JDK自带方法实现RSA非对称加密

package jdbc.pro.lin;

import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
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;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;

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

public class MyRSA {
    public static final String KEY_ALGORITHM = "RSA";
    /** 貌似默认是RSA/NONE/PKCS1Padding，未验证 */
    public static final String CIPHER_ALGORITHM = "RSA/ECB/PKCS1Padding";
    public static final String PUBLIC_KEY = "publicKey";
    public static final String PRIVATE_KEY = "privateKey";

    /** RSA密钥长度必须是64的倍数，在512~65536之间。默认是1024 */
    public static final int KEY_SIZE = 2048;

    public static final String PLAIN_TEXT = "MANUTD is the greatest club in the world";

    public static void main(String[] args) {
        Map<String, byte[]> keyMap = generateKeyBytes();

        // 加密
        PublicKey publicKey = restorePublicKey(keyMap.get(PUBLIC_KEY));
        
        byte[] encodedText = RSAEncode(publicKey, PLAIN_TEXT.getBytes());
        System.out.println("RSA encoded: " + Base64.encodeBase64String(encodedText));

        // 解密
        PrivateKey privateKey = restorePrivateKey(keyMap.get(PRIVATE_KEY));
        System.out.println("RSA decoded: "
                + RSADecode(privateKey, encodedText));
    }

    /**
     * 生成密钥对。注意这里是生成密钥对KeyPair，再由密钥对获取公私钥
     * 
     * @return
     */
    public static Map<String, byte[]> generateKeyBytes() {

        try {
            KeyPairGenerator keyPairGenerator = KeyPairGenerator
                    .getInstance(KEY_ALGORITHM);
            keyPairGenerator.initialize(KEY_SIZE);
            KeyPair keyPair = keyPairGenerator.generateKeyPair();
            RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
            RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();

            Map<String, byte[]> keyMap = new HashMap<String, byte[]>();
            keyMap.put(PUBLIC_KEY, publicKey.getEncoded());
            keyMap.put(PRIVATE_KEY, privateKey.getEncoded());
            return keyMap;
        } catch (NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 还原公钥，X509EncodedKeySpec 用于构建公钥的规范
     * 
     * @param keyBytes
     * @return
     */
    public static PublicKey restorePublicKey(byte[] keyBytes) {
        X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(keyBytes);

        try {
            KeyFactory factory = KeyFactory.getInstance(KEY_ALGORITHM);
            PublicKey publicKey = factory.generatePublic(x509EncodedKeySpec);
            return publicKey;
        } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 还原私钥，PKCS8EncodedKeySpec 用于构建私钥的规范
     * 
     * @param keyBytes
     * @return
     */
    public static PrivateKey restorePrivateKey(byte[] keyBytes) {
        PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(
                keyBytes);
        try {
            KeyFactory factory = KeyFactory.getInstance(KEY_ALGORITHM);
            PrivateKey privateKey = factory
                    .generatePrivate(pkcs8EncodedKeySpec);
            return privateKey;
        } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 加密，三步走。
     * 
     * @param key
     * @param plainText
     * @return
     */
    public static byte[] RSAEncode(PublicKey key, byte[] plainText) {

        try {
            Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
            cipher.init(Cipher.ENCRYPT_MODE, key);
            return cipher.doFinal(plainText);
        } catch (NoSuchAlgorithmException | NoSuchPaddingException
                | InvalidKeyException | IllegalBlockSizeException
                | BadPaddingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;

    }

    /**
     * 解密，三步走。
     * 
     * @param key
     * @param encodedText
     * @return
     */
    public static String RSADecode(PrivateKey key, byte[] encodedText) {

        try {
            Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
            cipher.init(Cipher.DECRYPT_MODE, key);
            return new String(cipher.doFinal(encodedText));
        } catch (NoSuchAlgorithmException | NoSuchPaddingException
                | InvalidKeyException | IllegalBlockSizeException
                | BadPaddingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;

    }
}

几点注意：

1.用到了KeyFactory。

2.用到了公私钥的规范。

3.RSA密钥长度从512~65536，必须是64的整数倍