说明：  　实现RC4加密算法，其是密钥长度可变的流加密算法簇。之所以称其为簇，是由于其核心部分的S-box长度可为任意，但一般为256字节。该算法的速度可以达到DES加密的10倍左右。RC4算法的原理很简单，包括初始化算法和伪随机子密码生成算法两大部分。
(RC4 encryption algorithm to achieve, it is the variable key length stream cipher algorithm clusters. It is called a cluster, is due to the core part of the S-box can be any length, but generally 256 bytes. The speed of the algorithm can achieve about 10 times DES encryption. The principle is very simple RC4 algorithm, including pseudo-random initialization algorithm and the two major sub-cipher algorithm.)