Research And Improvement Of RC4 Stream Cipher Algorithm

Stream cipher is an important branch of modern cryptography. RC4 Stream cipher is efficient to implement and easy to use, so that it is widely used in network security, database security areas. With the rapid development and applications popularization of Internet, the higher for network security is required, so that it is the security of RC4 stream cipher algorithm is facing serious challenges and have become one of research focuses.This dissertation introduces the related theories and mathematical knowledge about Stream cipher, makes an intensive studies the Working principle and design methods for Stream cipher, analyzes some classic RC4 attack chemes, and lays emphasis on the study of the internal state of RC4, the output function, design principles and typical attack analysis. RC4 stream cipher algorithm is vulnerable to weakness-key attack, distinguishing attack. Against above attacks, This dissertation proposes a improved RC4 algorithm RC4_n_m based on random permutation, the algorithm has the following characteristics:(1) Based on random permutation, which can uses the dynamic status table to make nonlinear transformation operation, extend sp value apace of the elements in the state table and makes the state table of the elements are constantly being updated,which guarantees the reusability of state table.(2) In the process of Key Sehedule Algorithim, introduce a secret number, which is changed with the transformation of state table. In the Pseudo-Random Sequence Generation Algorithm, the secret number participate in the transformation of the state table, which, ensure uniformity of the state table.(3) RC4_n_m keystream will be made by both the previous state and the next state of table, which enhances the randomness of keystream sequence. RC4_n_m outputs 32bit which is much larger than 8 bits of RC4, Therefore, efficiency of RC4_n_m is superior to RC4 algorithm.At last, this dissertation test the correctness, keystream randomness and efficiency of RC4_n_m stream cipher algorithim. Experiment results show that RC4_n_m is correct feasible, the keystream randomness and efficiency is superior to RC4 algorithm.