非对称的特点是加密和解密时使用的是不同的钥匙。密钥分为公钥和私钥,用公钥加密的数据只能用私钥进行解密,反之亦然。
另外,密钥还可以用于数字签名。数字签名跟上文说的消息摘要是一个道理,通过一定方法对数据内容进行处理得到一个签名,查看这个签名是否与对方传递的签名一致。
在非对称加密中用密钥来指公钥和私钥。
RSA
RAS是最早的非对称签名,是1977年由罗纳德·李维斯特(Ron Rivest)、阿迪·萨莫尔(Adi Shamir)和伦纳德·阿德曼(Leonard Adleman)一起提出的。1987年7月首次在美国公布,当时他们三人都在麻省理工学院工作实习。RSA就是他们三人姓氏开头字母拼在一起组成的。
对于非对称加密,在Java中可以用KeyPairGenerator工具类来负责生成密钥对:
public class RSAUtil { public final static String ALGORITHM = "RSA"; public static KeyPair getKey() throws Exception{ KeyPairGenerator generator = KeyPairGenerator.getInstance(ALGORITHM); return generator.generateKeyPair(); } public static void main(String[] args) throws Exception{ KeyPair keyPair = getKey(); RSAPrivateKey privateKey = (RSAPrivateKey)keyPair.getPrivate(); RSAPublicKey publicKey = (RSAPublicKey)keyPair.getPublic(); String privateKeyStr = Base64.encode(privateKey.getEncoded()); String publicKeyStr = Base64.encode(publicKey.getEncoded()); System.out.println("私钥:" + privateKeyStr); System.out.println("公钥:" + publicKeyStr); } }
使用公钥加密:
public static String encryptByPublicKey(String data,String key)throws Exception{ X509EncodedKeySpec keySpec = new X509EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); Key k = keyFactory.generatePublic(keySpec); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.ENCRYPT_MODE, k); byte[] bytes = cipher.doFinal(data.getBytes("UTF-8")); return Base64Util.encode(bytes); }
加密的时候用X509EncodedKeySpec来获取公钥,不要害怕X509,其实没有别的X508或者X609,就这么一个X509。X.509是一种非常通用的证书格式。所有的证书都符合ITU-T X.509国际标准。
和之前的DES类似,使用私钥解密的代码如下:
public static String decryptByPrivateKey(String data,String key)throws Exception{ X509EncodedKeySpec keySpec = new X509EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); Key k = keyFactory.generatePrivate(keySpec); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.DECRYPT_MODE, k); byte[] bytes = cipher.doFinal(Base64Util.decode(data)); return new String(bytes,"UTF-8"); }
还用X509去读私钥就不行了,会报下面这个错误:
Exception in thread "main" java.security.spec.InvalidKeySpecException: Only RSAPrivate(Crt)KeySpec and PKCS8EncodedKeySpec supported for RSA private keys
意思是只能用RSAPrivate(Crt)KeySpec 或者 PKCS8EncodedKeySpec去读私钥,改成下面这样就好了:
public static String decryptByPrivateKey(String data,String key)throws Exception{ PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); Key k = keyFactory.generatePrivate(keySpec); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.DECRYPT_MODE, k); byte[] bytes = cipher.doFinal(Base64Util.decode(data)); return new String(bytes,"UTF-8"); }
使用私钥加密和公钥解密的方法就不用多说了,只需要在加密和解密时换成另外一个钥匙就行了。
签名和签名验证
/** * 使用私钥进行签名 * @param data * @param key * @return * @throws Exception */ public static String sign(String data,String key)throws Exception{ PrivateKey k = (PrivateKey)getPrivateKey(key); Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM); signature.initSign(k); signature.update(data.getBytes("UTF-8")); return Base64.encode(signature.sign()); } /** * 使用公钥进行签名验证 * @param data * @param key * @return * @throws Exception */ public static boolean signVerify(String data,String key,String sign)throws Exception{ PublicKey k = (PublicKey)getPublicKey(key); Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM); signature.initVerify(k); signature.update(data.getBytes("UTF-8")); return signature.verify(Base64.decode(sign)); }
