Searchable Symmetric Encryption (SSE)

The problem being discussed is how to search for a specific word, “W”, within a set of encrypted documents that are stored on an untrusted server. The documents are encrypted by the user, Alice, to protect them from the untrusted server, Bob. The documents are divided into “words” which can be any token, such as a 64-bit block or an English word, depending on the context. The goal is to design a scheme where the server can determine if a document contains the specific word “W” without learning any other information about the document. This is necessary because Alice may have a low-bandwidth connection to the server. There seem to be two types of approaches. The first method involves creating an index that lists all documents containing a specific word. The second method involves searching through the documents sequentially without using an index. The advantage of using an index is that it can be faster when working with large amounts of data, but the disadvantage is that it can take a lot of resources to store and update the index. Therefore, using an index is more appropriate for data that is mostly read and not often modified.