With the rapid proliferation of the Internet of Things (IoT), the security of IoT devices has become an increasingly critical concern, particularly in the context of lightweight cryptographic algorithms designed for resource-constrained environments. Lightweight cryptography is indispensable for ensuring the confidentiality and integrity of communications across IoT networks. This paper presents a thorough security evaluation of the Sycon algorithm, focusing on its susceptibility to a range of cryptographic attacks. We begin by introducing Meet-in-the-Middle (MitM) preimage and collision attacks on 3-round and 4-round Sycon-Hash. These attacks are the first published analysis results on reduced-round Sycon-Hash. By employing an SMT-based modeling approach in conjunction with the STP solver, we successfully construct and validate MitM attack paths, thereby providing novel insights into the resilience of Sycon against such threats. In addition, we propose and implement a committing attack on the 2-round Sycon-AEAD-64 using the CMT-3 framework, which uncovers potential vulnerabilities within its authenticated encryption mechanism. Our analysis not only advances the understanding of Sycon’s cryptographic robustness but also offers valuable methodologies for the future assessment of lightweight cryptographic solutions in resource-constrained contexts.

The key collision attack was proposed as an open problem in key-committing security in Authenticated Encryption (AE) schemes like AES-GCM and ChaCha20Poly1305. In ASIACRYPT 2024, Taiyama et al. introduce a novel type of key collision—target-plaintext key collision (TPKC) for AES. Depending on whether the plaintext is fixed, TPKC can be divided into fixed-TPKC and free-TPKC, which can be directly converted into collision attacks and semi-free-start collision attacks on the Davies-Meyer (DM) hashing mode. In this paper, we propose a new rebound attack framework leveraging a time-memory tradeoff strategy, enabling practical key collision attacks with optimized complexity. We also present an improved automatic method for findingrebound-friendlydifferential characteristics by controlling the probabilities in the inbound and outbound phases, allowing the identified characteristics to be directly used inrebound-basedkey collision attacks. Our analysis reveals that the 2-round AES-128 fixed-TPKC attack proposed by Taiyama et al. is, in fact, a free-TPKC attack. This distinction is significant, as fixed-TPKC attacks are substantially more difficult than their free-TPKC counterparts. By integrating our improved automatic method with a new rebound attack framework, we successfully identify a new differential characteristic for the 2-round AES-128 fixed-TPKC attack and develope the first practical fixed-TPKC attack against 2-round AES-128. Additionally, we present practical fixed-TPKC attacks against 5-round AES-192 and 3-round Kiasu-BC, along with a practical free-TPKC attack against 6-round Kiasu-BC. Furthermore, we reduce time complexities for free-TPKC and fixed-TPKC attacks on other AES variants.

The advent of 6G communications technology will bring about a transition from the “Internet of Everything” to the “Intelligent Connection of Everything”. 6G-enabled vehicular ad hoc networks (VANETs) will enjoy lower latency, higher speed, and greater capacity network services. Nevertheless, achieving secure data sharing will be an even tougher challenge. Given this, we propose an attribute-based data sharing scheme with blockchain for 6G-enabled VANETs. First, we propose an efficient multi-tree-based user revocation mechanism. With the Chinese remainder theorem, our mechanism supports user batch revocation and batch joining. Second, we achieve distributed data storage by utilizing the blockchain and smart contracts. To solve the problem of insufficient storage capacity on the blockchain, we adopt a combination of on-chain and off-chain storage. Third, to reduce the computation burden on users, our proposal supports online/offline encryption and verifiable outsourced decryption. Meanwhile, our mechanism supports policy hiding, data revocation, and cross-domain data sharing. The proposed scheme is proven to satisfy the indistinguishability under chosen plaintext attack (IND-CPA) in the standard model. Theoretical analysis shows that our mechanism outperforms existing schemes in functionality and security. Simulation experiments show that our proposal is efficient and suitable for 6G-enabled VANETs.

Vehicular ad hoc network (VANET), as one of the bases of intelligent transport systems, plays an essential role in improving road traffic safety. Nevertheless, in such a complicated, distributed, and highly mobile network structure, how to achieve secure data sharing is a great challenge. The ciphertext-policy attribute-based encryption (CP-ABE) is a potential method to realize one-to-many data sharing for VANET. However, the key abuse problems of users and attribute authorities (AAs) incur many security concerns for VANET. Both issues are extremely important because the attribute keys directly affect users’ access to shared data. To solve the above issues, we propose an accountable attribute-based data-sharing scheme with the blockchain technology (AT-DS-VAHN, in short). For AAs key abuse, we use the consortium blockchain maintained by AAs to achieve distributed key storage and distribution. The attribute keys generated by each AA and its key distribution records are recorded on the blockchain in the form of transactions. Based on the traceability of blockchain, the key abuse behavior of AAs can be caught and prosecuted. For user key abuse, we achieve white-box traceability and efficient user revocation. Based on the principle of traceable-then-revocable, malicious users can be tracked and then revoked directly from the system without complex operations. Besides, to reduce the computation burden on users, our proposal supports online/offline encryption and verifiable outsourced decryption. Security and efficiency analyses show that our proposal is secure and efficient, with high practicability and reliability for VANET.

Vehicular fog computing (VFC), as an extended model of fog computing, combines fog computing with traditional in-vehicle networks to provide real-time response services for users. However, in such a dynamic system architecture, achieving secure and efficient data sharing is an enormous challenge. Ciphertext-policy attribute-based encryption (CP-ABE) is widely regarded as an excellent way of achieving one-to-many data sharing. Nevertheless, several practical challenges hinder its widespread application in VFC, such as inefficient attribute revocation, single-factor access control, and centralized data storage. For this purpose, we design a multifactor combined data sharing scheme for VFC with CP-ABE and blockchain (MC-DS-VFC, in short). We first propose an efficient attribute revocation mechanism that does not require complex key update operations. We then embed time, user attributes, and access interests into data sharing for more fine-grain access control, which enables users with sufficient attributes to efficiently access real-time shared data according to their access interests. Finally, we combine the interplanetary file system (IPFS) and the blockchain maintained by roadside units (RSUs) to achieve distributed collaborative storage. Furthermore, our mechanism also supports user traceability, attribute joining, online/offline encryption, and verifiable outsourced decryption. Our proposal is shown to satisfy the indistinguishability under chosen plaintext attack (IND-CPA) in the standard model. Theoretical analysis and simulation experiments indicate that the MC-DS-VFC scheme is efficient and practical for VFC.