简单的文件加密系统C语言代码

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我是靠谱客的博主俊秀小甜瓜，最近开发中收集的这篇文章主要介绍简单的文件加密系统C语言代码，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

用C语言实现一个简易的文件加密/解密系统。该系统采用对称加密体制，由用户指定自己的密钥key，加密函数可描述为M = P + key，对应的解密函数可描述为M = P - key。

代码如下：

#include <stdio.h>
#include <stdlib.h>

void encryption(char buffer[], int file_size, int key);
void decryption(char buffer[], int file_size, int key);
void Process(int a);
int openScrcFile(char **buffer);
void saveDstFile(char *buffer);
void menu();
char filename[20];

void main()
{
char flag;
menu();
flag = getchar();
getchar();
while(flag != 'Q' || flag != 'q')
{
  switch(flag)
  {
  case 'e':
  case 'E':
   Process(0);
   break;
  case 'd':
  case 'D':
   Process(1);
   break;
  }
  flag = getchar();
  getchar();
}
if (flag == 'Q' || flag == 'q')
  exit(0);
}

void menu()
{
printf("*********************************************************n");
printf("===========A STMPLE ENCRYPTION/DECRYPTION SYSTEM=========n");
printf(" ENCRYPTION press 'E' DECRYPTION press 'D' QUIT press 'Q'n");
printf("*********************************************************n");
}

int openScrcFile(char **buffer)
{
FILE *myfile_src;
//char filename[20];
long file_size;
printf("please input the path and filename of the file you want to processn");
scanf("%s", filename);
if (!(myfile_src = fopen(filename, "rb")))
{
printf("errorn");
}

fseek(myfile_src, 0, SEEK_END);
file_size = ftell(myfile_src);
fseek(myfile_src, 0, SEEK_SET);
*buffer = (char *)malloc(file_size);
fread(*buffer, 1, file_size, myfile_src);
fclose(myfile_src);
return file_size;
}

void saveDstFile(char *buffer, long file_size)
{
FILE *myfile_dst;

//printf("please input the path and filename of the file you have processedn");
//scanf("%s", filename);

if (!(myfile_dst = fopen(filename, "wb")))
{
printf("errorn");
}
fwrite(buffer, 1, file_size, myfile_dst);
printf("OK!n");
fclose(myfile_dst);
}

void Process(int a )
{
FILE *myfile_dst;
char * buffer;
int key;
long file_size;
file_size =openScrcFile(&buffer);
printf("please input the key (a integer) for encryption or decryptionn");
scanf("%d", &key);
if (a == 0)
{
  encryption(buffer, file_size, key);
}
else
{
  decryption(buffer, file_size, key);
}
saveDstFile(buffer, file_size);
}
void encryption(char buffer[], int file_size, int key)
{
int i;
for(i = 0; i < file_size; i ++)
{
  buffer[i] = buffer[i] + key;
}
}
void decryption(char buffer[], int file_size, int key)
{
int i;
for(i = 0; i < file_size; i ++)
{
  buffer[i] = buffer[i] - key;
}
}