الفهرس 
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Abstract
Matter can neither be created nor destroyed. Matter, it is said, obeys a low of conservation.If it is stolen,its loss may be detected ,for in taking it a gap is left. Not so with information.Information is abstract—it can be both created and destroyed,It can be copied without depleting the source,and it can sometimes be obtained by guessing.The strange abstract properties of information are lustrated by the form of information known as money.It too can be printed and burned,it can be forged without depleting the original,and it can sometimes be obtained by speculation!
To protect information,complex abstractions are required.Some general studies concerned with the protection of money and other informational transactions fall under the heading of
cryptology.Thus,while material objects are protected by physical means such as a strongbox of a standard design but with a unique customizedy,abstractions such as messages are protected by abstract means, such as an encipherment function of standard design but with a unique customized key. Electronic computers have evolved from exiguous experimental enterprises in the 1940s to prolific practical data processing systems in the 1980s .As we have come to rely on these systems to process and store data,we have also come to wonder about their ability to protect valuable data. Data security is the science and study of methods of protecting data in computer and communication systems from UflO.Uthorized disclosure and modification.Data security has evolved rapidly since 1975. We have seen exciting developments in cryptography:public key encryption,digital signatures,the Data Encryption Standard (DES) ,key safeguarding schemes ,and key distribution protocols.
Because data security field is evolving so rapidly,it has been difficult to write this researth in such a way that it both coherent and current.Even as it was in production,there were new developments in the field.Some areas are still unsetelled,and we were only able to include references.