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我们将使用DES对称加密算法对密钥进行生成，然后利用它来加密和解密我们的类文件。以下是一个简单的操作步骤和实现代码。

首先，我们需要生成一个密钥。这个过程可以通过以下代码实现：

package com.neusoft.jiami;import Java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.security.SecureRandom;import javax.crypto.Cipher;import javax.crypto.SecretKey;import javax.crypto.SecretKeyFactory;import javax.crypto.spec.DESKeySpec;public class KeyGenerator {    public static void main(String[] args) throws Exception {        SecureRandom sr = new SecureRandom();        FileInputStream fi = new FileInputStream(new File("key.txt"));        byte rawKeyData[] = new byte[fi.available()];        fi.read(rawKeyData);        fi.close();        DESKeySpec dks = new DESKeySpec(rawKeyData);        SecretKeyFactory.getInstance("DES").generateSecret(dks);    }}

接着，我们需要对类文件进行加密。以下是一个完整的加密过程：

package com.neusoft.jiami;import Java.io.File;import Java.io.FileInputStream;import Java.io.FileOutputStream;import Java.security.SecureRandom;import javax.crypto.Cipher;import javax.crypto.SecretKey;import javax.crypto.SecretKeyFactory;import javax.crypto.spec.DESKeySpec;public class Encrypt {    public static void main(String[] args) throws Exception {        SecureRandom sr = new SecureRandom();        FileInputStream fi = new FileInputStream(new File("key.txt"));        byte rawKeyData[] = new byte[fi.available()];        fi.read(rawKeyData);        fi.close();        DESKeySpec dks = new DESKeySpec(rawKeyData);        SecretKey key = SecretKeyFactory.getInstance("DES").generateSecret(dks);        Cipher cipher = Cipher.getInstance("DES");        cipher.init(Cipher.ENCRYPT_MODE, key, sr);        FileInputStream in = new FileInputStream(new File("DigestPass.class"));        byte data[] = new byte[in.available()];        in.read(data);        in.close();        byte encryptedData[] = cipher.doFinal(data);        FileOutputStream out = new FileOutputStream(new File("DigestPass.class"));        out.write(encryptedData);        out.close();    }}

最后，我们需要解密并重新加载加密后的类文件。以下是一个解密并加载的实现：

package com.neusoft.jiami;import Java.io.File;import Java.io.FileInputStream;import Java.io.FileOutputStream;import Java.security.SecureRandom;import javax.crypto.Cipher;import javax.crypto.SecretKey;import javax.crypto.SecretKeyFactory;import javax.crypto.spec.DESKeySpec;public class DecryptLoader {    public static void main(String[] args) throws Exception {        SecureRandom sr = new SecureRandom();        FileInputStream fi = new FileInputStream(new File("key.txt"));        byte rawKeyData[] = new byte[fi.available()];        fi.read(rawKeyData);        fi.close();        DESKeySpec dks = new DESKeySpec(rawKeyData);        SecretKey key = SecretKeyFactory.getInstance("DES").generateSecret(dks);        Cipher cipher = Cipher.getInstance("DES");        cipher.init(Cipher.DECRYPT_MODE, key, sr);        FileInputStream in = new FileInputStream(new File("DigestPass.class"));        byte encryptedData[] = new byte[in.available()];        in.read(encryptedData);        in.close();        byte decryptedData[] = cipher.doFinal(encryptedData);        FileOutputStream out = new FileOutputStream(new File("DigestPass.class"));        out.write(decryptedData);        out.close();        MyClassLoader mcl = new MyClassLoader("E:/");        Class cl = mcl.loadClass(decryptedData, "com.neusoft.jiami.DigestPass");        Object dp = cl.newInstance();    }}

上述代码展示了如何使用DES对称加密算法来生成和使用密钥进行文件加密和解密。整个过程可以通过以下步骤实现：

通过以上步骤，我们可以有效地保护我们的类文件，使其在传播过程中更加安全。