Public key encryption with equality test (PKEET) is a cryptographic primitive that enables a tester to determine whether two ciphertexts encrypted with same or different public keys have been generated from the same message without decryption. Previous studies extended PKEET to public key encryption with designated-position fuzzy equality test (PKE-DFET), enabling testers to verify whether plaintexts corresponding to two ciphertexts are equal while ignoring specific bits at designated positions. In this work, we have filled the research gap in the identity-based encryption (IBE) cryptosystems for this primitive. Furthermore, although our authorization method is the all-or-nothing (AoN) type, it overcomes the shortcomings present in the majority of AoN-type authorization schemes. In our scheme, equality tests can only be performed between a ciphertext and a given plaintext. Specifically, even if a tester acquires multiple AoN-type authorizations, it cannot conduct unpermitted equality tests between users. This significantly reduces the risk of user privacy leaks when handling sensitive information in certain scenarios, while still retaining the flexible and simple characteristics of AoN-type authorizations. We use the Chinese national cryptography standard SM9-IBE algorithm to provide the concrete construction of our scheme, enhancing the usability and security of our scheme, while making deployment more convenient. Finally, we prove that our scheme achieves F-OW-ID-CCA security when the adversary has the trapdoor of the challenge ciphertext, and achieves IND-ID-CCA security when the adversary does not have the trapdoor of the challenge ciphertext.

Universal composability (UC) is a primary security flavor for designing oblivious transfer (OT) due to its advantage of arbitrary composition. However, the study of UC-secure OT over lattices is still far behind compared with constructions over prequantum assumptions. Relying on the learning with errors (LWE) assumption, Quach proposes a dual-mode encryption scheme (SCN’20) for deriving a two-round OT whose security is provably UC-secure in the common reference string (CRS) model. Due to its use of a randomized rounding function proposed by Benhamouda et al. (PKC’18), this OT can only be limited to transmitting single-bit messages. Therefore, conducting trivial repetitions of Quach’s OT when transmitting multibit strings would be very costly. In this work, we put forward a modified dual-mode encryption cryptosystem under the decisional LWE assumption, from which we can derive a UC-secure string OT with both full-fledged dual-mode security and better efficiency on transmitting strings. The key technique we adopt is a key reconciliation scheme proposed by Jiang et al. (PKC’20), which is utilized to extend the single-bit symmetric encryption key (produced by the aforementioned rounding function) to a multibit case. Through a comprehensive performance analysis, we demonstrate that our proposal can indeed strike a balance between security and efficiency.

Abstract Recently, Gong et al. put forward a certificateless signcryption (CLSC) scheme suitable for Internet of things. The authors demonstrated that their scheme is confidential, unforgeable and forward secure, and it meets known session-specific temporary information security under the attacks of two Types of adversaries. More recently, Xu et al. constructed a CLSC mechanism suitable for edge computing on the basis of blockchain, and proved that their mechanism satisfies unforgeability and confidentiality. In this article, we first demonstrate Gong et al.’s scheme can be totally broken: every user can calculate the master secret key from the partial private key sent by Key Generation Center. Moreover, we prove that Gong et al.’s scheme is not confidential, unforgeable and forward secure, and it cannot enjoy known session-specific temporary information security, either. Next, we declare that Xu et al.'s mechanism is able to be universally forged by anyone, that is, everyone can forge valid signcryption ciphertexts of a sender on any message without knowing the sender’s secret information. Furthermore, Xu et al.’s mechanism is not CCA2 secure against two Types of adversaries.

