Searchable symmetric encryption (SSE) is a form of encryption that allows one to efficiently search over a collection of encrypted documents or files without the ability to decrypt them. SSE can be used to outsource files to an untrusted cloud storage server without ever revealing the files in the clear but while preserving the server's ability to search over them. Description A searchable symmetric encryption scheme is a symmetric-key encryption scheme that encrypts a collection of documents , where each document is viewed as a set of keywords from a keyword space . Given the encryption key and a keyword , one can generate a search token with which the encrypted data collection can be searched for . The result of the search is the subset of encrypted documents that contain the keyword . Static SSE A static SSE scheme consists of three algorithms that work as follows: takes as input a security parameter and a document collection and outputs a symmetric key , an encrypted index , and an encrypted document collection takes as input the secret key and a keyword and outputs a search token takes as input the encrypted index , the encrypted document collection and a search token and outputs a set of encrypted documents A static SSE scheme is used by a client and an untrusted server as follows. The client encrypts its data collection using the algorithm which returns a secret key and an encrypted document collection . The client keeps secret and sends and to the untrusted server. To search for a keyword , the client runs the algorithm on and to generate a search token which it sends to the server. The server runs Search with , , and and returns the resulting encrypted documents back to the client. Dynamic SSE A dynamic SSE scheme supports, in addition to search, the insertion and deletion of documents. A dynamic SSE scheme consists of seven algorithms where , and are as in the static case and the remaining algorithms work as follows: takes as input the secret key and a new document and outputs an insert token takes as input the encrypted document collection EDC and an insert token and outputs an updated encrypted document collection takes as input the secret key and a document identifier and outputs a delete token takes as input the encrypted data collection and a delete token and outputs