[32] Write a program which accepts a filename as a command-line argument [-32].

Question

[32] Write a program which accepts a filename as a command-line argument [-32]. It should then ask for a password via stdin (but it should not visible when entered; use getpass for this) [4]. The program should encrypt the file using a block-cipher algorithm (see encryption.rst for details) [12] if it was not already encrypted by the program, and rename it with a .enc extension. If it was already encrypted, it should decrypt the file and remove the .enc extension [12]. Under no circumstance should the program multiply encrypt the file [4]. Call the program encrypt.cpp. here is encrypt.rst Suppose I have an input file to encrypt: .. raw: The only true wisdom is in knowing you know nothing. (A quote by Socrates.) What I can do then is ask the user for a password. Suppose the user enters kitties. Then what I may do is pre-pend the password to an output file, and add kitties in rounds to the file: .. raw: kittiesThe only true wisdom is in knowing you know nothing. + kittieskittieskittieskittieskittieskittieskittieskittieskit ----------------------------------------------------------- = fhdkalhfioepwahfkdsanklvcxznkjvpwipqnkxlkdlajsflkjkljkljlkd When I add the characters in the string kitties, I get what appears to be jumbled garbage. Without the password, it is hard to decrypt the file. To decrypt the file, I ask the user for the password. Suppose they enter bubbles (the wrong password). .. raw: fhdkalhfioepwah... - bubbles ------------------ = ueiaqnv I see that by subtracting bubbles off the encrypted text, I do not get the string bubbles back, so bubbles is not the password. If the user enters kitties (the correct password): .. raw: fhdkalhfioepwah... - kitties ------------------ = kitties Then I see that what I get back is kitties, and since it matches the user password entered, I may proceed to decrypt the rest of the file simply by subtracting kitties off it in rounds. .. raw: = fhdkalhfioepwahfkdsanklvcxznkjvpwipqnkxlkdlajsflkjkljkljlkd - kittieskittieskittieskittieskittieskittieskittieskittieskit ----------------------------------------------------------- kittiesThe only true wisdom is in knowing you know nothing. Thus I obtain the original message. Notice the user-supplied password itself is a necessary element of the decryption. This type of algorithm is called a block cipher algorithm. MUST BE IN C++ AND MUST BE THE ACTUAL CODE

Explanation / Answer

#include<iostream.h>

#include<stdio.h>

#include<conio.h>

#include<fstream.h>

void main()

{

   char c,fname[10];

   ofstream out;

   cout<<"Enter File name:";

   cin>>fname;

   out.open(fname);

   cout<<"Enter contents to store in file (Enter # at end): ";

   while((c=getchar())!='#')

   {

   out<<c;

   }

   out.close();

   getch();

}

Related Questions

Navigate

• Browse (All)
• Browse #
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.