package src;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.SignatureException;

import javax.crypto.Cipher;

public class RSA_Exercise_4373 extends RSA_Basics implements RSA_ExerciseInterface{

	private static String text="first exercise";
	
	private Key privatekey;
	private Key publickey;
	
	
	public Key getPrivate() {
		return privatekey;
	}
	
	public Key getPublic() {
		return publickey;
	}
	
	public void generateRSAKeypair() {
		// Get a KeyPair Generator
		KeyPairGenerator gen;
		try {	gen = KeyPairGenerator.getInstance("RSA");}
		catch (NoSuchAlgorithmException e) { 
			//This should not be the case ;-)
			privatekey 	= null;
			publickey 	= null;
			return;}
		
		//set to 1024bit
		gen.initialize(1024);

		//Generate the Pair
		KeyPair keypair = gen.genKeyPair();

		//Assign class vars
		privatekey = keypair.getPrivate();
		publickey  = keypair.getPublic();
	}
	
	public String sign(String value, Key key) throws Exception
	{
		// Instance
		Signature signature = Signature.getInstance("SHA1withRSA");
		
		signature.initSign((PrivateKey) key);		
		signature.update(value.getBytes());		
		return asHex(signature.sign());	
	}
	
	public boolean verify(String value,String sigtoverify, Key key) throws NoSuchAlgorithmException, NoSuchProviderException, InvalidKeyException, SignatureException
	{
		// Instance
		Signature signature = Signature.getInstance("SHA1withRSA");
		
		signature.initVerify((PublicKey) key);
		signature.update(value.getBytes());
		return signature.verify(asByteArray(sigtoverify));
	}
	
	public String encrypt(String value, Key key) throws Exception
	{
		// Instance
		Cipher cip = Cipher.getInstance("RSA");
	
		// Set mode + finalize
		cip.init(Cipher.ENCRYPT_MODE, key);
		return asHex(cip.doFinal(value.getBytes()));
	}
	
	public String decrypt(String value, Key key) throws Exception
	{
		// Instance
		Cipher cip = Cipher.getInstance("RSA");
		
		// Set mode + finalize
		cip.init(Cipher.DECRYPT_MODE, key);
		return new String(cip.doFinal(asByteArray(value)));
	}
	
	
	public static void main(String[] args) throws Exception
	{
		String output="";
		
		//Generate Instance
		RSA_Exercise_4373 rsa=new RSA_Exercise_4373();
		
		//Generate new Keypair
		rsa.generateRSAKeypair();
		
		String studid="4373"; //Please change me to your own four last digits of the student id
		
		//Signature Checks
		output="Signature of "+text+" is:"+rsa.sign(studid+text,rsa.getPrivate())+"\n";
		output+="The signature of "+text+" is :"+rsa.verify(studid+text, rsa.sign(studid+text,rsa.getPrivate()), rsa.getPublic())+"\n";
		
		output+="Ciphertext:" +rsa.encrypt(studid+text,rsa.getPublic())+"\n";
		output+="Decrypted Text:"+rsa.decrypt(rsa.encrypt(studid+text,rsa.getPublic()),rsa.getPrivate())+"\n";
		
		System.out.println(output);
		
		// Write current Public and Private key for solution hand-in
		writeData(rsa.getClass().getName(), rsa.getPrivate(), rsa.getPublic(),output);
		
	}
	
	
	
}