自己写的RC4加密算法

为了方便研究802.11数据帧的加密格式，自己写了个RC4算法的程序，只输出密钥流的第一个字节，用来和LLC头的第一个字节做异或运算，没什么技术含量，呵呵

 

/*code by zhaoxiaobu
#include <stdio.h>

/*RC4加密算法 */
unsigned char RC4(unsigned char *IV,unsigned char *key)
{
    unsigned char K[256];
    unsigned char S[256];
    unsigned char seed[16];
    int i,j,k,t;


    for(k=0;k<3;k++)
    {
        seed[k]=IV[k];
    }

    for(k=0;k<13;k++)
    {
        seed[k+3]=key[k];
    }



    for(k=0;k<256;k++)
    {
        S[k]=k;
        K[k]=seed[k%16];
    }

    j=0;
    for(i=0;i<256;i++)
    {
        j=(j+S[i]+K[i])%256;
        t=S[i];
        S[i]=S[j];
        S[j]=t;
    }


    i=0;
    j=0;

    i=i+1;
    j=j+S[i];

    t=S[i];
    S[i]=S[j];
    S[j]=t;

    k=(S[i]+S[j])%256;
    return S[k];

}


int main(int argc,char *argv[])
{
    unsigned char K[256];
    unsigned char S[256];

    unsigned char IV[3]={0x1d,0x9c,0xea}; //3个字节的初始向量(IV)
    unsigned char key[13]={0x30,0x39,0x38,0x37,0x36,0x35,0x34,0x33,0x32,0x31,0x32,0x33,0x34};    //13个字节的密钥(假如采用的是128位加密算法)
    unsigned char seed[16];

    int i,j,k,t,x,A;
    unsigned char keystream;

    keystream=RC4(IV,key);
    printf("Using IV: (%d,%d,%d), first keystream byte is %02x\n",IV[0],IV[1],IV[2],keystream); //输出RC4加密流的第一个字节，用来和LLC头的第一个字节做异或运算
}