Java Cipher - PBE 线程安全问题

Question

Cipher 和/或 PBEKeySpec 似乎存在线程安全问题。

• JDK:1.8.0_102、1.8.0_151 和 9.0.1+11
• PBKDF2算法:PBKDF2WithHmacSHA1
• 密码算法:AES/CFB/NoPadding
• key 算法:AES

我知道如果我们使用相同的实例，这些类就不是安全的，但事实并非如此，我在每次解码时都会得到一个新实例。 但即便如此，有时解码也会失败，无一异常(exception)，只是一个意外的解码值。

我已经能够重现问题:

@Test
public void shouldBeThreadSafe() {

    final byte[] encoded = {
        27, 26, 18, 88, 84, -87, -40, -91, 70, -74, 87, -21, -124,
        -114, -44, -24, 7, -7, 104, -26, 45, 96, 119, 45, -74, 51
    };
    final String expected = "dummy data";
    final Charset charset = StandardCharsets.UTF_8;

    final String salt = "e47312da-bc71-4bde-8183-5e25db6f0987";
    final String passphrase = "dummy-passphrase";

    // Crypto configuration
    final int iterationCount = 10;
    final int keyStrength = 128;
    final String pbkdf2Algorithm = "PBKDF2WithHmacSHA1";
    final String cipherAlgorithm = "AES/CFB/NoPadding";
    final String keyAlgorithm = "AES";

    // Counters
    final AtomicInteger succeedCount = new AtomicInteger(0);
    final AtomicInteger failedCount = new AtomicInteger(0);

    // Test
    System.setProperty("java.util.concurrent.ForkJoinPool.common.parallelism", "10");
    IntStream.range(0, 1000000).parallel().forEach(i -> {
        try {

            SecretKeyFactory factory = SecretKeyFactory.getInstance(pbkdf2Algorithm);
            KeySpec spec = new PBEKeySpec(passphrase.toCharArray(), salt.getBytes(charset), iterationCount, keyStrength);
            SecretKey tmp = factory.generateSecret(spec);
            SecretKeySpec key = new SecretKeySpec(tmp.getEncoded(), keyAlgorithm);
            Cipher cipher = Cipher.getInstance(cipherAlgorithm);


            int blockSize = cipher.getBlockSize();
            IvParameterSpec iv = new IvParameterSpec(Arrays.copyOf(encoded, blockSize));
            byte[] dataToDecrypt = Arrays.copyOfRange(encoded, blockSize, encoded.length);
            cipher.init(Cipher.DECRYPT_MODE, key, iv);
            byte[] utf8 = cipher.doFinal(dataToDecrypt);

            String decoded = new String(utf8, charset);
            if (!expected.equals(decoded)) {
                System.out.println("Try #" + i + " | Unexpected decoded value: [" + decoded + "]");
                failedCount.incrementAndGet();
            } else {
                succeedCount.incrementAndGet();
            }
        } catch (Exception e) {
            System.out.println("Try #" + i + " | Decode failed");
            e.printStackTrace();
            failedCount.incrementAndGet();
        }
    });

    System.out.println(failedCount.get() + " of " + (succeedCount.get() + failedCount.get()) + " decodes failed");
}

输出:

Try #656684 | Unexpected decoded value: [�jE    |S���]
Try  #33896 | Unexpected decoded value: [�jE    |S���]

2 of 1000000 decodes failed

我不明白这段代码怎么会失败，Cipher 和/或 PBEKeySpec 类中是否存在错误？还是我在测试中遗漏了什么？

我们非常欢迎任何帮助。

---

更新

OpenJDK 问题:https://bugs.openjdk.java.net/browse/JDK-8191177

Answer 1

这确实是 PBKDF2KeyImpl.getEncoded() 方法中的 JDK 错误。

错误报告中有更多详细信息 https://bugs.openjdk.java.net/browse/JDK-8191177和相关问题https://bugs.openjdk.java.net/browse/JDK-8191002 .

它已在 Java 2018 年 1 月 CPU 版本中得到修复和交付。

更新:JDK 9 及更高版本已通过使用 reachabilityFence() 修复此问题。

由于较早版本的 JDK 中缺少此防护栏，您应该使用解决方法:« as first discovered by Hans Boehm, it just so happens that one way to implement the equivalent of reachabilityFence(x) even now is "synchronized(x) {}" »

在我们的例子中，解决方法是:

SecretKeyFactory factory = SecretKeyFactory.getInstance(pbkdf2Algorithm);
KeySpec spec = new PBEKeySpec(passphrase.toCharArray(), salt.getBytes(charset), iterationCount, keyStrength);
SecretKey secret = factory.generateSecret(spec);
SecretKeySpec key;
//noinspection SynchronizationOnLocalVariableOrMethodParameter
synchronized(secret) {
  key = new SecretKeySpec(secret.getEncoded(), keyAlgorithm);
}