BlackBox.java

/*
 * Copyright (C) 2017 Drakeet <drakeet.me@gmail.com>
 *
 * This file is part of rebase-android
 *
 * rebase-android is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * rebase-android is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with rebase-android. If not, see <http://www.gnu.org/licenses/>.
 */

package com.drakeet.rebase.tool;

import android.content.Context;
import android.security.KeyPairGeneratorSpec;
import android.util.Base64;
import android.util.Log;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.math.BigInteger;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.KeyStore;
import java.util.ArrayList;
import java.util.Calendar;
import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.security.auth.x500.X500Principal;

/**
 * @author drakeet
 */
public class BlackBox {

    static final String TAG = BlackBox.class.getSimpleName();

    public static final String ANDROID_KEY_STORE = "AndroidKeyStore";
    public static final String RSA_ALGORITHM = "RSA/ECB/PKCS1Padding";
    public static final String TYPE_RSA = "RSA";

    final String alias;
    final Context context;


    public BlackBox(Context context, String alias) {
        this.context = context;
        this.alias = alias;
    }


    /**
     * Creates a public and private key and stores it using the AndroidKeyStore,
     * so that only this application will be able to access the keys.
     */
    @SuppressWarnings("deprecation")
    public void createKeys() throws Exception {
        KeyStore keyStore = KeyStore.getInstance(ANDROID_KEY_STORE);
        keyStore.load(null);
        if (keyStore.containsAlias(alias)) {
            Log.d(TAG, "[containsAlias]");
            return;
        }

        Calendar start = Calendar.getInstance();
        Calendar end = Calendar.getInstance();
        end.add(Calendar.YEAR, 30);
        KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(context)
            .setAlias(alias)
            .setSubject(new X500Principal("CN=" + alias))
            .setSerialNumber(BigInteger.TEN)
            .setStartDate(start.getTime())
            .setEndDate(end.getTime())
            .build();
        KeyPairGenerator generator = KeyPairGenerator.getInstance(TYPE_RSA, ANDROID_KEY_STORE);
        generator.initialize(spec);
        KeyPair keyPair = generator.generateKeyPair();
        Log.d(TAG, "Public Key is: " + keyPair.getPublic().toString());
    }


    /**
     * Encrypt the secret with RSA.
     *
     * @param secret the secret.
     * @return the encrypted secret.
     * @throws Exception
     */
    public String encrypt(String secret) throws Exception {
        KeyStore keyStore = KeyStore.getInstance(ANDROID_KEY_STORE);
        keyStore.load(null);
        KeyStore.PrivateKeyEntry privateKeyEntry =
            (KeyStore.PrivateKeyEntry) keyStore.getEntry(alias, null);

        Cipher inputCipher = Cipher.getInstance(RSA_ALGORITHM);
        inputCipher.init(Cipher.ENCRYPT_MODE, privateKeyEntry.getCertificate().getPublicKey());

        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        CipherOutputStream cipherOutputStream = new CipherOutputStream(outputStream, inputCipher);
        cipherOutputStream.write(secret.getBytes());
        cipherOutputStream.close();

        return Base64.encodeToString(outputStream.toByteArray(), Base64.DEFAULT);
    }


    /**
     * Decrypt the encrypted secret.
     *
     * @param encrypted the encrypted secret.
     * @return the decrypted secret.
     * @throws Exception
     */
    public String decrypt(String encrypted) throws Exception {
        byte[] encryptedBytes = Base64.decode(encrypted, Base64.DEFAULT);
        KeyStore keyStore = KeyStore.getInstance(ANDROID_KEY_STORE);
        keyStore.load(null);
        KeyStore.PrivateKeyEntry privateKeyEntry =
            (KeyStore.PrivateKeyEntry) keyStore.getEntry(alias, null);
        Cipher output = Cipher.getInstance(RSA_ALGORITHM);
        output.init(Cipher.DECRYPT_MODE, privateKeyEntry.getPrivateKey());
        CipherInputStream cipherInputStream = new CipherInputStream(
            new ByteArrayInputStream(encryptedBytes), output);
        ArrayList<Byte> values = new ArrayList<>();
        int nextByte;
        while ((nextByte = cipherInputStream.read()) != -1) {
            values.add((byte) nextByte);
        }

        byte[] bytes = new byte[values.size()];
        for (int i = 0; i < bytes.length; i++) {
            bytes[i] = values.get(i);
        }
        return new String(bytes);
    }
}