如何使用 Java 从 CryptoJS 解密加密的 AES-256 字符串？

How to decrypt an encrypted AES-256 string from CryptoJS using Java?

提问by kientux

I have an encrypted AES-256 string from CryptoJS with a passphrase. I need to decrypt it in Java but can't figure out how to do it. It seems that you need IV, key and salt to decrypt, and as in CryptoJS mainpage, the encrypted data already contains all of them, and CryptoJS can somehow parse them out of encrypted input.

我有一个来自 CryptoJS 的带有密码的加密 AES-256 字符串。我需要用 Java 解密它，但不知道怎么做。似乎您需要 IV、密钥和盐来解密，并且就像在CryptoJS mainpage 中一样，加密数据已经包含所有这些，并且 CryptoJS 可以以某种方式从加密输入中解析它们。

Anyone know how to do that? I've seen so much example about CryptoJS - Java encrypt/decrypt but most of them use hardcoded IV/key, or just send IV/key from cryptoJS side to Java side. All I have is a passphrase, just like what this sitedo!

有谁知道怎么做？我见过很多关于 CryptoJS 的例子——Java 加密/解密，但大多数使用硬编码的 IV/key，或者只是将 IV/key 从 cryptoJS 端发送到 Java 端。我只有一个密码，就像这个网站所做的一样！

回答by Artjom B.

When a message is encrypted in this way:

当以这种方式加密消息时：

CryptoJS.AES.encrypt("message", "passphrase")

a password-based approach is used. For that CryptoJS generates a new salt and uses this salt in conjunction with the passphrase to derive the key and IV (I've written a derivation function for this question).
After the ciphertext is produced a special OpenSSL formatteris used to encode the ciphertext including the used salt:

使用基于密码的方法。为此，CryptoJS 生成一个新的盐，并将此盐与密码短语结合使用来派生密钥和 IV（我已为此问题编写了派生函数）。
生成密文后，使用特殊的 OpenSSL 格式化程序对密文进行编码，包括使用的盐：

var wordArray = WordArray.create([0x53616c74, 0x65645f5f]).concat(salt).concat(ciphertext);

You can need to decode the Base64 encoded string to get the byte array out if it. Then you can check if the header matches:

您可能需要解码 Base64 编码的字符串以获取字节数组。然后您可以检查标题是否匹配：

byte[] ctBytes = Base64.getDecoder().decode(ciphertext.getBytes("UTF-8"));
System.out.println("Is salted: " + new String(Arrays.copyOf(ctBytes, 8)).equals("Salted__"));

After that you can get the recover the salt and ciphertext from it:

之后，您可以从中恢复盐和密文：

byte[] saltBytes = Arrays.copyOfRange(ctBytes, 8, 16);
byte[] ciphertextBytes = Arrays.copyOfRange(ctBytes, 16, ctBytes.length);

Derive the key+IV:

导出密钥+IV：

byte[] key = new byte[keySize/8];
byte[] iv = new byte[ivSize/8];
EvpKDF(password.getBytes("UTF-8"), keySize, ivSize, saltBytes, key, iv);

And decrypt the ciphertext:

并解密密文：

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"),
        new IvParameterSpec(iv));
byte[] recoveredPlaintextBytes = cipher.doFinal(ciphertextBytes);
String recoveredPlaintext = new String(recoveredPlaintextBytes);

Full complete code:

完整完整的代码：

public static void main(String[] args) throws UnsupportedEncodingException, GeneralSecurityException {
    String ciphertext = "U2FsdGVkX1+0m/gle/XQX1shjnpveUrl1fO3oOlurPMlTks6+oQlEPfOrucihzEz";
    String plaintext = "This is some example plaintext";
    String password = "This is a very strong password";
    int keySize = 256;
    int ivSize = 128;

