Subscription music platforms, like many web applications, increasingly rely on Progressive Web Apps (PWAs) to enhance user experience. These PWAs function by exchanging data with servers or REST APIs. However, the current reliance on REST APIs poses significant security risks due to vulnerabilities in data transmission. To address this issue, this research integrates the El Gamal cryptographic algorithm into the architecture of a subscription music platform. By incorporating the El Gamal cryptographic algorithm, this research endeavors to fortify the security posture of data exchanged between users and servers through REST APIs. This encryption method was selected for its robust resistance to various cryptographic attacks, providing a strong defense against unauthorized interception and tampering of sensitive information. To evaluate the efficacy of the El Gamal integration, a rigorous white box testing regimen was employed, encompassing metrics such as cyclomatic complexity and basic path testing. These assessments comprehensively examined the code's structure and execution to identify potential vulnerabilities and ensure the correct implementation of the cryptographic algorithm. The findings of the white box testing unequivocally demonstrated the successful integration of El Gamal cryptography on both the client and server components of the subscription music platform, effectively safeguarding the confidentiality and integrity of data transmitted via REST APIs. This research contributes to the advancement of secure communication protocols within web applications, particularly subscription-based platforms. Through the implementation of robust encryption, the study enhances data integrity and confidentiality, ultimately building user trust.