使用 AES 加密和解密大文件

Question

我正在尝试使用 AES 加密一个大文件，然后对其解密并与原始文件进行比较。

本课总结了这项工作。它适用于 .txt 文件，但不是适用于 .mp3、.pdf 等。

我们将不胜感激。

import java.io.FileInputStream;
import java.io.FileOutputStream;

public class LargeFileEncryptionTest7 {

    protected static String FOLDER_PATH = "C:/temp/";
    protected static String FILE = "some-large-file";
    protected static String EXT = ".mp3"; //Works for .txt, but not for .mp3 or .pdf

    public static void main(String[] args) throws Exception {

        //Load file to encrypt
        byte[] largeFileBytes = loadFile(FOLDER_PATH + FILE + EXT);
        String largeFileString = new String(largeFileBytes);

        //Encrypt file with AES
        AESUtils aesUtils = new AESUtils();
        byte[] secretKey = aesUtils.generateSecretKey();
        aesUtils.setSecretKey(secretKey);
        byte[] largeFileEncBytes = aesUtils.encrypt(largeFileString);

        //Save encrypted file
        saveFile(largeFileEncBytes, FOLDER_PATH + FILE + "-encrypted" + EXT);

        //Load encrypted file
        byte[] largeFileEncBytesToCheck = loadFile(FOLDER_PATH + FILE + "-encrypted" + EXT);

        //Decrypt file      
        byte[] largeFileBytesToCheck = aesUtils.decrypt(largeFileEncBytesToCheck);
        String largeFileStringToCheck = new String(largeFileBytesToCheck);

        //Save decrypted file
        saveFile(largeFileBytesToCheck, FOLDER_PATH + FILE + "-decrypted" + EXT);

        //Check strings
        //System.out.println("Original content: " + largeFileStringToCheck);
        if (largeFileStringToCheck.equals(largeFileString)) {
            System.out.println("OK  :-) ");
        } else {
            System.out.println("KO  :-( ");
        }                       
    }

    private static void saveFile(byte[] bytes, String fileName) throws Exception {
        FileOutputStream fos = new FileOutputStream(fileName);
        fos.write(bytes);
        fos.close();
    }

    private static byte[] loadFile(String fileName) throws Exception {
        FileInputStream fis = new FileInputStream(fileName);
        int numBtyes = fis.available();
        byte[] bytes = new byte[numBtyes];
        fis.read(bytes);
        fis.close();
        return bytes;
    }

}

Answer 1

我发现您的解决方案存在 2 个问题：

您的代码：

   int numBtyes = fis.available();
    byte[] bytes = new byte[numBtyes];
    fis.read(bytes);

这实际上并不能保证阅读全部内容。同样，在加密大文件时（当不能保证它可以放入内存时），您可能不想将所有内容读入内存。

在加密/解密大型内容（无限制）时，您可能需要使用以下内容：

byte[] buff = new byte[BUFFERSIZE];
for(int readBytes=in.read(buff); readBytes>-1;readBytes=in.read(buff)) {
  out.write(cipher.update(buff,0, readBytes);
}
out.write(cipher.doFinal());

或查看 CipherOutputStream 和 CipherInputStream

另一个问题是比较：

String largeFileStringToCheck = new String(largeFileBytesToCheck);

如前所述，这是一种比较内容的糟糕方式。在 Java 中，字符串仅用于可打印字符，当尝试“字符串化”任何字节数组时，将应用编码并且不可打印字符可能会被“丢弃”。

为了简单的比较（有字节数组），你可以使用Arrays.equals方法

在比较非常大的内容时（当您可能不确定它是否适合您的 RAM 内存时），通常最好创建一个 message hash 并比较哈希值

编辑：如果您真的想查看/打印/比较密文为字符串，您可以对二进制数据进行编码，您可以查看Base64 encoding。

Answer 2

如果有人感兴趣，我会在这里提出最终解决方案。

它的灵感来自于人们所做的一些 cmets。主要避免使用Strings，使用byte[]：

import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Arrays;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

public class LargeFileEncryptionTest11 {

    private static final String FOLDER_PATH = "C:/temp/";
    private static final String FILE = "some-large-file";
    private static final String EXT = ".pdf";

    private static final String ENCRYPTION_ALGORITHM = "AES";
    private static final int KEY_SIZE = 128; // 192 and 256 bits may not be available

    public static void main(String[] args) throws Exception {
        //Common stuff to encrypt/decrypt
        KeyGenerator kgen = KeyGenerator.getInstance(ENCRYPTION_ALGORITHM);
        kgen.init(KEY_SIZE); 
        SecretKey skey = kgen.generateKey();
        byte[] secretKey = skey.getEncoded();
        SecretKeySpec skeySpec = new SecretKeySpec(secretKey, ENCRYPTION_ALGORITHM);
        Cipher cipher = Cipher.getInstance(ENCRYPTION_ALGORITHM);

        //Load file to encrypt
        byte[] largeFileBytes = Files.readAllBytes(Paths.get(FOLDER_PATH + FILE + EXT));

        //Encrypt file
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
        byte[] largeFileEncBytes = cipher.doFinal(largeFileBytes);

        //Save encrypted file
        Files.write(Paths.get(FOLDER_PATH + FILE + "-encrypted" + EXT), largeFileEncBytes);

        //Load encrypted file
        byte[] largeFileEncBytesToCheck = Files.readAllBytes(Paths.get(FOLDER_PATH + FILE + "-encrypted" + EXT));

        //Decrypt file      
        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
        byte[] largeFileBytesToCheck = cipher.doFinal(largeFileEncBytesToCheck);

        //Save decrypted file
        Files.write(Paths.get(FOLDER_PATH + FILE + "-decrypted" + EXT), largeFileBytesToCheck);

        //Compare results
        if (Arrays.equals(largeFileBytes, largeFileBytesToCheck)) {
            System.out.println("OK  :-) ");
        } else {
            System.out.println("KO  :-( ");
        }                       
    }

}