学步园

用JAVA实现RSA加密过程，有以下几个步骤： 

    1、甲方构建密钥对（公钥和私钥，公钥给对方，私钥留给自己） 
    2、甲方使用私钥加密数据，然后用私钥对加密后的数据签名，并把这些发送给乙方；乙方使用公钥、签名来验证待解密数据是否有效，如果有效使用公钥对数据解密。 
    3、乙方使用公钥加密数据，向甲方发送经过加密后的数据；甲方获得加密数据，通过私钥解密。 

 示例代码如下：

package com.rsa.core;

import java.security.Key;
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;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class RSACoder {

	public static PublicKey getPublicKey(String key) throws Exception {
		byte[] keyBytes;
		keyBytes = (new BASE64Decoder()).decodeBuffer(key);
		X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
		KeyFactory keyFactory = KeyFactory.getInstance("RSA");
		PublicKey publicKey = keyFactory.generatePublic(keySpec);
		return publicKey;
	}

	public static PrivateKey getPrivateKey(String key) throws Exception {
		byte[] keyBytes;
		keyBytes = (new BASE64Decoder()).decodeBuffer(key);
		PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
		KeyFactory keyFactory = KeyFactory.getInstance("RSA");
		PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
		return privateKey;
	}

	/**
	* 得到密钥字符串（经过base64编码）
	* @return
	*/
	public static String getKeyString(Key key) throws Exception {
		byte[] keyBytes = key.getEncoded();
		String s = (new BASE64Encoder()).encode(keyBytes);
		return s;
	}

	public static void main(String[] args) throws Exception {
		KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
		//密钥位数
		keyPairGen.initialize(1024);
		//密钥对
		KeyPair keyPair = keyPairGen.generateKeyPair();
		// 公钥
		PublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
		// 私钥
		PrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
		String publicKeyString = getKeyString(publicKey);
		System.out.println("public:\n" + publicKeyString);
		String privateKeyString = getKeyString(privateKey);
		System.out.println("private:\n" + privateKeyString);
		//加解密类
		Cipher cipher = Cipher.getInstance("RSA");//Cipher.getInstance("RSA/ECB/PKCS1Padding");
		//明文
		byte[] plainText = "91686280721609".getBytes();
		//加密
		cipher.init(Cipher.ENCRYPT_MODE, publicKey);
		byte[] enBytes = cipher.doFinal(plainText);
		String s1 = new String(enBytes);
		System.out.println("加密后的密文：" + s1);
		//通过密钥字符串得到密钥
		publicKey = getPublicKey(publicKeyString);
		privateKey = getPrivateKey(privateKeyString);
		//解密
		cipher.init(Cipher.DECRYPT_MODE, privateKey);
		byte[]deBytes = cipher.doFinal(enBytes);
		publicKeyString = getKeyString(publicKey);
		System.out.println("public:\n" +publicKeyString);
		privateKeyString = getKeyString(privateKey);
		System.out.println("private:\n" + privateKeyString);
		String s = new String(deBytes);
		System.out.println(s);
	}

}