JDK中有专门用于签名的工具类Signature,可用的签名算法如下:
完整代码重构如下:
public class RSAUtil { public final static String ALGORITHM = "RSA"; public final static String SIGNATURE_ALGORITHM = "MD5withRSA"; /** * 获取公钥密钥对 * @return * @throws Exception */ public static KeyPair getKey() throws Exception{ KeyPairGenerator generator = KeyPairGenerator.getInstance(ALGORITHM); return generator.generateKeyPair(); } private static Key getPublicKey(String key)throws Exception{ X509EncodedKeySpec keySpec = new X509EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); Key k = keyFactory.generatePublic(keySpec); return k; } private static Key getPrivateKey(String key)throws Exception{ PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); Key k = keyFactory.generatePrivate(keySpec); return k; } /** * 使用公钥进行加密 * @param data * @param key * @return * @throws Exception */ public static String encryptByPublicKey(String data,String key)throws Exception{ Key k = getPublicKey(key); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.ENCRYPT_MODE, k); byte[] bytes = cipher.doFinal(data.getBytes("UTF-8")); return Base64Util.encode(bytes); } /** * 使用私钥进行加密 * @param data * @param key * @return * @throws Exception */ public static String encryptByPrivateKey(String data,String key)throws Exception{ Key k = getPrivateKey(key); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.ENCRYPT_MODE, k); byte[] bytes = cipher.doFinal(data.getBytes("UTF-8")); return Base64Util.encode(bytes); } /** * 使用密钥进行解密 * @param data * @param key * @return * @throws Exception */ public static String decryptByPrivateKey(String data,String key)throws Exception{ Key k = getPrivateKey(key); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.DECRYPT_MODE, k); byte[] bytes = cipher.doFinal(Base64Util.decode(data)); return new String(bytes,"UTF-8"); } /** * 使用公钥进行解密 * @param data * @param key * @return * @throws Exception */ public static String decryptByPublicKey(String data,String key)throws Exception{ Key k = getPublicKey(key); Cipher cipher = Cipher.getInstance(ALGORITHM); cipher.init(Cipher.DECRYPT_MODE, k); byte[] bytes = cipher.doFinal(Base64Util.decode(data)); return new String(bytes,"UTF-8"); } /** * 使用私钥进行签名 * @param data * @param key * @return * @throws Exception */ public static String sign(String data,String key)throws Exception{ PrivateKey k = (PrivateKey)getPrivateKey(key); Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM); signature.initSign(k); signature.update(data.getBytes("UTF-8")); return Base64.encode(signature.sign()); } /** * 使用公钥进行签名验证 * @param data * @param key * @return * @throws Exception */ public static boolean signVerify(String data,String key,String sign)throws Exception{ PublicKey k = (PublicKey)getPublicKey(key); Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM); signature.initVerify(k); signature.update(data.getBytes("UTF-8")); return signature.verify(Base64.decode(sign)); } public static void main(String[] args) throws Exception{ KeyPair keyPair = getKey(); RSAPrivateKey privateKey = (RSAPrivateKey)keyPair.getPrivate(); RSAPublicKey publicKey = (RSAPublicKey)keyPair.getPublic(); String privateKeyStr = Base64.encode(privateKey.getEncoded()); String