如何使用从密码派生的密钥正确加密和解密文件

Question

我正在尝试找出使用“PBEWithHmacSHA256AndAES_256”标准加密和解密文件的正确过程。

据我了解来自 Oracle 的 example code。

我了解到需要加盐，以及迭代计数和哈希标准。

所以我有我的主要方法，传入加密方法：

用户定义的密码new String(key).toCharArray()作为字节数组（使用此方法进行其他加密运行）
作为字节数组的安全随机 IV initVector
作为字符串的纯文本文件inputFile
要创建的密文文件的名称outputFile作为字符串

我按照代码示例编写了我认为对加密方法正确的代码。我通过将盐和 IV 附加到密文来存储用于解密的盐和 IV。

private static void encrypt(byte[] key, byte[] initVector, String inputFile, String outputFile) //exceptions for throws... {
    //Initalisation for encryption
    Cipher cipher;

    byte[] salt = new byte[16];

        SecureRandom rand = new SecureRandom();

        // Salt randomly generated with base64
        rand.nextBytes(salt);
        System.out.println("my salt should be" + Base64.getEncoder().encodeToString(salt));
        salt = Base64.getEncoder().encode(salt);

        // Iteration count
        int count = 1000;

        IvParameterSpec iv = new IvParameterSpec(initVector);
        
        // Create PBE parameter set
        PBEParameterSpec pbeParamSpec = new PBEParameterSpec(Base64.getDecoder().decode(salt), count, iv);                
        // Convert pass into SecretKey object
        PBEKeySpec pbeKeySpec = new PBEKeySpec(new String(key).toCharArray());
        SecretKeyFactory keyFac = SecretKeyFactory.getInstance("PBEWithHmacSHA256AndAES_256");
        SecretKey pbeKey;
        try {
            pbeKey = keyFac.generateSecret(pbeKeySpec);
        } catch (InvalidKeySpecException e) {
            System.out.println("Sorry, the password specified cannot be used as a secret key");
            System.out.println("Please check that your password uses valid characters");
            return;
        }

        // Create PBE Cipher
        cipher = Cipher.getInstance("PBEWithHmacSHA256AndAES_256");

        // Initialize PBE Cipher with key and parameters
        cipher.init(Cipher.ENCRYPT_MODE, pbeKey, pbeParamSpec);
    }

    //File error checking and file handling (i.e. generating file paths)...

    System.out.println("Secret key is " + Base64.getEncoder().encodeToString(key));
    System.out.println("IV is " + Base64.getEncoder().encodeToString(initVector));

    //Special file reading and writing with 'Cipher Stream'
    try (InputStream fin = FileEncryptor.class.getResourceAsStream(loadFile.getName());
            OutputStream fout = Files.newOutputStream(saveFile);

            CipherOutputStream cipherOut = new CipherOutputStream(fout, cipher) {
            }) {
        final byte[] bytes = new byte[1024];
        for(int length=fin.read(bytes); length!=-1; length = fin.read(bytes)){

                fout.write(initVector);
                fout.write(salt);

            cipherOut.write(bytes, 0, length);

        }
    } catch (IOException e) {
        System.out.println("Something went wrong with reading and writing these files!");
        System.out.println("Please check you have the latest version of this program");
        System.out.println("Contact your IT admin to make sure you have sufficient privileges");
    }
    System.out.println("SUCCESS! Encryption finished, saved at specified location");
}

然后还有我的main方法，传入解密方法：

一个用户定义的密码String inputKEY作为一个字符串（其他解密运行也使用此方法）
inputIV 的字符串，已作为 null 传入，因为未用于 PBE。
密文文件inputFile作为字符串

要创建的以字符串形式显示明文文件的名称outputFile

private static void decrypt(String inputKEY, String inputIV, String inputFile, String outputFile) { 密码 cipher = null;

 //File error checking and file handling (i.e. generating file paths)...

 InputStream encryptedData = Files.newInputStream(loadFilePath);


     PBEKeySpec pbeKeySpec = new PBEKeySpec(inputKEY.toCharArray());
     SecretKeyFactory keyFac = SecretKeyFactory.getInstance("PBEWithHmacSHA256AndAES_256");
     SecretKey pbeKey = null;
     try {
         pbeKey = keyFac.generateSecret(pbeKeySpec);
     } catch (InvalidKeySpecException e) {
         // TODO Auto-generated catch block
         e.printStackTrace();
     }
     byte[] initVect = new byte[16];
     encryptedData.read(initVect);

     IvParameterSpec iv = new IvParameterSpec(Base64.getDecoder().decode(initVect);

     byte[] salt = new byte[16];
     encryptedData.read(salt);

     PBEParameterSpec pbeParamSpec = new PBEParameterSpec(Base64.getDecoder().decode(salt), 1000, iv);  
     cipher = Cipher.getInstance("PBEWithHmacSHA256AndAES_256");

