indistinguishability against chosen ciphertext attacks. Hence, it is natural to require that a policy-based encryption scheme also satisfies this strong notion of security. However, the definition of this security notion must be adapted to the policy-based setting. Our first contribution is the definition of policy-oriented security model for policy-based encryption schemes as well as the development of an efficient policy-based encryption scheme that is provably secure under our security model in the random oracle model.2. Policy-based encryption schemes may suffer from the key-escrow property i.e. in addition to the legitimate holder of the credentials fulfilling the encryption policy, any collusion of credential issuers who are able to issue a set of credentials fulfilling the policy can decrypt the message. Our second contribution is to address this issue through the notion of policy-based public-key encryption. The latter allows encrypting a message not only with respect to a policy but also according to a public-key so that only an entity fulfilling the policy and having access to the corresponding private-key is able to decrypt the message. We developed a policy-based public-key encryption scheme from bilinear pairings and proved its security under the corresponding security model. Our proposal improves related work in terms of both security and efficiency.

In recent years, as video technologies have been broadly used in TV, communication and multimedia, video security has been gaining in importance. This paper proposes a real-time selective video encryption using context-key control. The new context-key control encryption in this scheme is modified from ElGamal encryption. Using context-key control, our scheme can perform a low exponent operation and secure encryption. We apply our encryption scheme to perform selective encryption on video DCT coefficients. In our performance and security analysis, our scheme is a secure and efficient video encryption scheme, and can be well applied to the video protection.

Specific attack and security enhancement to optical image cryptosystem based on two random masks and interference

Secure distribution of digital goods is now a significantly important issue for protecting publishers' copyrights. In this paper, we study a useful primitive for constructing a secure and efficient digital rights management system (DRM) where a server which encrypts digital content and one which issues the corresponding decryption key works independently, and existing schemes lack this property. We first argue the desired property necessary of an encryption scheme for constructing an efficient DRM, and formally define an encryption scheme as split encryption scheme containing such property. Also, we show that an efficient split encryption scheme can be constructed from any identity-based scheme. However, since currently there is no identity-based encryption scheme which is based on well-known computational assumption and/or provable security without the random oracle, by reasonably tuning the system parameter, we show another construction of split encryption which is secure against chosen ciphertext attacks in the standard model assuming that the decision Diffie-Hellman problem is hard to solve.

A quantum public-key encryption scheme is presented in this paper. In the proposed scheme, ciphertext is described by quantum states and security of this scheme is based on the assumption that NP-complete (NP-C) problems are intractable against quantum (probabilistic) polynomial-time Turing machines (QPTM). One of the main properties of our scheme is that it is immune to off-line attack, in which the adversaries can copy all the ciphertext on channel and analyze them at a later time. We call this type of encryption scheme the computationally secure uncloneable encryption scheme. It is shown that the presented scheme can also be used to encrypt quantum states.

Anonymous certificate-based broadcast encryption with constant decryption cost

Although getting a CPA secure IBE scheme is quite easy, achieving a fully secure IBE scheme against CCA is still a challenging problem nowadays. We get such a IBE scheme. First we propose a fully secure HIBE against CPA based on Waters' IBE [23]. And then, as IBE is a special case of HIBE, we use Boneh's result and technique [6] to construct a fully secure IBE against CCA.

Liskov proposed several weakened versions of the random oracle model, called weakened random oracle models (WROMs), to capture the vulnerability of ideal compression functions, which are expected to have the standard security of hash functions, i.e., collision resistance, second-preimage resistance, and one-wayness properties. The WROMs offer additional oracles to break such properties of the random oracle. In this paper, we investigate whether public-key encryption schemes in the random oracle model essentially require the standard security of hash functions by the WROMs. In particular, we deal with four WROMs associated with the standard security of hash functions; the standard, collision tractable, second-preimage tractable, first-preimage tractable ones (ROM, CT-ROM, SPT-ROM, and FPT-ROM, respectively), done by Numayama et al. for digital signature schemes in the WROMs. We obtain the following results: (1) The OAEP is secure in all the four models. (2) The encryption schemes obtained by the Fujisaki-Okamoto conversion (FO) are secure in the SPT-ROM. However, some encryption schemes with FO are insecure in the FPT-ROM. (3) We consider two artificial variants wFO and dFO of FO for separation of the WROMs in the context of encryption schemes. The encryption schemes with wFO (dFO, respectively) are secure in the CT-ROM (ROM, respectively). However, some encryption schemes obtained by wFO (dFO, respectively) are insecure in the SPT-ROM (CT-ROM, respectively). These results imply that standard encryption schemes such as the OAEP and FO-based one do not always require the standard security of hash functions. Moreover, in order to make our security proofs complete, we construct an efficient sampling algorithm for the binomial distribution with exponentially large parameters, which was left open in Numayama et al.’s paper.

