信息加密之非对称加密算法RSA

　　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。