Code :
//Header File--RSA Application
//Miller & Rabin Algorithm--Test for Primality
//PseudoRandom Number Generator Algorithm
//Relatively Prime--Euclid's Algorithm
#include<iostream.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<conio.h>
#include<math.h>
#include<process.h>
class RSA
{
public:
int pr1,pr2,x1,n,n1;
int e,d,pt;
int a[20],b[10];
int len; //binary array length
RSA();
//Miller & Rabin Algorithm--Test for Primality
void testprimality();
//PseudoRandom Number Generator Algorithm
void pseudo1();
int pseudo2();
//Relatively Prime--Euclid's Algorithm
//GCD of two numbers-their common factor is '1'
void relprime();
int gcd(int c,int d);
//Key Generation
int keygenerate1(int ptext);//for Encryption
int keygenerate2(int ctext);//for Decryption
void decitobin(int x);
//Encryption
int encrypt(int num);
//Decryption
int decrypt(int ctext);
};
//Interface File--RSA Application
//Miller & Rabin Algorithm--Test for Primality
//PseudoRandom Number Generator Algorithm
//Relatively Prime--Euclid's Algorithm
#include"rh1.h"
RSA::RSA()
{
x1=1;
pr1=0;
pr2=0;
}
//Miller & Rabin Algorithm--Test for Primality
void RSA::testprimality()
{
int a,j,p1,q,x;
int t1,t2;
int k,flag,ch;
ch=1;
flag=0;
k=0;
//(n-1)=pow(2,k)*q
//divide (n-1) by 2 until result is odd number
while(ch)
{
x=(n-1)/(int)(pow(2,k));
if(fmod(x,2)==1)
{
ch=0;
break;
}
k++;
}
q=(int)((n-1)/(pow(2,k)));
//to pick an integer randomly which
//should be less than 'n';
//That's why calling pseudo2()
a=pseudo2();
if(a>1 && a<(n-1))
{
t1=(int)(pow(a,q));
if((t1%n)==1)
flag=1;
else
{
for(j=0;j<=(k-1);j++)
{
p1=((int)(pow(2,j)))*q;
t2=(int)pow(a,p1);
if((t2%n)==(n-1))
flag=1;
}
}
}
if(flag==1)
if(pr1==0)
pr1=n;
else if(pr1!=0 && pr2==0)
pr2=n;
}
//PseudoRandom Number Generator Algorithm
void RSA::pseudo1()
{
//to select 'n' pseudorandomly and pass to testprimality();
//'n' is to be proved either prime or not prime
int a,c,y;
unsigned int m;
y=0;
a=(int)pow(7,5); //(7,2),*(7,4),(7,5)
//(int)pow(7,5) used in IBM 360
//m should be assigned a "prime" no.
//up to pow(2,31) should be used.
//(2,5)-1;(2,7)-1;(2,13)-1;
//(2,17)-1;(2,19)-1;(2,31)-1 are primes
m=((int)pow(2,7))-1; //(2,7)
n=1;c=0;
for(int i=0;i<50;i++)
{
n=((a*n)+c)%m;
testprimality();
//n will be computed in textprimality()
}
// cout<<"
pr1 = "<<pr1;
// cout<<"
pr2 = "<<pr2;
}
int RSA::pseudo2()
{
//to pick an integer randomly which
//should be less than 'n'
int a,ret;
unsigned int m;
a=(int)pow(7,4); //(7,3),*(7,4) for a's (7,5)in pseudo1
m=(int)pow(2,5)-1; //(2,5)
ret=(a*x1)%m;
x1=ret;
return ret;
}
//Relatively Prime--Euclid's Algorithm
//GCD of two numbers-their common factor is '1'
void RSA::relprime()
{
//Finding 'e' & 'd' value
int fin,ret,ret1,ret2,ch,ex,dx;
ch=1;ex=2;dx=1;
n1=pr1*pr2;
fin=(pr1-1)*(pr2-1);
//Finding 'e' alone
x1=1; //for pseudo2
while(ch)
{
ex=pseudo2();
if(ex>1 && ex<fin)
{
ret1=gcd(ex,fin);
ret2=gcd(fin,(ex%fin));
if(ret1==1 && ret2==1)
{
e=ex;
ch=0;
break;
}
}
}
// cout<<"
Relative Prime : e value: "<<e;
//Finding 'd' alone
//de=(1 mod fin) where fin=(pr1-1)*(pr2-1);
ch=1;
while(ch)
{
ret=(e*dx)%fin;
if(ret==1)
{
d=dx;
ch=0;
break;
}
dx=dx+1;
}
// cout<<"
d value : "<<d;
}
int RSA::gcd(int c,int d)
{
int r;
r=d%c;
while(r!=0)
{
d=c;
c=r;
r=d%c;
}
return c;
}
int RSA::keygenerate1(int ptext)
{
//Encryption
int i,c;
int entext;
c=0;entext=1;
decitobin(e); //public key with 'e'
//b[]->array contains binary value of 'e'
for(i=len;i>=0;i--)
{
c=2*c;
entext=(entext*entext)%n1; //187->n1
if(a[i]==1)
{
c=c+1;
entext=(entext*ptext)%n1; //187->n1
}
}
// cout<<"
Encrypted 'c' : "<<c;
return entext;
}
int RSA::keygenerate2(int ctext)
{
//Decryption
int i,dntext,c;
dntext=1;
c=0;
decitobin(d); //Private Key with 'd'
//b[]->array contains binary value of 'd'
for(i=len;i>=0;i--)
{
c=2*c;
dntext=(dntext*dntext)%n1;
if(a[i]==1)
{
c=c+1;
dntext=(dntext*ctext)%n1;
}
}
// cout<<"
Decrypted 'c' := "<<c;
return dntext;
}
void RSA::decitobin(int x)
{
int k,i=0;
while(x>0)
{
a[i]=x%2;
i++;
x=x/2;
}
//when exit from above loop, i value is incremented by 1
k=i-1;
len=i-1;
}
int RSA::encrypt(int num)
{
int ctext,i;
pt=num;
ctext=keygenerate1(num);
return(ctext);
}
int RSA::decrypt(int ctext)
{
int dectext,i;
dectext=keygenerate2(ctext);
return(dectext);
}
//Application File--RSA Application
//Miller & Rabin Algorithm--Test for Primality
//PseudoRandom Number Generator Algorithm
//Relatively Prime--Euclid's Algorithm
#include"rh1.h"
#include<stdio.h>
void main()
{
int i,det,det1,len,k,k1,cnt;
int con=0,c;
char ch[100],cipher[20],orig[20];
RSA r;
c=1;
cout<<endl<<endl;
for(i=0;i<70;i++)
cout<<'*';
cout<<"
RSA APPLICATION
";
for(i=0;i<70;i++)
cout<<'*';
cout<<endl;
r.pseudo1();
r.relprime();
cout<<"
Enter the String : ";
cnt=0;
char chr;
scanf ( "%[^
]s", ch ) ;
len=strlen(ch);
k=0;k1=0;
for(i=0;i<len;i++)
{
con=(int)ch[i];
det=r.encrypt(con);
cipher[k]=char(det);
k++;
det1=r.decrypt(det);
orig[k1]=char(det1);
k1++;
}
cipher[k]='
