Abstract: This paper describes the implementation of a secure cloud storage application. Cloud service providers often have access to the files of their customers. To prevent this and other security risks, a novel variant of the RSA encryption algorithm is employed. The application is web-based and therefore platform-independent. It is possible to create, open and edit text files directly in the browser. The files are encrypted and decrypted only locally on the computer of the user. A special role in the implementation plays the user’s Smartphone which is used as a security token. The project comprises an Android application that basically generates and holds the decryption key. To open and decrypt a file, the user has to scan a QR code which is shown on the computer screen.

Keywords: Cloud Platform, Android Application, Security, AES, RSA, Token Generation.