Exploring queriability of encrypted and compressed XML data

When large XML documents are shared, documents compression and encryption become simultaneously important for efficient and secure access. Existing approaches for compressing and encrypting large XML documents provide a non-queriable intermediate document representation, creating a need to decompress and decrypt the whole document before any access, which simply wastes computing resources (such as memory, time, and power) especially in mobile environment. To overcome this limitation, this paper proposes a new approach for compressing and encrypting large XML documents while maintaining queriability over the intermediate document representation. The proposed approach separates document structure from its contents using a variation of the Ctree XML indexing approach (known as the Ctree⁺), then applies context-free lossless encryption and compression techniques over the resulting Ctree⁺ intermediate representations. Experiments results show that the proposed approach dramatically enhances queries response times when compared with existing approaches. However, the proposed approach provides lesser compression ratios when compared with context-based compression techniques.