Tight chosen ciphertext attack (CCA)-secure hybrid encryption scheme with full public verifiability

We present a new Authenticated Encryption (AE) scheme based on finite automata using the method Encrypt-then-MAC. The scheme is constructed from two cryptographic primitives, a symmetric encryption scheme based on finite automata known as FASKC and a Message Authentication Code (MAC) constructed from a finite automaton. The paper shows how the scheme works and how to construct a MAC from a finite automaton using a boolean function with good cryptographic properties. Due to the construction method and the assumption that the symmetric encryption scheme is secure under Chosen Plaintext Attack (CPA), it is shown that the MAC is unforgeable under Chosen Message Attack (UF-CMA) making the scheme secure under Chosen Ciphertext Attack (CCA).

We propose a practical key encapsulation mechanism with a simple and intuitive design concept. Security against chosen-ciphertext attacks can be proved in the standard model under a new assumption, the Gap Hashed Diffie-Hellman (GHDH) assumption. The security reduction is tight and simple. Secure key encapsulation, combined with an appropriately secure symmetric encryption scheme, yields a hybrid public-key encryption scheme which is secure against chosen-ciphertext attacks. The implied encryption scheme is very efficient: compared to the previously most efficient scheme by Kurosawa and Desmedt [Crypto 2004] it has 128 bits shorter ciphertexts, between 25-50% shorter public/secret keys, and it is slightly more efficient in terms of encryption/decryption speed. Furthermore, our scheme enjoys (the option of) public verifiability of the ciphertexts and it inherits all practical advantages of secure hybrid encryption.

This work presents the employment of graph theory for cryptographic applications. A Cartesian product graph (CPG) is used to propose new symmetric encryption schemes. On proposed encryption schemes, the ciphertexts of the plaintexts are sent to the receiver entity as the CPGs. The CPG is created based on two graphs G and H that are generated depending on the random choices of the plaintext bits. These bits are used as vertices of graphs G and H. The purpose of using the CPG is to increase the security level of the symmetric encryption schemes in comparison with other encryption schemes. Two study cases of the proposed symmetric Cartesian product graphic encryption (SCPGE) schemes are presented as new experimental results. The security issues of the proposed SCPGE schemes are determined. The SCPGE schemes consider as new insights for more secure communications.

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.

We introduce the notion of complementary-witness-soundness for a witness indistinguishable proof system. We then present a new general framework for public key encryption schemes, denoted as CWSWI-type encryption, based on a complementary-witness-sound witness indistinguishable (CWSWI) proof system. The construction of a CWSWI-type encryption scheme is relatively straight forward, while the security thereof against adaptive chosen cipher text attack (denoted CCA2) can be rigorously proven. Many existing CCA2 public key encryption schemes can be interpreted as being of CWSWI-type, including the schemes of Lindell, Cramer-Shoup and Peikert-Waters. Thus, our CWSWI approach provides a novel means for designing and analyzing CCA2 secure public key encryption schemes.

A new public key encryption scheme is proposed and analyzed, which is based on a vector space over some finite field with respect to a class of matrix semigroup action. The scheme is proved secure against adaptive chosen ciphertext attack under EDDH assumption. Since EDDH assumption is weaker than DDH assumption for generic bilinear groups, the new encryption scheme is a good replacement for Cramer-Shoup encryption scheme when bilinear group is adopted as construction platform.

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.

With the development of modern communication technology, an increasing number of people are choosing to communicate end-to-end over the network. However, the risk of information leakage and data tampering has also increased, and the issue of information confidentiality has become an increasing concern. Among the existing encryption algorithms, symmetric encryption algorithms cannot securely manage the key and share the key between communication parties; ECC and other public key encryption algorithms have problems such as slow encryption and decryption speed, low encryption strength, etc. In addition, key management is still not guaranteed to be very secure; conventional hybrid encryption algorithms need to manage two different types of keys, and key management may be very complicated and prone to key leakage or theft. Based on the problems of the above algorithms, this paper proposes RSA-Co-CP-ABE Architecture, which uses socket communication, encrypts the RSA public key passed from Client to Server with CP-ABE, encrypts the confidential message with the public key passed from Client at Server, and finally sends the encrypted message to Client. This scheme has higher flexibility than the traditional symmetric encryption and public key encryption schemes, and by using CP-ABE encryption, it can realize attribute-based access control. And RSA encryption can make the scheme make a better balance between encryption and decryption efficiency and encryption strength. In addition, because the communication is transmitted in full cipher text during the communication, the scheme can effectively resist tampering or stealing by man-in-the-middle attacks.

