Question

背景我正在处理的应用程序应该脱机工作。我应该使用密码作为Java服务器端的密钥加密一些文本数据。加密数据传递到HTML5页面，在客户端使用crypto-js库，应解密服务器加密数据。

我的问题： 为了加密我的消息，客户端可以使用crypt-js（使用用户输入的密码）对其进行解密，我需要知道加密消息时crypto-js所期望的确切步骤。

我需要知道的事情： 我有以下加密代码，使用crypto-js在客户端加密消息。

var message = "my message text";
var password = "user password";
var encrypted = CryptoJS.AES.encrypt( message ,password );
console.log(encrypted.toString());

我需要知道加密消息时CryptoJS使用的AES参数（不确定它们是什么，但听起来像：密钥大小（256），填充（pkcs5），模式（CBC），PBE算法（PBKDF2），盐（随机），迭代计数（100））。如果有人能证实这一点会有很大的帮助......过去几天我一直试图解开这个谜团。

我需要知道CryptoJS在AES加密消息时执行的不同步骤

Answer 1

CryptoJS uses用于密钥派生的非标准化OpenSSL KDF（EvpKDF），其中 MD5 作为散列算法和 1 迭代。 IV也来自密码，这意味着在Java端只需要实际的密文，密码和盐来解密它。

换句话说，PBKDF2不用于CryptoJS的密码模式中的密钥派生。默认情况下，AES-256在CBC模式下使用PKCS5填充（same as PKCS7 padding）。请注意，您可能需要JCE Unlimited Strength Jurisdiction Policy Files。另请参阅Why there are limitations on using encryption with keys beyond certain length?

以下代码在Java中重新创建KDF（keySize和ivSize分别为8和4，用于AES-256并来自）。

public static byte[] evpKDF(byte[] password, int keySize, int ivSize, byte[] salt, int iterations, String hashAlgorithm, byte[] resultKey, byte[] resultIv) throws NoSuchAlgorithmException {
    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
}

以下是完整的参考类：

public class RecreateEVPkdfFromCryptoJS {
    public static void main(String[] args) throws UnsupportedEncodingException, GeneralSecurityException {
        String msg = "hello";
        String password = "mypassword";
        String ivHex = "aab7d6aca0cc6ffc18f9f5909753aa5f";
        int keySize = 8; // 8 words = 256-bit
        int ivSize = 4; // 4 words = 128-bit
        String keyHex = "844a86d27d96acf3147aa460f535e20e989d1f8b5d79c0403b4a0f34cebb093b";
        String saltHex = "ca35168ed6b82778";
        String openSslFormattedCipherTextString = "U2FsdGVkX1/KNRaO1rgneK9S3zuYaYZcdXmVKJGqVqk=";
        String cipherTextHex = "af52df3b9869865c7579952891aa56a9";
        String padding = "PKCS5Padding";

        byte[] key = hexStringToByteArray(keyHex);
        byte[] iv = hexStringToByteArray(ivHex);
        byte[] salt = hexStringToByteArray(saltHex);
        byte[] cipherText = hexStringToByteArray(cipherTextHex);

        byte[] javaKey = new byte[keySize * 4];
        byte[] javaIv = new byte[ivSize * 4];
        evpKDF(password.getBytes("UTF-8"), keySize, ivSize, salt, javaKey, javaIv);
        System.out.println(Arrays.equals(key, javaKey) + " " + Arrays.equals(iv, javaIv));

        Cipher aesCipherForEncryption = Cipher.getInstance("AES/CBC/PKCS5Padding"); // Must specify the mode explicitly as most JCE providers default to ECB mode!!

