import java.math.BigInteger ;
import java.util.* ;
import java.io.* ;
import java.sql.*;

/**
 * Class for RSA Algorithm (RSA.java).
 *
 * Generates Prime numbers and Public/Private Keys. Performs Encryption and Decryption.
 *
 * @author  Chue Wai Lian
 * @version
 *
 * 1.0.0	11 Apr 2001
 * <br>		1st release.
 */
/**
 * Modifiled by Shweta Agrawal 
 * Assignement 1 
 * Network Security	
 * Date: 15 Aug, 2003
 * */
 
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 ;

	/**
	* Certainity that new BigInteger represensts a prime
	*/
	public static int certainity = 10; // initialized to a default value

	/**
	 * Constructor.
	 *
	 * @param	primeSize		Bit length of each prime number.
	 */
	public RSA( int primeSize )
	{
		this.primeSize = primeSize ;

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

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


	/**
	 * Generate two distinct large prime numbers p and q.
	 */
	public void generatePrimeNumbers()
	{
		//System.out.println("Starting time is ");
		//long start=getCurrentTime();
		p = new BigInteger( primeSize, certainity, new Random() ) ;
		do
		{
			q = new BigInteger( primeSize, certainity, new Random() ) ;
		} while( q.compareTo( p ) == 0 ) ;
		System.out.println("Prime number search competed");
		//long end=getCurrentTime();
		//System.out.println("Total elapsed time = "+(new Timestamp(end-start)).getNanos());
            
                
	}
	public static long getCurrentTime()
	{
		/*java.util.Date date=Calendar.getInstance().getTime();
		Timestamp a=new Timestamp(date.getTime()); 
		long currentTime=Calendar.getInstance().getTimeInMillis();*/
		long currentTime = System.currentTimeMillis();
		System.out.println("Time: "+ currentTime);
		return currentTime;
	}
            


	/**
	 * 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 ) ) ) ;


		// 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 ) ;
	}


	/**
	 * Encrypts the plaintext (Using Public Key).
	 *
	 * @param	message			String containing the plaintext message to be encrypted.
	 * @return	The ciphertext as a BigInteger array.
	 */
	public BigInteger[] encrypt( String message )
	{
		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 ) ;


		return( encrypted ) ;
	}


	/**
	 * Decrypts the ciphertext (Using Private Key).
	 *
	 * @param	encrypted		BigInteger array containing the ciphertext to be decrypted.
	 * @return	The decrypted plaintext.
	 */
	public String decrypt( BigInteger[] encrypted )
	{
		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() ) ;


		return( new String( charArray ) ) ;
	}


	/**
	 * 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 ) ;
	}



	/**
	 * RSA Main program for Unit Testing.
	 */
	public static void main( String[] args ) throws IOException
	{
		/*Argguments processing*/
		
		if( args.length < 2)
		{
			System.out.println( "Syntax: java RSA <PrimeSize> <y / n / (message size in bytes)> [certainity value]" ) ;
			System.out.println( "e.g. java RSA 512 y" ) ;
			System.out.println( "e.g. java RSA 512 1024" ) ;
			System.out.println( "e.g. java RSA 512 y 15" ) ;
			System.exit( -1 ) ;
		}
		
		// Get bit length of each prime number
		int primeSize = Integer.parseInt( args[0] ) ;
		
		if (args.length == 3)
		{
			//the certainity value for prime numbers
			try {
				certainity = Integer.parseInt(args[2]);
			} catch(Exception e) {
				System.out.println("Exception in accepting certainity argument: " + e);
				System.exit(-1);
			}
		}
		
		// Generate Public and Private Keys
		System.out.println( "Generating the key pair .........." ) ;
		long start = getCurrentTime();
		RSA rsa = new RSA( primeSize ) ;
		long end = getCurrentTime();
		System.err.println("Key Generation Time: " + (end-start));
		
		
		System.out.println( "Key Size: [" + primeSize + "]" ) ;
		System.out.println( "" ) ;
		
