Question

Caesar Cipher v3 Decription

Description A Caesar cipher is one of the first and most simple encryption methods. It works by shifting all letters in the original message (plaintext) by a certain fixed amount (the amounts represents the encryption key). The resulting encoded text is called ciphertext.

Example Key (Shift): 3 Plaintext: Abc Ciphertext: Def

Task Your goal is to implement a Caesar cipher program that receives the key and an encrypted paragraph (with uppercase and lowercase letters, punctuations, and spaces) and decrypt it.

Requirements Only letters must be decrypted, any other character must remain unchanged

Note: The whole paragraph is going to be given to you as a string (char array). Review the template code for more details.

//Code Given

#include <stdio.h>

#include <stdbool.h>

#include <string.h>

#include <ctype.h>

// ---------------------- DO NOT MODIFY THIS SECTION --------------------------------

#define MAX_PGRAPH_LENGTH 100

#define MAX_WORD_LENGHT 20

int main(void) {

// definitions

char plaintext[MAX_PGRAPH_LENGTH];

char ciphertext[MAX_PGRAPH_LENGTH] = "";

char input[MAX_WORD_LENGHT];

// read the key

int key;

scanf("Key: %d, ", &key);

// read text

scanf("Input: ");

while (true)

{

scanf("%s", input);

if (strlen(ciphertext) + strlen(input) + 1 > MAX_PGRAPH_LENGTH)

break;

strcat(ciphertext, input);

strcat(ciphertext, " ");

}

ciphertext[strlen(ciphertext) - 1] = '\0';

// ---------------------- -----------------------------------------------------------

/*

Your code goes here!

*/

// ---------------------- DO NOT MODIFY THIS SECTION --------------------------------

printf(" Key: %d\n", key);

printf(" Input: %s\n", ciphertext);

printf("Output: %s\n", plaintext);

// ---------------------- -----------------------------------------------------------

}

Answer 1

//Code Given

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>

// ---------------------- DO NOT MODIFY THIS SECTION --------------------------------
#define MAX_PGRAPH_LENGTH 100
#define MAX_WORD_LENGHT 20

int main(void) {

        // definitions
        char plaintext[MAX_PGRAPH_LENGTH];
        char ciphertext[MAX_PGRAPH_LENGTH] = "";
        char input[MAX_WORD_LENGHT];

        // read the key
        int key;
        scanf("Key: %d, ", &key);

        // read text
        scanf("Input: ");
        while (true) {
                scanf("%s", input);
                if (strlen(ciphertext) + strlen(input) + 1 > MAX_PGRAPH_LENGTH)
                        break;

                strcat(ciphertext, input);
                strcat(ciphertext, " ");
        }

        ciphertext[strlen(ciphertext) - 1] = '\0';
        // ---------------------------------------------------------------------------------

        int len = strlen(ciphertext);
        //key = key % 26;
        for(int i=0; i<len; i++) {
                if(ciphertext[i] <= 'Z' && ciphertext[i] >= 'A') {
                        plaintext[i] = 'A' + (((int)(ciphertext[i] - 'A') - key + 26) % 26);
                } else if(ciphertext[i] <= 'z' && ciphertext[i] >= 'a') {
                        // if lower case letters
                        plaintext[i] = 'a' + (((int)(ciphertext[i] - 'a') - key + 26) % 26);
                } else {
                        // it is not alphabate.. do not decrypt
                        plaintext[i] = ciphertext[i];
                }
        }

        // ----------------------DO NOT MODIFY THIS SECTION-------------------------------

        printf("   Key: %d\n", key);
        printf(" Input: %s\n", ciphertext);
        printf("Output: %s\n", plaintext);

        // ---------------------- -----------------------------------------------------------

}

Hi. please find the complete code.. i have given code comments so that it is very easy for you to understand the flow. In case of any doubts, please ask in comments. If the answer helps you, please upvote. Thanks!

saved share gcc version 4.6.3 Key: 4, kadjksanjd adsaj dsadjsa jdas jksndjnajskd j asjd sa dhjas djksa hd djhsa djsa djh ashdas dhas das dh sajd sajh 13 14 15 16 17 18 19 28 21 dsahj djhas dsadj sajd saj dsajhd definitions char plaintext[MAX PGRAPH LENGTH]: char ciphertext[MAX PGRAPH_LENGTH] char input[HAX_WORD_LENGHT: Key: 4 Input: kadjksanjd adsaj dsadjsa jdas jksndjnajskd j asjd sa dhjas djksa hd djhsa djsa djh ashdas dhas das zfd wodzwo zdwo zwo // read the key int key; scant( "Key: %d. ", &key); 23 24 25- 26 27 28 29 38 31 32 // read text scanf Input: " while (true) scanf("%s", input); if (strlen(ciphertext) strlen(input) 1 > MAX PGRAPH LENGTH) break; strcat(ciphertext, input); strcat(ciphertext,"); 34 35 36 37 38 39 40- 41 42 13 ciphertexttrien(ciphertext) 1-e int len strlen(ciphertext); //key-key % 26; for(int i-e; ilen; i+) { if(ciphertext[1] "Z" && ciphertext[1] 'A. { (((int)(ciphertext[i] >- 'A') plaintext[1] 'A') key + 26) % 26); - . - else if(ciphertext[i] <-z & ciphertext[i]- a) // İf lower case letters plaintext[1] 'a, + (((int)(ciphertext[1] 'a') key + 26) % 26); - - else ( 46 47 /I it is not alphabate.. do not decrypt plaintexti] ciphertext[i]: