###### Abstract
This paper presents a practical and structured evaluation of the integration between smart contracts of Ethereum and wallet interfaces through a case study of BlockScribe, a prototype decentralized application designed to manage subscriptions. The overarching objective of this study is not just to analyze a single instance but to develop a generalizable security assessment framework for Ethereum-based applications that interact with cryptocurrency wallets. BlockScribe serves as a controlled, reproducible environment for testing security assumptions, identifying architectural risks, and validating mitigation strategies. The framework itself is designed to be applicable across a broad range of Ethereum dApps with similar interaction patterns. The insights derived from this case aim to inform the secure design and auditing of decentralized applications in a more general way. Instead of proposing a new cryptographic primitive or formal verification method, this work contributes to the field by providing reproducible testing practices, code-level insights, and security recommendations derived from a complete contract-frontend workflow. The intended audience includes researchers in applied blockchain security, developers of decentralized applications, and auditors tasked with reviewing production smart contract deployments. The main contributions of this paper are as follows:  
* We propose a generalizable security assessment framework for evaluating the integration of cryptocurrency wallets with Ethereum-based decentralized applications, with a focus on identifying architectural vulnerabilities in the wallet-contract interaction layer. * We identify and examine the security risks and vulnerabilities associated with cryptocurrency wallets in web applications. * We investigate the role of smart contracts in enhancing the security of decentralized applications, with an emphasis on how they can be used to automate trustless operations while minimizing security risks. * We develop a prototype Ethereum-based web application, BlockScribe, to demonstrate how MetaMask and Ethereum smart contracts can be integrated effectively, followed by a comprehensive security analysis to identify key vulnerabilities and suggest solutions. * We conduct experiments and propose best practices for developers working with Ethereum-based applications. In Section 2, we provide an overview of the fundamental technologies behind blockchain, Ethereum, smart contracts, and cryptocurrency wallets, examining their role in enabling decentralized applications. Section 3 reviews the latest developments in Ethereum-compatible wallet architectures, highlights key attack vectors, and integrates a comparison with related academic work on smart contract security assessment. In Section 4, we present a case study of BlockScribe, a prototype Ethereum-based subscription management system, used to demonstrate common integration patterns between wallets and smart contracts. Section 5 covers the results of our empirical evaluation, including structured manual testing, static analysis with automated tools, and severity-based classification. Finally, Section 6 concludes the study with key findings and best practices and also outlines future research directions, including performance benchmarking and the broader applicability of the proposed framework across platforms.