Abstract
Company data are very often outsourced to cloud service providers in order to lower costs of maintaining hardware. If the outsourced data are to be kept secure from a third party, the connection between the cloud service provider and the company could be secured by a protocol similar to SSL. This, however, requires that the data is stored at the cloud service provider in plaintext form, meaning the company has to trust the cloud service provider and its administrators in order to perform search on the outsourced data. Alternatively, the data themselves could be encrypted, however, the outputs of typical cryptographic algorithms are not amenable to search. For example, if a client wishes to retrieve only documents containing certain words, it was not previously known how to let the data storage server perform the search and answer the query without loss of data confidentiality. By the advantage of our cryptography scheme a query generated at the client-side, is transformed into a representation so that it can be evaluated directly on encrypted data at the could storage server. The results might be processed by the client after decryption to determine the final answers. Additionally, we introduce an efficient common prefix keyword search which makes the scheme more tolerant of minor typos and format inconsistencies when exact keyword matching fails.