import java.io.*;
import java.security.*;
import javax.crypto.*;

class EncryptAndDecrypt {

public static void main (String[] args) throws Exception{
KeyPairGenerator keygenerator = KeyPairGenerator.getInstance("RSA");
SecureRandom random = SecureRandom.getInstance("SHA1PRNG", "SUN");
keygenerator.initialize(1024, random);

KeyPair keypair = keygenerator.generateKeyPair();
PrivateKey privateKey = keypair.getPrivate();
PublicKey publicKey = keypair.getPublic();
Cipher cipher = Cipher.getInstance("RSA");

cipher.init(Cipher.ENCRYPT_MODE, publicKey);
BufferedReader br=new BufferedReader(new FileReader(new File("data.txt")));
String st,str;
while((st=br.readLine()) != null)   {
    str+=st+" ";
}
byte[] cleartext = null;
cleartext = str.getBytes();
byte[] ciphertext = null;
ciphertext = cipher.doFinal(cleartext);
System.out.println("the encrypted text is: " + ciphertext.toString());

cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] cleartext1 = cipher.doFinal(ciphertext);
System.out.println("the decrypted cleartext is: " + new String(cleartext1));
}
}