先贴个我手打的源码

RC4

#include <stdio.h>
#include <string.h> 

#define LEN 256

void Swap(unsigned char * a, unsigned char * b);
void Rc4_Init(unsigned char * s, unsigned char * key, int klen);
void Rc4_Crypt(unsigned char * s, unsigned char * p, int plen);

int main(void) 
{
	unsigned char s[LEN] = { 0 };
	unsigned char ss[LEN] = { 0 };
	unsigned char key[LEN] = { "20220127" };
	unsigned char p[LEN * 2] = { "20211205" };
	int i, j;
	
	Rc4_Init(s, key, strlen(key));
	for ( i = 0; i < LEN; i++ )
	{
		ss[i] = s[i];
//		printf("%d %d ", s[i], ss[i]);	
	} 
	
	printf("Encrypt:");
	Rc4_Crypt(s, p, strlen(p));
	for ( i = 0; i < strlen(p); i++ )
		printf("0x%X, ", p[i]);
		
	puts("\n");
	
	printf("Decrypt:");
	Rc4_Crypt(ss, p, strlen(p));
	for ( i = 0; i < strlen(p); i++ )
		printf("0x%X, ", p[i]);
	
	return 0;
}

void Swap(unsigned char * a, unsigned char * b)
{
//	Swap((unsigned char *)&key[0], (unsigned char *)&key[1]);
//	printf("%c %c", key[0], key[1]);
//	printf("%d %d\n", *(__int8 *)&a, *(__int8 *)&b);
//	Swap((__int8 *)&a, (__int8 *)&b);		//以int8来读取这个地址的值 并不是解引用 
//	printf("%c %c\n", a, b);
//	printf("%c %c\n", *a, *b);
	*a ^= *b;					//可以加个异或的混淆 
	*b ^= *a;
	*a ^= *b;
}

void Rc4_Init(unsigned char * s, unsigned char * key, int klen)
{
	unsigned char k[LEN] = {  };
	unsigned char t = 0;
	int i, j;
	
	for ( i = 0; i < LEN; i++ )
	{
		s[i] = i;					//向量S 
		k[i] = key[i % klen];		//向量T 由key组成 用来打乱S 
	}
	for ( i = 0, j = 0; i < LEN; i++ )
	{
		j = (j + s[i] + k[i]) % 256;
		Swap(&s[i], &s[j]); //以int8来读取这个地址的值 并不是解引用 
	}
}

void Rc4_Crypt(unsigned char * s, unsigned char * p, int plen)
{
	int i, j, k, t;
	
	for ( i = 0, j = 0, k = 0; k < plen; k++ )
	{
		i = (i + 1) % 256;
		j = (j + s[i]) % 256;
		Swap(&s[i], &s[j]);
		t = (s[i] + s[j]) % 256;				//有点不理解RC4为什么要交换了再加
//		printf("%d %d\n", p[k], s[t]); 
		p[k] ^= s[t];	
	} 
}