Encrypting and Decrypting password in java

Question

Im Trying to do my homework to create a class called Password that implements the Encryptable interface.

Im trying using RSA Algorythm.

I use some RSA code references from the Google and resulting my code below.

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.Key;
import java.util.Arrays;
import javax.crypto.Cipher;
import java.util.Scanner;
public class Password
{
    public static void main(String[] args) 
    {
        Scanner sc = new Scanner(System.in);
        String password = sc.nextLine();
        KeyPair keyPair = RSAKeyPair.keyPairRSA();
        Key publicKey = keyPair.getPublic();
        Key privateKey = keyPair.getPrivate();
        System.out.println("Original: " + password);
        byte[] encrypted = RSAEncryptDecrypt.encrypt(password, privateKey);
        System.out.println("Encrypted: " + new String(encrypted));
        byte[] decrypted = RSAEncryptDecrypt.decrypt(encrypted, publicKey);
        System.out.println("Decrypted: " + new String(decrypted));
    }
}
final class RSAConstants {
    private RSAConstants() {
    }
    public static final String ALGORITHM = "RSA";
    public static final int ALGORITHM_BITS = 2048;
}
class RSAKeyPair {
    public static KeyPair keyPairRSA() {
        KeyPairGenerator generator = null;
        try {
            generator = KeyPairGenerator.getInstance(RSAConstants.ALGORITHM);
        } catch (Exception e) {
            e.printStackTrace();
        }
        if (generator != null) {
            generator.initialize(RSAConstants.ALGORITHM_BITS);
            KeyPair keyPair = generator.genKeyPair();
            return keyPair;
        }
        return null;
    }
}

class RSAEncryptDecrypt {
    public static byte[] encrypt(String original, Key privateKey) {
        if (original != null && privateKey != null) {
            byte[] bs = original.getBytes();
            byte[] encData = convert(bs, privateKey, Cipher.ENCRYPT_MODE);
            return encData;
        }
        return null;
    }
    public static byte[] decrypt(byte[] encrypted, Key publicKey) {
        if (encrypted != null && publicKey != null) {
            byte[] decData = convert(encrypted, publicKey, Cipher.DECRYPT_MODE);
            return decData;
        }
        return null;
    }
    private static byte[] convert(byte[] data, Key key, int mode) {
        try {
            Cipher cipher = Cipher.getInstance(RSAConstants.ALGORITHM);
            cipher.init(mode, key);
            byte[] newData = cipher.doFinal(data);
            return newData;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

My Input is:

InterstellarGalactica

All goes smooth except for the result of Encrypted Password Resulting below

Original: InterstellarGalactica
Encrypted: Sªë/H?ù,X?U4??A???ìñáQ
÷?      *?7*??d?'å?Ñ¡w °??? Pè???«{?D÷??cB???'É »???qªîÉDë??~hb??z8?çÿ?hí?{mè?{*îèGê??WÅ{x??ï.5¼?úü;e??G?-F?shèn?FI
áh`UƒIàB!?åäô+D<&"?)?????ß!??3ä?¬???â???<?¬Ü?{ @ó12B?òt?ƒòÆr²Ä·oHQ?ë?«ú?°?î??Äy?:X^<?
&:ryb\?¼
Decrypted: InterstellarGalactica

Why do it is became a meaningless character?

Is there anything wrong with my code?

Can you explain how to do it in proper way(if there is)?

Thanks in advance.

Answer 1

You are using RSA in the wrong way:

In RSA you use the public key for encryption and the private key for decryption.

You however use the private key for encryption and the public key for decryption:

    byte[] encrypted = RSAEncryptDecrypt.encrypt(password, privateKey);
    byte[] decrypted = RSAEncryptDecrypt.decrypt(encrypted, publicKey);

Additionally please never convert a byte[] that contains binary data to String. If you want to print binary data convert it for example to a hexadecimal or base64 String instead. Or if you want to print it as a number use BigInteger.

// output Base64 encoded    
System.out.println(java.util.Base64.getEncoder().encode(encrypted));

// out hexadecimal (uses Apache commons codec library
System.out.println(org.apache.commons.codec.binary.Hex.encodeHexString(encrypted));

// out hexadecimal without external library)    
System.out.println(new java.math.BigInteger(1, encrypted).toString(16))

// Output as large number (useful for manual RSA calculations)
System.out.println(new java.math.BigInteger(1, encrypted));