Vehicular ad hoc networks (VANETs) can effectively provide vehicle driving safety, high-speed data communication, intelligent traffic management, and vehicle entertainment. However, compared with traditional networks, VANETs are more vulnerable to attacks from adversaries, such as eavesdropping, tampering, tracking users’ privacy, etc. In order to provide security and privacy protection for VANET communication, many conditional privacy protection (CPP) authentication schemes have been reported. In 2021, Cai et al. designed a novel CPP scheme based on ring signcryption suitable for VANETs. They proved that their scheme enjoys confidentiality, unforgeability, anonymity of sender’s identity, and traceability of malicious vehicle users. But we demonstrate their scheme has some defects in construction and security. First, there is a small flaw in the ring signcryption algorithm in the scheme, which makes a legitimate receiver unable to get the original message sent by the sender from the received valid ciphertext. Second, Cai et al.’s scheme cannot provide anonymous protection of an honest sender’s identity. At the same time, it is unable to reveal the identity of a malicious vehicle user. Finally, we present an improved scheme of Cai et al.’s scheme and supply its security proofs in the random oracle model, and analyze its performance. Ours is superior to the original scheme in security and efficiency. It is very suitable for providing security and privacy protection for vehicular users in VANETs.

Public key encryption with equality test (PKEET) is a cryptographic primitive that enables a tester to determine, without decryption, whether two ciphertexts encrypted with different public keys generate from the same message. In previous research, public key encryption with equality test (PKEET) was extended to include identity-based encryption with equality test (IBEET), thereby broadening the application of PKEET. Subsequently, certificateless encryption with equality test (CLEET) was introduced to address the key escrow problem in IBEET. However, existing CLEET schemes suffer from inefficiency and potential information leakage when dealing with multiple ciphertexts due to the need for pairwise equality tests. To address this issue, we propose a concept of certificateless encryption supporting multi-ciphertext equality test with proxy-assisted authorization (CLE-MET-PA). CLE-MET-PA incorporates the functionality of the multi-ciphertext equality test into CLEET, enabling a tester to perform a single equality test on multiple ciphertexts to determine whether the underlying plaintexts are equal, without revealing any additional information. This enhances the security of our scheme while significantly reducing the computational overhead compared to multiple pairwise equality tests, making our scheme more efficient. Additionally, our approach integrates proxy-assisted authorization, allowing users to delegate a proxy to grant authorizations for equality tests on their behalf when offline. Importantly, the proxy token used in our scheme does not include any portion of the user’s private key, providing enhanced protection compared to traditional PKEET schemes in which the user token is often part of the user’s private key. We construct a concrete CLE-MET-PA scheme and prove that it achieves CPA security and attains CCA security through an FO transformation.

. On CRYPTO2021, Nishanth Chandran, Bhavana Kanukurthi, Sai Lakshmi Bha-vana Obattu, and Sruthi Sekar presented a novel secret sharing scheme, called CKO+21 scheme. This scheme makes use of Shamir secret sharing schemes and randomness extractors as its basic components, to generate a multi-layer encapsulation structure. The authors claimed that CKO+21 scheme satisfied “leakage resilience”, that is, the privacy still held under both “not enough revealing” and “appropriate leakage”. More important is that authors presented a bulky proof for the security of CKO+21 scheme. In this paper we only consider the simple case of ( n, t ) threshold secret sharing. We find following 5 facts about CKO+21 scheme, which are the basic reasons we negate the security proof of CKO+21 scheme. (1) In the expression of share of CKO+21 scheme, some bottom Shamir share is simply included, rather than encapsulated. (2) The leakage of the share is not a random leakage, but rather related to the inquiry of the attacker, that is, a chosen leakage. (3) The permitted leakage length of each share is proportional to the share length. (4) The bottom Shamir scheme has such special feature: when the length of the share l ∗ is kept unchanged, it can make the number of shares n , the threshold value t , and the difference value n − t + 1 any large, as long as t < n . (5) There is no additional assumption for the bottom Shamir scheme, especially no clear negating its “leakage recoverability” and “contaminated leakage irrecoverability”, defined in this paper. In

Vehicular ad hoc networks (VANETs) create an vital platform for communication between vehicles, which can realize accident warning, auxiliary driving, road traffic information query, passenger communication and other applications. While providing convenient services for people, VANETs also bring some security risks. Security and privacy are the primary issues in the research of VANETs. Signcryption is an ideal way to transfer messages in a logical step in a secure and authenticated way. We design a Certificateless signcryption (CLSC) scheme to provide confidentiality, authentication, integrity, non-repudiation and user privacy preservation for the information transmitted between vehicle communication units. We demonstrate the confidentiality and unforgeability of the proposed scheme in the random oracle model. Moreover, compared with the existing CLSC schemes, ours realizes the perfect combination of efficiency, security and privacy, and it is particularly well adapted to the secure communication of vehicle networks.

