After many incidents of cloud services being attacked and personal user data leaking, a secure way of storing data on the cloud would be to encrypt. Even if an attacker would have access to the files he/she would not be able to decrypt the files without the secret key. In this thesis a software will be developed and works by securing user data by encrypting, prior uploading to the cloud. This software is a potential solution to the existing threat. The thesis presents many different methods of encryption but narrows it down to two, AES and XOR, which will be implemented into the software. This is done by statistically comparing the speed of each system. As well as comparing the expected time by using a student’s t-test calculating what degree of certainty one will be faster than the other. The thesis discusses and highlights level of security regarding cloud security. Comparisons of the algorithms are made to determine which method to be used under what circumstances.

Cloud-based collaborative editors enable real-time document processing via remote connections. Their common application is to allow Internet users to collaboratively work on their documents stored in the cloud, even if these users are physically a world apart. However, this convenience comes at a cost in terms of user privacy. Hence, the growth of popularity of cloud computing application stipulates the growth in importance of cloud security. A major concern with the cloud is who has access to user data. In order to address this issue, various third-party services offer encryption mechanisms for protection of the user data in the case of insider attacks or data leakage. However, these services often only encrypt data-at-rest, leaving the data which is being processed potentially vulnerable. The purpose of this study is to propose a prototype software system that encrypts collaboratively edited data in real-time, preserving the user experience similar to that of, e.g., Google Docs.