A General Two-Server Framework for Ciphertext-Checkable Encryption Against Offline Message Recovery Attack

Cloud computing enables users to remove the necessity of the need of local hardware architecture, which removes the burden of the users from high computation costs. Therefore, it has attracted much attention and research has been conducted heavily on it. To protect users’ privacy, data is usually encrypted prior to being sent to the cloud server. As the resulting system is unusable, since the cloud can no longer search throughout the data, new cryptographic primitive such as public-key encryption with equality test (PKEET) has been introduced. In PKEET, users can test whether the underlying messages of two ciphertexts encrypted under different public keys are equal or not without the need to decrypt those ciphertexts. This is a very useful tool, especially for the cloud database, since PKEET mainly focuses on the equality test between two ciphertexts. However, in practice, the cloud server may need to verify the equivalence among more than two ciphertexts. This leads to disclosing unnecessary information of users and redundant computation cost will also occur when using traditional PKEET schemes. How to make this more efficient and practical remains an interesting research problem. In this article, to solve the aforementioned problems by providing a novel concept of public-key encryption with multi-ciphertext equality test (PKE-MET). In PKE-MET, each ciphertext can designate a number <inline-formula><tex-math notation="LaTeX">$s$</tex-math></inline-formula> such that the cloud server can only perform equality test on this ciphertext with other <inline-formula><tex-math notation="LaTeX">$s-1$</tex-math></inline-formula> ciphertexts, where all their designated numbers are <inline-formula><tex-math notation="LaTeX">$s$</tex-math></inline-formula> . For PKE-MET, besides traditional OW-CPA and IND-CPA security, we specially define Number security. We instantiate PKE-MET to a concrete scheme and give its security proof. Furthermore, to enable the primitive to be more practical in applications, we extend it to the concept of PKE with flexible MET (PKE-FMET). In PKE-FMET, the cloud server can perform equality test on any number of ciphertexts as long as the maximum number of their designated numbers is less than or equal to the number of ciphertexts. We construct a PKE-FMET scheme based on our PKE-MET construction and prove its security under the defined security models. Besides, the performance analysis mainly of efficiency and security between our constructions and existing equality test schemes in cloud computing show that our proposed schemes are more efficient and secure in the multi-ciphertext scenario.

Public key encryption with equality test (PKEET) has been widely adopted in applications such as private health record management, secure outsourced data processing, and email filtering, owing to its ability to test equality on ciphertexts encrypted under different public keys. However, existing PKEET schemes often fall short in specialized settings, such as case-insensitive matching. Moreover, their security guarantees remain inadequate. In particular, many existing schemes are vulnerable to offline message recovery attacks (OMRA), which present a significant security challenge to PKEET. Furthermore, the existing IND-CCA security model is incomplete, as it fails to model all potential attacks that an adversary could exploit to execute the OMRA. To address these challenges, we propose a new variant of PKEET, termed public key encryption with case-insensitive fuzzy equality test (PKE-CIFET). To analyze security, we propose a unified security model that more closely aligns with IND-CCA security than previous works. This model includes more comprehensive oracles and considers adversaries launching the OMRA through multi-hop testing. Based on this model, we provide a comprehensive and rigorous security proof. Furthermore, experimental results demonstrate that the proposed PKE-CIFET scheme is efficient in terms of computational cost.

We investigate public key encryption that allows the originator of a ciphertext to retrieve a forgotten plaintext from the ciphertext. This type of public key encryption with contrasts more widely analyzed public key encryption with forward secrecy. We advocate that together they form the two sides of a whole coin, whereby offering complementary roles in data security, especially in cloud computing, 3G/4G communications and other emerging computing and communication platforms. We formalize the notion of public key encryption with backward recovery, and present two construction methods together with formal analyses of their security. The first method embodies a generic public key encryption scheme with backward recovery using the encrypt then sign paradigm, whereas the second method provides a more efficient scheme that is built on Hofheinz and Kiltz's public key encryption in conjunction with target collision resistant hashing. Security of the first method is proved in a two-user setting, whereas the second is in a more general multi-user setting.

