import java.math.BigInteger ;
import java.util.Random ;
import java.io.* ;
import java.io.*;
import java.util.*;
import java.sql.*;
import javax.swing.*;

public class RSA
{
/**
* Bit length of each prime number.
*/
int primeSize ;

/**
* Two distinct large prime numbers p and q.
*/
BigInteger p, q ;

/**
* Modulus N.
*/
BigInteger N ;

/**
* r = ( p – 1 ) * ( q – 1 )
*/
BigInteger r ;

/**
* Public exponent E and Private exponent D
*/
BigInteger E, D ;

String nt,dt,et;
/**
* Constructor.
*
* @param primeSize Bit length of each prime number.
*/

String publicKey;
String privateKey;
String randomNumber;

BigInteger[] ciphertext;
int m[] = new int[1000];
String st[] = new String[1000];
String str = "";
String sarray1[] = new String[100000];

StringBuffer sb1 = new StringBuffer();
String inputMessage,encryptedData,decryptedMessage;

public RSA( int primeSize )
{

this.primeSize = primeSize ;

// Generate two distinct large prime numbers p and q.
generatePrimeNumbers() ;

// Generate Public and Private Keys.
generatePublicPrivateKeys() ;

BigInteger publicKeyB = getE();
BigInteger privateKeyB = getD();
BigInteger randomNumberB = getN();
publicKey = publicKeyB.toString();
privateKey = privateKeyB.toString();
randomNumber = randomNumberB.toString();
System.out.println("Public Key (E,N): "+publicKey+","+randomNumber);
System.out.println("Private Key (D,N): "+privateKey+","+randomNumber);

//Encrypt data
inputMessage=JOptionPane.showInputDialog(null,"Enter message to encrypt");
encryptedData=RSAencrypt(inputMessage);
System.out.println("Encrypted message"+encryptedData);
JOptionPane.showMessageDialog(null,"Encrypted Data "+"\n"+encryptedData);

//Decrypt data
decryptedMessage=RSAdecrypt();
JOptionPane.showMessageDialog(null,"Decrypted Data "+"\n"+decryptedMessage);

}

/**
* Generate two distinct large prime numbers p and q.
*/
public void generatePrimeNumbers()
{
p = new BigInteger( primeSize, 10, new Random() ) ;

do
{
q = new BigInteger( primeSize, 10, new Random() ) ;
}
while( q.compareTo( p ) == 0 ) ;
}

/**
* Generate Public and Private Keys.
*/
public void generatePublicPrivateKeys()
{
// N = p * q
N = p.multiply( q ) ;

// r = ( p – 1 ) * ( q – 1 )
r = p.subtract( BigInteger.valueOf( 1 ) ) ;
r = r.multiply( q.subtract( BigInteger.valueOf( 1 ) ) ) ; //(p-1)(q-1)

// Choose E, coprime to and less than r
do
{
E = new BigInteger( 2 * primeSize, new Random() ) ;
}
while( ( E.compareTo( r ) != -1 ) || ( E.gcd( r ).compareTo( BigInteger.valueOf( 1 ) ) != 0 ) ) ;

// Compute D, the inverse of E mod r
D = E.modInverse( r ) ;

}

/**
* Get prime number p.
*
* @return Prime number p.
*/
public BigInteger getp()
{
return( p ) ;
}

/**
* Get prime number q.
*
* @return Prime number q.
*/
public BigInteger getq()
{
return( q ) ;
}

/**
* Get r.
*
* @return r.
*/
public BigInteger getr()
{
return( r ) ;
}

/**
* Get modulus N.
*
* @return Modulus N.
*/
public BigInteger getN()
{
return( N ) ;
}

/**
* Get Public exponent E.
*
* @return Public exponent E.
*/
public BigInteger getE()
{
return( E ) ;
}

/**
* Get Private exponent D.
*
* @return Private exponent D.
*/
public BigInteger getD()
{
return( D ) ;
}

/** Encryption */

public String RSAencrypt(String info) {

E = new BigInteger(publicKey);
N = new BigInteger(randomNumber);
try {
ciphertext = encrypt( info ) ;
for( int i = 0 ; i < ciphertext.length ; i++ )
{
m[i] = ciphertext[i].intValue();
st[i] = String.valueOf(m[i]);
sb1.append(st[i]);
sb1.append(" ");
str = sb1.toString();

}
}
catch (Exception e) {
System.out.println(e);
}

return str;
}
public BigInteger[] encrypt( String message )
{
int i ;
byte[] temp = new byte[1] ;
byte[] digits = new byte[8];
try {
digits = message.getBytes() ;
String ds = new String(digits);

System.out.println("ds="+ds);

}
catch (Exception e) {
System.out.println(e);
}
BigInteger[] bigdigits = new BigInteger[digits.length] ;
for( i = 0 ; i < bigdigits.length ; i++ )
{
temp[0] = digits[i] ;
bigdigits[i] = new BigInteger( temp ) ;
}
BigInteger[] encrypted = new BigInteger[bigdigits.length] ;
for( i = 0 ; i < bigdigits.length ; i++ )
encrypted[i] = bigdigits[i].modPow( E, N ) ;

return( encrypted ) ;
}

/** Decrption */

public String RSAdecrypt() {
D = new BigInteger(privateKey);
N = new BigInteger(randomNumber);

System.out.println("D = " + D);
System.out.println("N = " + N);

int k1= 0;
StringTokenizer st = new StringTokenizer(encryptedData);
while (st.hasMoreTokens()) {
sarray1[k1] = st.nextToken(" ");
k1++;
}

BigInteger[] ciphertext1 = new BigInteger[100000];

for( int i = 0 ; i ciphertext1[i] = new BigInteger(sarray1[i]);
}
String recoveredPlaintext = decrypt( ciphertext1,D,N,k1) ;
System.out.println(recoveredPlaintext);
return recoveredPlaintext;
}
public String decrypt( BigInteger[] encrypted,BigInteger D,BigInteger N,int size )
{
int i ;
String rs="";
BigInteger[] decrypted = new BigInteger[size] ;
for( i = 0 ; i < decrypted.length ; i++ ) {
decrypted[i] = encrypted[i].modPow( D, N ) ;
}
char[] charArray = new char[decrypted.length] ;
byte[] byteArray = new byte[decrypted.length] ;
for( i = 0 ; i < charArray.length ; i++ ) {
charArray[i] = (char) ( decrypted[i].intValue() ) ;
Integer iv = new Integer(0);
iv=decrypted[i].intValue() ;
byteArray[i] = iv.byteValue();
}
try {
rs=new String( byteArray );
}
catch (Exception e) {
System.out.println(e);
}
return(rs) ;
}

/**
* KeyGeneration Main program for Unit Testing.
*/
public static void main( String[] args ) throws IOException
{
RSA akg = new RSA(8);

}

}