and Emily Shen Substring - Searchable Symmetric Encryption

In this paper, we consider a setting where aclient wants to outsource storage of a large amount ofprivate data and then perform substring search querieson the data – given a data string s and a search stringp, find all occurrences of p as a substring of s. First, weformalize an encryption paradigm that we call queryableencryption, which generalizes searchable symmetric en-cryption (SSE) and structured encryption. Then, weconstruct a queryable encryption scheme for substringqueries. Our construction uses suffix trees and achievesasymptotic efficiency comparable to that of unencryptedsuffix trees. Encryption of a string of length n takesO(λn) time and produces a ciphertext of size O(λn),and querying for a substring of length m that occurs ktimes takes O(λm + k) time and three rounds of com-munication. Our security definition guarantees correct-ness of query results and privacy of data and queriesagainst a malicious adversary. Following the line of workstarted by Curtmola et al. (ACM CCS 2006), in orderto construct more efficient schemes we allow the queryprotocol to leak some limited information that is cap-tured precisely in the definition. We prove security ofour substring-searchable encryption scheme against ma-licious adversaries, where the query protocol leaks lim-ited information about memory access patterns throughthe suffix tree of the encrypted string.