Hill Cipher Algorithm Program in C

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Today we will learn Hill Cipher algorithm program in c with the output. Hill Cipher algorithm was invented in 1929 by Lester S. Hill. Hill cipher was the first polygraphic cipher. In Hill cipher, each letter is represented by a number modulo 26. To encrypt a message, each n block of letters will be multiplied by the n*n matrix, against modulus 26. The matrix is called a cipher key.


Below is the Hill Cipher program example to know how to compute cipher text from plain text.

Hill Cipher Example

/*Hill Cipher Algorithm Program in C */

#include<stdio.h>
#include<conio.h>
void main()
{
    int i,j,ans[25][1],sum=0,mtrx[25][25],end;
    char txt[25];
    clrscr();
    printf("\nEnter the string : ");
    scanf("%s",txt);

    for(i=0;i<25;i++)
    {
        if(txt[i]>=97 && txt[i]<122) {

        }
        else
        {
            end=i;
            break;
        }
    }

    for(i=0;i<end;i++)
    {
        txt[i]=txt[i]-'a';
    }

    printf("\nEnter %dX%d key matrix row by row.\n",end,end);

    for(i=0;i<end;i++)
    {
        for(j=0;j<end;j++)
        {
    printf("key[%d][%d] : ",i,j);
            scanf("%d",&mtrx[i][j]);
        }
    }
    printf("\n");

    printf("Key matrix is :\n");
    for(i = 0; i <end; i++) {
        for(j = 0; j <end; j++)
    printf("%d\t", mtrx[i][j]);

        printf("\n");
    }

    for(i=0;i<end;i++)
    {
        sum=0;
        for(j=0;j<end;j++)
        {
            sum+=mtrx[i][j]*(int)txt[j];
        }
        ans[i][0]=sum;
    }

    printf("\nCipher Text is: ");
    for(i=0;i<end;i++)
    {
        printf(" %c",((ans[i][0])%26)+97);
    }

    getch();
}

Output:

Hill Cipher Algorithm Program in C - Encryption - Output