publicKeyStr = Base64.encode(publicKey.getEncoded()); System.out.println("私钥:" + privateKeyStr); System.out.println("公钥:" + publicKeyStr); String data = "Hello,RSA,Hello,RSAHello,RSAHello,RSAHello,RSAHello,RSAHello,RSA"; System.out.println("---------------公钥加密,私钥解密-----------------"); String encryptedData = encryptByPublicKey(data,publicKeyStr); System.out.println("加密后:" + encryptedData); String decryptedData = decryptByPrivateKey(encryptedData, privateKeyStr); System.out.println("解密后:" + decryptedData); System.out.println("---------------私钥加密,公钥解密-----------------"); encryptedData = encryptByPrivateKey(data,privateKeyStr); System.out.println("加密后:" + encryptedData); decryptedData = decryptByPublicKey(encryptedData, publicKeyStr); System.out.println("解密后:" + decryptedData); String sign = sign(data,privateKeyStr); System.out.println("签名:" + sign); System.out.println("签名验证:" + signVerify(data,publicKeyStr,sign)); } }
DH(Diffie-Hellman)
非对称加密的算法比较耗时,所以不能用它来传输大数据。通常情况下会是这样:
- 因为对称加密算法中没法安全传递密钥,所以用非对称加密算法来传递对称加密的密钥;
- 等对称加密的秘钥传递成功之后,正式的数据就用对称加密算法来传递了。
DH算法就是为了实现这个目的而产生的。DH能实现甲乙双方的密钥沟通。
假设客户端要发送数据到服务端,在Java中DH加密的完整步骤:
服务端先生成自己的密钥对:
/** * 数据处理服务端*/public class Server { private String publicKey; private String privateKey; private SecretKey key; public Server(){ try { String[] keyPair = DHUtil.getStringKeyPair(); publicKey = keyPair[0]; privateKey = keyPair[1]; } catch (Exception e) { e.printStackTrace(); } } ...
服务端的私钥自己保持,公布公钥,客户端则需要根据服务端的公钥生成自己的密钥对:
/** * 数据传输客户端*/public class Client { private String publicKey; private String privateKey;private Server server; public Client(Server server){ this.server = server; String serverPublicKey = server.getPublicKey();//明文获取到公钥 try{ String[] keyPair = DHUtil.getStringKeyPair(serverPublicKey); publicKey = keyPair[0]; privateKey = keyPair[1]; }catch(Exception e){ e.printStackTrace(); } } ...
客户端在和服务端通信时,使用的加密算法是对称加密。对称加密的密钥是根据服务端的公钥和客户端的私钥生成的。
public class Client { private String publicKey; private String privateKey; private SecretKey key; private Server server; public Client(Server server){ this.server = server; String serverPublicKey = server.getPublicKey(); try{ String[] keyPair = DHUtil.getStringKeyPair(serverPublicKey); publicKey = keyPair[0]; privateKey = keyPair[1]; key = DHUtil.getAgreementSecretKey(serverPublicKey, privateKey); }catch(Exception e){ e.printStackTrace(); } }...
好了,现在可以往服务端发送数据了,比如有一个登录操作:
public class Client { ... public boolean login(String user,String pwd){ String data = "user=" + user + "&pwd=" + pwd; try { data = DHUtil.encrypt(data, key); } catch (Exception e) { e.printStackTrace(); } String response = server.service(data,publicKey); System.out.println("Login Response:" + response); return response.equals("OK"); }}
可见,公钥是通过明文的形式发送给服务端的。服务端对数据进行处理:
/** * 数据处理服务端 * @author huqiao */public class Server { ... public String service(String data,String clientPublicKey){ try { key = DHUtil.getAgreementSecretKey(clientPublicKey, privateKey);//根据客户端的publicKey生成本地密钥 String decryptedData = DHUtil.decrypt(data, key); System.out.println("Data decryped:" + decryptedData); if(verfiy(decryptedData)){ return "OK"; }else{ return "Error"; } } catch (Exception e) { e.printStackTrace(); return e.getMessage(); } } ...
