Translating Algorithms to handle Fully Homomorphic Encrypted Data on the Cloud

Description

Cloud provides large shared resources where users (or foundations) can enjoy the facility of storing data or executing applications. In spite of gaining convenience of large resources, storing critical data in cloud is not secured. Hence, cloud security is an important issue to make cloud useful at the enterprise level. Data encryption is a primary solution for providing confidentiality to sensitive data. However, processing of encrypted data requires extra overhead, since repeated encryption-decryption need to be performed for every simple processing on encrypted data. Hence, direct processing on encrypted cloud data is advantageous, which is supported by homomorphic encryption schemes. Fully Homomorphic Encryption (FHE) provides a method of performing arbitrary operations directly on encrypted data. This seemingly magical idea is a welcome to cloud computing. However, there are several challenges to overcome for making the technology viable in practical applications. In this paper, we make an initial effort to highlight the problem of translating algorithms that can run on unencrypted or normal data to those which operate on encrypted data. Here, we show that although FHE provides the ability to perform arbitrary computations, its complete benefit can only be obtained if they also allow to execute arbitrary algorithms on encrypted data. In this pursuit, we provide techniques to translate basic operators (like bitwise, arithmetic and relational operators), which are used for implementation of algorithms in any high-level language like C. Subsequently, we address decision making and loop handling and related data structures which are vital to realize when the controlling variables are encrypted. Since, termination is a major challenge while handling encrypted data, we propose a method of handling termination by message passing between server and client.