Question

In this lab, you will write a C program to encrypt a file. The program prompts the user to enter a key (maximum of 5 bytes), then the program uses the key to encrypt the file. Note that the user might enter more than 5 characters, but only the first 5 are used. If a new line before the five characters, the key is padded with 'a'; Note that the new line is not a part of the key, but the a space or tab is. The encryption is the Exclusive-OR of the text with the key. Specification • Input file name is lab62.txt • Output file name is lab62enc.txt • The prompt is "Please enter the key : " without the quotes lab62.txt is a regular text file that may include spaces, tabs, or new lines.

Answer 1

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

void main()
{
   #pragma warning(disable : 4996)
   FILE* input = fopen("lab62.txt", "r");
   #pragma warning(disable : 4996)
   FILE* output = fopen("lab62enc.txt", "w");
   char key[1000];

   //initializion to null string
   for (int i = 0; i < 1000; i++)
   {
       key[i] = '\0';
   }
   printf("Please enter the key: ");
   gets(key);
   //calculate length
   int length = 0;
   while (key[length]!='\0')
   {
       length++;
   }
   //pad a's if length is less than 5
   while (length < 5)
   {
       key[length++] = 'a';
   }
   // if user enters longer key end string at length 5
   length = 5;
   key[length] = '\0';
   int ch;
   int i = 0;
   if (input == NULL)
   {
       printf("Error opining file.");
       return 0;
   }
   while ((ch = fgetc(input)) != EOF)
   {
       ch = ((char)ch )^ key[i++];
       i = i % 5;// key length is five
       fputc(ch, output);
   }

   fclose(input);
   fclose(output);
   return 0;
}

A i ce char kewf10001 Bina - ] ccomputer Science que v lab62.txt - Notepad File Edit Format View Help I like c programming. X CA Microsoft Visual Studio Debug Console Please enter the key: secret - .. xwimmaress 11672) exite lab62encbit - Notepad File Edit Format View Help : ENTE RII Ln 3, Col 4 100% Windows (CRLF) UTF-8 Skip to next question Type here to search A ote 0 U 07:12 AM (44 ENG 30-10-2019

//To check the correctness of program give encripted text as input with same key

//original text will be generated as this is xor encription.