接下来我们介绍对称加密算法，最常用的莫过于DES数据加密算法。
DES DES-Data Encryption Standard,即数据加密算法。是IBM公司于1975年研究成功并公开发表的。DES算法的入口参数有三个:Key、Data、Mode。其中Key为8个字节共64位,是DES算法的工作密钥;Data也为8个字节64位,是要被加密或被解密的数据;Mode为DES的工作方式,有两种:加密或解密。 DES算法把64位的明文输入块变为64位的密文输出块,它所使用的密钥也是64位。
通过java代码实现如下：Coder类见 Java加密算法（一） import java.security.Key;import java.security.SecureRandom;import javax.crypto.Cipher;import javax.crypto.KeyGenerator;import javax.crypto.SecretKey;import javax.crypto.SecretKeyFactory;import javax.crypto.spec.DESKeySpec;/** * DES安全编码组件 * ** 支持 DES、DESede(TripleDES,就是3DES)、AES、Blowfish、RC2、RC4(ARCFOUR) * DES key size must be equal to 56 * DESede(TripleDES) key size must be equal to 112 or 168 * AES key size must be equal to 128, 192 or 256,but 192 and 256 bits may not be available * Blowfish key size must be multiple of 8, and can only range from 32 to 448 (inclusive) * RC2 key size must be between 40 and 1024 bits * RC4(ARCFOUR) key size must be between 40 and 1024 bits * 具体内容 需要关注 JDK Document http://.../docs/technotes/guides/security/SunProviders.html ** */public abstract class DESCoder extends Coder { /** * ALGORITHM 算法 * 可替换为以下任意一种算法，同时key值的size相应改变。 * ** DES key size must be equal to 56 * DESede(TripleDES) key size must be equal to 112 or 168 * AES key size must be equal to 128, 192 or 256,but 192 and 256 bits may not be available * Blowfish key size must be multiple of 8, and can only range from 32 to 448 (inclusive) * RC2 key size must be between 40 and 1024 bits * RC4(ARCFOUR) key size must be between 40 and 1024 bits ** * 在Key toKey(byte[] key)方法中使用下述代码 *SecretKey secretKey = new SecretKeySpec(key, ALGORITHM);替换 ** DESKeySpec dks = new DESKeySpec(key); * SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(ALGORITHM); * SecretKey secretKey = keyFactory.generateSecret(dks); **/ public static final String ALGORITHM = "DES"; /** * 转换密钥 * * @param key * @return * @throws Exception */ private static Key toKey(byte[] key) throws Exception { DESKeySpec dks = new DESKeySpec(key); SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(ALGORITHM); SecretKey secretKey = keyFactory.generateSecret(dks); // 当使用其他对称加密算法时，如AES、Blowfish等算法时，用下述代码替换上述三行代码 // SecretKey secretKey = new SecretKeySpec(key, ALGORITHM); return secretKey; } /** * 解密 * * @param data * @param key * @return * @throws Exception */ public static byte[] decrypt(byte[] data, String key) throws Exception { Key k = toKey(decryptBASE64(key)); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.DECRYPT_MODE, k); return cipher.doFinal(data); } /** * 加密 * * @param data * @param key * @return * @throws Exception */ public static byte[] encrypt(byte[] data, String key) throws Exception { Key k = toKey(decryptBASE64(key)); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.ENCRYPT_MODE, k); return cipher.doFinal(data); } /** * 生成密钥 * * @return * @throws Exception */ public static String initKey() throws Exception { return initKey(null); } /** * 生成密钥 * * @param seed * @return * @throws Exception */ public static String initKey(String seed) throws Exception { SecureRandom secureRandom = null; if (seed != null) { secureRandom = new SecureRandom(decryptBASE64(seed)); } else { secureRandom = new SecureRandom(); } KeyGenerator kg = KeyGenerator.getInstance(ALGORITHM); kg.init(secureRandom); SecretKey secretKey = kg.generateKey(); return encryptBASE64(secretKey.getEncoded()); }}
延续上一个类的实现，我们通过MD5以及SHA对字符串加密生成密钥，这是比较常见的密钥生成方式。
再给出一个测试类：import static org.junit.Assert.*;import org.junit.Test;/** * *DES测试 * */public class DESCoderTest { @Test public void test() throws Exception { String inputStr = "DES"; String key = DESCoder.initKey(); System.err.println("原文:\t" + inputStr); System.err.println("密钥:\t" + key); byte[] inputData = inputStr.getBytes(); inputData = DESCoder.encrypt(inputData, key); System.err.println("加密后:\t" + DESCoder.encryptBASE64(inputData)); byte[] outputData = DESCoder.decrypt(inputData, key); String outputStr = new String(outputData); System.err.println("解密后:\t" + outputStr); assertEquals(inputStr, outputStr); }} 得到的输出内容如下：
原文: DES密钥: f3wEtRrV6q0=加密后: C6qe9oNIzRY=解密后: DES
由控制台得到的输出，我们能够比对加密、解密后结果一致。这是一种简单的加密解密方式，只有一个密钥。
其实DES有很多同胞兄弟，如DESede(TripleDES)、AES、Blowfish、RC2、RC4(ARCFOUR)。这里就不过多阐述了，大同小异，只要换掉ALGORITHM换成对应的值，同时做一个代码替换SecretKey secretKey = new SecretKeySpec(key, ALGORITHM);就可以了，此外就是密钥长度不同了。/** * DES key size must be equal to 56 * DESede(TripleDES) key size must be equal to 112 or 168 * AES key size must be equal to 128, 192 or 256,but 192 and 256 bits may not be available * Blowfish key size must be multiple of 8, and can only range from 32 to 448 (inclusive) * RC2 key size must be between 40 and 1024 bits * RC4(ARCFOUR) key size must be between 40 and 1024 bits **/
来源于：http://snowolf.iteye.com/blog