服务器拿到客户端的公钥之后生成本地的密钥,然后对数据进行解密。为了简单起见,这里服务器往客户度返回数据时没有做加密。
非常重要的DHUtil.java完整代码:
public class DHUtil { public final static String ALGORITHM = "DH"; public final static String SYMMETRIC_SECRET_ALGORITHM = "AES";//对称加密算法名称 /** * 产生密钥对 * @return * @throws Exception */ public static KeyPair getKeyPair()throws Exception{ KeyPairGenerator generator = KeyPairGenerator.getInstance(ALGORITHM); generator.initialize(1024); return generator.generateKeyPair(); } /** * 获取字符串类型的密钥对 * @return * @throws Exception */ public static String[] getStringKeyPair()throws Exception{ KeyPair keyPair = getKeyPair(); return keyPairToStringArray(keyPair); } public static String[] getStringKeyPair(String publicKey)throws Exception{ KeyPair keyPair = getKeyPairByPublicKey(publicKey); return keyPairToStringArray(keyPair); } private static String[] keyPairToStringArray(KeyPair keyPair){ String[] res = new String[2]; PublicKey pubKey = keyPair.getPublic(); PrivateKey priKey = keyPair.getPrivate(); res[0] = Base64Util.encode(pubKey.getEncoded()); res[1] = Base64Util.encode(priKey.getEncoded()); return res; } /** * 由一个公钥产生密钥对 * @param publicKey * @return * @throws Exception */ public static KeyPair getKeyPairByPublicKey(String publicKey)throws Exception{ PublicKey pKey = getPublicKey(publicKey); KeyPairGenerator generator = KeyPairGenerator.getInstance(pKey.getAlgorithm()); DHParameterSpec dhGenParam = ((DHPublicKey) pKey).getParams(); generator.initialize(dhGenParam); return generator.generateKeyPair(); } private static PublicKey getPublicKey(String key)throws Exception{ X509EncodedKeySpec keySpec = new X509EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); PublicKey k = keyFactory.generatePublic(keySpec); return k; } private static PrivateKey getPrivateKey(String key)throws Exception{ PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); PrivateKey k = keyFactory.generatePrivate(keySpec); return k; } /** * 根据一方公钥和另外一方私钥构建本地密钥 * @param publicKey * @param privateKey * @return * @throws Exception */ public static SecretKey getAgreementSecretKey(String publicKey,String privateKey)throws Exception{ PublicKey pubKey = getPublicKey(publicKey); PrivateKey priKey = getPrivateKey(privateKey); return getAgreementSecretKey(pubKey,priKey); } public static SecretKey getAgreementSecretKey(PublicKey pubKey,PrivateKey priKey)throws Exception{ KeyAgreement argeement = KeyAgreement.getInstance(pubKey.getAlgorithm()); argeement.init(priKey); argeement.doPhase(pubKey, true); SecretKey secretKey = argeement.generateSecret(SYMMETRIC_SECRET_ALGORITHM); return secretKey; } /** * 加密 * @param data * @param key * @return * @throws Exception */ public static String encrypt(String data,SecretKey key)throws Exception{ Cipher cipher = Cipher.getInstance(key.getAlgorithm()); cipher.init(Cipher.ENCRYPT_MODE, key); byte[] encryptedData = cipher.doFinal(data.getBytes("UTF-8")); return Base64Util.encode(encryptedData); } /** * 解密 * @param data * @param key * @return * @throws Exception */ public static String decrypt(String data,SecretKey key)throws Exception{ byte[] encryptedData = Base64Util.decode(data); Cipher cipher = Cipher.getInstance(key.getAlgorithm()); cipher.init(Cipher.DECRYPT_MODE, key); byte[] decryptedData = cipher.doFinal(encryptedData); return new String(decryptedData,"UTF-8"); }}
