例3-3.c

这是用C编写的伪随机数加密算法

/* Note:Your choice is C IDE */
#include <stdio.h>
#include <stdlib.h>
union
{
	int value; 
	struct
	{
		char first;
		char second;
	}fran;
}num;
main()
{   
	FILE *fp,*name2;         /* name2位加密存放的文件 */
	int i,t,len,k1,k2,k3,k4,k5;
	float j;
	char name1,buf[60000];   /* name1位用户输入的要进行加密的文件 */
	printf("\n input filename that you want to lock or open:");
	scanf("%s",name1); 
	if((fp=fopen(name1,"rb"))==NULL)      /* 以只读的方式打开一个二进制文件 */
 	{
 		printf("File cannot be opened\n");
 		exit(1);
 	}
	else
 		printf("File opened for encrypt\n");
	j=filelength(name1);
	printf("\ninput key1:"); 
	gets(k1);
	printf("\ninput key2:"); 
	gets(k2);
	printf("\ninput key3:"); 
	gets(k3);  
	srand(k1);
	for(i=0;i<k2;i++)
	{
		k4=rand();
	}
	k5=(k3+k2)/2;
	for(i=0;i<j;i++)
	{
		num.value=rand();
		if(num.fran.first<=33)
			num.fran.first=num.fran.first+33;
		buf[i]=num.fran.first^buf[i];        /* 进行异或运算 */
	} 
	fopen(name2,"wb");   /* 以只写的方式建立一个二进制文件存放加密后的文件 */
	fputs(buf,name2);              
	printf("\nFile is already encrypted");
	fclose(name1);      /* 关闭文件 */
	fclose(name2);
}