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Use dynamic PBE iteration count.

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Fixes #184
Fixes #247
This commit is contained in:
Moxie Marlinspike 2014-06-03 17:59:11 -07:00
parent 5785860631
commit 12d217991c
1 changed files with 110 additions and 79 deletions
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177
src/org/thoughtcrime/securesms/crypto/MasterSecretUtil.java
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@ -19,7 +19,6 @@ package org.thoughtcrime.securesms.crypto;
import android.content.Context; import android.content.Context;
import android.content.SharedPreferences; import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.util.Log; import android.util.Log;
import org.whispersystems.textsecure.crypto.InvalidKeyException; import org.whispersystems.textsecure.crypto.InvalidKeyException;
@ -36,6 +35,7 @@ import java.io.IOException;
import java.security.GeneralSecurityException; import java.security.GeneralSecurityException;
import java.security.NoSuchAlgorithmException; import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom; import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;
import java.util.Arrays; import java.util.Arrays;
import javax.crypto.Cipher; import javax.crypto.Cipher;
@ -66,10 +66,20 @@ public class MasterSecretUtil {
String newPassphrase) String newPassphrase)
{ {
try { try {
byte[] combinedSecrets = combineSecrets(masterSecret.getEncryptionKey().getEncoded(), byte[] combinedSecrets = Util.combine(masterSecret.getEncryptionKey().getEncoded(),
masterSecret.getMacKey().getEncoded()); masterSecret.getMacKey().getEncoded());
encryptWithPassphraseAndSave(context, combinedSecrets, newPassphrase); 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; return masterSecret;
} catch (GeneralSecurityException gse) { } catch (GeneralSecurityException gse) {
@ -93,10 +103,13 @@ public class MasterSecretUtil {
{ {
try { try {
byte[] encryptedAndMacdMasterSecret = retrieve(context, "master_secret"); byte[] encryptedAndMacdMasterSecret = retrieve(context, "master_secret");
byte[] encryptedMasterSecret = verifyMac(context, encryptedAndMacdMasterSecret, passphrase); byte[] macSalt = retrieve(context, "mac_salt");
byte[] combinedSecrets = decryptWithPassphrase(context, encryptedMasterSecret, passphrase); int iterations = retrieve(context, "passphrase_iterations", 100);
byte[] encryptionSecret = getEncryptionSecret(combinedSecrets); byte[] encryptedMasterSecret = verifyMac(macSalt, iterations, encryptedAndMacdMasterSecret, passphrase);
byte[] macSecret = getMacSecret(combinedSecrets); 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"), return new MasterSecret(new SecretKeySpec(encryptionSecret, "AES"),
new SecretKeySpec(macSecret, "HmacSHA1")); new SecretKeySpec(macSecret, "HmacSHA1"));
@ -155,9 +168,18 @@ public class MasterSecretUtil {
try { try {
byte[] encryptionSecret = generateEncryptionSecret(); byte[] encryptionSecret = generateEncryptionSecret();
byte[] macSecret = generateMacSecret(); byte[] macSecret = generateMacSecret();
byte[] masterSecret = combineSecrets(encryptionSecret, macSecret); 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);
encryptWithPassphraseAndSave(context, masterSecret, 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"), return new MasterSecret(new SecretKeySpec(encryptionSecret, "AES"),
new SecretKeySpec(macSecret, "HmacSHA1")); new SecretKeySpec(macSecret, "HmacSHA1"));
@ -169,7 +191,6 @@ public class MasterSecretUtil {
public static boolean hasAsymmericMasterSecret(Context context) { public static boolean hasAsymmericMasterSecret(Context context) {
SharedPreferences settings = context.getSharedPreferences(PREFERENCES_NAME, 0); SharedPreferences settings = context.getSharedPreferences(PREFERENCES_NAME, 0);
return settings.contains(ASYMMETRIC_LOCAL_PUBLIC_DJB); return settings.contains(ASYMMETRIC_LOCAL_PUBLIC_DJB);
} }
@ -178,48 +199,25 @@ public class MasterSecretUtil {
