import org.apache.tomcat.util.codec.binary.Base64;
import javax.crypto.Cipher;
import java.nio.charset.StandardCharsets;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;
public class RSAEncrypt {
    //用于封裝隨機產(chǎn)生的公鑰與私鑰
    private static Map<Integer, String> keyMap = new HashMap<Integer, String>();
    public static void main(String[] args) throws Exception {
        //生成公鑰和私鑰
        genKeyPair();
        //加密字符串
        String message = "123456";
        System.out.println("隨機生成的公鑰為:" + keyMap.get(0));
        System.out.println("隨機生成的私鑰為:" + keyMap.get(1));
        String messageEn = encrypt(message, keyMap.get(0));
        System.out.println(message + "\t加密后的字符串為:" + messageEn);
        String messageDe = decrypt(messageEn, keyMap.get(1));
        System.out.println("還原后的字符串為:" + messageDe);
    }
    /**
     * 隨機生成密鑰對
     *
     * @throws NoSuchAlgorithmException
     */
    public static void genKeyPair() throws NoSuchAlgorithmException {
        // KeyPairGenerator類用于生成公鑰和私鑰對，基于RSA算法生成對象
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
        // 初始化密鑰對生成器，密鑰大小為96-1024位
        keyPairGen.initialize(1024, new SecureRandom());
        // 生成一個密鑰對，保存在keyPair中
        KeyPair keyPair = keyPairGen.generateKeyPair();
        // 得到私鑰
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        // 得到公鑰
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        //得到公鑰字符串
        String publicKeyString = new String(Base64.encodeBase64(publicKey.getEncoded()), StandardCharsets.UTF_8);
        // 得到私鑰字符串
        String privateKeyString = new String(Base64.encodeBase64((privateKey.getEncoded())), StandardCharsets.UTF_8);
        // 將公鑰和私鑰保存到Map
        keyMap.put(0, publicKeyString);  //0表示公鑰
        keyMap.put(1, privateKeyString);  //1表示私鑰
    }
    /**
     * RSA公鑰加密
     *
     * @param str       加密字符串
     * @param publicKey 公鑰
     * @return 密文
     * @throws Exception 加密過程中的異常信息
     */
    public static String encrypt(String str, String publicKey) throws Exception {
        //base64編碼的公鑰
        byte[] decoded = Base64.decodeBase64(publicKey);
        RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(decoded));
        //RSA加密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, pubKey);
        return Base64.encodeBase64String(cipher.doFinal(str.getBytes(StandardCharsets.UTF_8)));
    }
    /**
     * RSA私鑰解密
     *
     * @param str        加密字符串
     * @param privateKey 私鑰
     * @return 銘文
     * @throws Exception 解密過程中的異常信息
     */
    public static String decrypt(String str, String privateKey) throws Exception {
        //64位解碼加密后的字符串
        byte[] inputByte = Base64.decodeBase64(str.getBytes(StandardCharsets.UTF_8));
        //base64編碼的私鑰
        byte[] decoded = Base64.decodeBase64(privateKey);
        RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(decoded));
        //RSA解密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, priKey);
        return new String(cipher.doFinal(inputByte));
    }
}