不要被它的长度吓到,它做的事情其实很简单,就是生成密钥对和加密解密。生成密钥对,加密和解密在之前都见过,这里最重要的方法是使用来自两方的公钥和私钥生成一个本地密钥:
/** * 根据一方公钥和另外一方私钥构建本地密钥 * @param publicKey * @param privateKey * @return * @throws Exception */ public static SecretKey getAgreementSecretKey(String publicKey,String privateKey)throws Exception{ PublicKey pubKey = getPublicKey(publicKey); PrivateKey priKey = getPrivateKey(privateKey); return getAgreementSecretKey(pubKey,priKey); } public static SecretKey getAgreementSecretKey(PublicKey pubKey,PrivateKey priKey)throws Exception{ KeyAgreement argeement = KeyAgreement.getInstance(pubKey.getAlgorithm()); argeement.init(priKey); argeement.doPhase(pubKey, true); SecretKey secretKey = argeement.generateSecret(SYMMETRIC_SECRET_ALGORITHM); return secretKey; }
完整客户端和服务端代码如下:
/** * 数据传输客户端 * @author huqiao */public class Client { private String publicKey; private String privateKey; private SecretKey key; private Server server; public Client(Server server){ this.server = server; String serverPublicKey = server.getPublicKey(); try{ String[] keyPair = DHUtil.getStringKeyPair(serverPublicKey); publicKey = keyPair[0]; privateKey = keyPair[1]; key = DHUtil.getAgreementSecretKey(serverPublicKey, privateKey); }catch(Exception e){ e.printStackTrace(); } } public boolean login(String user,String pwd){ String data = "user=" + user + "&pwd=" + pwd; try { data = DHUtil.encrypt(data, key); } catch (Exception e) { e.printStackTrace(); } String response = server.service(data,publicKey); System.out.println("Login Response:" + response); return response.equals("OK"); }}
/** * 数据处理服务端 * @author huqiao */public class Server { private String publicKey; private String privateKey; private SecretKey key; public Server(){ try { String[] keyPair = DHUtil.getStringKeyPair(); publicKey = keyPair[0]; privateKey = keyPair[1]; } catch (Exception e) { e.printStackTrace(); } } public String service(String data,String clientPublicKey){ System.out.println("----------------Data received at Server:----------------\r\n"+ data); System.out.println("----------------Client PublicKey received at Server:----------------\r\n"+clientPublicKey); try { key = DHUtil.getAgreementSecretKey(clientPublicKey, privateKey); String decryptedData = DHUtil.decrypt(data, key); System.out.println("Data decryped:" + decryptedData); if(verfiy(decryptedData)){ return "OK"; }else{ return "Error"; } } catch (Exception e) { e.printStackTrace(); return e.getMessage(); } } private boolean verfiy(String decryptedData) { //解析用户名和密码,进行验证 return true; } /** * 明文拿到服务端公钥 * @return */ public String getPublicKey(){ return publicKey; }}
测试:
public class DHTest { public static void main(String[] args) { Server server = new Server(); Client client = new Client(server); boolean loginSuccess = client.login("admin", "123456"); System.out.println("login success:" + loginSuccess); }}
测试结果:
----------------Data received at Server:----------------pVWbVMP57wkLftZN3bXx1mf4631yTMlxJ+hnMm4Dwmg=----------------Client PublicKey received at Server:----------------MIIBpzCCARsGCSqGSIb3DQEDATCCAQwCgYEA/X9TgR11EilS30qcLuzk5/YRt1I870QAwx4/gLZRJmlFXUAiUftZPY1Y+r/F9bow9subVWzXgTuAHTRv8mZgt2uZUKWkn5/oBHsQIsJPu6nX/rfGG/g7V+fGqKYVDwT7g/bTxR7DAjVUE1oWkTL2dfOuK2HXKu/yIgMZndFIAccCgYEA9+GghdabPd7LvKtcNrhXuXmUr7v6OuqC+VdMCz0HgmdRWVeOutRZT+ZxBxCBgLRJFnEj6EwoFhO3zwkyjMim4TwWeotU fI0o4KOuHiuzpnWRbqN/C/ohNWLx+2J6ASQ7zKTxvqhRkImog9/hWuWfBpKLZl6Ae1UlZAFMO/7P SSoCAgIAA4GFAAKBgQC+WT4qNq/Yay1WFA89n5IOy+hJa8JQh4R0uyy5Yfo2ckgQ4cjh/u5GPKev Ua2B3vQVFEifKSn7tfP5bmYMQ5IZLPJ3JrP2m/QAjQ1T7swG/Kbtfc4eTgq+wpnb2LbDoznKGN28 Mcrbf4HkwZ8QK0M26CySSEQCFliWydd6u/vl0A== Data decryped:user=admin&pwd=123456 Login Response:OK login success:true
