Group ID Authorized -Based Certificateless Encryption with Equality Test

Since certificateless public key cryptosystem can solve the complex certificate management problem in the traditional public key cryptosystem and the key escrow problem in identity-based cryptosystem and the pairing computation is slower than scalar multiplication over the elliptic curve, how to design certificateless signature (CLS) scheme without bilinear pairings is a challenge. In this paper, we first propose a new pairing-free CLS scheme, and then the security proof is presented in the random oracle model (ROM) under the discrete logarithm assumption. The proposed scheme is more efficient than the previous CLS schemes in terms of computation and communication costs and is more suitable for the applications of low-bandwidth environments.

In this paper, we propose a certificateless noninteractive key exchange protocol. No message exchange is required in the protocol, and this feature will facilitate the applications where the communication overhead matters, for example, the communications between the satellites and the earth. The public key certificate is removed as well as the key escrow problem using the certificateless public key cryptosystem. The security of the protocol rests on the bilinear Diffie–Hellman problem, and it could be proved in the random oracle model. Compared with previous protocols, the new protocol reduces the running time by at least 33.0%.

Code-based public key cryptosystems have been found to be an interesting option in the area of Post-Quantum Cryptography. In this work, we present a key encapsulation mechanism (KEM) using a parity check matrix of the Generalized Srivastava code as the public key matrix. Generalized Srivastava codes are privileged with the decoding technique of Alternant codes as they belong to the family of Alternant codes. We exploit the dyadic structure of the parity check matrix to reduce the storage of the public key. Our encapsulation leads to a shorter ciphertext as compared to DAGS proposed by Banegas et al. in Journal of Mathematical Cryptology which also uses Generalized Srivastava code. Our KEM provides IND-CCA security in the random oracle model. Also, our scheme can be shown to achieve post-quantum security in the quantum random oracle model.

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.

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.

In [1], Bellare, Boldyreva, and Micali addressed the security of public-key encryptions (PKEs) in a multi-user setting (called the BBM model in this paper). They showed that although the indistinguishability in the BBM model is induced from that in the conventional model, its reduction is far from tight in general, and this brings a serious key length problem. In this paper, we discuss PKE schemes in which the IND-CCA security in the BBM model can be obtained tightly from the IND-CCA security. We call such PKE schemes IND-CCA secure in the BBM model with invariant security reductions (briefly, SR-invariant IND-CCABBM secure). These schemes never suffer from the underlying key length problem in the BBM model. We present three instances of an SR-invariant IND-CCABBM secure PKE scheme: the first is based on the Fujisaki-Okamoto PKE scheme [7], the second is based on the Bellare-Rogaway PKE scheme [3], and the last is based on the Cramer-Shoup PKE scheme [5].

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.

In this paper, we study the problem of secure integrating public key encryption with keyword search (PEKS) with public key data encryption (PKE). We argue the previous security model is not complete regarding keyword privacy and the previous constructions are secure only in the random oracle model. We solve these problems by first defining a new security model, then give a generic construction which is secure in the new security model without random oracles. Our construction is based on secure PEKS and tag-KEM/DEM schemes and achieves modular design. We also give some applications and extensions for our construction. For example, instantiate our construction with proper components, we have a concrete scheme without random oracles, whose performance is even competitive to the previous schemes with random oracles.

Efficient public-key encryption with equality test from lattices

Blind signatures allow a signer to issue signatures on messages chosen by the signature recipient. The main property is that the recipient’s message is hidden from the signer. There are many applications, including Chaum’s e-cash system and Privacy Pass, where no special distribution of the signed message is required, and the message can be random. Interestingly, existing notions do not consider this practical use case separately. In this paper, we show that constraining the recipient’s choice over the message distribution spawns a surprising new primitive that improves the well-established state-of-the-art. We formalize this concept by introducing the notion of non-interactive blind signatures ( $$\textsf{NIBS}$$ ). Informally, the signer can create a presignature with a specific recipient in mind, identifiable via a public key. The recipient can use her secret key to finalize it and receive a blind signature on a random message determined by the finalization process. The key idea is that online interaction between the signer and recipient is unnecessary. We show an efficient instantiation of $$\textsf{NIBS}$$ in the random oracle model from signatures on equivalence classes. The exciting part is that, in this case, for the recipient’s public key, we can use preexisting keys for Schnorr, ECDSA signatures, El-Gamal encryption scheme or even the Diffie-Hellman key exchange. Reusing preexisting public keys allows us to distribute anonymous tokens similarly to cryptocurrency airdropping. Additional contributions include tagged non-interactive blind signatures ( $$\textsf{TNIBS}$$ ) and their efficient instantiation. A generic construction in the random oracle or common reference string model based on verifiable random functions, standard signatures, and non-interactive proof systems.

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.

Identity-based encryption with equality test (IBE-ET) allows the detection of whether two different ciphertexts encrypt the same plaintext without decryption within the conventional identity-based encryption (IBE) model. This property ensures the confidentiality of communication and reduces the storage overhead of ciphertexts in cryptosystems. However, IBE-ET schemes based on traditional assumptions, such as discrete logarithm and integer factoring, are vulnerable to quantum algorithm attacks, highlighting the importance of designing lattice-based IBE-ET schemes. To address this, researchers have proposed several lattice-based IBE-ET schemes that utilize outdated lattice IBE paradigms and are inefficient in terms of parameter size. In this work, we construct a new lattice-based IBE-ET scheme using the most compact lattice IBE framework known to date. Our new proposal significantly improves the parameters compared to previous constructions. Furthermore, we provide a security reduction in the random oracle model, along with corresponding parameter selection and the comparison between our scheme and known constructions. The results imply that our scheme is efficient.

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.

Certificateless cryptography eliminates the key escrow problem inherent in identity based cryptosystem. Certificatateless systems are preferred in public cloud to offer security because it solves two different problems simultaneously, namely, the key escrow problem and the cumbersome certificate management. A stateful public key encryption scheme is a cryptographic primitive, in which the sender maintains state information to perform encryption. The encryption algorithm takes the intended message, receiver’s public key and the current state information to produce the ciphertext, and possibly updates the state information. Decryption is straightforward and depends only on the ciphertext and secret key of the receiver. In this paper, we propose the first stateful certificateless public key encryption scheme and prove the security of the scheme in the random oracle model. This scheme finds very interesting application for sharing data in an encrypted cloud storage system.

Code-based public key encryption (PKE) is a popular choice to achieve post-quantum security, partly due to its capability to achieve fast encryption/decryption. However, code-based PKE has larger ciphertext and public key sizes in comparison to conventional PKE schemes (e.g., those based on RSA). In 2018, Lau and Tan proposed a new rank metric code-based PKE scheme, which has smaller public key and ciphertext sizes compared to other code-based PKE schemes. They also proved that their scheme achieves IND-CPA security, assuming the intractability of the decisional rank syndrome decoding problem. It is known that IND-CCA2 security is the strongest and most popular security assurance for PKE schemes. Therefore, in this paper, we obtain a new code-based PKE scheme from Lau and Tan’s scheme, in order to inherit the underlying small public key and ciphertext sizes. However, our new scheme is shown to achieve IND-CCA2 security, instead of the weaker IND-CPA security. Specifically, the respective public key size and ciphertext size in our new scheme are 15.06 KB and 1.37 KB under 141-bit security level, and 16.76 KB and 1.76 KB under 154-bit security level. We then present a use case for the proposed scheme, that is for secure cloud storage.