A leakage-resilient public-key encryption (PKE) scheme provides security even if an adversary obtains some information on the secret key. In recent years, much attention has been focused on designing provably secure PKE in the presence of key-leakage and almost all the constructions rely on an important building block namely hash proof system (HPS). However, in the setting of adaptive chosen-ciphertext attacks (CCA2), there are not many HPS-based leakage-resilient PKE schemes available. Moreover, most of them have an unsatisfactory leakage rate. In this study, the authors propose a new method of constructing leakage-resilient CCA2-secure PKE scheme from any tag-based strongly universal 2 HPS. The striking advantage of the authors scheme is the leakage rate, which is the best one among all known HPS-based indistinguishability key leakage CCA2-secure constructions. In particular, they present an instantiation under the n -linear assumption. In the cases of n = 1 (resp. n = 2), they actually obtain a decisional Diffie-Hellman (DDH)-based [resp. decisional linear (DLIN)-based] PKE scheme, where the leakage rate can be made to 1/4 (resp. 1/6). The authors DDH-based scheme achieves the best leakage rate among all known DDH-based (Cramer-Shoup-type) schemes. Their DLIN-based scheme is the first one that can achieve leakage of L /6 bits without pairing, where L is the length of the secret key.

Quite recently, Tseng and Tsai proposed a revocable identity (ID)-based encryption (RIBE) with a public channel, in which the private key generator (PKG) can efficiently revoke misbehaving/compromised users by using a public channel. Considering the problem where a sender would like to encrypt an identical message for n receivers, the sender must re-encrypt the message n times using Tseng and Tsai’s RIBE scheme. In such a case, n expensive pairing operations are required for the re-encrypting procedure. In this paper, for reducing the pairing operations, we extend Tseng and Tsai’s RIBE to propose an efficient revocable multi-receiver ID-based encryption (RMIBE) scheme. Our scheme only needs one pairing operation to encrypt an identical message for n receivers while remaining the merit of user revocability in Tseng and Tsai’s RIBE scheme. We demonstrate that the RMIBE scheme is semantically secure against adaptive chosen ciphertext attacks (CCA) in the random oracle model.DOI: http://dx.doi.org/10.5755/j01.itc.42.2.2244

Non-malleability is an important and intensively studied security notion for many cryptographic primitives. In the context of public key encryption, this notion means it is infeasible for an adversary to transform an encryption of some message m into one of a related message m' under the given public key. Although it has provided a strong security property for many applications, it still does not suffice for some scenarios like the system where the users could issue keys on-the-fly. In such settings, the adversary may have the power to transform the given public key and the ciphertext. To withstand such attacks, Fischlin introduced a stronger notion, known as complete non-malleability, which requires that the non-malleability property be preserved even for the adversaries attempting to produce a ciphertext of some related message under the transformed public key. To date, many schemes satisfying this stronger security have been proposed, but they are either inefficient or proved secure in the random oracle model. In this work, we put forward a new encryption scheme in the common reference string model. Based on the standard DBDH assumption, the proposed scheme is proved completely non-malleable secure against adaptive chosen ciphertext attacks in the standard model. In our scheme, the well-formed public keys and ciphertexts could be publicly recognized without drawing support from unwieldy techniques like non-interactive zero knowledge proofs or one-time signatures, thus achieving a better performance.

The first practical public-key encryption scheme and digital signature scheme were proposed in 1978 by Rivest et al. [165]. While the original public-key encryption scheme would not be considered secure by modern standards, the RSARSA transform has been the basis of dozens of public-key encryption schemes and digital signature schemes. These schemes have proven very successful and have been very widely deployed in industry. However, despite being widely used in the design of public-key encryption and digital signature schemes, the RSARSA transform has not been widely used in the construction of signcryption schemes.

Public-key encryption scheme with optimal continuous leakage resilience

Leakage of private information including private key has become a threat to the security of computing systems. It has become a common security requirement that a cryptographic scheme should withstand various leakage attacks, including continuous leakage attacks. In order to obtain an Identity-based encryption (IBE) scheme which can keep its original security in the continuous leakage setting, we propose a new construction method of IBE scheme with Chosen-ciphertext attacks (CCA) security, which can tolerate continuous leakage attacks on many private keys of each identity, and whose security is proved based on the hardness of the classical Decisional bilinear Diffie-Hellman (DBDH) assumption in the standard model. The leakage parameter is independent of the plaintext space and has the constant size.