FastLogin/src/main/java/com/github/games647/fastlogin/Encryption.java

package com.github.games647.fastlogin;

import com.google.common.base.Charsets;

import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

/**
 * Encryption and decryption minecraft util for connection between servers
 * and paid minecraft account clients.
 *
 * Source: https://github.com/bergerkiller/CraftSource/blob/master/net.minecraft.server/MinecraftEncryption.java
 *
 * Remapped by: https://github.com/Techcable/MinecraftMappings/tree/master/1.8
 */
public class Encryption {

    public static KeyPair generateKeyPair() {
        try {
            KeyPairGenerator keypairgenerator = KeyPairGenerator.getInstance("RSA");

            keypairgenerator.initialize(1024);
            return keypairgenerator.generateKeyPair();
        } catch (NoSuchAlgorithmException nosuchalgorithmexception) {
            //Should be existing in every vm
            return null;
        }
    }

    public static byte[] getServerIdHash(String serverId, PublicKey publickey, SecretKey secretkey) {
        return digestOperation("SHA-1"
                , new byte[][]{serverId.getBytes(Charsets.ISO_8859_1), secretkey.getEncoded(), publickey.getEncoded()});
    }

    private static byte[] digestOperation(String algo, byte[]... content) {
        try {
            MessageDigest messagedigest = MessageDigest.getInstance(algo);
            for (byte[] data : content) {
                messagedigest.update(data);
            }

            return messagedigest.digest();
        } catch (NoSuchAlgorithmException nosuchalgorithmexception) {
            nosuchalgorithmexception.printStackTrace();
            return null;
        }
    }

    public static PublicKey decodePublicKey(byte[] encodedKey) {
        try {
            X509EncodedKeySpec x509encodedkeyspec = new X509EncodedKeySpec(encodedKey);
            KeyFactory keyfactory = KeyFactory.getInstance("RSA");

            return keyfactory.generatePublic(x509encodedkeyspec);
        } catch (NoSuchAlgorithmException | InvalidKeySpecException nosuchalgorithmexception) {
            ;
        }

        System.err.println("Public key reconstitute failed!");
        return null;
    }

    public static SecretKey decryptSharedKey(PrivateKey privatekey, byte[] encryptedSharedKey) {
        return new SecretKeySpec(decryptData(privatekey, encryptedSharedKey), "AES");
    }

    public static byte[] decryptData(Key key, byte[] abyte) {
        return cipherOperation(Cipher.DECRYPT_MODE, key, abyte);
    }

    private static byte[] cipherOperation(int operationMode, Key key, byte[] data) {
        try {
            return createCipherInstance(operationMode, key.getAlgorithm(), key).doFinal(data);
        } catch (IllegalBlockSizeException | BadPaddingException illegalblocksizeexception) {
            illegalblocksizeexception.printStackTrace();
        }

        System.err.println("Cipher data failed!");
        return null;
    }

    private static Cipher createCipherInstance(int operationMode, String cipherName, Key key) {
        try {
            Cipher cipher = Cipher.getInstance(cipherName);

            cipher.init(operationMode, key);
            return cipher;
        } catch (InvalidKeyException | NoSuchAlgorithmException | NoSuchPaddingException invalidkeyexception) {
            invalidkeyexception.printStackTrace();
        }

        System.err.println("Cipher creation failed!");
        return null;
    }

    public static Cipher createBufferedBlockCipher(int operationMode, Key key) {
        try {
            Cipher cipher = Cipher.getInstance("AES/CFB8/NoPadding");

            cipher.init(operationMode, key, new IvParameterSpec(key.getEncoded()));
            return cipher;
        } catch (GeneralSecurityException generalsecurityexception) {
            throw new RuntimeException(generalsecurityexception);
        }
    }

    private Encryption() {
        //utility
    }
}