/**
* Copyright (C) 2011 Whisper Systems
* Copyright (C) 2013 Open Whisper Systems
*
* This program 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.
*
* This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.thoughtcrime.SMP.crypto;
import android.content.Context;
import android.content.SharedPreferences;
import android.text.TextUtils;
import android.util.Log;
import org.thoughtcrime.SMP.util.Base64;
import org.thoughtcrime.SMP.util.Util;
import org.whispersystems.libaxolotl.InvalidKeyException;
import org.whispersystems.libaxolotl.ecc.Curve;
import org.whispersystems.libaxolotl.ecc.ECKeyPair;
import org.whispersystems.libaxolotl.ecc.ECPrivateKey;
import org.whispersystems.libaxolotl.ecc.ECPublicKey;
import java.io.IOException;
import java.security.GeneralSecurityException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;
import java.util.Arrays;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;
import javax.crypto.spec.SecretKeySpec;
/**
* Helper class for generating and securely storing a MasterSecret.
*
* @author Moxie Marlinspike
*/
public class MasterSecretUtil {
public static final String UNENCRYPTED_PASSPHRASE = "unencrypted";
public static final String PREFERENCES_NAME = "SecureSMS-Preferences";
private static final String ASYMMETRIC_LOCAL_PUBLIC_DJB = "asymmetric_master_secret_curve25519_public";
private static final String ASYMMETRIC_LOCAL_PRIVATE_DJB = "asymmetric_master_secret_curve25519_private";
public static MasterSecret changeMasterSecretPassphrase(Context context,
MasterSecret masterSecret,
String newPassphrase)
{
try {
byte[] combinedSecrets = Util.combine(masterSecret.getEncryptionKey().getEncoded(),
masterSecret.getMacKey().getEncoded());
byte[] encryptionSalt = generateSalt();
int iterations = generateIterationCount(newPassphrase, encryptionSalt);
byte[] encryptedMasterSecret = encryptWithPassphrase(encryptionSalt, iterations, combinedSecrets, newPassphrase);
byte[] macSalt = generateSalt();
byte[] encryptedAndMacdMasterSecret = macWithPassphrase(macSalt, iterations, encryptedMasterSecret, newPassphrase);
save(context, "encryption_salt", encryptionSalt);
save(context, "mac_salt", macSalt);
save(context, "passphrase_iterations", iterations);
save(context, "master_secret", encryptedAndMacdMasterSecret);
save(context, "passphrase_initialized", true);
return masterSecret;
} catch (GeneralSecurityException gse) {
throw new AssertionError(gse);
}
}
public static MasterSecret changeMasterSecretPassphrase(Context context,
String originalPassphrase,
String newPassphrase)
throws InvalidPassphraseException
{
MasterSecret masterSecret = getMasterSecret(context, originalPassphrase);
changeMasterSecretPassphrase(context, masterSecret, newPassphrase);
return masterSecret;
}
public static MasterSecret getMasterSecret(Context context, String passphrase)
throws InvalidPassphraseException
{
try {
byte[] encryptedAndMacdMasterSecret = retrieve(context, "master_secret");
byte[] macSalt = retrieve(context, "mac_salt");
int iterations = retrieve(context, "passphrase_iterations", 100);
byte[] encryptedMasterSecret = verifyMac(macSalt, iterations, encryptedAndMacdMasterSecret, passphrase);
byte[] encryptionSalt = retrieve(context, "encryption_salt");
byte[] combinedSecrets = decryptWithPassphrase(encryptionSalt, iterations, encryptedMasterSecret, passphrase);
byte[] encryptionSecret = Util.split(combinedSecrets, 16, 20)[0];
byte[] macSecret = Util.split(combinedSecrets, 16, 20)[1];
return new MasterSecret(new SecretKeySpec(encryptionSecret, "AES"),
new SecretKeySpec(macSecret, "HmacSHA1"));
} catch (GeneralSecurityException e) {
Log.w("keyutil", e);
return null; //XXX
} catch (IOException e) {
Log.w("keyutil", e);
return null; //XXX
}
}
public static AsymmetricMasterSecret getAsymmetricMasterSecret(Context context,
MasterSecret masterSecret)
{
try {
byte[] djbPublicBytes = retrieve(context, ASYMMETRIC_LOCAL_PUBLIC_DJB);
byte[] djbPrivateBytes = retrieve(context, ASYMMETRIC_LOCAL_PRIVATE_DJB);
ECPublicKey djbPublicKey = null;
ECPrivateKey djbPrivateKey = null;
if (djbPublicBytes != null) {
