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The thesis describes the Wallenc mobile application — a client wallet for storing data on untrusted backends without a dedicated application server. Data is encrypted on the device before upload; decryption is performed only when the user enters a valid key. The work includes analysis of analogues, requirements, architecture and UI design, Kotlin implementation for Android, testing, and a brief economic assessment.

The application uses MVVM and Clean Architecture. Main features are local and remote vault management, client-side AES encryption, Room metadata storage, and Yandex OAuth integration.

Keywords: mobile application, client-side encryption, Android, vault, OAuth, Room.