return preferences.getBoolean("passphrase_initialized", false); return preferences.getBoolean("passphrase_initialized", false);
} }
private static void encryptWithPassphraseAndSave(Context context, byte[] masterSecret, String passphrase) throws GeneralSecurityException { private static void save(Context context, String key, int value) {
byte[] encryptedMasterSecret = encryptWithPassphrase(context, masterSecret, passphrase); context.getSharedPreferences(PREFERENCES_NAME, 0)
byte[] encryptedAndMacdMasterSecret = macWithPassphrase(context, encryptedMasterSecret, passphrase); .edit()
.putInt(key, value)
save(context, "master_secret", encryptedAndMacdMasterSecret); .commit();
save(context, "passphrase_initialized", true);
}
private static byte[] getEncryptionSecret(byte[] combinedSecrets) {
byte[] encryptionSecret = new byte[16];
System.arraycopy(combinedSecrets, 0, encryptionSecret, 0, encryptionSecret.length);
return encryptionSecret;
}
private static byte[] getMacSecret(byte[] combinedSecrets) {
byte[] macSecret = new byte[20];
System.arraycopy(combinedSecrets, 16, macSecret, 0, macSecret.length);
return macSecret;
}
private static byte[] combineSecrets(byte[] encryptionSecret, byte[] macSecret) {
byte[] combinedSecret = new byte[encryptionSecret.length + macSecret.length];
System.arraycopy(encryptionSecret, 0, combinedSecret, 0, encryptionSecret.length);
System.arraycopy(macSecret, 0, combinedSecret, encryptionSecret.length, macSecret.length);
return combinedSecret;
} }
private static void save(Context context, String key, byte[] value) { private static void save(Context context, String key, byte[] value) {
SharedPreferences settings = context.getSharedPreferences(PREFERENCES_NAME, 0); context.getSharedPreferences(PREFERENCES_NAME, 0)
Editor editor = settings.edit(); .edit()
.putString(key, Base64.encodeBytes(value))
editor.putString(key, Base64.encodeBytes(value)); .commit();
editor.commit();
} }
private static void save(Context context, String key, boolean value) { private static void save(Context context, String key, boolean value) {
SharedPreferences settings = context.getSharedPreferences(PREFERENCES_NAME, 0); context.getSharedPreferences(PREFERENCES_NAME, 0)
Editor editor = settings.edit(); .edit()
.putBoolean(key, value)
editor.putBoolean(key, value); .commit();
editor.commit();
} }
private static byte[] retrieve(Context context, String key) throws IOException { private static byte[] retrieve(Context context, String key) throws IOException {
@ -230,6 +228,11 @@ public class MasterSecretUtil {
else return Base64.decode(encodedValue); 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() { private static byte[] generateEncryptionSecret() {
try { try {
KeyGenerator generator = KeyGenerator.getInstance("AES"); KeyGenerator generator = KeyGenerator.getInstance("AES");
@ -255,43 +258,74 @@ public class MasterSecretUtil {
private static byte[] generateSalt() throws NoSuchAlgorithmException { private static byte[] generateSalt() throws NoSuchAlgorithmException {
SecureRandom random = SecureRandom.getInstance("SHA1PRNG"); SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
byte[] salt = new byte[8]; byte[] salt = new byte[16];
random.nextBytes(salt); random.nextBytes(salt);
return salt; return salt;
} }
private static SecretKey getKeyFromPassphrase(String passphrase, byte[] salt) throws GeneralSecurityException { private static int generateIterationCount(String passphrase, byte[] salt) {
PBEKeySpec keyspec = new PBEKeySpec(passphrase.toCharArray(), salt, 100); 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"); SecretKeyFactory skf = SecretKeyFactory.getInstance("PBEWITHSHA1AND128BITAES-CBC-BC");
return skf.generateSecret(keyspec); return skf.generateSecret(keyspec);
} }
private static Cipher getCipherFromPassphrase(String passphrase, byte[] salt, int opMode) throws GeneralSecurityException { private static Cipher getCipherFromPassphrase(String passphrase, byte[] salt, int iterations, int opMode)