     System.out.println("my salt should be" + Base64.getEncoder().encodeToString(Base64.getDecoder().decode(salt)));

     cipher.init(Cipher.DECRYPT_MODE, pbeKey, pbeParamSpec); 

 try (CipherInputStream decryptStream = new CipherInputStream(encryptedData, cipher);    
         OutputStream decryptedOut = Files.newOutputStream(saveFile)){
     final byte[] bytes = new byte[1024];
     for(int length=decryptStream.read(bytes); length!=-1; length = decryptStream.read(bytes)){
         decryptedOut.write(bytes, 0, length);
     }
 } catch (IOException e) { //This is caught when decryption is run
     System.out.println("Something went wrong with reading and writing these files!");
     System.out.println("Please check you have the latest version of this program");
     System.out.println("Contact your IT admin to make sure you have sufficient privileges");
 }

 System.out.println("SUCESS! Decryption finished, saved at specified location");

}

我认为我对PBE的理解有些不对，因此我实现它的方式可能是错误的。谁能指出似乎有什么问题？

Answer 1

主要问题是：

IV 和 Salt 不能写在 for 循环中。
IV 存储在 encrypt 中，未进行 Base64 编码，但在 decrypt 中进行了 Base64 解码。
16 字节的 salt 以 encrypt（不必要地）Base64 编码存储，即存储 24 字节。然而在 decrypt 中只加载了 16 个字节。

还有：

在encoding/decoding之后，有时没有指定编码，所以使用默认编码。
encrypt 和 decrypt 对密钥和 IV 使用不同的参数类型。
代码中有很多 copy/paste 个错误。

注意：与您的代码不同，linked 代码除了确定密钥外，还确定来自密码和盐的 IV。在您的代码中，IV 已通过。因此，您必须确保 key/IV 对只能使用一次。通常每次加密都会生成一个随机IV。

在下面的代码中（基于您的代码，但为简单起见，没有进行异常处理）这些问题是 fixed/optimized。此外，代码应用 FileInputStream 和 FileOutputStream 而不是您的类（但这不是必需的）：

private static void encrypt(String key, byte[] initVector, String inputFile, String outputFile) throws Exception {

    // Key
    PBEKeySpec pbeKeySpec = new PBEKeySpec(key.toCharArray());
    SecretKeyFactory keyFac = SecretKeyFactory.getInstance("PBEWithHmacSHA256AndAES_256");
    SecretKey pbeKey = keyFac.generateSecret(pbeKeySpec);

    // IV
    IvParameterSpec iv = new IvParameterSpec(initVector);

    // Salt
    SecureRandom rand = new SecureRandom();
    byte[] salt = new byte[16];
    rand.nextBytes(salt);

    // ParameterSpec
    int count = 1000; // should be larger, see Michael Fehr's comment
    PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt, count, iv);

    // Cipher
    Cipher cipher = Cipher.getInstance("PBEWithHmacSHA256AndAES_256");
    cipher.init(Cipher.ENCRYPT_MODE, pbeKey, pbeParamSpec);

    try (FileInputStream fin = new FileInputStream(inputFile);
         FileOutputStream fout = new FileOutputStream(outputFile);
         CipherOutputStream cipherOut = new CipherOutputStream(fout, cipher)) {
    
        // Write IV, Salt
        fout.write(initVector);
        fout.write(salt);
    
        // Encrypt
        final byte[] bytes = new byte[1024];
        for (int length = fin.read(bytes); length != -1; length = fin.read(bytes)) {
            cipherOut.write(bytes, 0, length);
        }
    } 
}

private static void decrypt(String key, byte[] initVect, String inputFile, String outputFile) throws Exception {

    try (FileInputStream encryptedData = new FileInputStream(inputFile);
         FileOutputStream decryptedOut = new FileOutputStream(outputFile)) {

        // Key
        PBEKeySpec pbeKeySpec = new PBEKeySpec(key.toCharArray());
        SecretKeyFactory keyFac = SecretKeyFactory.getInstance("PBEWithHmacSHA256AndAES_256");
        SecretKey pbeKey = keyFac.generateSecret(pbeKeySpec);

        // Read IV
        if (initVect == null) {
            initVect = encryptedData.readNBytes(16);
        }
        IvParameterSpec iv = new IvParameterSpec(initVect);

        // Read salt
        byte[] salt = encryptedData.readNBytes(16);

        // ParameterSpec
        int count = 1000;
        PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt, count, iv);

        // Cipher
        Cipher cipher = Cipher.getInstance("PBEWithHmacSHA256AndAES_256");
        cipher.init(Cipher.DECRYPT_MODE, pbeKey, pbeParamSpec);

        try (CipherInputStream decryptStream = new CipherInputStream(encryptedData, cipher)) {
        
            // Decrypt
            final byte[] bytes = new byte[1024];
            for (int length = decryptStream.read(bytes); length != -1; length = decryptStream.read(bytes)) {
                decryptedOut.write(bytes, 0, length);
            }
        } 
    }
}

编辑 - 关于decrypt中盐和IV的读数：
正如GPI指出的在他们的评论中，FileInputStream.read(byte[] b) generally reads b.length bytes, but this is not guaranteed. More robust is to determine the length of the read data and call the method in a loop until the data is complete. Another alternative is the use of InputStream.readNBytes(int len)，保证读取len字节（除非遇到流结束或抛出异常），因为Zabuzard 已建议。在代码中，现在使用后者，即 read 被替换为 readNBytes.

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