    // var wordArray = WordArray.create([0x53616c74, 0x65645f5f]).concat(salt).concat(ciphertext);
    byte[] ctBytes = Base64.getDecoder().decode(ciphertext.getBytes("UTF-8"));
    System.out.println("Is salted: " + Arrays.equals(Arrays.copyOf(ctBytes, 8), new byte[]{0x53, 0x61, 0x6c, 0x74, 0x65, 0x64, 0x5f, 0x5f}));
    System.out.println("Is salted: " + new String(Arrays.copyOf(ctBytes, 8)).equals("Salted__"));

    byte[] saltBytes = Arrays.copyOfRange(ctBytes, 8, 16);
    System.out.println("Salt matches: " + Arrays.equals(saltBytes, hexStringToByteArray("b49bf8257bf5d05f")));

    byte[] ciphertextBytes = Arrays.copyOfRange(ctBytes, 16, ctBytes.length);
    System.out.println("CT matches: " + Arrays.equals(ciphertextBytes, hexStringToByteArray("5b218e7a6f794ae5d5f3b7a0e96eacf3254e4b3afa842510f7ceaee722873133")));

    byte[] key = new byte[keySize/8];
    byte[] iv = new byte[ivSize/8];
    EvpKDF(password.getBytes("UTF-8"), keySize, ivSize, saltBytes, key, iv);

    Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"), new IvParameterSpec(iv));
    byte[] recoveredPlaintextBytes = cipher.doFinal(ciphertextBytes);
    String recoveredPlaintext = new String(recoveredPlaintextBytes);

    System.out.println("Recovered Plaintext: " + recoveredPlaintext);
    System.out.println("Expected Plaintext: " + plaintext);
}

public static byte[] EvpKDF(byte[] password, int keySize, int ivSize, byte[] salt, byte[] resultKey, byte[] resultIv) throws NoSuchAlgorithmException {
    return EvpKDF(password, keySize, ivSize, salt, 1, "MD5", resultKey, resultIv);
}

public static byte[] EvpKDF(byte[] password, int keySize, int ivSize, byte[] salt, int iterations, String hashAlgorithm, byte[] resultKey, byte[] resultIv) throws NoSuchAlgorithmException {
    keySize = keySize / 32;
    ivSize = ivSize / 32;
    int targetKeySize = keySize + ivSize;
    byte[] derivedBytes = new byte[targetKeySize * 4];
    int numberOfDerivedWords = 0;
    byte[] block = null;
    MessageDigest hasher = MessageDigest.getInstance(hashAlgorithm);
    while (numberOfDerivedWords < targetKeySize) {
        if (block != null) {
            hasher.update(block);
        }
        hasher.update(password);
        block = hasher.digest(salt);
        hasher.reset();

        // Iterations
        for (int i = 1; i < iterations; i++) {
            block = hasher.digest(block);
            hasher.reset();
        }

        System.arraycopy(block, 0, derivedBytes, numberOfDerivedWords * 4,
                Math.min(block.length, (targetKeySize - numberOfDerivedWords) * 4));

        numberOfDerivedWords += block.length/4;
    }

    System.arraycopy(derivedBytes, 0, resultKey, 0, keySize * 4);
    System.arraycopy(derivedBytes, keySize * 4, resultIv, 0, ivSize * 4);

    return derivedBytes; // key + iv
}

/**
 * Copied from https://stackoverflow.com/a/140861
 * */
public static byte[] hexStringToByteArray(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

JavaScript code:

JavaScript 代码：

var pw = "This is a very strong password";
var pt = "This is some example plaintext";
var encrypted = CryptoJS.AES.encrypt(pt, pw);
encrypted.toString(); // U2FsdGVkX1+0m/gle/XQX1shjnpveUrl1fO3oOlurPMlTks6+oQlEPfOrucihzEz
encrypted.salt.toString(); // b49bf8257bf5d05f
encrypted.ciphertext.toString(); // 5b218e7a6f794ae5d5f3b7a0e96eacf3254e4b3afa842510f7ceaee722873133