Question

I NEED HELP WITH DEBUGGING A C PROGRAM! PLEASE HEAR ME OUT AND READ THIS. I just have to explain a lot so you understand how the program should work.

In C programming, write a simple program to take a text file as input and encrypt/decrypt it by reading the text bit by bit, and swap the bits if it is specified by the first line of the text file to do so (will explain below, and please let me know if you need more information).

An example of running the program on a linux machine.

@loki:/home/wmahoney/CYBR2250/tablecrypt$ cat ok_data3 Example of an already encrypted text file as input. vvv SNSSNNSSNSNSSNSS IC?u?x?[?Q?T? x?Y y?Y_ _??_?Y??^??U?T?r??_ p?_?Y?x s?S?Y?s, ?Y?Q??T?y?Q?X??Z u?Q?s Q?_-?^?U??Y?Y?x X?S?X?s, ?x T?s R?Y??T??x?r??Z {?Q?) I?U?T??Y S?\?Y??\?s?U??r?p?_?r?p?u ?@? x?Q??,?Z ]?x?_?s _??^?r?p?U?^ x?Q??s??Y??^??Q?Y? _??Y?T?p??U?p?Y ]?S?Q?U?Q??U?s-?^ x?Y Y?r? ju 20x??Y?x?r? x?Y U?z?^?U?^ _??_?p?Y??Y?T?^?S?\ Q?X Y?Y?x?_?Y?T?^?S?\ ]?S?U?Y? s?S??s x?Y I?U?]??_?_??Q?T?^? p?_?U?Y??_?Y s?p T?U?x?S?x?X Q?X Y?Z?S?Y?x ]?Q?s ??^?r?p?U?^;?^??T??y?s?q?Y?x U?x?_?y?x? ??Z Y?Y?x?_?U?s Q?X S?]?y?U?[ T?s Q?\?{ ?X Y?Q? ?Q?Y s?T [?]?s ??x?\??r?Q?Y??_?p?Y?U?u,?_?x _??T?S??r??^?U?Y?u y?s?U?Y??_ p?^ Q?x_p?p?r- L?_?s \?W??Q?R??_?r p?_?r?] {?r?s? 6. Qloki: /home/wmahoney/CYBR2250/tablecrypt$ ./tablecrypt sok data3 SNSSNNSSNSNSSNSS <- Example of decrypting the text by swapping the bits, bit by bit as the first line shows. Cryptography, the use of codes and ciphers to protect secrets, began thousands of years ago. Until recent decades, it has been the story of what might be called classic cryptography – that is, of methods of encryption that use pen and paper, or perhaps simple mechanical aids. In the early 20th century, the invention of complex mechanical and electromechanical machines, such as the Enigma rotor machine, Program should take as input a text file where the provided more sophisticated and efficient means of encryption; and the first 16 bytes are as shown in the example, they subsequent introduction of electronics and computing has allowed stand for SWAP and NOT SWAP. The program elaborate schemes of still greater complexity, most of which are should read that, then read the text in the file bit by entirely unsuited to pen and paper. bit and swap the bits or not, according to the first line. This is an example run. It should be able to Looks like maybe your program works? encrypt and decrypt as shown. @loki:/home/wmahoney/CYBR2250/tablecrypt$ |

The program should:

Accept as input from “stdin” a file of data. Please do not open the file, just read from the standard input. The first 16 bytes are as shown below in the example, four characters for row zero, four more for row one, etc. After this initial string there is a newline character, and then the data to encrypt. You can read these (and everything else) with “getchar”, and print everything with just “putchar”.

We need to start doing error checking. If there’s fewer than 16 bytes on the first line, or greater than 16 bytes on the first line, print an appropriate error message and abandon ship. If things look OK, keep going to ...

Output the original 16 bytes as well as the newline character.

For each byte of the rest of the data, encrypt the byte and print it, then after each byte rotate the table 90 degrees left (counterclockwise).

Repeat this byte by byte until you encounter the end of the file.

You must use the following functions for this program:

main – in charge of running the show.

rotate – it takes one parameter, the 4x4 table, and rotates it 90 degrees left. It is a “void” function.

encrypt – it takes two parameters, the character to encrypt and the table. It returns a “char” as the result.

Make sure the program compiles with the following:

gcc -Wall -pedantic -std=c1x -o tablecrypt tablecrypt.c

Encrypting one byte can be done with something like this.