SecretKey key = getKeyFromPassphrase(passphrase, salt); throws GeneralSecurityException
{
SecretKey key = getKeyFromPassphrase(passphrase, salt, iterations);
Cipher cipher = Cipher.getInstance(key.getAlgorithm()); Cipher cipher = Cipher.getInstance(key.getAlgorithm());
cipher.init(opMode, key, new PBEParameterSpec(salt, 100)); cipher.init(opMode, key, new PBEParameterSpec(salt, iterations));
return cipher; return cipher;
} }
private static byte[] encryptWithPassphrase(Context context, byte[] data, String passphrase) throws GeneralSecurityException { private static byte[] encryptWithPassphrase(byte[] encryptionSalt, int iterations, byte[] data, String passphrase)
byte[] encryptionSalt = generateSalt(); throws GeneralSecurityException
Cipher cipher = getCipherFromPassphrase(passphrase, encryptionSalt, Cipher.ENCRYPT_MODE); {
byte[] cipherText = cipher.doFinal(data); Cipher cipher = getCipherFromPassphrase(passphrase, encryptionSalt, iterations, Cipher.ENCRYPT_MODE);
save(context, "encryption_salt", encryptionSalt);
return cipherText;
}
private static byte[] decryptWithPassphrase(Context context, byte[] data, String passphrase) throws GeneralSecurityException, IOException {
byte[] encryptionSalt = retrieve(context, "encryption_salt");
Cipher cipher = getCipherFromPassphrase(passphrase, encryptionSalt, Cipher.DECRYPT_MODE);
return cipher.doFinal(data); return cipher.doFinal(data);
} }
private static Mac getMacForPassphrase(String passphrase, byte[] salt) throws GeneralSecurityException { private static byte[] decryptWithPassphrase(byte[] encryptionSalt, int iterations, byte[] data, String passphrase)
SecretKey key = getKeyFromPassphrase(passphrase, salt); 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(); byte[] pbkdf2 = key.getEncoded();
SecretKeySpec hmacKey = new SecretKeySpec(pbkdf2, "HmacSHA1"); SecretKeySpec hmacKey = new SecretKeySpec(pbkdf2, "HmacSHA1");
Mac hmac = Mac.getInstance("HmacSHA1"); Mac hmac = Mac.getInstance("HmacSHA1");
@ -300,9 +334,8 @@ public class MasterSecretUtil {
return hmac; return hmac;
} }
private static byte[] verifyMac(Context context, byte[] encryptedAndMacdData, String passphrase) throws InvalidPassphraseException, GeneralSecurityException, IOException { private static byte[] verifyMac(byte[] macSalt, int iterations, byte[] encryptedAndMacdData, String passphrase) throws InvalidPassphraseException, GeneralSecurityException, IOException {
byte[] macSalt = retrieve(context, "mac_salt"); Mac hmac = getMacForPassphrase(passphrase, macSalt, iterations);
Mac hmac = getMacForPassphrase(passphrase, macSalt);
byte[] encryptedData = new byte[encryptedAndMacdData.length - hmac.getMacLength()]; byte[] encryptedData = new byte[encryptedAndMacdData.length - hmac.getMacLength()];
System.arraycopy(encryptedAndMacdData, 0, encryptedData, 0, encryptedData.length); System.arraycopy(encryptedAndMacdData, 0, encryptedData, 0, encryptedData.length);
@ -316,16 +349,14 @@ public class MasterSecretUtil {
else throw new InvalidPassphraseException("MAC Error"); else throw new InvalidPassphraseException("MAC Error");
} }
private static byte[] macWithPassphrase(Context context, byte[] data, String passphrase) throws GeneralSecurityException { private static byte[] macWithPassphrase(byte[] macSalt, int iterations, byte[] data, String passphrase) throws GeneralSecurityException {
byte[] macSalt = generateSalt(); Mac hmac = getMacForPassphrase(passphrase, macSalt, iterations);
Mac hmac = getMacForPassphrase(passphrase, macSalt);
byte[] mac = hmac.doFinal(data); byte[] mac = hmac.doFinal(data);
byte[] result = new byte[data.length + mac.length]; byte[] result = new byte[data.length + mac.length];
System.arraycopy(data, 0, result, 0, data.length); System.arraycopy(data, 0, result, 0, data.length);
System.arraycopy(mac, 0, result, data.length, mac.length); System.arraycopy(mac, 0, result, data.length, mac.length);
save(context, "mac_salt", macSalt);
return result; return result;
} }
} }