The software-as-a-service (SaaS) market is growing very fast, but still many clients are concerned about the condentiality
of their data in the cloud. Motivated hackers or malicious insiders could try to steal the clients' data. Encryption is a potential solution, but supporting the necessary functionality also in existing applications is dicult. In this paper, we examine encrypting analytical web applications that perform extensive number processing operations in the database. Existing solutions for encrypting data in web applications poorly support such encryption. We employ a proxy that adjusts the encryption to the level necessary for the client's usage and also supports additively homomorphic encryption. This proxy is deployed at the client and all encryption keys are stored and managed there, while the application is running in the cloud. Our proxy is stateless and we only need to modify the database driver of the application.
We evaluate an instantiation of our architecture on an exemplary application. We only slightly increase page load time on average from 3:1 seconds to 4:7. However, roughly 40% of all data columns remain probabilistic encrypted. The client can set the desired security level for each column using our policy mechanism. Hence our proxy architecture oers a solution to increase the condentiality of the data at the cloud provider at a moderate performance penalty.