Research About Several Questions Such As Expansion Of Pseudo-random Sequence In The Stream Cipher

The stream cipher is also known as periodic sequence, which is a kind of symmetric algorithm and has a long history. There are many good characteristics. Such as the hardware and software is easy to implement, the encryption and decryption speeds quickly and the transmission error is limited. Especially in the military, diplomatic and other fields, It is important to the use of confidential.Based on the principle of expansion of the stream cipher, It provades two methods of design of the stream cipher.The focus of the article is discussed about the imorpance of handling text before encryption ,the watermarking system of sequence spread spectrum in discrete cosine domain and other related issues.Ultimately it is better to achieve stream cipher encrypted security. In this paper, the author obtains main results as follows :1,Stream cipher increase in the process of designing electronic switch so that it is easy to change the cycle of pseudo-random sequence under the conditions of limited text.It is effective way to resist the attacked method based on the analysis of a single cycle.2,Using electronic switches, it improves Geffe system so that it can produce more high complexity of the pseudo-random sequence.3,According to the uniform expansion of the pseudo-random sequence, the dynamic scheduling sequence code structure is found that the sequence is generated different length by the algorithm and that made an analysis of its code.4,From information theory and the attacked methods, the author discuss the need to the handling text before encryption and propose to eliminate redundant data with data compression or filled random code to improve the security of confidential papers.5,With the use of spread spectrum on static images ,the author products discrete cosine domain watermarking and does numerous attacked experiment to test the effect of this sequence watermark. 6,To enhance the confidentiality of secret and encrypted transmission system,the author proposes a three-step thinking,that is expressly the handling text -encryption-secret transmission.