Question

C Programming

I have this function to i want to return the cipher text, but its not working, can anyone try to see what i'm doing wrong.

I need it to return the cipher text.

char* vigenereCipher(char *plainText, char *k)

{

int i;

char cipher;

int cipherValue;

int len = strlen(k);

char *cipherText = (char *)malloc(sizeof(plainText) * sizeof(char));

//Loop through the length of the plain text string

for (i = 0; i < strlen(plainText); i++)

{

//if the character is lowercase, where range is [97 -122]

if (islower(plainText[i]))

{

cipherValue = ((int)plainText[i] - 97 + (int)tolower(k[i % len]) - 97) % 26 + 97;

cipher = (char)cipherValue;

}

else // Else it's upper case, where letter range is [65 - 90]

{

cipherValue = ((int)plainText[i] - 65 + (int)toupper(k[i % len]) - 65) % 26 + 65;

cipher = (char)cipherValue;

}

//Print the ciphered character if it is alphanumeric (a letter)

if (isalpha(plainText[i]))

{

// Assign the cipher to the cipherText instead of printing it.

*cipherText = cipher;

cipherText++;

}

else //if the character is not a letter then print the character (e.g. space)

{

// Assign the character to the cipherText instead of printing it.

*cipherText = plainText[i];

cipherText++;

}

}

printf("%s", cipherText); //<------TRY PRINTING IT HERE AND NOTHING!!!!!

//return cipherText;

return strdup(cipherText);

}

Answer 1

Here, you can check my C++ code.

// C++ code to implement Vigenere Cipher 
#include<bits/stdc++.h> 
using namespace std; 
  
// This function generates the key in 
// a cyclic manner until it's length isi'nt 
// equal to the length of original text 
string generateKey(string str, string key) 
{ 
    int x = str.size(); 
  
    for (int i = 0; ; i++) 
    { 
        if (x == i) 
            i = 0; 
        if (key.size() == str.size()) 
            break; 
        key.push_back(key[i]); 
    } 
    return key; 
} 
  
// This function returns the encrypted text 
// generated with the help of the key 
string cipherText(string str, string key) 
{ 
    string cipher_text; 
  
    for (int i = 0; i < str.size(); i++) 
    { 
        // converting in range 0-25 
        char x = (str[i] + key[i]) %26; 
  
        // convert into alphabets(ASCII) 
        x += 'A'; 
  
        cipher_text.push_back(x); 
    } 
    return cipher_text; 
} 
  
// This function decrypts the encrypted text 
// and returns the original text 
string originalText(string cipher_text, string key) 
{ 
    string orig_text; 
  
    for (int i = 0 ; i < cipher_text.size(); i++) 
    { 
        // converting in range 0-25 
        char x = (cipher_text[i] - key[i] + 26) %26; 
  
        // convert into alphabets(ASCII) 
        x += 'A'; 
        orig_text.push_back(x); 
    } 
    return orig_text; 
} 
  
// Driver program to test the above function 
int main() 
{ 
    string str = "GEEKSFORGEEKS"; 
    string keyword = "AYUSH"; 
  
    string key = generateKey(str, keyword); 
    string cipher_text = cipherText(str, key); 
  
    cout << "Ciphertext : "
         << cipher_text << "\n"; 
  
    cout << "Original/Decrypted Text : "
         << originalText(cipher_text, key); 
    return 0; 
}