An image encryption scheme based on chaotic systems is proposed in this paper. By combining the spatial-domain encryption of digital images and the traditional stream ciphers technology, the security of the encryption scheme is enhanced effectively. Instead of encrypting an image in a chaotic signal directly, the proposed scheme uses two chaotic systems based on the thought of higher secrecy of multi-system. One of the chaotic systems is used to generate a chaotic sequence. Then this chaotic sequence is transformed into a binary stream by a threshold function. The other chaotic system is used to construct a permutation matrix. Firstly, the pixel values of a plain image are modified randomly using the binary stream as a key stream. Secondly, the modified image is encrypted again by permutation matrix. The security of encryption scheme is analyzed in detail. And the simulation results show that the proposed scheme has a better efficiency than others' and a high security performance

A fast and secure public-key image encryption scheme based on Mordell elliptic curves

This paper proposes a visually secure asymmetric image encryption scheme based on Rivest–Shamir–Adlemen (RSA) algorithm and hyperchaotic map. It combines the advantages of the RSA and chaos-based image encryption algorithms. First, to fully encrypt the image information, the plain image is encrypted into a cipher image by applying the row and column encryption algorithms. Second, the image secret key is converted into a ciphertext by utilizing the RSA algorithm to increase the security, and then the ciphertext is transformed into an image and permuted using the Arnold map to enhance the robustness of the embedded image. We then obtain the key cipher image. Finally, the cipher image and the key cipher image are embedded into a carrier image (CI) to obtain a visually secure image. It simultaneously achieves the image information security and image visually security. To further improve the security, the RSA keys management technique is applied and the initial conditions of the hyperchaotic map are updated in real time based on the plain image. In addition, the encryption scheme is suitable for multi-user image transmission with high security requirements and image transmission without the secure channel for key transmission. The simulation results and performance analysis validate the effectiveness, security and robustness of the proposed scheme.

The Fujisaki-Okamoto (FO) conversion is a generic conversion to enhance a public key encryption scheme with security of one-way against chosen plaintext attacks (OW-CPA) to security of indistinguishable against adaptive chosen ciphertext attacks (IND-CCA) in the random oracle model. Existing works have shown that the FO conversion also can generically upgrade the security of the identity-based encryption (IBE) schemes or certificateless public key encryption (CL-PKE) schemes. However, it is still unknown if the same holds for certificate-based encryption (CBE) schemes. In this paper, we investigate the generic security of the CBE scheme obtained by applying the FO conversion to an arbitrary underlying OW-CBE-CPA secure CBE scheme and confirm that the FO conversion can generically convert any OW-CBE-CPA secure CBE into an IND-CBE-CCA secure CBE. We also note that the straightforward application of the FO conversion only leads to a CBE scheme with a loose reduction. To solve this problem, we propose an enhanced FO conversion which just introduces minor extra computation overhead, but results in considerably more efficient security reduction.

QC-MDPC McEliece attracted significant attention as promising alternative public-key encryption scheme believed to be resistant against quantum computing attacks. Compared to binary Goppa codes, it achieves practical key sizes and was shown to perform well on constrained platforms such as embedded microcontrollers and FPGAs. However, so far none of the published QC-MDPC McEliece/Niederreiter implementations provide indistinguishability under chosen plaintext or chosen ciphertext attacks. Common ways for the McEliece and Niederreiter encryption schemes to achieve IND-CPA/IND-CCA security are surrounding constructions that convert them into secured schemes. In this work we take a slightly different approach presenting 1 an efficient implementation of QC-MDPC Niederreiter for ARM Cortex-M4 microcontrollers and 2 the first implementation of Persichetti's IND-CCA hybrid encryption scheme from PQCrypto'13 instantiated with QC-MDPC Niederreiter for key encapsulation and AES-CBC/AES-CMAC for data encapsulation. Both implementations achieve practical performance for embedded microcontrollers, at 80-bit security hybrid encryption takes 16.5i¾źms, decryption 111i¾źms and key-generation 386.4i¾źms.