Java用密码加密文件

Question

嗨，我是新用户，这是我的第一个问题：我声明我没有广泛的密码学知识。 我正在尝试使用用户提供的密码加密文件，我发现了这种方法：

fileProcessor(Cipher.ENCRYPT_MODE,key,inputFile,newFile);

static void fileProcessor(int cipherMode,String key,File inputFile,File outputFile) {
    try {
        Key secretKey = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(cipherMode, secretKey);

        FileInputStream inputStream = new FileInputStream(inputFile);
        byte[] inputBytes = new byte[(int) inputFile.length()];
        inputStream.read(inputBytes);

        byte[] outputBytes = cipher.doFinal(inputBytes);

        FileOutputStream outputStream = new FileOutputStream(outputFile);
        outputStream.write(outputBytes);

        inputStream.close();
        outputStream.close();

        } catch (NoSuchPaddingException | NoSuchAlgorithmException 
                     | InvalidKeyException | BadPaddingException
                 | IllegalBlockSizeException | IOException e) {
        e.printStackTrace();
            }
}

问题是该程序仅在我输入 16 字节密码时才有效（我认为即使是它的倍数也可以）。 如何使用不一定是 16 字节倍数的密码？

Answer 1

密钥 ( SecretKeySpec ) 是一个加密密钥，而不是用户提供的简单明文密码。 AES 标准指定以下密钥大小：128、192 或 256 位。 可以使用密钥派生函数（例如PBKDF2 ）从文本密码创建密钥。

正如评论中提到的Maarten- Cipher.getInstance("AES") ， Cipher.getInstance("AES")导致 AES 加密在 ECB 模式下是不安全的。 AES-GCM是基于 AES 算法的强大认可的认证加密模式。

此外，在继续示例代码之前，您需要了解以下概念：

• 盐
• PBKDF2 密码算法
• 什么是信息安全中的机密性、完整性和真实性
• 密码强度建议

示例代码：

// The number of times that the password is hashed during the derivation of the symmetric key
private static final int PBKDF2_ITERATION_COUNT = 300_000;
private static final int PBKDF2_SALT_LENGTH = 16; //128 bits
private static final int AES_KEY_LENGTH = 256; //in bits
// An initialization vector size
private static final int GCM_NONCE_LENGTH = 12; //96 bits
// An authentication tag size
private static final int GCM_TAG_LENGTH = 128; //in bits

private static byte[] encryptAES256(byte[] input, String password) {
  try {
    SecureRandom secureRandom = SecureRandom.getInstanceStrong();
    // Derive the key, given password and salt
    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA512");
    // A salt is a unique, randomly generated string
    // that is added to each password as part of the hashing process
    byte[] salt = new byte[PBKDF2_SALT_LENGTH];
    secureRandom.nextBytes(salt);
    KeySpec keySpec =
        new PBEKeySpec(password.toCharArray(), salt, PBKDF2_ITERATION_COUNT, AES_KEY_LENGTH);
    byte[] secret = factory.generateSecret(keySpec).getEncoded();
    SecretKey key = new SecretKeySpec(secret, "AES");

    // AES-GCM encryption
    Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
    // A nonce or an initialization vector is a random value chosen at encryption time
    // and meant to be used only once
    byte[] nonce = new byte[GCM_NONCE_LENGTH];
    secureRandom.nextBytes(nonce);
    // An authentication tag
    GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH, nonce);
    cipher.init(Cipher.ENCRYPT_MODE, key, gcmParameterSpec);
    byte[] encrypted = cipher.doFinal(input);
    // Salt and nonce can be stored together with the encrypted data
    // Both salt and nonce have fixed length, so can be prefixed to the encrypted data
    ByteBuffer byteBuffer = ByteBuffer.allocate(salt.length + nonce.length + encrypted.length);
    byteBuffer.put(salt);
    byteBuffer.put(nonce);
    byteBuffer.put(encrypted);
    return byteBuffer.array();
  } catch (Exception e) {
    throw new RuntimeException(e);
  }
}

private static byte[] decryptAES256(byte[] encrypted, String password) {
  try {
    // Salt and nonce have to be extracted
    ByteBuffer byteBuffer = ByteBuffer.wrap(encrypted);
    byte[] salt = new byte[PBKDF2_SALT_LENGTH];
    byteBuffer.get(salt);
    byte[] nonce = new byte[GCM_NONCE_LENGTH];
    byteBuffer.get(nonce);
    byte[] cipherBytes = new byte[byteBuffer.remaining()];
    byteBuffer.get(cipherBytes);

    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA512");
    KeySpec keySpec =
        new PBEKeySpec(password.toCharArray(), salt, PBKDF2_ITERATION_COUNT, AES_KEY_LENGTH);
    byte[] secret = factory.generateSecret(keySpec).getEncoded();
    SecretKey key = new SecretKeySpec(secret, "AES");

    Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
    // If encrypted data is altered, during decryption authentication tag verification will fail
    // resulting in AEADBadTagException
    GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH, nonce);
    cipher.init(Cipher.DECRYPT_MODE, key, gcmParameterSpec);
    return cipher.doFinal(cipherBytes);
  } catch (Exception e) {
    throw new RuntimeException(e);
  }
}

public static void main(String[] args) throws Exception {
  String password = "Q8yRrM^AvV5r8Yx+"; //Password still has to be strong ehough
  String input = "Sample text to encrypt";
  byte[] encrypted = encryptAES256(input.getBytes(UTF_8), password);
  System.out.println(Base64.getEncoder().encodeToString(encrypted));
  //s+AwwowLdSb3rFZ6jJlxSXBvzGz7uB6+g2e97QXGRKUY5sHPgf94AOoybkzuR3rNREMj56Ik1+Co682s4vT2sAQ/
  byte[] decrypted = decryptAES256(encrypted, password);
  System.out.println(new String(decrypted, UTF_8));
  //Sample text to encrypt
}

再说几句随机 nonce 。 如果只有少数记录使用相同的密钥加密，那么随机数不会带来风险。 但是，如果大量记录使用相同的密钥加密，则风险可能变得相关。

单个重复随机数通常足以完全恢复连接的身份验证密钥。 在此类错误实现中，真实性丢失，攻击者能够操纵受 TLS 保护的内容。

出于安全原因，应避免随机数，并应使用计数器。

Answer 2

我正在尝试使用用户提供的密码加密文件
如何使用不一定是 16 字节倍数的密码？

要从用户提供的密码创建加密密钥，您可以查看一些示例，通常搜索“基于密码的加密”

这是如何使用用户密码创建加密密钥的示例

 private static final String PBKDF_ALG = "PBKDF2WithHmacSHA256";
 private static final int PBKDF_INTERATIONS = 800000;

// create key from password
 SecretKeyFactory secKeyFactory = SecretKeyFactory.getInstance(PBKDF_ALG);
 KeySpec pbeSpec = new PBEKeySpec(password.toCharArray(), psswdSalt, PBKDF_INTERATIONS, SYMMETRIC_KEY.length*8);
 SecretKey pbeSecretKey = secKeyFactory.generateSecret(pbeSpec);
SecretKey secKey = new SecretKeySpec(pbeSecretKey.getEncoded(), SYMMETRIC_KEY_ALG);

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(cipherMode, secKey) ;