Hill Cipher Implementation > C Program

Hill Cipher Implementation > C Program

Cryptography and System Security

Program:

#include<stdio.h>

int check(int x)

{

if(x%3==0)

return 0;

int a=x/3;

int b=3*(a+1);

int c=b-x;

return c;

}

void main()

{

int l,i,j;

int temp1;

int k[3][3];

int p[3][1];

int c[3][1];

char ch;

printf("\nThe cipher has a key of length 9. ie. a 3*3 matrix.\nEnter the 9 character key. ");

for(i=0;i<3;++i)

{

for(j=0;j<3;++j)

{

scanf("%c",&ch);

if(65<=ch && ch<=91)

k[i][j]=(int)ch%65;

else

k[i][j]=(int)ch%97;

}

}

for(i=0;i<3;++i)

{

for(j=0;j<3;++j)

{

printf("%d ",k[i][j]);

}

printf("\n");

}

printf("\nEnter the length of string to be encoded(without spaces). ");

scanf("%d",&l);

temp1=check(l);

if(temp1>0)

printf("You have to enter %d bogus characters.",temp1);

char pi[l+temp1];

printf("\nEnter the string. ");

for(i=-1;i<l+temp1;++i)

{

scanf("%c",&pi[i]);

}

int temp2=l;

int n=(l+temp1)/3;

int temp3;

int flag=0;

int count;

printf("\n\nThe encoded cipher is : ");

while(n>0)

{

count=0;

for(i=flag;i<flag+3;++i)

{

if(65<=pi[i] && pi[i]<=91)

temp3=(int)pi[i]%65;

else

temp3=(int)pi[i]%97;

p[count][0]=temp3;

count=count+1;

}

int k1;

for(i=0;i<3;++i)

c[i][0]=0;

for(i=0;i<3;++i)

{

for(j=0;j<1;++j)

{

for(k1=0;k1<3;++k1)

c[i][j]+=k[i][k1]*p[k1][j];

}

}

for(i=0;i<3;++i)

{

c[i][0]=c[i][0]%26;  

printf("%c ",(char)(c[i][0]+65));

}

n=n-1;

flag=flag+3;

}

}

/*OUTPUT

[prat2@localhost Desktop]$ gcc hill.c

[prat2@localhost Desktop]$ ./a.out

The cipher has a key of length 9. ie. a 3*3 matrix.

Enter the 9 character key. GYBNQKURP

6 24 1 

13 16 10 

20 17 15 

Enter the length of string to be encoded(without spaces). 6

Enter the string. actCAt

The encoded cipher is : P O H F I N 

[prat2@localhost Desktop]$ gcc hill.c

[prat2@localhost Desktop]$ ./a.out

The cipher has a key of length 9. ie. a 3*3 matrix.

Enter the 9 character key. GYBNQKURP

6 24 1 

13 16 10 

20 17 15 

Enter the length of string to be encoded(without spaces). 7

You have to enter 2 bogus characters.

Enter the string. actcatact

The encoded cipher is : P O H F I N P O H  

*/