3223

3139

كارشناسي ارشد

﴿مخابرات ﴾

اصفهان : دانشگاه صنعتي اصفهان ، دانشكده برق و كامپيوتر

1385

نه ، 97 ، [II] ، ص : جدول ، نمودار

ص . ع : به فارسي و انگليسي

سيد محمود مدرس هاشمي

محمد دخيل عليان

1395/08/25

مهندسي برق و كامپيوتر

ID3139

به فارسي و انگليسي : قابل رويت در نسخه ديجيتالي

Abstract In recent years various aspects of human life have been influenced by informationtechnology Consequently the importance of information transsmission security has beenincreased Thus the need for efficient cryptograghy algorithms that can satisfy specificrequirements and stand against attacks is felt much more than the past Among these stream ciphers because of high speed and simple implementation have many applicationsin cryptosystems and so their efficiency and security improvement are always under theconsideration It is clear that the investigation of different attacks is necessary for securityanalysis of cryptosystems In this thesis after the introduction of stream ciphers and important attacks againstthem we emphasize on algebraic attack which is basically solving nonlinear equations ofthe stream ciphers algorithms Then a new method is proposed for counting the number ofextra equations in relinearization method Therefore algebraic attack is considered againstregular clocking systems After this we consider algebraic attack against systems withmemory and this attack is employed against BSRA systems Finally this attack isconsidered for clock controlled cipher systems and new algebraic attacks are proposedagainst A5 systems

سيد محمود مدرس هاشمي

محمد دخيل عليان