We introduce the notion of public key encryption with secure key leasing (PKE-SKL). Our notion supports the leasing of decryption keys so that a leased key achieves the decryption functionality but comes with the guarantee that if the quantum decryption key returned by a user passes a validity test, then the user has lost the ability to decrypt. Our notion is similar in spirit to the notion of secure software leasing (SSL) introduced by Ananth and La Placa (Eurocrypt 2021) but captures significantly more general adversarial strategies. (In more detail, our adversary is not restricted to use an honest evaluation algorithm to run pirated software.) Our results can be summarized as follows: Prior to our work, the notion of single decryptor encryption (SDE) has been studied in the context of PKE (Georgiou and Zhandry, Eprint 2020) and FE (Kitigawa and Nishimaki, Asiacrypt 2022) but all their constructions rely on strong assumptions including indistinguishability obfuscation. In contrast, our constructions do not require any additional assumptions, showing that PKE/IBE/ABE/FE can be upgraded to support secure key leasing for free.

Efficient public-key encryption with equality test from lattices

Attribute-based encryption is a popular cryptographic technology to protect the privacy of clients' data in cloud computing. In order to make the scheme have the functionality of comparing ciphertext, Zhu et al. combined concepts of key-policy attributed-based encryption with public key encryption with equality test and proposed key-policy attributed-based encryption with equality test. They defined its security model and put forward a scheme from bilinear pairing. In this paper, we first use two methods to show that their scheme is not secure for one-way under chosen ciphertext attack. Next, we show that the scheme is not secure for a test under chosen ciphertext attack defined in their paper yet. Finally, we point out the definition of a test under chosen ciphertext attack is very strong, which causes no scheme to satisfy the model.

The emergence of 5G networks will allow cloud computing providers to offer more convenient services. However, security and privacy issues of cloud services in 5G networks represent huge challenges. Recently, to improve security and privacy, a novel primitive was proposed by Ma et al. in TIFS 2015, called public key encryption with equality test supporting flexible authorization (PKEET-FA). However, the PKEET scheme lacks verification for equality test results to check whether the cloud performed honestly. In this paper, we expand the study of PKEET-FA and propose a verifiable PKEET (V-PKEET) scheme, which, to the best of our knowledge, is the first work that achieves verification in PKEET. Moreover, V-PKEET has been designed for three types of authorization to dynamically protect the privacy of data owners. Therefore, it further strengthens security and privacy in 5G networks.

In this paper, we present a new public key encryption scheme with equality test (PKEwET). Compared to other PKEwET schemes, we find that its security can be improved since the proposed scheme is based on non-Abelian factorization problems. To our knowledge, it is the first scheme regarding equality test that can resist quantum algorithm attacks. We show that our scheme is one-way against chosen-ciphertext attacks in the case that the computational Diffie-Hellman problem is hard for a Type-I adversary. It is indistinguishable against chosen-ciphertext attacks in the case that the Decisional Diffie-Hellman problem is hard in the random oracle model for a Type-II adversary. To conclude the paper, we demonstrate that our scheme is more efficient.

Ciphertext equivalence test can compare data encrypted by different public keys. In electronic medical applications, only users within the patient group are expected to be able to test the equivalence of ciphertext. Based on certificateless public key cryptosystem and group user authorization mechanism, this paper designs a ciphertext equivalence test encryption scheme with group user authorization. Firstly, the framework of group id authorized-based certificateless encryption with equality test (GACLEET) is proposed. Secondly, this paper proposes a specific GACLEET scheme and analyzes the correctness of the scheme. Finally, based on the random oracle model, it is proved that the scheme has OW-CCA and IND-CCA security. The scheme can not only solve the key escrow problem of group id-based encryption with equality test scheme, but also realize group granularity authorization and equivalent testing functions.

In recent years, a lot of research has been carried out on the privacy protection of heterogeneous Internet of Vehicles (IoV). However, cloud servers in the IoV store a large amount of ciphertext data, so how to efficiently search ciphertext data encrypted by different public keys is also an urgent problem to be solved. This paper proposes a heterogeneous signcryption scheme with equality test from CLC to PKI (CPHS-ET) for the complex IoV environment. It allows roadside units to encrypt sensitive data in the CLC cryptosystem, which is then sent to the vehicle in the PKI cryptosystem and uploaded to the cloud server at the same time. Further, the cloud server can perform equality tests on different ciphertexts. In the random oracle model, our designed CPHS-ET is proved to satisfy confidentiality, unforgeability, one-way. Performance analysis shows that our CPHS-ET scheme is more efficient.

