import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.Random;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;

/**
 * PBE 全称为Password-Based Encrypt（基于密码的加密）。
 */
public class PBE_Encrypt {
 private static String ALGORITHM1 = "PBE";
 private static String ALGORITHM2 = "PBEWithMD5AndDES";
 private static int ITERATIONCOUNT = 1000; // 迭代计数。

/**
 * 根据自定义密码生成密钥
 */
 public static SecretKey generateKey(String password) throws Exception {
 PBEKeySpec keySpec = new PBEKeySpec(password.toCharArray());
 SecretKeyFactory kf = SecretKeyFactory.getInstance(ALGORITHM1);
 return kf.generateSecret(keySpec);
 }

/**
 * 加密文件
 * @param key密钥
 * @param sourceFile源文件
 * @param secretFile目标加密文件
 */
 public static void encryptFile(SecretKey key, File sourceFile, File secretFile)
 throws Exception {
 /** 产生一个随机盐 */
 byte[] salt = new byte[8];
 Random random = new Random();
 random.nextBytes(salt);

/** 为 PKCS #5 标准中所定义的基于密码的加密法构造一个参数集合 salt:复制该 salt 的内容来防止后续修改;1000:迭代计数 */
 PBEParameterSpec spec = new PBEParameterSpec(salt, ITERATIONCOUNT);
 /** 得到Cipher对象来实现对源数据的PBEWithMD5AndDES加密 */
 Cipher cipher = Cipher.getInstance(ALGORITHM2);
 cipher.init(Cipher.ENCRYPT_MODE, key, spec);
 /** 构造文件缓冲输出流，并将随机盐写入密文头 */
 BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(secretFile));
 out.write(salt);
 /** 构造源文件读取流 */
 BufferedInputStream in = new BufferedInputStream(new FileInputStream(sourceFile));

/** 构造密文输出流，将源文件内容加密写入目标加密文件 */
 CipherOutputStream cos = new CipherOutputStream(out, cipher);
 int b = -1;
 while ((b = in.read()) != -1) {
 cos.write(b);
 }
 cos.close();
 in.close();
 }

/**
 * 解密文件
 * @param key 密钥
 * @param secretFile 加密文件
 * @param decryptFile 解密后文件
 */
 public static void decryptFile(SecretKey key, File secretFile, File decryptFile)
 throws Exception {
 /** 从加密文件中读取随机盐 */
 byte[] salt = new byte[8];
 BufferedInputStream bis = new BufferedInputStream(new FileInputStream(secretFile));
 bis.read(salt);

PBEParameterSpec spec = new PBEParameterSpec(salt, ITERATIONCOUNT);
 /** 得到Cipher对象来实现对加密数据的PBEWithMD5AndDES解密 */
 Cipher cipher = Cipher.getInstance(ALGORITHM2);
 cipher.init(Cipher.DECRYPT_MODE, key, spec);

BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(decryptFile));
 CipherInputStream in = new CipherInputStream(bis, cipher);

int b = -1;
 while ((b = in.read()) != -1) {
 out.write(b);
 }
 out.close();
 in.close();
 }

public static void main(String[] args) throws Exception {
 SecretKey key = generateKey("MySecretKey");// 用自定义的字符串生成一个可信密钥
 File sourceFile = new File("D:\\test.jpg");// 源文件
 File secretFile = new File("D:\\secret");// 加密目标文件
 File decryptFile = new File("D:\\decrypt.jpg");// 解密目标文件

/** 加密文件 */
 encryptFile(key, sourceFile, secretFile);

/** 解密文件 */
 decryptFile(key, secretFile, decryptFile);
 }
}

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