file_encrpyt.c

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

void file_encryption(char key[])
{
    char c,sentence[20];
    printf("\nDo you want to input string(y/n): ");
    scanf("%c",&c);
    if(c=='y')
    {
        printf("\nenter string: ");
        scanf("%[^/n]s",sentence);
      
        int keyLen = strlen(key), i, j;
        int n= strlen(sentence);
        int ciphertext_len = 0;
        for (int i = 0;i<n; i++)
        {
            if ((sentence[i] >= 'A') && (sentence[i] <= 'Z'))
                ciphertext_len++;
        }
        //printf("cipher text length: %d\n", ciphertext_len);

        char newKey[ciphertext_len];

        //generating new key
        for (i = 0, j = 0; i < ciphertext_len; ++i, ++j)
        {
            if (j == keyLen)
                j = 0;

            newKey[i] = key[j];
        }
        newKey[i] = '\0';
        printf("\nNew Generated Key: %s\n", newKey); 
    }
    else
    {
        FILE *f1 = fopen("plaintext.txt", "r");

        if (f1 == NULL)
            printf("error in opening the file");

        else
        {
            char ch;
            int keyLen = strlen(key), i, j;

            int ciphertext_len = 0;
            for (int i = 0; (ch = fgetc(f1)) != EOF; i++)
            {
                if ((ch >= 'A') && (ch <= 'Z'))
                    ciphertext_len++;
            }
            //printf("cipher text length: %d\n", ciphertext_len);

            char newKey[ciphertext_len];

            //generating new key
            for (i = 0, j = 0; i < ciphertext_len; ++i, ++j)
            {
                if (j == keyLen)
                    j = 0;

                newKey[i] = key[j];
            }
            newKey[i] = '\0';
            printf("\nNew Generated Key: %s\n", newKey);
            fclose(f1);
    }
}