给文件加密的技术很多,其中又分为不同等级,以适合不同场合的需要.这里给出最简单的文件加密技术,即采用文件逐字节与密码异或方式对文件进行加密,当解密时,只需再运行一遍加密程序即可.
下面是一个实例程序,能对任意一个文件进行加密,密码要求用户输入,限8位以内(当然你可以再更改).程序有很好的容错设计,这是我们应该学习的.
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/**//* Turbo 2.0 pass. give file a password! */
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#include<stdio.h>
#include<stdlib.h>
#include<conio.h>
#include<string.h>
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void dofile(char *in_fname,char *pwd,char *out_fname);/**//*对文件进行加密的具体函数*/
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void main(int argc,char *argv[])/**//*定义main()函数的命令行参数*/
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{
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char in_fname[30];/**//*用户输入的要加密的文件名*/
char out_fname[30];
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char pwd[8];/**//*用来保存密码*/
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if(argc!=4)
{/**//*容错处理*/
printf("\nIn-fname:\n");
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gets(in_fname);/**//*得到要加密的文件名*/
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printf("Password:\n");
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gets(pwd);/**//*得到密码*/
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printf("Out-file:\n");
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gets(out_fname);/**//*得到加密后你要的文件名*/
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dofile(in_fname,pwd,out_fname);
}
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else
{/**//*如果命令行参数正确,便直接运行程序*/
strcpy(in_fname,argv[1]);
strcpy(pwd,argv[2]);
strcpy(out_fname,argv[3]);
dofile(in_fname,pwd,out_fname);
}
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}
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/**//*加密子函数开始*/
void dofile(char *in_fname,char *pwd,char *out_file)
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{
FILE *fp1,*fp2;
register char ch;
int j=0;
int j0=0;
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fp1=fopen(in_fname,"rb");
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if(fp1==NULL)
{
printf("cannot open in-file.\n");
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exit(1);/**//*如果不能打开要加密的文件,便退出程序*/
}
fp2=fopen(out_file,"wb");
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if(fp2==NULL)
{
printf("cannot open or create out-file.\n");
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exit(1);/**//*如果不能建立加密后的文件,便退出*/
}
while(pwd[++j0]);
ch=fgetc(fp1);
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/**//*加密算法开始*/
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while(!feof(fp1))
{
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fputc(ch^pwd[j>=j0?j=0:j++],fp2);/**//*异或后写入fp2文件*/
ch=fgetc(fp1);
}
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fclose(fp1);/**//*关闭源文件*/
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fclose(fp2);/**//*关闭目标文件*/
}
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/**//*程序结束*/
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