VIGENERE CIPHER in C

VIGENERE CIPHER

For theory purpose you can refer to any standard book or NPTEL Video lecture.

#include<stdio.h>
#include<string.h>
#define max 30

char key[max],CT[max];
int k;

void enterKey(void);
void senderText(void);
void receiverText(void);


void enterKey()
{
  printf("Enter the key: ");
    scanf("%s",key);
//printf("key: %s",key);
k=strlen(key);
  //printf("\nKey length: %d",k);
}

void senderText()
{
printf("\n\n\t*****SENDER-ENCODING*****\n");

char text[max];
int t,i,j=0;
int aci_ct[max];

  printf("\nEnter the text: ");
scanf("%s",text);
//printf("Entered text is: %s",text);
   t=strlen(text);
//printf("\nText length: %d",t);
enterKey();

  for(i=0;i<t;i++)
  {
    aci_ct[i]=(((text[i]-97)+(key[j]-97))%26)+97;
    j++;
    if(j>=k)
      j=0;
  }

  for(i=0;i<t;i++)
    {
    CT[i]=aci_ct[i];
  }
  printf("\n\tCipher Text: %s",CT);
}

void receiverText()
{
printf("\n\n\t*****RECEIVER-DECODING*****\n");
char PT[max];
int t,i,j=0;
int aci_pt[max];

t=strlen(CT);
//printf("\nText length: %d",t);

for(i=0;i<t;i++)
  {
    aci_pt[i]=(((CT[i]-97)-(key[j]-97)+26)%26)+97;
        j++;
        if(j>=k)
          j=0;
  }
  for(i=0;i<t;i++)
    {
      PT[i]=aci_pt[i];
  }
  printf("\n\tPlain Text: %s",PT);
}

main()
{
  printf("\n\n\t\t\t.........VIGENERE-CIPHER.........\n");

senderText();
receiverText();

   printf("\n\n");
}

Output:

.........VIGENERE-CIPHER.........


*****SENDER-ENCODING*****

Enter the text: welcometounicoderz
Enter the key: unicoderz

Cipher Text: qrtecpiknoaqecgiiy

*****RECEIVER-DECODING*****

Plain Text: welcometounicoderz

For any query, please comment below.
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