教你用Java實現RSA非對稱加密算法

package com.ljt.rsa.util;

import org.apache.commons.codec.binary.Base64;
import org.apache.commons.io.IOUtils;

import javax.crypto.Cipher;
import java.io.ByteArrayOutputStream;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

/**
 * @ClassName: RSAUtil
 * @Description:  RSA非對稱加密算法工具類
 * @Author: 寒山月初°C
 * @Date 2021/5/16 17:47
 * @Version 1.0
 */

public class RSAUtil {

    public static final String CHARSET = "UTF-8";
    public static final String RSA_ALGORITHM = "RSA";


    public static Map<String, String> createKeys(int keySize){
        //為RSA算法創建一個KeyPairGenerator對象（KeyPairGenerator，密鑰對生成器，用於生成公鑰和私鑰對）
        KeyPairGenerator kpg;
        try{
            kpg = KeyPairGenerator.getInstance(RSA_ALGORITHM);
        }catch(NoSuchAlgorithmException e){
            throw new IllegalArgumentException("No such algorithm-->[" + RSA_ALGORITHM + "]");
        }

        //初始化KeyPairGenerator對象,密鑰長度
        kpg.initialize(keySize);
        //生成密匙對
        KeyPair keyPair = kpg.generateKeyPair();
        //得到公鑰
        Key publicKey = keyPair.getPublic();
        String publicKeyStr = Base64.encodeBase64URLSafeString(publicKey.getEncoded()); //返回一個publicKey經過二次加密後的字符串
        //得到私鑰
        Key privateKey = keyPair.getPrivate();
        String privateKeyStr = Base64.encodeBase64URLSafeString(privateKey.getEncoded()); 返回一個privateKey經過二次加密後的字符串

        Map<String, String> keyPairMap = new HashMap<String, String>();
        keyPairMap.put("publicKey", publicKeyStr);
        keyPairMap.put("privateKey", privateKeyStr);

        return keyPairMap;
    }

    /**
     * 得到公鑰
     * @param publicKey 密鑰字符串（經過base64編碼）
     * @throws Exception
     */
    public static RSAPublicKey getPublicKey(String publicKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
        //通過X509編碼的Key指令獲得公鑰對象
        KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(Base64.decodeBase64(publicKey));
        RSAPublicKey key = (RSAPublicKey) keyFactory.generatePublic(x509KeySpec);
        return key;
    }

    /**
     * 得到私鑰
     * @param privateKey 密鑰字符串（經過base64編碼）
     * @throws Exception
     */
    public static RSAPrivateKey getPrivateKey(String privateKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
        //通過PKCS#8編碼的Key指令獲得私鑰對象
        KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(Base64.decodeBase64(privateKey));
        RSAPrivateKey key = (RSAPrivateKey) keyFactory.generatePrivate(pkcs8KeySpec);
        return key;
    }

    /**
     * 公鑰加密
     * @param data
     * @param publicKey
     * @return
     */
    public static String publicEncrypt(String data, RSAPublicKey publicKey){
        try{
            Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
            cipher.init(Cipher.ENCRYPT_MODE, publicKey);
            return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET), publicKey.getModulus().bitLength()));
        }catch(Exception e){
            throw new RuntimeException("加密字符串[" + data + "]時遇到異常", e);
        }
    }

    /**
     * 私鑰解密
     * @param data
     * @param privateKey
     * @return
     */

    public static String privateDecrypt(String data, RSAPrivateKey privateKey){
        try{
            Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
            cipher.init(Cipher.DECRYPT_MODE, privateKey);
            return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data), privateKey.getModulus().bitLength()), CHARSET);
        }catch(Exception e){
            throw new RuntimeException("解密字符串[" + data + "]時遇到異常", e);
        }
    }

    /**
     * 私鑰加密
     * @param data
     * @param privateKey
     * @return
     */

    public static String privateEncrypt(String data, RSAPrivateKey privateKey){
        try{
            Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
            cipher.init(Cipher.ENCRYPT_MODE, privateKey);
            return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET), privateKey.getModulus().bitLength()));
        }catch(Exception e){
            throw new RuntimeException("加密字符串[" + data + "]時遇到異常", e);
        }
    }

    /**
     * 公鑰解密
     * @param data
     * @param publicKey
     * @return
     */

    public static String publicDecrypt(String data, RSAPublicKey publicKey){
        try{
            Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
            cipher.init(Cipher.DECRYPT_MODE, publicKey);
            return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data), publicKey.getModulus().bitLength()), CHARSET);
        }catch(Exception e){
            throw new RuntimeException("解密字符串[" + data + "]時遇到異常", e);
        }
    }

    private static byte[] rsaSplitCodec(Cipher cipher, int opmode, byte[] datas, int keySize){
        int maxBlock = 0;
        if(opmode == Cipher.DECRYPT_MODE){
            maxBlock = keySize / 8;
        }else{
            maxBlock = keySize / 8 - 11;
        }
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] buff;
        int i = 0;
        try{
            while(datas.length > offSet){
                if(datas.length-offSet > maxBlock){
                    buff = cipher.doFinal(datas, offSet, maxBlock);
                }else{
                    buff = cipher.doFinal(datas, offSet, datas.length-offSet);
                }
                out.write(buff, 0, buff.length);
                i++;
                offSet = i * maxBlock;
            }
        }catch(Exception e){
            throw new RuntimeException("加解密閥值為["+maxBlock+"]的數據時發生異常", e);
        }
        byte[] resultDatas = out.toByteArray();
        IOUtils.closeQuietly(out);
        return resultDatas;
    }
}

class Test{
    public static void main (String[] args) throws Exception {
        Map<String, String> keyMap = RSAUtil.createKeys(1024);
        String  publicKey = keyMap.get("publicKey");
        String  privateKey = keyMap.get("privateKey");
        System.out.println("公鑰: \n\r" + publicKey);
        System.out.println("私鑰： \n\r" + privateKey);

        System.out.println("公鑰加密——私鑰解密");
        String str = "寒山月初℃";
        System.out.println("\r明文：\r\n" + str);
        System.out.println("\r明文大小：\r\n" + str.getBytes().length);
        String encodedData = RSAUtil.publicEncrypt(str, RSAUtil.getPublicKey(publicKey));
        System.out.println("密文：\r\n" + encodedData);
        String decodedData = RSAUtil.privateDecrypt(encodedData, RSAUtil.getPrivateKey(privateKey));
        System.out.println("解密後文字: \r\n" + decodedData);
    }

}