		System.out.println( "Generated prime numbers p and q" ) ;
		System.out.println( "p: [" + rsa.getp().toString( 16 ).toUpperCase() + "]" ) ;
		System.out.println( "q: [" + rsa.getq().toString( 16 ).toUpperCase() + "]" ) ;
		System.out.println( "" ) ;

		System.out.println( "The public key is the pair (N, E) which will be published." ) ;
		System.out.println( "N: [" + rsa.getN().toString( 16 ).toUpperCase() + "]" ) ;
		System.out.println( "E: [" + rsa.getE().toString( 16 ).toUpperCase() + "]" ) ;
		System.out.println( "" ) ;

		System.out.println( "The private key is the pair (N, D) which will be kept private." ) ;
		System.out.println( "N: [" + rsa.getN().toString( 16 ).toUpperCase() + "]" ) ;
		System.out.println( "D: [" + rsa.getD().toString( 16 ).toUpperCase() + "]" ) ;
		System.out.println( "" ) ;
		
		
		//Only key generation for different certainities being checked
		if (args.length == 3)
			System.exit(-1);
		
		//Get the message to be encrypted/decrypted
		String plaintext = "";
		if (args[1].equals("y"))
		{
			// A message of 1 KB approximately 
			plaintext = "Many web users monitor dynamic data such as stock prices, weather information and traffic data for making online decisions. Algorithms for creating a resilient and efficient content distribution network for such dynamically changing data have been discussed in the literature. The focus of the above work is on maintaining coherency of dynamic data-items in a network of repositories: data disseminated to one repository is filtered by that repository and disseminated to repositories dependent on it, according to their respective data and coherency requirements. These repositories can, in turn, serve the clients and hence reduce the load on the servers. In this paper, we pose and solve the problem of determining the repository to which a client must be connected to satisfy its data needs. We formulate the problem of mapping clients to repositories in the network as a linear optimization problem and discuss the constraints and objective function for it.  Given the complexity of this assignment, we also offer a heuristic solution to it. Experimental evaluation using real world traces demonstrate that the fidelity achieved by clients, using the heuristic assignment, is close to that achieved using linear optimization.";
		}
		else if(!args[1].equals("n"))
			// create message of required message size
		{
			try {
			int message_size = Integer.parseInt(args[1]);
			plaintext = "";
			for (int m=0; m<message_size; m++) 	
			plaintext += "s"; 
			} catch(Exception e) {
				System.out.println("Exception in accepting message argument: " + e);
				System.exit(-1);
			}
		}
		
		// Check if the message is to input from user
		if (args[1].equals("n") )
		{
		// Get message (plaintext) from user
		System.out.println( "Please enter message (plaintext):" ) ;
		plaintext = ( new BufferedReader( new InputStreamReader( System.in ) ) ).readLine() ;
		System.out.println( "" ) ;
		}
		
		// Encrypt Message
		System.out.println( "Encrypting the message .........." ) ;
		start = getCurrentTime();
		BigInteger[] ciphertext = rsa.encrypt( plaintext ) ;
		end = getCurrentTime();
		System.err.println("Encryption Time: " + (end-start));

		
		System.out.print( "Ciphertext: [" ) ;
		for( int i = 0 ; i < ciphertext.length ; i++ )
		{
			System.out.print( ciphertext[i].toString( 16 ).toUpperCase() ) ;

			if( i != ciphertext.length - 1 )
				System.out.print( " " ) ;
		}
		System.out.println( "]" ) ;
		System.out.println( "" ) ;
	

		//Decrypt the message back
		System.out.println( "Decrypting back the message .........." ) ;
		start = getCurrentTime();
		String recoveredPlaintext = rsa.decrypt( ciphertext ) ;
		end = getCurrentTime();
		System.err.println("Decryption Time: " + (end-start));

		System.out.println( "Recovered plaintext: [" + recoveredPlaintext + "]" ) ;
	}
}