The development of smart contracts remains in its early stages, with significant differences in underlying programming languages and application platforms resulting in a lack of standardization. This lack of standardization increases the susceptibility to vulnerabilities and associated financial losses. To address security vulnerabilities in smart contracts on the Ethereum blockchain platform, this paper proposes a security audit method based on formal verification. The method integrates an input module, static analysis module, formal verification module, analog execution module, and report and recommendation module, which can accurately discover the security vulnerabilities and logical flaws of smart contracts through formal verification and other analysis techniques, thus realizing correctness detection. During the experiment, the method detects 8 types of common vulnerabilities in 148 smart contracts and marks 21 smart contracts with vulnerabilities. After manual review and analysis, it is found that 17 of these 21 marked smart contracts do have security vulnerabilities. The experimental results show that the proposed method can accurately detect security vulnerabilities and logic flaws in smart contracts through formal verification and other analysis techniques before smart contracts are deployed, thus significantly improving the security of smart contracts and reducing the economic losses that may be caused by code defects.

Ratchet protocols are a class of secure protocols based on ratcheting encryption mechanisms, widely employed in instant messaging. Against the backdrop of frequent incidents of communication privacy breaches, ratchet protocols have become a vital technology for ensuring secure end-to-end communication. This paper presents a formal analysis framework for ratchet protocols grounded in Logic of Events theory (LoET). We further extend LoET by introducing dedicated Diffie–Hellman (DH) and ratchet event classes, along with tailored axioms and inference rules, to support precise modeling of ratcheted encryption. Using the Signal protocol as a case study, we construct a bidirectional authentication model and rigorously prove that both its symmetric and asymmetric ratchet phases satisfy strong authentication properties. Compared with existing formal approaches, our method enables more expressive modeling of key update sequences and supports structured reasoning over causality and authentication flows. The proposed framework lays a theoretical foundation for analyzing the security of modern ratcheted protocols and holds potential for future automated verification.