الفهرس 
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Abstract
Encryption provides strong security for databases. To develop a database encryption strategy, many factors must be taken into consideration. Unfortunately, the integration of existing encryption techniques with database systems causes undesirable performance degradation. It is a crucial technique in the security mechanisms of database. Organizations must balance between the requirement for security and for excellent performance. A novel encryption algorithm is proposed “Reverse Encryption Algorithm (REA)”. It is simple and yet leads to a cipher. The proposed algorithm REA is implemented and tested on the database. Its results are compared with the most common encryption algorithms namely: DES, 3DES, RC2, AES and Blowfish. The REA algorithm provides maximum security and limits the added time cost for encryption and decryption. The proposed algorithm REA achieves balance between the security and the performance. In addition, evaluating the query processing performance over encrypted database with the proposed algorithm REA and with the algorithm AES. The results of a set of experiments validate the functionality and usability of the proposed algorithm REA. Another problem, conventional encryption schemes do not better work for images because of their large size and high redundancy. Therefore images cryptosystem of the databases based on chaotic maps (chaotic confusion and diffusion of the pixel values) are used on this thesis. It is implemented by development our database encryption simulation by adding chaotic confusion-diffusion, which using chaotic standard and henon map has been widely used in images encryption. Experimental results demonstrate that the image cryptosystem has satisfactory efficient and very secure, which makes it a possible candidate for images encryption in the databases. iii