CNS Practical-7

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

// Function to encrypt the message using Rail Fence Cipher
void railFenceEncrypt(char text[], int rails) {
    int len = strlen(text);
    char grid[rails][len];
    int row = 0, col = 0;
    int dir_down = 0; // flag to determine the direction (down or up)

    // Initialize grid with empty spaces
    for (int i = 0; i < rails; i++) {
        for (int j = 0; j < len; j++) {
            grid[i][j] = '\n';
        }
    }

    // Fill the grid with the message in a zigzag pattern
    for (int i = 0; i < len; i++) {
        grid[row][col++] = text[i];
        if (row == 0 || row == rails - 1) {
            dir_down = !dir_down;
        }
        row += dir_down ? 1 : -1;
    }

    // Read the grid row by row to form the ciphertext
    printf("Encrypted Text: ");
    for (int i = 0; i < rails; i++) {
        for (int j = 0; j < len; j++) {
            if (grid[i][j] != '\n') {
                printf("%c", grid[i][j]);
            }
        }
    }
    printf("\n");
}

int main() {
    char text[] = "HELLO";
    int rails = 3;  // Number of rails (rows)
    
    railFenceEncrypt(text, rails);
    
    return 0;
}

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

// Function to encrypt the message using Columnar Transposition Cipher
void columnarEncrypt(char text[], char key[]) {
    int len = strlen(text);
    int keyLen = strlen(key);
    int rows = (len + keyLen - 1) / keyLen;  // Calculate the number of rows needed
    char grid[rows][keyLen];

    // Fill the grid with text, row by row
    int k = 0;
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < keyLen; j++) {
            if (k < len) {
                grid[i][j] = text[k++];
            } else {
                grid[i][j] = 'X';  // Padding with 'X' if the grid is not full
            }
        }
    }

    // Sort the key to determine the column order
    int order[keyLen];
    for (int i = 0; i < keyLen; i++) {
        order[i] = i;
    }

    // Sorting by key values
    for (int i = 0; i < keyLen - 1; i++) {
        for (int j = i + 1; j < keyLen; j++) {
            if (key[order[i]] > key[order[j]]) {
                int temp = order[i];
                order[i] = order[j];
                order[j] = temp;
            }
        }
    }

    // Print the encrypted message by reading columns in sorted order
    printf("Encrypted Text: ");
    for (int i = 0; i < keyLen; i++) {
        for (int j = 0; j < rows; j++) {
            printf("%c", grid[j][order[i]]);
        }
    }
    printf("\n");
}

int main() {
    char text[] = "HELLO";
    char key[] = "ZEBRAS";  // Keyword to determine the column order
    
    columnarEncrypt(text, key);
    
    return 0;
}