jiami.cpp

Vigenere加密算法的小程序,可以实现字符的加解密

//本程序是实现Vigenere加密算法的小程序

#include<conio.h>
#include<process.h>
#include<stdio.h>
#include<iostream.h>

#define File_Len 10//定义文件名长度
#define Key_Len  20//定义密匙长度

void encrypt()//加密函数
{
	char infile[File_Len];
	char key[Key_Len];

	cout<<"\nInput the filename:";
	cin>>infile;
	cout<<"Input the key:";
	cin>>key;

	FILE *fp;
	int i=0;
	char *p=key,ch;

	if((fp=fopen(infile,"r+"))==NULL)
	{
		printf("cannot open file\n");
 		exit(0);
	}

	ch=fgetc(fp);

	while(ch!=EOF)
	{
		if(*p=='\0') /*如果密钥长度结束*/
	      		p=key;/*重新赋值*/

		if(ch>='a'&&ch<='z')
	 		{
				if(*p>='a'&&*p<='z')  				    			       
					ch=((ch-96)+(*p-96))%26+95;
	 			else   
					ch=((ch-96)+(*p-64))%26+95;
			}
		else if(ch>='A'&&ch<='Z')
	 		{
				if(*p>='A'&&*p<='Z') 						       	       
					ch=((ch-64)+(*p-64))%26+63;
		  		else   
					ch=((ch-64)+(*p-96))%26+63;
			}
		else ;
		p++,i++;
		fseek(fp,i-1,0); /*定位到将要写入字符的位置*/
		fputc(ch,fp); /*把加密的字符写入文件中*/
		fseek(fp,i,0); /*定位到下一个字符所在的位置*/
		ch=fgetc(fp);
	}
	fclose(fp);
}
/*****************************************************************/
void decrypt()//解密函数
{
	char infile[File_Len];
	char key[Key_Len];

	cout<<"\nInput the filename:";
	cin>>infile;
	cout<<"Input the key:";
	cin>>key;

	FILE *fp;
	int i=0;
	char *p=key,ch;

	if((fp=fopen(infile,"r+"))==NULL)
	{
		printf("cannot open file\n");
 		exit(0);
	}

	ch=fgetc(fp);

	while(ch!=EOF)
	{
		if(*p=='\0')
		 	p=key;//Loop of key

		if(ch>='a'&&ch<='z')
		{
			if(*p>='a'&&*p<='z') 		     			       
				ch=((ch-96)+26-(*p-96))%26+97;
	  		else  
				ch=((ch-96)+26-(*p-64))%26+97;
		}
		else if(ch>='A'&&ch<='Z')
				{
					if(*p>='A'&&*p<='Z') 				    				

						ch=((ch-64)+26-(*p-64))%26+65;
	   				else    
						ch=((ch-64)+26-(*p-96))%26+65;
				}
		     else

		p++,i++;
		fseek(fp,i-1,0);
		fputc(ch,fp);
		fseek(fp,i,0);
		ch=fgetc(fp);
	}
		fclose(fp);
}
/*****************************************************************/
void main()//主函数
{
	int choice;

Loop:
	do
	{
  	//clrscr(); 
  	cout<<"Welcome to use!\n";
  	cout<<"Author:DengJianguo(Icerain)\n";
 	cout<<"E-mail:[e-mail] \n";

 	cout<<"\nPlease make a choice from fallowing options:\n";
 	cout<<"0)Exit \n";
  	cout<<"1)Encrypt \n";
  	cout<<"2)Decrypt \n";
  	cout<<"\n Please input a option number[0-2]:";
  	choice=getchar();
  	}while(choice!='0'&&choice!='1'&&choice!='2');
	
	if(choice=='0') exit(0);
	if(choice=='1')
	{
		encrypt();
		goto Loop;
	}
	if(choice=='2')
	{
		decrypt();
		goto Loop;
	}
}