Playfair Cipher Implementation > C Program
Playfair Cipher Implementation > C Program
Cryptography and System Security
Program:
#include<stdio.h>
int check(char table[5][5],char k)
{
int i,j;
for(i=0;i<5;++i)
for(j=0;j<5;++j)
{
if(table[i][j]==k)
return 0;
}
return 1;
}
void main()
{
int i,j,key_len;
char table[5][5];
for(i=0;i<5;++i)
for(j=0;j<5;++j)
table[i][j]='0';
printf("**********Playfair Cipher************\n\n");
printf("Enter the length of the Key. ");
scanf("%d",&key_len);
char key[key_len];
printf("Enter the Key. ");
for(i=-1;i<key_len;++i)
{
scanf("%c",&key[i]);
if(key[i]=='j')
key[i]='i';
}
int flag;
int count=0;
// inserting the key into the table
for(i=0;i<5;++i)
{
for(j=0;j<5;++j)
{
flag=0;
while(flag!=1)
{
if(count>key_len)
goto l1;
flag=check(table,key[count]);
++count;
}// end of while
table[i][j]=key[(count-1)];
}// end of inner for
}// end of outer for
l1:printf("\n");
int val=97;
//inserting other alphabets
for(i=0;i<5;++i)
{
for(j=0;j<5;++j)
{
if(table[i][j]>=97 && table[i][j]<=123)
{}
else
{
flag=0;
while(flag!=1)
{
if('j'==(char)val)
++val;
flag=check(table,(char)val);
++val;
}// end of while
table[i][j]=(char)(val-1);
}//end of else
}// end of inner for
}// end of outer for
printf("The table is as follows:\n");
for(i=0;i<5;++i)
{
for(j=0;j<5;++j)
{
printf("%c ",table[i][j]);
}
printf("\n");
}
int l=0;
printf("\nEnter the length length of plain text.(without spaces) ");
scanf("%d",&l);
printf("\nEnter the Plain text. ");
char p[l];
for(i=-1;i<l;++i)
{
scanf("%c",&p[i]);
}
for(i=-1;i<l;++i)
{
if(p[i]=='j')
p[i]='i';
}
printf("\nThe replaced text(j with i)");
for(i=-1;i<l;++i)
printf("%c ",p[i]);
count=0;
for(i=-1;i<l;++i)
{
if(p[i]==p[i+1])
count=count+1;
}
printf("\nThe cipher has to enter %d bogus char.It is either 'x' or 'z'\n",count);
int length=0;
if((l+count)%2!=0)
length=(l+count+1);
else
length=(l+count);
printf("\nValue of length is %d.\n",length);
char p1[length];
//inserting bogus characters.
char temp1;
int count1=0;
for(i=-1;i<l;++i)
{
p1[count1]=p[i];
if(p[i]==p[i+1])
{
count1=count1+1;
if(p[i]=='x')
p1[count1]='z';
else
p1[count1]='x';
}
count1=count1+1;
}
//checking for length
char bogus;
if((l+count)%2!=0)
{
if(p1[length-1]=='x')
p1[length]='z';
else
p1[length]='x';
}
printf("The final text is:");
for(i=0;i<=length;++i)
printf("%c ",p1[i]);
char cipher_text[length];
int r1,r2,c1,c2;
int k1;
for(k1=1;k1<=length;++k1)
{
for(i=0;i<5;++i)
{
for(j=0;j<5;++j)
{
if(table[i][j]==p1[k1])
{
r1=i;
c1=j;
}
else
if(table[i][j]==p1[k1+1])
{
r2=i;
c2=j;
}
}//end of for with j
}//end of for with i
if(r1==r2)
{
cipher_text[k1]=table[r1][(c1+1)%5];
cipher_text[k1+1]=table[r1][(c2+1)%5];
}
else
if(c1==c2)
{
cipher_text[k1]=table[(r1+1)%5][c1];
cipher_text[k1+1]=table[(r2+1)%5][c1];
}
else
{
cipher_text[k1]=table[r1][c2];
cipher_text[k1+1]=table[r2][c1];
}
k1=k1+1;
}//end of for with k1
printf("\n\nThe Cipher text is:\n ");
for(i=1;i<=length;++i)
printf("%c ",cipher_text[i]);
}
/*OUTPUT
[prat@localhost Desktop]$ gcc playfair.c
[prat@localhost Desktop]$ ./a.out
**********Playfair Cipher************
Enter the length of the Key. 15
Enter the Key. playfairexample
The table is as follows:
p l a y f
i r e x m
b c d g h
k n o q s
t u v w z
Enter the length length of plain text.(without spaces) 25
Enter the Plain text. hidethegoldinthetreestump
The replaced text(j with i)
h i d e t h e g o l d i n t h e t r e e s t u m p
The cipher has to enter 1 bogus char.It is either 'x' or 'z'
Value of length is 26.
The final text is:
h i d e t h e g o l d i n t h e t r e x e s t u m p
The Cipher text is:
b m o d z b x d n a b e k u d m u i x m m o u v i f
*/
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