Hash and Boolean logic

Another key element that needs to be to be considered is the hash functions that have to be combined with tree graphs. We have already covered hash functions in Chapter 4, Introducing Hash Functions and Digital Signatures, of this book. In the same chapter, we have also seen more Boolean operators useful for hash function in the section: Logic and notations to implement hash functions. However, while in cryptography hashes are employed for a digital signature to avoid exposing the content of the message, [M], here we use hashes for a different scope. The object of a query is also called the keyword. Another definition of a keyword could be the result of a process of indexing a string or a group of strings in a database.

If our search engine is efficient, it will be indexing (a similar process to encoding) as few strings as possible, recognizing and discarding the double-indexed ones. In a search engine that works with encrypted data, the query itself is encrypted...