Suppose that you need to flip two bits, say bit 7 and bit 6. Obviously if both are zero there's nothing you have to do, and if both are 1, same story. Only for 01 or 10 do you need to invert them, and this can be done with XOR. So for bits 7 and 6, and variable X, something like this ought to be fine:

if ( ( X & 0xc0 == 0x80 ) || ( X & 0xc0 == 0x40 ) )

X ^= 0xc0;

So if you had

SNSS NSNS SNNS SNNS (SNSSNSNSSNNSSNNS)

01 01 00 10 (01010010)... it would become

10 01 00 10 (10010010).

You can count the number of S's in every 4, and if there are an odd number of S's, then swap. If it is even like SNNS then it won't be changed.

HERE IS THE CODE I HAVE THAT I DONT KNOW HOW TO FIX OR WHAT IS WRONG.

#include <stdio.h>

#include <stdlib.h>

#include <math.h>

//function to convert char into its binary

void getBinaryFromChar(char c, char binary[])

{

for (int i = 7; i >= 0; --i)

{

binary[7 - i] = ((c & (1 << i)) ? '1' : '0');

}

}

//function to convert binary into its character

char getCharFromBinary(char binary[])

{

int n = 0;

for(int i = 0; i < 8; i++)

{

if(binary[i] == '1')

{

n += pow(2, 7 - i);

}

}

n %= 128;

char c = (char)n;

return c;

}

//function to encrypt the char

char encrypt(char binary[], char table[4][4])

{

int count = 0;

// loop for the encryption

for(int i = 0; i < 4; i++)

{

for(int j = 0; j < 4; j++)

{

if(table[i][j] == 'S')

{

count++;

}

}

//if count is odd then swap

if(count % 2)

{

char ch = binary[2 * i];

binary[2 * i] = binary[2 * i + 1];

binary[2 * i + 1] = ch;

}

count = 0;

}

//return the encrypted character

return getCharFromBinary(binary);

}

//function to rotate the table 90 degree left

void rotateTable(char table[4][4])

{

int N = 4;

for (int x = 0; x < N / 2; x++)

{

for (int y = x; y < N - x - 1; y++)

{

int temp = table[x][y];

table[x][y] = table[y][N - 1 - x];

table[y][N - 1 - x] = table[N - 1 - x][N - 1 - y];

table[N - 1 - x][N - 1 - y] = table[N - 1 - y][x];

table[N - 1 - y][x] = temp;

}

}

}

//main function to implement the encryption of data

int main()

{

int count = 0;

char ch, string[16];

//loop to store the first 16 characters

while((ch = getchar()) != '\n')

{

string[count] = ch;

count++;

putchar(ch);

if(count == 16)

{

break;

}

}

//condition to check that char before newline are exactly 16 or not

if(count == 16 && getchar() == '\n')

{

putchar('\n');

}

else

{

printf("Data is corrupted can't encrypt the data\n");

exit(0);

}

//create table for the first 16 characters

char table[4][4];

for(int i = 0; i < 4; i++)

{

for(int j = 0; j < 4; j++)

{

table[i][j] = string[i * 4 + j];

}

}

//to store the binary value of the characters

char binary[8],encryptedch;

//loop to read each byte or character one by one until the EOF

while((ch = getchar()) != EOF)

{

//function to get the binary value of ch into binary string

getBinaryFromChar(ch, binary);

//encrypt function returns the encrypted value of ch character

encryptedch = encrypt(binary, table);

//print the encrypted charater

printf("%c", encryptedch);

//rotate the table to 90 degree left each time

rotateTable(table);

}

//all the data is encrypted now

}

$//loop to store the first 16 characters while((ch = getchar()) != \n) string[count] = ch; count++; putchar(ch); if(count ==$

$else printf(Data is corrupted cant encrypt the data\n); exit(0); //create table for the first 16 characters char table[4][$

The program appears to encrypt correctly. But not decrypt. You should be able to pipe in the output of the initial encryption as input and see the original text. Any help is very much appreciated please I am stuck on this.

Answer 1

I guess you have to declare the arrays you are using as global, else how are you updating the values. This may be the only problem with your code. So I will request you to declare the arrays globally,then modify the code according to it. Rest everything looks fine.