非对称加密算法之Java RSA算法应用

  · RSA算法简介

  RSA公开密钥密码体制是一种使用不同的加密密钥与解密密钥，“由已知加密密钥推导出解密密钥在计算上是不可行的”密码体制。

​  在公开密钥密码体制中，加密密钥（即公开密钥）PK是公开信息，而解密密钥（即秘密密钥）SK是需要保密的。加密算法E和解密算法D也都是公开的。虽然解密密钥SK是由公开密钥PK决定的，但却不能根据PK计算出SK。

  RSA允许你选择公钥的大小。512位的密钥被视为不安全的；768位的密钥不用担心受到除了国家安全管理（NSA）外的其他事物的危害；1024位的密钥几乎是安全的。

  关于RSA概念性的内容不做过多介绍，大家可以自行百度。

  · Maven 依赖

​  工具类对于加密后使用Base64进行编码，所以需要依赖Apache Commons Codec。

<dependency>
    <groupId>commons-codec</groupId>
    <artifactId>commons-codec</artifactId>
    <version>1.9</version>
</dependency>

  · 工具类实现

package com.arhorchin.securitit.enordecryption.rsa;

import java.io.ByteArrayOutputStream;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
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;

import javax.crypto.Cipher;

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

/**
 * @author Securitit.
 * @version 1.0.
 * @note RSA公钥/私钥/签名工具包. 
 *       字符串格式的密钥在未在特殊说明情况下都为BASE64编码格式. 
 *       由于非对称加密速度极其缓慢，一般文件不使用它来加密而是使用对称加密.
 *       非对称加密算法可以用来对对称加密的密钥加密，这样保证密钥的安全也就保证了数据的安全.
 */
public class RSAUtil {

    /**
     * 加密算法RSA.
     */
    public static final String KEY_ALGORITHM = "RSA";

    /**
     * 获取公钥的key.
     */
    private static final String PUBLIC_KEY = "RSAPublicKey";

    /**
     * 获取私钥的key.
     */
    private static final String PRIVATE_KEY = "RSAPrivateKey";

    /**
     * RSA最大加密明文大小.
     */
    private static final int MAX_ENCRYPT_BLOCK = 117;

    /**
     * RSA最大解密密文大小.
     */
    private static final int MAX_DECRYPT_BLOCK = 128;

    /**
     * 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 = 1024;

    /**
     * 生成密钥对(公钥和私钥).
     * @return .
     * @throws Exception .
     */
    public static Map<String, Object> genKeyPair() throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        keyPairGen.initialize(KEY_SIZE);
        KeyPair keyPair = keyPairGen.generateKeyPair();
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put(PUBLIC_KEY, publicKey);
        keyMap.put(PRIVATE_KEY, privateKey);
        return keyMap;
    }

    /**
     * 获取公钥.
     * @param keyMap 密钥对.
     * @return .
     * @throws Exception .
     */
    public static String getPublicKey(Map<String, Object> keyMap) throws Exception {
        Key key = (Key) keyMap.get(PUBLIC_KEY);
        return Base64.encodeBase64String(key.getEncoded());
    }

    /**
     * 获取私钥.
     * @param keyMap 密钥对.
     * @return .
     * @throws Exception .
     */
    public static String getPrivateKey(Map<String, Object> keyMap) throws Exception {
        Key key = (Key) keyMap.get(PRIVATE_KEY);
        return Base64.encodeBase64String(key.getEncoded());
    }

    /**
     * 公钥加密.
     * @param data 源数据.
     * @param publicKey 公钥(BASE64编码).
     * @return .
     * @throws Exception .
     */
    public static byte[] encryptByPublicKey(byte[] data, String publicKey) throws Exception {
        byte[] keyBytes = new Base64().decode(publicKey);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        // 对数据加密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, publicK);
        int inputLen = data.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 对数据分段加密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                cache = cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(data, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }

    /**
     * 私钥加密.
     * @param data 源数据.
     * @param privateKey 私钥(BASE64编码).
     * @return .
     * @throws Exception .
     */
    public static byte[] encryptByPrivateKey(byte[] data, String privateKey) throws Exception {
        byte[] keyBytes = new Base64().decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, privateK);
        int inputLen = data.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 对数据分段加密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {
                cache = cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(data, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }

    /**
     * 公钥解密.
     * @param encryptedData 已加密数据.
     * @param publicKey 公钥(BASE64编码).
     * @return .
     * @throws Exception .
     */
    public static byte[] decryptByPublicKey(byte[] encryptedData, String publicKey) throws Exception {
        byte[] keyBytes = new Base64().decode(publicKey);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, publicK);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 对数据分段解密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return decryptedData;
    }

    /**
     * 私钥解密.
     * @param encryptedData 已加密数据.
     * @param privateKey 私钥(BASE64编码).
     * @return .
     * @throws Exception .
     */
    public static byte[] decryptByPrivateKey(byte[] encryptedData, String privateKey) throws Exception {
        byte[] keyBytes = new Base64().decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, privateK);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 对数据分段解密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return decryptedData;
    }

