Question

In modern operating systems, kernel processes messages are communicated securely by using several encryption mechanisms such as Zig-Zag cipher which divides the message into two parts: the first part contains the odd-positions characters, while the second part contains the even-positions characters. Eventually, the cipher is constructed by concatenating the first part with second part. Using traditional pipes, write a program to produce a full duplex parent/child relationship in which processes can send/receive user data encrypted with Zig-Zag cipher. The communication should cease if either process sends the message “Bye

Answer 1

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#define VAL(PTR) (*PTR)

typedef char* STRING;

typedef char** STRING_REF;

void flush_stdin()

{

while(fgetc(stdin) != '\n');

}

void rail_fence_encrypt(STRING_REF str, int depth)

{

STRING old_str = VAL(str);

int len_str = strlen(old_str), itr_str, rows, cols;

STRING res_str = (STRING)malloc(sizeof(char)*len_str);

for(rows = 0, itr_str = 0 ; rows < depth ; ++rows)

{

for(cols = rows ; cols < len_str ; cols += depth)

{

res_str[itr_str] = old_str[cols];

++itr_str;

}

}

res_str[itr_str] = '\0';

free(VAL(str));

VAL(str) = res_str;

}

void rail_fence_decrypt(STRING_REF str, int depth)

{

STRING old_str = VAL(str);

int len_str = strlen(old_str), itr_str, rows, counter;

STRING res_str = (STRING)malloc(sizeof(char)*len_str);

for(counter = 0, itr_str = 0 ; counter < len_str/depth ; ++counter)

{

for(rows = counter ; rows < len_str ; rows+=(len_str/depth))

{

res_str[itr_str] = old_str[rows];

++itr_str;

}

}

free(VAL(str));

VAL(str) = res_str;

}

int main(void)

{

STRING str;

int txt_length, key;

printf("Enter the depth: ");

scanf("%d",&key);

printf("Enter the length of the text: ");

scanf("%d",&txt_length);

printf("Input the string you want to encrypt: ");

flush_stdin();

str = (char*)malloc((txt_length+1)*sizeof(char));

fgets(str,txt_length+1,stdin);

if(&str == "Bye" || &str =="bye")

return 0;

else

rail_fence_encrypt(&str,key);

printf("\nThe encrypted text is: %s",str);

rail_fence_decrypt(&str,key);

printf("\nThe decrypted text is: %s",str);

return 0;

}