一、概述
3DES,即3重DES(Triple DES),也称为DESede,是一种对称密钥加密算法。DESede是通过对每个数据块应用三次DES加密算法来实现加密。由于DESede采用了多次加密的方法,因此算法更为安全,在现今网络通信安全中广泛应用。
二、原理
DESede的加密过程主要分为三个步骤:密钥的生成、加密和解密。
1. 密钥的生成
DESede算法使用长度为24个字节的密钥,其中包含3个单独的8字节密钥K1, K2, K3。密钥生成的过程如下:
private static byte[][] generateKey(byte[] key) throws Exception { byte[][] keys = new byte[3][8]; byte[] keyBytes = paddingKey(key); DESedeKeySpec desKeySpec = new DESedeKeySpec(keyBytes); SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DESede"); SecretKey secretKey = keyFactory.generateSecret(desKeySpec); byte[] secretKeyBytes = secretKey.getEncoded(); System.arraycopy(secretKeyBytes, 0, keys[0], 0, 8); System.arraycopy(secretKeyBytes, 8, keys[1], 0, 8); System.arraycopy(secretKeyBytes, 16, keys[2], 0, 8); return keys; }
2. 加密
加密是指将明文经过一定的方法转换为密文,使得第三方无法直接读取到明文。在DESede算法中,加密分为两个步骤:DES加密和反向DES加密。
(1)DES加密
首先将明文输入到第一轮DES加密中,使用密钥K1加密。得到的结果作为第二轮DES加密的明文,使用密钥K2加密。得到的结果作为第三轮DES加密的明文,使用密钥K3加密。加密过程如下:
private static byte[] encrypt(byte[] data, byte[] key) throws Exception { byte[][] keys = generateKey(key); Cipher cipher = Cipher.getInstance("DESede"); cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(keys[0], "DESede")); byte[] encrypted = cipher.doFinal(data); cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(keys[1], "DESede")); byte[] decrypted = cipher.doFinal(encrypted); cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(keys[2], "DESede")); return cipher.doFinal(decrypted); }
(2)反向DES加密
DESede算法采用了反向DES加密方式,即解密与加密使用的密钥相反。这样做的目的是增强算法的安全性。
3. 解密
解密是指将密文经过一定的方法还原为明文。DESede的解密过程与加密过程刚好相反,主要由反向DES加密和DES解密两部分组成。具体可参考DESede的加密过程。
三、应用
DESede算法的应用非常广泛,可以用于文件加密、数据传输加密以及数字签名等场景。在Java中,DESede算法可以通过Java Cryptography Extension (JCE) 来实现。以下是一个简单的DESede加解密示例:
import javax.crypto.Cipher; import javax.crypto.SecretKey; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.DESedeKeySpec; import javax.crypto.spec.SecretKeySpec; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.util.Base64; public class DESedeDemo { private static final String KEY = "my_key"; public static void main(String[] args) throws Exception { String data = "hello world"; String encrypted = encrypt(data, KEY); System.out.println(encrypted); String decrypted = decrypt(encrypted, KEY); System.out.println(decrypted); } private static byte[][] generateKey(byte[] key) throws Exception { byte[][] keys = new byte[3][8]; byte[] keyBytes = paddingKey(key); DESedeKeySpec desKeySpec = new DESedeKeySpec(keyBytes); SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DESede"); SecretKey secretKey = keyFactory.generateSecret(desKeySpec); byte[] secretKeyBytes = secretKey.getEncoded(); System.arraycopy(secretKeyBytes, 0, keys[0], 0, 8); System.arraycopy(secretKeyBytes, 8, keys[1], 0, 8); System.arraycopy(secretKeyBytes, 16, keys[2], 0, 8); return keys; } private static byte[] paddingKey(byte[] key) throws Exception { MessageDigest md5 = MessageDigest.getInstance("MD5"); byte[] md5Bytes = md5.digest(key); byte[] keyBytes = new byte[24]; if (md5Bytes.length < 24) { System.arraycopy(md5Bytes, 0, keyBytes, 0, md5Bytes.length); } else { System.arraycopy(md5Bytes, 0, keyBytes, 0, 24); } return keyBytes; } private static String encrypt(String data, String key) throws Exception { byte[] dataBytes = data.getBytes(StandardCharsets.UTF_8); byte[] keyBytes = key.getBytes(StandardCharsets.UTF_8); byte[] encryptedBytes = encrypt(dataBytes, keyBytes); return Base64.getEncoder().encodeToString(encryptedBytes); } private static byte[] encrypt(byte[] data, byte[] key) throws Exception { byte[][] keys = generateKey(key); Cipher cipher = Cipher.getInstance("DESede"); cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(keys[0], "DESede")); byte[] encrypted = cipher.doFinal(data); cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(keys[1], "DESede")); byte[] decrypted = cipher.doFinal(encrypted); cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(keys[2], "DESede")); return cipher.doFinal(decrypted); } private static String decrypt(String encrypted, String key) throws Exception { byte[] encryptedBytes = Base64.getDecoder().decode(encrypted); byte[] keyBytes = key.getBytes(StandardCharsets.UTF_8); byte[] decryptedBytes = decrypt(encryptedBytes, keyBytes); return new String(decryptedBytes, StandardCharsets.UTF_8); } private static byte[] decrypt(byte[] encrypted, byte[] key) throws Exception { byte[][] keys = generateKey(key); Cipher cipher = Cipher.getInstance("DESede"); cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(keys[2], "DESede")); byte[] decrypted = cipher.doFinal(encrypted); cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(keys[1], "DESede")); byte[] encrypted1 = cipher.doFinal(decrypted); cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(keys[0], "DESede")); return cipher.doFinal(encrypted1); } }
四、总结
DESede算法是一种更为安全的对称加密算法,应用广泛。在实现DESede算法时,需要注意密钥的生成、加密和解密的流程,以及采用反向DES加密方式增强算法的安全性。