Hill Cipher in C - Sanfoundry

This is a C Program to implement Hill Cipher. Hill cipher is a polygraphic substitution cipher based on linear algebra.

Here is source code of the C Program to Implement the Hill Cypher. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include<stdio.h>
```
```
#include<string.h>
```
```
int main() {
```

    unsigned int a[3][3] = { { 6, 24, 1 }, { 13, 16, 10 }, { 20, 17, 15 } };

    unsigned int b[3][3] = { { 8, 5, 10 }, { 21, 8, 21 }, { 21, 12, 8 } };

```
    int i, j;
```
```
    unsigned int c[20], d[20];
```
```
    char msg[20];
```
```
    int determinant = 0, t = 0;
```
```
    ;
```
```
    printf("Enter plain text\n ");
```
```
    scanf("%s", msg);
```
```
    for (i = 0; i < 3; i++) {
```
```
        c[i] = msg[i] - 65;
```
```
        printf("%d ", c[i]);
```
```
    }
```
```
    for (i = 0; i < 3; i++) {
```
```
        t = 0;
```
```
        for (j = 0; j < 3; j++) {
```
```
            t = t + (a[i][j] * c[j]);
```
```
        }
```
```
        d[i] = t % 26;
```
```
    }
```

    printf("\nEncrypted Cipher Text :");

```
    for (i = 0; i < 3; i++)
```
```
        printf(" %c", d[i] + 65);
```
```
    for (i = 0; i < 3; i++) {
```
```
        t = 0;
```
```
        for (j = 0; j < 3; j++) {
```
```
            t = t + (b[i][j] * d[j]);
```
```
        }
```
```
        c[i] = t % 26;
```
```
    }
```

    printf("\nDecrypted Cipher Text :");

```
    for (i = 0; i < 3; i++)
```
```
        printf(" %c", c[i] + 65);
```
```
    return 0;
```
```
}
```

Output:

$ gcc HillCipher.c
$ ./a.out
 
Enter plain text: SAN
 18 0 13 
Encrypted Cipher Text : R A J
Decrypted Cipher Text : S A N

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