DSA
DSA的全称为数字签名算法(Digital Signature Algorithm),它与RSA的区别在于它只用于签名,并且它的速度比RSA要快。在安全性上两者差不多。
因为在RSA中已经说到过签名以及验证的过程,DSA和它完全类似:
public class DSAUtil { static final String ALGORITHM = "DSA"; private static KeyPair getKeyPair()throws Exception{ KeyPairGenerator generator = KeyPairGenerator.getInstance(ALGORITHM); generator.initialize(1024); return generator.genKeyPair(); } /** * 用私钥签名 * @param data * @param privateKey * @return */ public static String sign(String data,String privateKey)throws Exception{ PrivateKey priKey = getPrivateKey(privateKey); Signature sign = Signature.getInstance(ALGORITHM); sign.initSign(priKey); sign.update(data.getBytes("UTF-8")); byte[] signBytes = sign.sign(); return Base64Util.encode(signBytes); } /** * 用公钥进行签名验证 * @param data * @param publicKey * @param signData * @return * @throws Exception */ public static boolean verify(String data,String publicKey,String signData)throws Exception{ PublicKey pubKey = getPublicKey(publicKey); Signature sign = Signature.getInstance(ALGORITHM); sign.initVerify(pubKey); sign.update(data.getBytes("UTF-8")); return sign.verify(Base64Util.decode(signData)); } private static PublicKey getPublicKey(String key)throws Exception{ X509EncodedKeySpec keySpec = new X509EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); PublicKey k = keyFactory.generatePublic(keySpec); return k; } private static PrivateKey getPrivateKey(String key)throws Exception{ PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(Base64Util.decode(key)); KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM); PrivateKey k = keyFactory.generatePrivate(keySpec); return k; } /** * 获取字符串类型的密钥对 * @return * @throws Exception */ public static String[] getStringKeyPair()throws Exception{ KeyPair keyPair = getKeyPair(); return keyPairToStringArray(keyPair); } private static String[] keyPairToStringArray(KeyPair keyPair){ String[] res = new String[2]; PublicKey pubKey = keyPair.getPublic(); PrivateKey priKey = keyPair.getPrivate(); res[0] = Base64Util.encode(pubKey.getEncoded()); res[1] = Base64Util.encode(priKey.getEncoded()); return res; } public static void main(String[] args) throws Exception{ String data = "Hello,DSA"; String[] keyPair = getStringKeyPair(); String pubKey = keyPair[0]; String priKey = keyPair[1]; System.out.println("原文:" + data); System.out.println("---------Public Key----------"); System.out.println(pubKey); System.out.println("---------Private Key----------"); System.out.println(priKey); System.out.println(); String signData = sign(data, priKey); System.out.println("Sign Data:" + signData); System.out.println("Verify Result:" + verify(data, pubKey, signData)); }}
ECC
ECC-Elliptic Curves Cryptography,椭圆曲线密码编码学,是目前已知的公钥体制中,对每比特所提供加密强度最高的一种体制。ECC算法相当耗费资源,如果单纯使用CPU进行加密/解密,效率低下。目前JDK9都没有实现ECC的加密解密,仅仅提供ECC的秘钥生成。
可以自己去实现ECC的Provider。因为Java的安全框架()提供了密钥生成的扩展机制()。参考这里如何实现一个Provider:
参考资料: