如何使用从密码派生的密钥正确加密和解​​密文件

Question

我正在尝试使用“PBEWithHmacSHA256AndAES_256”标准制定正确的过程来加密和解密文件。

从我从 Oracle 的这个示例代码中了解到。

我收集到需要一个盐，以及一个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：

1. 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）
2. initVector作为字节数组的安全随机 IV
3. 纯文本文件inputFile作为字符串
4. 要创建的密文文件的名称outputFile作为字符串

我已经按照代码示例编写了我认为对加密方法正确的内容。我通过将它们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");
}

然后我还有我的main方法，传入解密方法：

1. 用户定义的密码String inputKEY作为字符串（也将此方法用于其他 dencryption 运行）

2. , 的字符串inputIV已作为 null 传入，因为未用于 PBE。

3. 密文文件inputFile作为字符串

4. 将要创建的显示纯文本文件的名称outputFile作为字符串

   私有静态无效解密（字符串输入密钥，字符串输入IV，字符串输入文件，字符串输出文件）{密码密码=空；

    //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");
   

   }

我相信我对 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 不得写入for循环内。
• IVencrypt不是用 Base64 编码存储的，而是用 Base64 解码的decrypt.
• 16 个字节的盐存储在encrypt（不必要的）Base64 编码中，即存储了 24 个字节。在decrypt但是只有16字节加载。

还：

• 在编码/解码时，有时不指定编码，因此使用默认编码。
• encrypt并decrypt为 key 和 IV 使用不同的参数类型。
• 代码中有很多复制/粘贴错误。

注意：与您的代码相反，链接代码除了密钥之外还确定密码和盐的 IV。在您的代码中，IV 已通过。因此，您必须确保密钥/IV 对只能使用一次。通常为每个加密生成一个随机 IV。

在以下代码（基于您的代码，但为了简单起见，没有异常处理）中，这些问题已修复/优化。此外，代码适用FileInputStream，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- 关于盐和 IV 的读取decrypt：
正如GPI在他们的评论中指出的那样，FileInputStream.read(byte[] b)通常读取b.length字节，但这不能保证。更健壮的是确定读取数据的长度并在循环中调用该方法，直到数据完整。另一种选择是使用InputStream.readNBytes?(int len)，它保证读取len字节（除非遇到流结束或抛出异常），正如Zabuzard所建议的那样。在代码中，现在使用了后者，read即被替换为readNBytes?.