/* Program for Analization of performance of RSA Algorithm. */

import java.math.BigInteger ;/* Class to getnerate numbers of bit size 128 , 256 etc. */
import java.util.* ;
import java.io.* ;
import java.sql.*;

//RSA MAIN CLASS

public class RSA
{
	//prime number size
	int primeSize ;

	//TWO LARGE INTEGERS
	BigInteger p, q ;
	
	// Modulus 
	BigInteger N ;
	
	//r=(p-1) * (q-1)
	BigInteger r ;
	
	// (E,N) -encryption  (D,N) -decryption 
	BigInteger E, D ;
	int prob;/* The probability that a generated number if prime . given in % */

	//CONSTRUCTER FOR RSA

	public RSA( int primeSize, int prob )
	{
	
		this.primeSize = primeSize ;
		long start=getCurrentTime();
		//generate p and q
	
		generatePrimeNumbers(prob);

		// Generate Public and Private Keys
	
		generatePublicPrivateKeys();
		
		long end=getCurrentTime();
		 
	        //System.out.println("Total elapsed time for key generation= "+(new Timestamp(end-start).getNanos()));
	   	 System.out.print("     "+new Timestamp(end-start).getNanos());
            
	}

	//Generate distinct p and q
	
	public void generatePrimeNumbers(int prob)
	{
        p = new BigInteger( primeSize, prob, new Random() ) ;
	do
	{
		q = new BigInteger( primeSize, prob, new Random() ) ;
	}
	while( q.compareTo( p ) == 0 ) ;
        }

	// Gets the current time from the local system	

        public long getCurrentTime()
        {
          java.util.Date date=Calendar.getInstance().getTime();
          Timestamp a=new Timestamp(date.getTime()); 
          long currentTime=Calendar.getInstance().getTimeInMillis();
          return currentTime;
        }
            
	
	//generate keys E and D
	
	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 ) ) ) ;
		// 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 ) ;
	}


	//Encrypting the plain TEXT

	public BigInteger[] encrypt( String message )
	{
		long start=getCurrentTime();
		int i ;
		byte[] temp = new byte[1] ;
		byte[] digits = message.getBytes() ;
		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 ) ;
		long end=getCurrentTime();
		System.out.print("       "+(new Timestamp(end-start)).getNanos());
		return( encrypted ) ;
	}

	//Decryption of cipher text 

	public String decrypt( BigInteger[] encrypted )
	{			
		long start=getCurrentTime();
		int i ;
		

		BigInteger[] decrypted = new BigInteger[encrypted.length] ;

		for( i = 0 ; i < decrypted.length ; i++ )
			decrypted[i] = encrypted[i].modPow( D, N ) ;

		char[] charArray = new char[decrypted.length] ;

		for( i = 0 ; i < charArray.length ; i++ )
			charArray[i] = (char) ( decrypted[i].intValue() ) ;
		long end=getCurrentTime();
		System.out.print("        "+(new Timestamp(end-start)).getNanos());

		return( new String( charArray ) ) ;
	}


	// returns p
	public BigInteger getp()
	{
		return( p ) ;
	}


	//returns q
	public BigInteger getq()
	{
		return( q ) ;
	}


	//return r
	public BigInteger getr()
	{
		return( r ) ;
	}

	//return N
	public BigInteger getN()
	{
		return( N ) ;
	}

	//return E
	public BigInteger getE()
	{
		return( E ) ;
	}


	// returns D
	public BigInteger getD()
	{
		return( D ) ;
	}

	// Genarates the text automatically to the size given by length
	public String messageGenerator(int lengthOfText)
	{
		String mesg=" ";
		for (int  i=0; i<lengthOfText;i++)
		{
			mesg=mesg+(char)(i%256);
		}
		return(mesg);
	}

	
	public static void main( String[] args ) throws IOException
	{
	 		if( args.length != 3 )
		{
			System.out.println( "Syntax: java RSA PrimeSize Textsize Probabilty" ) ;
			System.out.println( "e.g. java RSA 512 1024 10 " ) ;
			System.out.println(" This means keysize=512 , textsize=1024 , probality of 10 % ");
      			System.exit( -1 ) ;//Unsuccessful exit
		}

		int keySize = Integer.parseInt( args[0] ) ;
		
		System.out.print(keySize+"      ") ;
		System.out.print(Integer.parseInt(args[1])+"      ") ;
		System.out.print(Integer.parseInt(args[2])+"        ");
		int primeSize=keySize/2;
		RSA rsa = new RSA( primeSize,Integer.parseInt(args[2]) ) ;
		
		String plaintext=rsa.messageGenerator(Integer.parseInt(args[1]));
		//System.out.println( "" ) ;
		
		// Encrypt Message
		BigInteger[] ciphertext = rsa.encrypt( plaintext ) ;
		String recoveredPlaintext = rsa.decrypt( ciphertext ) ;

		//Verification of correctness of recovered messasage
		if(recoveredPlaintext.equals(plaintext)) System.out.println("         Matched");
		else System.out.println("         NOT Matched");
		//	System.out.println( "Recovered plaintext: [" + recoveredPlaintext + "]" ) ;
	}
}