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前面为大家已经总结了，基于密钥交换的DH算法，现在就为大家再介绍一种基于因子分解的RSA算法，这种加密算法有两种实现形式：1、公钥加密，私钥解密；2、私钥加密，公钥解密。下面就为大家分析一下实现代码，相对于DH算法，RSA显得有些简单。
初始化密钥：
KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
keyPairGenerator.initialize(512);
KeyPair keyPair = keyPairGenerator.generateKeyPair();
RSAPrivateKey rsaprivateKey = (RSAPrivateKey)keyPair.getPrivate();//私有密钥
RSAPublicKey rsapublicKey = (RSAPublicKey)keyPair.getPublic();//公有密钥
System.out.println("privateKey : "+Base64.encodeBase64String(rsaprivateKey.getEncoded()));
System.out.println("publicKey : "+Base64.encodeBase64String(rsapublicKey.getEncoded()));
1、私钥加密，公钥解密：
//私钥加密，公钥解密--加密 PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaprivateKey.getEncoded()); KeyFactory privateKeyFactory = KeyFactory.getInstance("RSA"); PrivateKey privateKey = privateKeyFactory.generatePrivate(pkcs8EncodedKeySpec); Cipher privateCipher = Cipher.getInstance("RSA"); privateCipher.init(Cipher.ENCRYPT_MODE, privateKey); byte[] result = privateCipher.doFinal(src.getBytes()); System.out.println("私钥加密，公钥解密--加密:"+Base64.encodeBase64String(result)); //私钥加密，公钥解密--解密 X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(rsapublicKey.getEncoded()); KeyFactory publicKeyFactory = KeyFactory.getInstance("RSA"); PublicKey publicKey = publicKeyFactory.generatePublic(x509EncodedKeySpec); Cipher publicCipher = Cipher.getInstance("RSA"); publicCipher.init(Cipher.DECRYPT_MODE, publicKey); result = publicCipher.doFinal(result); System.out.println("私钥加密，公钥解密--解密:"+new String(result));
2、公钥加密，私钥解密：
//公钥加密，私钥解密---加密 x509EncodedKeySpec = new X509EncodedKeySpec(rsapublicKey.getEncoded()); publicKeyFactory = KeyFactory.getInstance("RSA"); publicKey = publicKeyFactory.generatePublic(x509EncodedKeySpec); publicCipher = Cipher.getInstance("RSA"); publicCipher.init(Cipher.ENCRYPT_MODE, publicKey); result = publicCipher.doFinal(src.getBytes()); System.out.println("公钥加密，私钥解密---加密:"+Base64.encodeBase64String(result)); //公钥加密，私钥解密---解密 pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaprivateKey.getEncoded()); privateKeyFactory = KeyFactory.getInstance("RSA"); privateKey = privateKeyFactory.generatePrivate(pkcs8EncodedKeySpec); privateCipher = Cipher.getInstance("RSA"); privateCipher.init(Cipher.DECRYPT_MODE, privateKey); result = privateCipher.doFinal(result); System.out.println("公钥加密，私钥解密---解密:"+new String(result));
根据输出的结果不难发现，公钥和私钥并不一致，私钥的长度要大于公钥。
到今天对于信息的加密算法：Base64、对称加密算法、消息摘要加密算法、非对称加密算法就全部总结完毕。
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原文地址：http://www.cnblogs.com/AndroidJotting/p/4290685.html