        IvParameterSpec ivSpec = new IvParameterSpec(javaIv);
        aesCipherForEncryption.init(Cipher.DECRYPT_MODE, new SecretKeySpec(javaKey, "AES"), ivSpec);

        byte[] byteMsg = aesCipherForEncryption.doFinal(cipherText);
        System.out.println(Arrays.equals(byteMsg, msg.getBytes("UTF-8")));
    }

    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 {
        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 http://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;
    }
}

以及用于在Java代码中生成值的JavaScript代码：

var msg = "hello";
var password = "mypassword"; // must be present on the server
var encrypted = CryptoJS.AES.encrypt( msg, password );
var ivHex = encrypted.iv.toString();
var ivSize = encrypted.algorithm.ivSize; // same as the blockSize
var keySize = encrypted.algorithm.keySize;
var keyHex = encrypted.key.toString();
var saltHex = encrypted.salt.toString(); // must be sent as well
var openSslFormattedCipherTextString = encrypted.toString(); // not used
var cipherTextHex = encrypted.ciphertext.toString(); // must be sent

Answer 2

在@Artjom B在此问题和here for python users上都给出了很好的答案之后，我加入了完整的Java代码，该代码可帮助我解密以这种方式加密的字符串

var encrypted = CryptoJS.AES.encrypt(message, password).toString();

当您仅知道密码（即未与加密字符串一起发送salt）时，这段Java代码非常有用：

public String decrypt(String encrypted, String password) throws Exception {
    int keySize = 8;
    int ivSize = 4;
    // Start by decoding the encrypted string (Base64)
    // Here I used the Android implementation (other Java implementations might exist)
    byte[] cipherText = Base64.decode(encrypted, Base64.DEFAULT);
    // prefix (first 8 bytes) is not actually useful for decryption, but you should probably check that it is equal to the string "Salted__"
    byte[] prefix = new byte[8];
    System.arraycopy(cipherText, 0, prefix, 0, 8);
    // Check here that prefix is equal to "Salted__"
    // Extract salt (next 8 bytes)
    byte[] salt = new byte[8];
    System.arraycopy(cipherText, 8, salt, 0, 8);
    // Extract the actual cipher text (the rest of the bytes)
    byte[] trueCipherText = new byte[cipherText.length - 16];
    System.arraycopy(cipherText, 16, trueCipherText, 0, cipherText.length - 16);
    byte[] javaKey = new byte[keySize * 4];
    byte[] javaIv = new byte[ivSize * 4];
    evpKDF(password.getBytes("UTF-8"), keySize, ivSize, salt, javaKey, javaIv);
    Cipher aesCipherForEncryption = Cipher.getInstance("AES/CBC/PKCS5Padding");
    IvParameterSpec ivSpec = new IvParameterSpec(javaIv);
    aesCipherForEncryption.init(Cipher.DECRYPT_MODE, new SecretKeySpec(javaKey, "AES"), ivSpec);

    byte[] byteMsg = aesCipherForEncryption.doFinal(trueCipherText);
    return new String(byteMsg, "UTF-8");
}

public  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  byte[] evpKDF(byte[] password, int keySize, int ivSize, byte[] salt, int iterations, String hashAlgorithm, byte[] resultKey, byte[] resultIv) throws NoSuchAlgorithmException {
    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
}

Answer 3

我在这里看at the documentation：

密钥大小：“如果您使用密码短语，那么它将生成一个256位密钥。”
padding：Pkcs7（默认值）
模式：CBC（默认）
iv：生成并存储在密文对象中：与“encrypted.iv”一起使用

生成密钥的东西：

salt：生成并存储在密文对象中：与“encrypted.salt”一起使用（虽然它没有真正说明，所以我在这里猜测）
pbe算法：不清楚。它没有记录。
迭代计数：我无法在任何地方找到此文档。代码中的示例似乎使用了1000。

您可以手动设置参数，这可能比依赖默认设置更安全，例如一些伪代码基于文档中的示例：

var salt = CryptoJS.lib.WordArray.random(128/8);
var iv = CryptoJS.lib.WordArray.random(128);
var key256Bits10000Iterations = CryptoJS.PBKDF2("Secret Passphrase", salt, { keySize: 256/32, iterations: 10000 }); //I don't know this is dividing by 32
var encrypted = CryptoJS.AES.encrypt("Message", key, { mode: CryptoJS.mode.CBC, padding: CryptoJS.pad.Pkcs7, iv:iv });

您可能需要进行实验。我一步一步走。通过摆弄这些参数来获取基于密码的密钥进行匹配，然后获取要匹配的密文，然后找出解密。避免简化跳过IV或使用ECB等事情的冲动。

在使用密码加密消息时，crypto-js内部使用的AES参数和步骤是什么？

3 个答案: