Question

我有来自CryptoJS的带密码的加密AES-256字符串。我需要用Java解密它，但无法弄清楚如何做到这一点。您似乎需要IV，密钥和盐来解密，并且在CryptoJS mainpage中，加密数据已经包含所有这些，并且CryptoJS可以某种方式将它们从加密输入中解析出来。

任何人都知道该怎么做？我已经看到了很多关于CryptoJS的例子 - Java加密/解密但是大多数都使用硬编码的IV /密钥，或者只是将密码/密钥从cryptoJS端发送到Java端。我所拥有的只是一个密码，就像this site所做的那样！

Answer 1

以这种方式加密邮件时：

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

使用基于密码的方法。因为CryptoJS会生成一个新的盐，并将此盐与密码结合使用以获得密钥和IV（我已经为this question编写了一个派生函数。）产生密文后，special OpenSSL formatter用于编码包含用过的盐的密文：

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

如果需要，可以解码Base64编码的字符串以获取字节数组。然后你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__"));

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);

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);

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);

完整的完整代码：

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

如何使用Java从CryptoJS解密加密的AES-256字符串？

1 个答案: