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RSA 工具类。提供加密，解密，生成密钥对等方法。

RSA加密原理概述 ：RSA的安全性依赖于大数的分解，公钥和私钥都是两个大素数（大于100的十进制位）的函数。据猜测，，从一个密钥和密文推断出明文的难度等同于分解两个大素数的积 密钥的产生： 1.选择两个大素数 p,q ,计算 n=p*q; 2.随机选择加密密钥 e ,要求 e 和 (p-1)*(q-1)互质 3.利用 Euclid 算法计算解密密钥 d , 使其满足 e*d = 1(mod(p-1)*(q-1)) (其中 n,d 也要互质) 4:至此得出公钥为 (n,e) 私钥为 (n,d) RSA速度 由于进行的都是大数计算，使得RSA最快的情况也比DES慢上100倍，无论 是软件还是硬件实现。 速度一直是RSA的缺陷。一般来说只用于少量数据 加密。

package com.security.rsa;import java.security.KeyFactory;import java.security.KeyPair;import java.security.KeyPairGenerator;import java.security.PrivateKey;import java.security.PublicKey;import java.security.interfaces.RSAPrivateKey;import java.security.interfaces.RSAPublicKey;import java.security.spec.PKCS8EncodedKeySpec;import java.security.spec.X509EncodedKeySpec;import javax.crypto.Cipher;public class RSAsecurity {public static String src="RSA 加密字符串";public void priENpubDE() {try {//1.初始化秘钥KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");//秘钥长度keyPairGenerator.initialize(512);//初始化秘钥对KeyPair keyPair = keyPairGenerator.generateKeyPair();//公钥RSAPublicKey rsaPublicKey = (RSAPublicKey) keyPair.getPublic();//私钥RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyPair.getPrivate();//2.私钥加密，公钥解密—-加密//生成私钥PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaPrivateKey.getEncoded());KeyFactory keyFactory =KeyFactory.getInstance("RSA");PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);//Cipher类为加密和解密提供密码功能，通过getinstance实例化对象Cipher cipher =Cipher.getInstance("RSA");//初始化加密cipher.init(Cipher.ENCRYPT_MODE,privateKey);byte[] result = cipher.doFinal(src.getBytes());System.out.println("私钥加密，公钥解密—-加密:"+Base64.encode(result));//3.私钥加密，公钥解密—-解密//生成公钥X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(rsaPublicKey.getEncoded());keyFactory=KeyFactory.getInstance("RSA");PublicKey publicKey= keyFactory.generatePublic(x509EncodedKeySpec);cipher = Cipher.getInstance("RSA");//初始化解密cipher.init(Cipher.DECRYPT_MODE,publicKey);result = cipher.doFinal(result);System.out.println("私钥加密，公钥解密—-解密:"+new String(result));} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace(); }}public void pubENpriDE() {try {//1.初始化秘钥KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");//秘钥长度keyPairGenerator.initialize(512);//初始化秘钥对KeyPair keyPair = keyPairGenerator.generateKeyPair();//公钥RSAPublicKey rsaPublicKey = (RSAPublicKey) keyPair.getPublic();//私钥RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyPair.getPrivate();//2.公钥加密，私钥解密—-加密X509EncodedKeySpec x509EncodedKeySpec=new X509EncodedKeySpec(rsaPublicKey.getEncoded());KeyFactory keyFactory = KeyFactory.getInstance("RSA");PublicKey publicKey = keyFactory.generatePublic(x509EncodedKeySpec);//初始化加密//Cipher类为加密和解密提供密码功能，通过getinstance实例化对象Cipher cipher =Cipher.getInstance("RSA");cipher.init(Cipher.ENCRYPT_MODE,publicKey);//加密字符串byte[] result = cipher.doFinal(src.getBytes());System.out.println("公钥加密，私钥解密—-加密:"+Base64.encode(result));//3.公钥加密，私钥解密—–解密 PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaPrivateKey.getEncoded());keyFactory=KeyFactory.getInstance("RSA"); PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);//初始化解密cipher.init(Cipher.DECRYPT_MODE, privateKey);//解密字符串result = cipher.doFinal(result);System.out.println("公钥加密，私钥解密—–解密:"+new String(result));} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}测试：package com.secutiry.rsa;import com.security.rsa.RSAsecurity;public class RSAtest {public static void main(String[] args) {RSAsecurity rsAsecurity = new RSAsecurity();System.out.println("私钥加密公钥解密例：");rsAsecurity.priENpubDE();System.out.println("公钥加密私钥解密例：");rsAsecurity.pubENpriDE();}}测试结果：

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