Study On AES Algorithm And Its Working Modes

Symmetrical cryptosystem is an important branch of modern cryptography, withits appearance and development there are wide applicant background and theorialvalue. There are lot theorial and applicant problems need to be studied and optimized,such as: how to design a provable safe cryptosystem, how to strengthen the safty ofalgorithms and working modules which are already available, how to test the safty ofa cipher algorithm, how to design safe components of a cryptosystem, as S-boxes,diffusing layers, and key-expanding processes, etc.The general architecture of symmetrical cryptosystem at present can be sorted asFeistel (CAST-256, DEAL, DFC E2, etc.), SP network (Safer+, Serpent, etc.) andother architectures (Frog, HPC). Symmetry is the most distinct character of Feistel,while SP network has a good deffuse capability. AES inherited SQUARE indesignation, and added in a lot of matrix operations. This causes a bit differentbetween encryption and decryption, but it optimizes the efficiency of the algorism.AES is a rapid progress in cryptosystem development, however, it needs to beameliorated yet. The efficiency of AES may be boosted, and new working module isalso necessary to be developed.This paper introuduces the theory of semmetrical cryptography and the workingprocess of AES algorithm, improves a conventional means of increasing theencrypting speed based on table-looking-up method, proposes its optimized algorism,which can greately increase the encrypting/decrypting speed, or save on memoryspace. Besides, a high-efficient method of generating S-box is proposed.And, the working module of AES is also a hot point of researching at present. Aworking module based on random block length is designed taking the advantage ofRijndael that it has a obvious agility in the length of block and cipher key, and thismodule can strengthen the safty of Rijndael algorithm. that completely crack thismodule is a imporsable case at the applicant level of present is proved. This module isalso able to be composed with CFB, CBC, and other available modules, strengtheningsafty and remaining aviable merits. And, other characters of this module are analysedin this paper, based this, some advices of applying it are proprsed.