Searchable Encryption with Substring Search I want to search substrings in encrypted string. To do that I have read “Implement Rabin-Karp Algorithm” and “Substring-Searchable Symmetric Encryption”. After that, I completed the Rabin-Karp implementation. But, those does not answer for my problem. Rabin-Karp requires both main string for searching substrings and substring to be searched. What I want to do is finding patterns in encrypted strings without decrypt it?
There are some works both theoretical and practical that they do solve your problem efficiently and in a secure way. By efficiently i mean the search efficiency is linear on the size of the searched substring. This is achieved by using auxiliary data structures known as suffix tree. Chase and Shen  follow this approach, by encrypting the suffix tree with symmetric primitives.

This work does not use any auxiliary data structure for efficiency. It encrypts consecutive n-grams and their positions.

A theoretical work follows another technique. By altering the subset sum problem to be easily solvable they issue subset sum instances to the cloud, and the cloud solves them polynomially and the solutions are the positions in the original string of the substring.

Stronger security guarantees with oblivious ram are presented here