}

  · 密钥生成测试类如下：

package com.arhorchin.securitit.enordecryption.rsa;

import java.util.Map;

import com.arhorchin.securitit.enordecryption.rsa.RSAUtil;

/**
 * @author Securitit.
 * @note RSA非对称密钥对生成.
 */
public class RsaKeyPairTester {

    public static void main(String[] args) throws Exception {
        Map<String, Object> keyPairMap = null;
        String publicKeyStr = null;
        String privateKeyStr = null;

        keyPairMap = RSAUtil.genKeyPair();
        publicKeyStr = RSAUtil.getPublicKey(keyPairMap);
        privateKeyStr = RSAUtil.getPrivateKey(keyPairMap);

        System.out.println("公钥：" + publicKeyStr);
        System.out.println("私钥：" + privateKeyStr);
    }

}

  · 密钥生成输出结果：

公钥：MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCrEC2uiS37eTAGlw4obsYIQ64c7UZgqiLETjv1ddU729kIQuLDOS+iq/RGoFsfPDSNfjTCBFMcYyFw3L2Ee9lsVGbfupztf1Ni9ZgVzlQ1d2v9xi15Ol/DGytMGxEmSIWPD8dL7yrQ9Cw9MlX1gT1YYFjB0M0FgwmBqZ7xv7CjaQIDAQAB
私钥：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

  · 加解密测试类如下：

package com.arhorchin.securitit.enordecryption.rsa;

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

import com.arhorchin.securitit.enordecryption.charset.Characters;

/**
 * @author Securitit.
 * @note RSAUtil测试类.
 */
public class RSAUtilTester {
    
    /**
     * 公钥.
     */
    private static String PUBLIC_KEY = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCrEC2uiS37eTAGlw4obsYIQ64c7UZgqiLETjv1ddU729kIQuLDOS+iq/RGoFsfPDSNfjTCBFMcYyFw3L2Ee9lsVGbfupztf1Ni9ZgVzlQ1d2v9xi15Ol/DGytMGxEmSIWPD8dL7yrQ9Cw9MlX1gT1YYFjB0M0FgwmBqZ7xv7CjaQIDAQAB";
    
    /**
     * 私钥.
     */
    private static String PRIVATE_KEY = "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";

    public static void main(String[] args) throws Exception {
        String plaintext = null;
        byte[] cipherBts = null;
        String ciphertext = null;
        byte[] dePlainBts = null;
        String dePlaintext = null;
        
        /********************************* 公钥加密、私钥解密 ************************************/
        plaintext = "这是一段数据原文-公钥原文.";
        // 公钥进行加密示例.
        cipherBts = RSAUtil.encryptByPublicKey(plaintext.getBytes(Characters.UTF8), PUBLIC_KEY);
        ciphertext = Base64.encodeBase64String(cipherBts);
        System.out.println("公钥加密密文：" + ciphertext);
        // 私钥进行解密示例.
        dePlainBts = RSAUtil.decryptByPrivateKey(Base64.decodeBase64(ciphertext), PRIVATE_KEY);
        dePlaintext = new String(dePlainBts, Characters.UTF8);
        System.out.println("私钥解密明文：" + dePlaintext);
        
        /********************************* 私钥加密、公钥解密 ************************************/
        plaintext = "这是一段数据原文-私钥原文.";
        // 私钥进行加密示例.
        cipherBts = RSAUtil.encryptByPrivateKey(plaintext.getBytes(Characters.UTF8), PRIVATE_KEY);
        ciphertext = Base64.encodeBase64String(cipherBts);
        System.out.println("私钥加密密文：" + ciphertext);
        // 公钥进行解密示例.
        dePlainBts = RSAUtil.decryptByPublicKey(Base64.decodeBase64(ciphertext), PUBLIC_KEY);
        dePlaintext = new String(dePlainBts, Characters.UTF8);
        System.out.println("公钥解密明文：" + dePlaintext);
    }
    
}

  · 加解密输出结果：

公钥加密密文：fslkNblfclqJQ0cTq5YjTGOOvioatFcbOJd8lFt2qMAWzyfUI/9Cish6VuVIRo4AogFFkJGYg7MtMr48YTdIdnwNpieOxh1emzEOTnR/rCwPvQG7rk7L6vntkwy1d7s/J3B1TcsY+0/52Gna702ksZgYjvNmry9dKJteAZSWnY0=
私钥解密明文：这是一段数据原文-公钥原文.
私钥加密密文：La+NYTDI3OAH4AofUh0BHY4u+NwtImPeTDBxsSKJZN1AtmLAnnxH2BPbHz/hiraHTbQK0QSsuUbW/vFOItk7x117caeQJaZm/MOHRBKlRlUJHKKa1Mc/2Hr7bFd5jpn7493PWuvJgBZw3MT7P6FyLaqVK+EGjzx7f+If+SvaelE=
公钥解密明文：这是一段数据原文-私钥原文.

  · 总结

  算法实现都很类似，本文只是对算法实现做了整理，在Maven依赖引入的情况下，RSAUtil已经做了简单测试，可以直接使用。