对称加密算法是以一种使用频率高的初等的加密算法,如你所想,之所以称之为对称加密算法,说明加密秘钥是相同,加密过程可逆,而前面介绍的base64加密,和消息摘要加密算法是不可逆的.一般的对称加密算法有DES,DES秘钥长度不够,易被破解,进而衍生出了3DES,在DES的基础上又出现了AES算法,还有PBE,IDEA等算法.
DES(Data Encryption Standrad)数据加密标准

秘钥长度	默认	工作模式	填充方式	实现方
56	56	ECB|CBC|PCBC|CTR|CTS| CFB|CFB8|到128|OFB|OFB8到128	NoPadding|PKCS5Padding| ISO10126Padding	jdk
64	56	同上	PKCS7Padding|ISO10126d2Padding| X932Padding|ISO7816d4Padding| ZeroBytePadding	bc

代码实现

• jdk实现

try {//生成keyKeyGenerator keyGenerator = KeyGenerator.getInstance("DES");keyGenerator.init(56);SecretKey secretKey = keyGenerator.generateKey();byte[] bytesKey = secretKey.getEncoded();//key转换KeySpec keySpec = new DESKeySpec(bytesKey);SecretKeyFactory factory = SecretKeyFactory.getInstance("DES");SecretKey convertSecretKey = factory.generateSecret(keySpec);//加密Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");cipher.init(Cipher.ENCRYPT_MODE, convertSecretKey);byte[] result = cipher.doFinal(str.getBytes());System.out.println("jdk des en:"+ Hex.toHexString(result));//解密cipher.init(Cipher.DECRYPT_MODE, convertSecretKey);byte[] raw = cipher.doFinal(result);System.out.println("jdk des de:"+ new String(raw)); } catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}

• bc的实现

try {Security.addProvider(new BouncyCastleProvider());//生成keyKeyGenerator keyGenerator = KeyGenerator.getInstance("DES","BC");keyGenerator.init(56);System.out.println(keyGenerator.getProvider());SecretKey secretKey = keyGenerator.generateKey();byte[] bytesKey = secretKey.getEncoded();//key转换KeySpec keySpec = new DESKeySpec(bytesKey);SecretKeyFactory factory = SecretKeyFactory.getInstance("DES");SecretKey convertSecretKey = factory.generateSecret(keySpec);//加密Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");cipher.init(Cipher.ENCRYPT_MODE, convertSecretKey);byte[] result = cipher.doFinal(str.getBytes());System.out.println("jdk des en:"+ Hex.toHexString(result));//解密cipher.init(Cipher.DECRYPT_MODE, convertSecretKey);byte[] raw = cipher.doFinal(result);System.out.println("bc des de:"+ new String(raw));} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}

3DES在实际应用中十分广泛,但效率比较低,下面是jdk实现3DES

try {//生成keyKeyGenerator keyGenerator = KeyGenerator.getInstance("DESede");
//          keyGenerator.init(168);keyGenerator.init(new SecureRandom());//生成默认长度SecretKey secretKey = keyGenerator.generateKey();byte[] bytesKey = secretKey.getEncoded();//key转换KeySpec keySpec = new DESedeKeySpec(bytesKey);SecretKeyFactory factory = SecretKeyFactory.getInstance("DESede");SecretKey convertSecretKey = factory.generateSecret(keySpec);//加密Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");cipher.init(Cipher.ENCRYPT_MODE, convertSecretKey);byte[] result = cipher.doFinal(str.getBytes());System.out.println("jdk 3des en:"+ Hex.toHexString(result));//解密cipher.init(Cipher.DECRYPT_MODE, convertSecretKey);byte[] raw = cipher.doFinal(result);System.out.println("jdk 3des de:"+ new String(raw));} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}

AES是DES算法的代替者,目前还没有被破解的消息.

java实现AES与实现DES相似

        try {//生成keyKeyGenerator keyGenerator = KeyGenerator.getInstance("AES");keyGenerator.init(new SecureRandom());SecretKey secretKye = keyGenerator.generateKey();byte[] keyBytes =  secretKye.getEncoded();//转换keySecretKeySpec keySpec= new SecretKeySpec(keyBytes, "AES");//加密Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");cipher.init(Cipher.ENCRYPT_MODE, keySpec);byte[] result = cipher.doFinal(str.getBytes());System.out.println("jdk aes en:"+ Base64.encodeBase64String(result));//解密cipher.init(Cipher.DECRYPT_MODE,  keySpec);byte[] raw = cipher.doFinal(result);System.out.println("jdk aes de:"+new String(raw));} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}

PBE(Password Based Encryption)基于口令的加密
算法结合了消息摘要算法和对称加密算法的特点,是对已有算法是包装(口令+盐)

代码实现

try {//初始化盐SecureRandom secureRandom = new SecureRandom();byte[] salt = secureRandom.generateSeed(8);salt = new byte[]{'a','a','a','a','a','a','a','a'};//口令与秘钥String password = "yexiu";PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray());SecretKeyFactory factory = SecretKeyFactory.getInstance("PBEWITHMD5andDES");Key key = factory.generateSecret(pbeKeySpec);//加密PBEParameterSpec parameter = new PBEParameterSpec(salt, 100);Cipher cipher = Cipher.getInstance("PBEWITHMD5andDES");cipher.init(Cipher.ENCRYPT_MODE, key, parameter);byte[] result = cipher.doFinal(str.getBytes());System.out.println("jdk pbe en:"+Base64.encodeBase64String(result));//解密cipher.init(Cipher.DECRYPT_MODE, key, parameter);byte[] raw = cipher.doFinal(result);System.out.println("jdk pbe de:"+new String(raw));} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}