With the rapid popularization of Internet of Things (IoT) in various fields, the security of the IoT has been widely concerned. Security authentication technology is the foundation of the security of the IoT. Certificateless signature, which removes the intricate certificate management and key escrow, is one of the practical methods to provide data integrity and identity authentication for the IoT. At present, many certificateless signature schemes have been put forward, but few of them are secure and suitable for the IoT. Recently, Jia et al. designed a certificateless signature scheme for the IoT deployment. The authors demonstrated that their scheme can withstand attacks of two types of super adversaries. However, we prove that Jia et al.'s scheme cannot resist attacks from a normal Type I adversary, not to mention a super Type I adversary. Then, we put forward a certificateless signature scheme on the basis of elliptic curve cryptosystem, and prove the scheme cannot be forged by two types of super adversaries. Our certificateless signature scheme performs better than the existing certificateless signature schemes, and it is the best combination of high security and efficiency so far and is more appropriate for the resource-constrained IoT environment.

Attribute-based encryption has broad application prospects. GVW'13 attribute-based encryption (ABE) scheme is one of the major candidates for ABE. The scheme has exquisite structure and proven security, and the crucial component is two-to-one recoding (TOR) algorithm. However, it has security risks in practical applications. In this paper, we describe this security risk, the collusion trap against GVW'13 ABE. In such a scenario: Alice and Bob collude to share decryption ability. In other words, when anyone can decrypt the ciphertext, he will tell the other one the corresponding plaintext. If Bob decrypts Alice's fake ciphertext and returns “corresponding plaintext” to Alice, Alice can attempt to gradually calculate Bob's secret key. We use the method of chosen-ciphertext attack of Jaulmes and Joux against NTRU to construct our attack. We show that whether for naked encryption or for calibrated encryption, Alice can obtain the equivalent secret key of Bob in polynomial time, although the size of the attack for calibrated encryption is much larger.

Wireless sensor network (WSN) can be widely used in the field of health care since it has many advantages, such as low cost, high efficiency, low latency, and so on. In healthcare wireless sensor network (HWSN), the patients' health information needs to be transmitted to health professionals in real time through the Internet, so it is vital to ensure the integrity and privacy of medical information. Aggregate signature (AS) cannot only provide message integrity and authentication for multiple users but also drastically improve the efficiency of signature transmission and verification. Certificateless public key cryptography (CLPKC) is superior to traditional public key infrastructure and identity-based cryptography. We combine the advantages of CLPKC and AS and construct a certificateless aggregate signature (CLAS) scheme without using pairings. Our CLAS scheme realizes the protection of the privacy and integrity of healthcare information for multiple patients in HWSN for the first time. Under the assumption of elliptic curve discrete logarithm, the proposed CLAS scheme is existentially unforgettable against two types of adversaries. In addition, the scheme has better performance than other CLAS schemes as for the security, communication overhead, and computational costs. So it is more suitable for green HWSN.

Certificateless public key cryptosystem (CLPKC) is a desirable cryptographic system because it refrains from both certificate management and key escrow. In CLPKC, how to revoke a misbehaving or compromised user is an important issue. However, the existing revocable methods in CLPKC are impractical because of the use of either an expensive mediator or a burdensome key generation center (KGC). In order to overcome this drawback, we introduce outsourcing computation into CLPKC for the first time and design an outsourced revocable certificateless signature (ORCLS) scheme, and the revocation functionality is outsourced to a cloud server. The amount of computation needed to revoke a user is borne by the cloud server, which greatly reduces the burden on the KGC. In the rest of this paper, we formalize the definition and the security model for an ORCLS scheme and construct the first ORCLS scheme without bilinear pairings. It is proved that our scheme is existential unforgeable against adaptive chosen-message attacks from Type I, Type II, Type III, and Type IV adversaries under the elliptic curve discrete logarithm problem. Moreover, our scheme needs less computational cost and communication overhead and thus is more efficient than the other proposed revocable certificateless signature schemes so far.