Secure substring search to filter encrypted data

Abstract

Secure substring searching on encrypted data may involve a first preprocessing comprising fragmenting a plaintext string slated for remote secure storage, in a plurality of overlapping plaintext substrings. A second preprocessing encrypts these substrings into ciphertexts (e.g., utilizing Frequency-Hiding Order Preserving Encryption) further including position information of the substring. A search index and a secret state result from the first and second preprocessing. The ciphertexts and search index are outsourced to a database within an unsecure server. An engine within the server determines candidate ciphertexts matching a query request received from a secure client. The engine returns ciphertexts to the client for decryption according to the secret state. Preprocessing may be delegated to a third party for outsourcing search index/ciphertexts to the server, and the secret state to the client. Filtering of candidate ciphertexts on the server-side, can eliminate false positives and reduce the volume of communication with remote clients.