Public-key encryption is extensively used to provide digital data confidentiality and deliver the security features, such as nonrepudiation (digital signature) and secure key exchange. Conventional public-key schemes are based on mathematical problems with inflexible constraints, and the security of digital contents relies on computational complexity. In the era of emerging technologies, most public-key image encryption schemes are susceptible to various threats. We propose a novel public-key encryption in this article with near-ring criteria and provide confidentiality to private data with the microstates of the Einstein crystal model. The virtual oscillator generated by microstates of initial oscillators for the common secrets with the public-key scheme produces unique states to encrypt digital data. The privacy-preserved structure, that mimics the data stream of digital content with the behavior of the improved Einstein crystal model, describes a system in terms of microstates to generate diffusion in the plain data with unique states of a virtual oscillator. The performance and digital forensic evaluations, such as randomness, histogram uniformity, pixels’ correlation, pixels’ similarity, visual strength, pixels’ incongruity, key sensitivity, linear and differential attacks, noise, and occlusion attacks analyses, certify the resistivity of the proposed algorithm against potential threats and provide superior capacity in comparison to existing methodologies to hostile certain attacks.

Simulation-sound trap-door commitment (SSTC) schemes are an essential ingredient for making non-malleable and universally composable protocols. In previous work, the SSTC schemes and their variants are all constructed in the same framework based on digital signatures. In this paper, we provide new constructions of SSTC schemes using encryption, which is somewhat surprising, because of the tight relationship between SSTC and digital signature schemes. Although our constructions require a few rounds of interactions between a committer and a receiver and the notion of public-key encryption could be stronger than digital signature, the resulting instantiations are much more efficient than these based on digital signature schemes. In particular, we present an efficient SSTC scheme under the CDH assumption in the bilinear groups, with a tight security reduction and short public key parameters, and the first efficient SSTC scheme under the factoring assumption. Our interactive SSTC schemes inherit properties of the non-interactive version of SSTC schemes to construct non-malleable and universally composable protocols.KeywordsSignature SchemeCommitment SchemeDigital Signature SchemeChallenge CiphertextDecryption OracleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

RETRACTED: A public key size homomorphic encryption scheme based on the sum of sparse subsets and integers

Public key encryption schemes developed based on learning with error problem became popular for homomorphic encryption, and are proved as secured schemes based on the worst-case hardness of short vector problems. Homomorphic encryption allows computations over the cipher text without decryption. Implementation of the scheme is not considered to be practical because of its larger public keys and larger cipher texts. Large public key and cipher texts require huge space in the cloud storages. However, there are some approaches proposed to shorten the cipher texts and public keys of LWE-based homomorphic encryption scheme. The objective of the paper is to introduce an idea to shorten the public keys and cipher texts in the storage. Also, support homomorphic addition operation on reduced cipher texts. The aim of the paper is not only to give the practical implementation of standard LWE-based homomorphic encryption operation (Addition) on the reduced cipher texts and also the performance of the proposed scheme.

Here we describe a public-key digital encryption scheme that does not require secret-key distribution — one of the Achilles’ heels of secret-key cryptographic systems because once the secret encrypting key becomes known, transmissions are no longer secret. In public-key encryption, every potential recipient of secret messages publishes his encrypting key (hence the name public key). But knowledge of the encrypting key is of no practical help in decryption. The public-key is the key to a “trap door” through which messages can vanish, not to be recovered — except through a different route to which only the legitimate receiver holds the required key, the decrypting key. (Trap door means easily in, but out only with the proper tools.) It is as if everyone had a (chained!) box in front of his house into which secret messages could be stuffed and to which only the owner had the proper opening key.KeywordsSecret MessageOriginal MessageEncrypt MessageProper ToolTrap DoorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.