file_encrypt.cpp

key.txt存放密钥

#include <fstream.h>
#include <stdlib.h>

void main(void)
{
	ifstream in_file;
	ofstream out_file;
	ifstream key_file;

	char *read_filename = "text.txt";
	char *write_filename = "result.txt";
	char *key_filename = "key.txt";
	char ch;
	char ch_key[80];
	int i,key_long,state;

	key_file.open(key_filename,ios::in);
	if(!key_file)
	{
		cout<<"Error: The file---key.txt open is fail.Check the disk and try again..."<<endl;
		exit(1);
	}
	else
	{
		cout<<"Reading key.txt......"<<endl;
		cout<<"File---key.txt read successful."<<endl<<endl;
		cout<<"key.txt = ";
	}

	key_file.get(ch);
	for(i=0; ch>='0'&&ch<='9'&&i<80; i++)
	{
		ch_key[i]=ch;
		key_file.get(ch);
	}
	if(i==0)
	{
		cout<<"File---key.txt read error: file's key is empty!"<<endl;
		exit(1);
	}
	else
	{
		key_long=i;
		for(i=0;i<key_long;i++)
			cout<<ch_key[i];
	}
	cout<<endl<<endl;
	key_file.close();

	in_file.open(read_filename,ios::in);
	out_file.open(write_filename,ios::out);
	if(!in_file)
	{
		cout<<"Error: The file---text.txt open is fail.Check the disk and try again..."<<endl;
		exit(1);
	}
	else
	{
		cout<<"Reading text.txt......"<<endl;
		cout<<"File---text.txt read successful."<<endl<<endl;
		cout<<"Writing result.txt......"<<endl;
		cout<<"File---result.txt write successful."<<endl<<endl;
	}

	for(i=0; !in_file.eof(); )
	{
		in_file.get(ch);
		if(ch>='0' && ch<='9')
		{
			if(i==key_long)
				i=0;
			ch = (char)( ( (int)ch - 48 + ((int)ch_key[i] - 48) ) % 10 + 48 );
			i++;
		}
		else
		{
			if(ch>='A' && ch<='Z')
			{
				if(i==key_long)
					i=0;
				ch = (char)( ( (int)ch - 65 + ((int)ch_key[i] - 48) ) % 26 + 65 );
				i++;
			}
			else
			{
				if(ch>='a' && ch<='z')
				{
					if(i==key_long)
						i=0;
					ch = (char)( ( (int)ch - 97 + ((int)ch_key[i] - 48) ) % 26 + 97 );
					i++;
				}
			}
		}
		out_file<<ch;
		if(out_file.fail())
		{
			cerr<<"File---result.txt write error!"<<endl;
			exit(1);
		}
	}
	in_file.close();
	out_file.close();
}