djbPublicKey = Curve.decodePoint(djbPublicBytes, 0);
}
if (masterSecret != null) {
MasterCipher masterCipher = new MasterCipher(masterSecret);
if (djbPrivateBytes != null) {
djbPrivateKey = masterCipher.decryptKey(djbPrivateBytes);
}
}
return new AsymmetricMasterSecret(djbPublicKey, djbPrivateKey);
} catch (InvalidKeyException | IOException ike) {
throw new AssertionError(ike);
}
}
public static AsymmetricMasterSecret generateAsymmetricMasterSecret(Context context,
MasterSecret masterSecret)
{
MasterCipher masterCipher = new MasterCipher(masterSecret);
ECKeyPair keyPair = Curve.generateKeyPair();
save(context, ASYMMETRIC_LOCAL_PUBLIC_DJB, keyPair.getPublicKey().serialize());
save(context, ASYMMETRIC_LOCAL_PRIVATE_DJB, masterCipher.encryptKey(keyPair.getPrivateKey()));
return new AsymmetricMasterSecret(keyPair.getPublicKey(), keyPair.getPrivateKey());
}
public static MasterSecret generateMasterSecret(Context context, String passphrase) {
try {
byte[] encryptionSecret = generateEncryptionSecret();
byte[] macSecret = generateMacSecret();
byte[] masterSecret = Util.combine(encryptionSecret, macSecret);
byte[] encryptionSalt = generateSalt();
int iterations = generateIterationCount(passphrase, encryptionSalt);
byte[] encryptedMasterSecret = encryptWithPassphrase(encryptionSalt, iterations, masterSecret, passphrase);
byte[] macSalt = generateSalt();
byte[] encryptedAndMacdMasterSecret = macWithPassphrase(macSalt, iterations, encryptedMasterSecret, passphrase);
save(context, "encryption_salt", encryptionSalt);
save(context, "mac_salt", macSalt);
save(context, "passphrase_iterations", iterations);
save(context, "master_secret", encryptedAndMacdMasterSecret);
save(context, "passphrase_initialized", true);
return new MasterSecret(new SecretKeySpec(encryptionSecret, "AES"),
new SecretKeySpec(macSecret, "HmacSHA1"));
} catch (GeneralSecurityException e) {
Log.w("keyutil", e);
return null;
}
}
public static boolean hasAsymmericMasterSecret(Context context) {
SharedPreferences settings = context.getSharedPreferences(PREFERENCES_NAME, 0);
return settings.contains(ASYMMETRIC_LOCAL_PUBLIC_DJB);
}
public static boolean isPassphraseInitialized(Context context) {
SharedPreferences preferences = context.getSharedPreferences(PREFERENCES_NAME, 0);
return preferences.getBoolean("passphrase_initialized", false);
}
private static void save(Context context, String key, int value) {
if (!context.getSharedPreferences(PREFERENCES_NAME, 0)
.edit()
.putInt(key, value)
.commit())
{
throw new AssertionError("failed to save a shared pref in MasterSecretUtil");
}
}
private static void save(Context context, String key, byte[] value) {
if (!context.getSharedPreferences(PREFERENCES_NAME, 0)
.edit()
.putString(key, Base64.encodeBytes(value))
.commit())
{
throw new AssertionError("failed to save a shared pref in MasterSecretUtil");
}
}
private static void save(Context context, String key, boolean value) {
if (!context.getSharedPreferences(PREFERENCES_NAME, 0)
.edit()
.putBoolean(key, value)
.commit())
{
throw new AssertionError("failed to save a shared pref in MasterSecretUtil");
}
}
private static byte[] retrieve(Context context, String key) throws IOException {
SharedPreferences settings = context.getSharedPreferences(PREFERENCES_NAME, 0);
String encodedValue = settings.getString(key, "");
if (TextUtils.isEmpty(encodedValue)) return null;
else return Base64.decode(encodedValue);
}
private static int retrieve(Context context, String key, int defaultValue) throws IOException {
SharedPreferences settings = context.getSharedPreferences(PREFERENCES_NAME, 0);
return settings.getInt(key, defaultValue);
}
private static byte[] generateEncryptionSecret() {
try {
KeyGenerator generator = KeyGenerator.getInstance("AES");
generator.init(128);
SecretKey key = generator.generateKey();
return key.getEncoded();
} catch (NoSuchAlgorithmException ex) {
Log.w("keyutil", ex);
return null;
}
}
private static byte[] generateMacSecret() {
try {
KeyGenerator generator = KeyGenerator.getInstance("HmacSHA1");
return generator.generateKey().getEncoded();
