用AES加密和解密大型文件

Question

我正在尝试用AES加密一个大文件，然后解密，与原件进行比较。

这堂课总结了工作。它适用于.txt文件，但不适用于.mp3、.pdf等文件。

我们将非常感谢你的帮助。

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

万一有人感兴趣，我把最后的解决方案放在这里。

它的灵感来自于人们所做的一些评论。主要避免使用字符串，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  :-( ");
        }                       
    }

}

Answer 2

我发现您的解决方案有两个问题：

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，当加密大文件时（当不能保证它能放入内存时），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，您可能希望使用以下内容：

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());

或者看一下CipherOutputStream和CipherInputStream

另一个问题是比较：

String largeFileStringToCheck = new String(largeFileBytesToCheck);

正如已经评论过的，这是一种可怕的内容比较方式。在Java，字符串只用于可打印的字符，当试图“字符串化”任何字节数组时，会应用一种编码，而不可打印的字符可能会被“丢弃”。

对于简单的比较（具有字节数组），可以使用arrays.equals方法

在比较真正大的内容时（当您可能不确定它是否适合您的RAM内存时），通常创建消息哈希并比较哈希是一个好主意

编辑：如果你真的想看到/打印/比较作为字符串的密文，你可以对二进制数据进行编码，你可以看一下Base64编码。