自动生成RSA密钥，并进行加密和解密1

/**
	 * 自动产生RSA512位密钥(可以在512到2048之间)
	 */
	public static void getA271() throws Exception{
		KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
		kpg.initialize(512);
		KeyPair kp = kpg.genKeyPair();
		PublicKey puk = kp.getPublic();
		PrivateKey prk = kp.getPrivate();
		System.out.println("公钥："+puk);
		System.out.println("私钥："+prk);
	}

	/**
	 * 自动产生RSA1024位密钥；并保持到文件里
	 */
	public static void getA272() throws Exception{
		KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
		kpg.initialize(512);
		KeyPair kp = kpg.genKeyPair();
		PublicKey puk = kp.getPublic();
		PrivateKey prk = kp.getPrivate();
		FileOutputStream pufos = new FileOutputStream("d:\\rsapublickey.txt");
		ObjectOutputStream puoos = new ObjectOutputStream(pufos);
		puoos.writeObject(puk);
		FileOutputStream prfos = new FileOutputStream("d:\\rsaprivatekey.txt");
		ObjectOutputStream proos = new ObjectOutputStream(prfos);
		proos.writeObject(prk);
	}

	/**
	 * 使用非对称生成的公钥进行加密RSA512
	 */
	public static void getA281() throws Exception{
		FileInputStream fis = new FileInputStream("d:\\rsapublickey.txt");
		ObjectInputStream ois = new ObjectInputStream(fis);
		RSAPublicKey pbk = (RSAPublicKey)ois.readObject();
		BigInteger e = pbk.getPublicExponent();
		BigInteger n = pbk.getModulus();

		String mingwen = "hello world";//明文
		byte[] ptext = mingwen.getBytes("UTF-8");
		BigInteger m = new BigInteger(ptext);
		BigInteger c = m.modPow(e, n);//因为RSA算法要求整型数m的值必须小于n，所以需要计算

		//保存密文
		String cs = c.toString();
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("d:\\rsapublickeyjiamihou.txt")));
		bw.write(cs);
		bw.flush();
	}

	/**
	 * 使用非对称生成的公钥和私钥进行解密RSA512
	 */
	public static void getA282() throws Exception{
		BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("d:\\rsapublickeyjiamihou.txt")));//加密后文件
		String ctext = br.readLine();
		BigInteger c = new BigInteger(ctext);

		FileInputStream fis = new FileInputStream("d:\\rsaprivatekey.txt");
		ObjectInputStream ois = new ObjectInputStream(fis);
		RSAPrivateKey prk = (RSAPrivateKey)ois.readObject();
		BigInteger d = prk.getPrivateExponent();
		BigInteger n = prk.getModulus();
		BigInteger m = c.modPow(d, n);
		byte[] mt = m.toByteArray();
		String s = "";
		for(int i=0;i			s+=(char)mt[i];
		}
		System.out.println(s);
	}