} catch (NoSuchAlgorithmException e) {
Log.w("keyutil", e);
return null;
}
}
private static byte[] generateSalt() throws NoSuchAlgorithmException {
SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
byte[] salt = new byte[16];
random.nextBytes(salt);
return salt;
}
private static int generateIterationCount(String passphrase, byte[] salt) {
int TARGET_ITERATION_TIME = 50; //ms
int MINIMUM_ITERATION_COUNT = 100; //default for low-end devices
int BENCHMARK_ITERATION_COUNT = 10000; //baseline starting iteration count
try {
PBEKeySpec keyspec = new PBEKeySpec(passphrase.toCharArray(), salt, BENCHMARK_ITERATION_COUNT);
SecretKeyFactory skf = SecretKeyFactory.getInstance("PBEWITHSHA1AND128BITAES-CBC-BC");
long startTime = System.currentTimeMillis();
skf.generateSecret(keyspec);
long finishTime = System.currentTimeMillis();
int scaledIterationTarget = (int) (((double)BENCHMARK_ITERATION_COUNT / (double)(finishTime - startTime)) * TARGET_ITERATION_TIME);
if (scaledIterationTarget < MINIMUM_ITERATION_COUNT) return MINIMUM_ITERATION_COUNT;
else return scaledIterationTarget;
} catch (NoSuchAlgorithmException e) {
Log.w("MasterSecretUtil", e);
return MINIMUM_ITERATION_COUNT;
} catch (InvalidKeySpecException e) {
Log.w("MasterSecretUtil", e);
return MINIMUM_ITERATION_COUNT;
}
}
private static SecretKey getKeyFromPassphrase(String passphrase, byte[] salt, int iterations)
throws GeneralSecurityException
{
PBEKeySpec keyspec = new PBEKeySpec(passphrase.toCharArray(), salt, iterations);
SecretKeyFactory skf = SecretKeyFactory.getInstance("PBEWITHSHA1AND128BITAES-CBC-BC");
return skf.generateSecret(keyspec);
}
private static Cipher getCipherFromPassphrase(String passphrase, byte[] salt, int iterations, int opMode)
throws GeneralSecurityException
{
SecretKey key = getKeyFromPassphrase(passphrase, salt, iterations);
Cipher cipher = Cipher.getInstance(key.getAlgorithm());
cipher.init(opMode, key, new PBEParameterSpec(salt, iterations));
return cipher;
}
private static byte[] encryptWithPassphrase(byte[] encryptionSalt, int iterations, byte[] data, String passphrase)
throws GeneralSecurityException
{
Cipher cipher = getCipherFromPassphrase(passphrase, encryptionSalt, iterations, Cipher.ENCRYPT_MODE);
return cipher.doFinal(data);
}
private static byte[] decryptWithPassphrase(byte[] encryptionSalt, int iterations, byte[] data, String passphrase)
throws GeneralSecurityException, IOException
{
Cipher cipher = getCipherFromPassphrase(passphrase, encryptionSalt, iterations, Cipher.DECRYPT_MODE);
return cipher.doFinal(data);
}
private static Mac getMacForPassphrase(String passphrase, byte[] salt, int iterations)
throws GeneralSecurityException
{
SecretKey key = getKeyFromPassphrase(passphrase, salt, iterations);
byte[] pbkdf2 = key.getEncoded();
SecretKeySpec hmacKey = new SecretKeySpec(pbkdf2, "HmacSHA1");
Mac hmac = Mac.getInstance("HmacSHA1");
hmac.init(hmacKey);
return hmac;
}
private static byte[] verifyMac(byte[] macSalt, int iterations, byte[] encryptedAndMacdData, String passphrase) throws InvalidPassphraseException, GeneralSecurityException, IOException {
Mac hmac = getMacForPassphrase(passphrase, macSalt, iterations);
byte[] encryptedData = new byte[encryptedAndMacdData.length - hmac.getMacLength()];
System.arraycopy(encryptedAndMacdData, 0, encryptedData, 0, encryptedData.length);
byte[] givenMac = new byte[hmac.getMacLength()];
System.arraycopy(encryptedAndMacdData, encryptedAndMacdData.length-hmac.getMacLength(), givenMac, 0, givenMac.length);
byte[] localMac = hmac.doFinal(encryptedData);
if (Arrays.equals(givenMac, localMac)) return encryptedData;
else throw new InvalidPassphraseException("MAC Error");
}
private static byte[] macWithPassphrase(byte[] macSalt, int iterations, byte[] data, String passphrase) throws GeneralSecurityException {
Mac hmac = getMacForPassphrase(passphrase, macSalt, iterations);
byte[] mac = hmac.doFinal(data);
byte[] result = new byte[data.length + mac.length];
System.arraycopy(data, 0, result, 0, data.length);
System.arraycopy(mac, 0, result, data.length, mac.length);
return result;
}
}