PreIndex: A Simple But Efficient Tree Index for Encrypted Databases

In this paper, we present a new index structure called PreIndex for encrypted databases. Unlike existing encrypted indexes that encrypt whole keys, PreIndex proposes to encrypt only the suffix of each key but leave a prefix of the key unencrypted. With this mechanism, we can efficiently accelerate queries over encrypted data while avoiding the leakage of confidential data. PreIndex offers an alternative for realizing a better trade-off between data encryption and query efficiency. We conduct experiments on various tailor-made workloads to compare PreIndex with the unencrypted B+-tree and the fully encrypted B+-tree, and the results show that PreIndex can achieve higher query performance than the fully-encrypted B+-tree. Moreover, by controlling the length of the prefix, PreIndex’s performance can be tuned according to different application scenarios.