Forward Secure Searchable Symmetric Encryption

Data outsourcing to third party clouds poses numerous data security threats. Access by unauthorized users is one of the security threat to the outsourced data. Unauthorized access can be avoided by encrypting the data before outsourcing. However, encrypting data before outsourcing renders it unsearchable to the data owner. Searchable encryption schemes are developed to specifically target this problem. A dynamic searchable encryption is the one that allows the data owner to add or delete a file after data outsourcing. Dynamic searchable encryption schemes are vulnerable to two specific security threats that are not applicable to the static searchable encryption schemes namely forward privacy and backward privacy. Forward privacy requires that the addition of a file should not reveal the presence of a previously searched keyword. Backward privacy requires that a search should not return the file identifier of a previously deleted file. In this paper, we propose a dynamic searchable scheme that guarantees forward privacy. It only uses the symmetric key algorithms hence reducing the requirements for storage and processing power on the client side. Furthermore, our proposed scheme is space reclaiming. After the deletion of a file, the redundant data nodes are also deleted from the secure index in the subsequent searches. Because of this space reclaiming capability of the scheme, the scheme is also partially backward private.