java 这个Java加密代码线程安全吗？

Is this Java encryption code thread safe?

提问by user646584

I want to use the following code for a high-concurrency application where certain data must be encrypted and decrypted. So I need to know what part of this code should be synchronized, if any, to avoid unpredictable issues.

我想将以下代码用于必须加密和解密某些数据的高并发应用程序。所以我需要知道这段代码的哪一部分应该同步，如果有的话，以避免出现不可预测的问题。

public class DesEncrypter {
    Cipher ecipher;
    Cipher dcipher;

    // 8-byte Salt
    byte[] salt = {
        (byte)0xA9, (byte)0x9B, (byte)0xC8, (byte)0x32,
        (byte)0x56, (byte)0x35, (byte)0xE3, (byte)0x03
    };

    int iterationCount = 19;

    DesEncrypter(String passPhrase) {
        try {
            // Create the key
            KeySpec keySpec = new PBEKeySpec(passPhrase.toCharArray(), salt, iterationCount);

            SecretKey key = SecretKeyFactory.getInstance( "PBEWithMD5AndDES").generateSecret(keySpec);
            ecipher = Cipher.getInstance(key.getAlgorithm());
            dcipher = Cipher.getInstance(key.getAlgorithm());

            // Prepare the parameter to the ciphers
            AlgorithmParameterSpec paramSpec = new PBEParameterSpec(salt, iterationCount);

            // Create the ciphers
            ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
            dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
        } catch (...)
    }

    public String encrypt(String str) {
        try {
            // Encode the string into bytes using utf-8
            byte[] utf8 = str.getBytes("UTF8");
            // Encrypt
            byte[] enc = ecipher.doFinal(utf8);
            // Encode bytes to base64 to get a string
            return new sun.misc.BASE64Encoder().encode(enc);

        } catch (...)
    }

    public String decrypt(String str) {
        try {
            // Decode base64 to get bytes
            byte[] dec = new sun.misc.BASE64Decoder().decodeBuffer(str);
            // Decrypt
            byte[] utf8 = dcipher.doFinal(dec);
            // Decode using utf-8
            return new String(utf8, "UTF8");
        } catch (...)
    }
}

If I create a new cipher in the encrypt() and decrypt() methods for each invocation, then I can avoid concurrency problems, I'm just not sure if there's a lot of overhead in getting a new instance of a cipher for each invocation.

如果我在 encrypt() 和decrypt() 方法中为每次调用创建一个新的密码，那么我可以避免并发问题，我只是不确定为每次调用获取一个新的密码实例是否有很多开销.

   public String encrypt(String str) {
        try {
            // Encode the string into bytes using utf-8
            byte[] utf8 = str.getBytes("UTF8");
            // Encrypt
            //new cipher instance
            ecipher = Cipher.getInstance(key.getAlgorithm());

            byte[] enc = ecipher.doFinal(utf8);
            // Encode bytes to base64 to get a string
            return new sun.misc.BASE64Encoder().encode(enc);

        } catch (...)

采纳答案by Nick Johnson

Things only need to be thread-safe if they're used by multiple threads at once. Since each instance of this class will presumably be used by only a single thread, there's no need to worry about whether it's threadsafe or not.

如果它们一次被多个线程使用，那么它们只需要是线程安全的。由于这个类的每个实例大概只会被一个线程使用，所以不必担心它是否是线程安全的。

On an unrelated note, having a hardcoded salt, nonce or IV is nevera good idea.

顺便提一下，使用硬编码的 salt、nonce 或 IV从来都不是一个好主意。

回答by Stephen C

The standard rule is - unless the Javadoc states explicitly that a class in the Java libraries is thread-safe, you should assumethat it is not.

标准规则是 - 除非 Javadoc 明确声明 Java 库中的类是线程安全的，否则您应该假设它不是。

In this particular instance:

在这个特定的例子中：

• The various classes are not documented as thread-safe.

• The Cipher.getInstance(...)and SecretKeyFactory.getInstance(...)methods ARE documented as returning new objects; i.e. not references to existing objects that other threads might have references to.

  UPDATE- The javadocsays this:

  "A new SecretKeyFactory object encapsulating the SecretKeyFactorySpi implementation from the first Provider that supports the specified algorithm is returned."

  Furthermore, the source codeplainly confirms that a new object is created and returned.

• 各种类没有被记录为线程安全的。

• 该Cipher.getInstance(...)和SecretKeyFactory.getInstance(...)方法被记录为返回新对象; 即不引用其他线程可能引用的现有对象。

  更新- javadoc说：

  “返回一个新的 SecretKeyFactory 对象，该对象封装了来自支持指定算法的第一个 Provider 的 SecretKeyFactorySpi 实现。”

  此外，源代码清楚地确认创建并返回了一个新对象。

In short, this means that your DesEncryptorclass is not currently thread-safe, but you should be able to make it thread-safe by synchronizing the relevant operations (e.g. encodeand decode), and not exposing the two Cipher objects. If making the methods synchronized is likely to create a bottleneck, then create a separate instance of DesEncryptorfor each thread.

简而言之，这意味着您的DesEncryptor类当前不是线程安全的，但是您应该能够通过同步相关操作（例如encode和decode）来使其成为线程安全的，并且不公开两个 Cipher 对象。如果使方法同步可能会造成瓶颈，DesEncryptor则为每个线程创建一个单独的实例。

回答by David Gelhar

The Cipherobject is not going to be thread-safe, because it retains internal state about the encryption process. That applies to your DesEncrypterclass as well - each thread will need to use its own instance of DesEncrypter, unless you synchonize the encodeand decodemethods.

该Cipher对象不会是线程安全的，因为它保留有关加密过程的内部状态。这也适用于您的DesEncrypter类 - 每个线程都需要使用自己的 实例DesEncrypter，除非您同步encode和decode方法。