摘要：非對(duì)稱(chēng)密碼概念發(fā)送者使用接收者的公鑰加密，接收者使用自己的私鑰解密。

發(fā)送者使用接收者的公鑰加密，接收者使用自己的私鑰解密。
需要兩個(gè)密鑰進(jìn)行加密或解密，分為公鑰和私鑰
特點(diǎn)：安全性高，速度慢

DH密鑰交換算法

RSA算法

ElGamal算法那

密鑰交換（DH）

雙方在沒(méi)有確定共同密鑰的情況下，生成密鑰，不提供加密工作，加解密還需要其他對(duì)稱(chēng)加密算法實(shí)現(xiàn)

加密/解密（RSA）

數(shù)字簽名（RSA）

import javax.crypto.KeyAgreement;
import javax.crypto.interfaces.DHPrivateKey;
import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;
import java.security.*;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

//1 生成源密鑰
//2 把源公鑰交給目標(biāo)，目標(biāo)通過(guò)源公鑰，生成目標(biāo)公鑰和私鑰
//3 把目標(biāo)公鑰交給源
//4 雙方使用對(duì)方的公鑰和和自己的私鑰，生成本地密鑰
//5 如果雙方生成本地密鑰相同則完成密鑰交換
public class DHUtil {

    public static final String PUBLIC_KEY = "DH_Public_Key";
    public static final String PRIVATE_KEY = "DH_Private_key";

    /**
     * 生成源密鑰對(duì)
     * @return
     * @throws Exception
     */
    public static Map initSourceKey() throws Exception{
        //創(chuàng)建KeyPairGenerator的實(shí)例，選用DH算法
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("DH");

        //初始化密鑰長(zhǎng)度，默認(rèn)1024，可選范圍512-65536 & 64的倍數(shù)
        keyPairGenerator.initialize(1024);

        //生成密鑰對(duì)
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        DHPublicKey dhPublicKey = (DHPublicKey) keyPair.getPublic();
        DHPrivateKey dhPrivateKey = (DHPrivateKey) keyPair.getPrivate();

        //將密鑰對(duì)放入Map
        Map keyMap = new HashMap();
        keyMap.put(PUBLIC_KEY, dhPublicKey);
        keyMap.put(PRIVATE_KEY, dhPrivateKey);
        return keyMap;
    }

    /**
     * 通過(guò)源公鑰 生成 目標(biāo)密鑰對(duì)
     * @param sourcePublicKey
     * @return
     * @throws Exception
     */
    public static Map initTargetKey(byte[] sourcePublicKey) throws Exception {

        KeyFactory keyFactory = KeyFactory.getInstance("DH");

        //通過(guò)源公鑰，生成keySpec，使用KeyFactory生成源PublicKey相關(guān)信息
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(sourcePublicKey);
        DHPublicKey sourcePublic = (DHPublicKey) keyFactory.generatePublic(keySpec);

        DHParameterSpec dhPublicKeyParams = sourcePublic.getParams();

        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("DH");
        keyPairGenerator.initialize(dhPublicKeyParams);

        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        DHPublicKey dhPublicKey = (DHPublicKey) keyPair.getPublic();
        DHPrivateKey dhPrivateKey = (DHPrivateKey) keyPair.getPrivate();

        //將密鑰對(duì)放入Map
        Map keyMap = new HashMap();
        keyMap.put(PUBLIC_KEY, dhPublicKey);
        keyMap.put(PRIVATE_KEY, dhPrivateKey);
        return keyMap;
    }

    /**
     * 使用一方的公鑰和另一方的私鑰，生成本地密鑰
     * @return
     */
    public static byte[] generateLocalSecretKey(byte[] aPublicKey, byte[] bPrivateKey) throws Exception{
        KeyFactory keyFactory = KeyFactory.getInstance("DH");

        //通過(guò)A公鑰，生成keySpec，使用KeyFactory生成A PublicKey相關(guān)信息
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(aPublicKey);
        PublicKey publicKey = keyFactory.generatePublic(keySpec);

        //通過(guò)B私鑰，生成B PrivateKey相關(guān)信息
        PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(bPrivateKey);
        PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);

        //通過(guò)KeyAgreement對(duì)A的PublicKey和B的PrivateKey進(jìn)行加密
        KeyAgreement keyAgreement = KeyAgreement.getInstance("DH");
        keyAgreement.init(privateKey);
        keyAgreement.doPhase(publicKey,true);


        return keyAgreement.generateSecret("AES").getEncoded();//算法使用對(duì)稱(chēng)加密算法（DES，DESede，AES）
        //return keyAgreement.generateSecret();                // 也可以不選擇算法，使用默認(rèn)方法計(jì)算
    }

    //獲取公鑰字節(jié)數(shù)組
    public static byte[] getPublicKey(Map map){
        return ((DHPublicKey) map.get(PUBLIC_KEY)).getEncoded();
    }

    //獲取私鑰字節(jié)數(shù)組
    public static byte[] getPrivateKey(Map map){
        return ((DHPrivateKey) map.get(PRIVATE_KEY)).getEncoded();
    }

    public static void main(String[] args) throws Exception {

        byte[] source_public_key;
        byte[] source_private_key;
        byte[] source_local_key;

        byte[] target_public_key;
        byte[] target_private_key;
        byte[] target_local_key;

        Map sourceKey = initSourceKey();
        source_public_key = getPublicKey(sourceKey);
        source_private_key = getPrivateKey(sourceKey);

        System.out.println("源公鑰："+BytesToHex.fromBytesToHex(source_public_key));
        System.out.println("源私鑰："+BytesToHex.fromBytesToHex(source_private_key));

        Map targetKey = initTargetKey(getPublicKey(sourceKey));
        target_public_key = getPublicKey(targetKey);
        target_private_key = getPrivateKey(targetKey);

        System.out.println("目標(biāo)公鑰："+BytesToHex.fromBytesToHex(target_public_key));
        System.out.println("目標(biāo)私鑰："+BytesToHex.fromBytesToHex(target_private_key));

        source_local_key = generateLocalSecretKey(target_public_key, source_private_key);
        target_local_key = generateLocalSecretKey(source_public_key, target_private_key);

        System.out.println("源本地密鑰："+BytesToHex.fromBytesToHex(source_local_key));
        System.out.println("目標(biāo)本地密鑰："+BytesToHex.fromBytesToHex(target_local_key));
    }
}

公鑰加密，私鑰解密

import javax.crypto.Cipher;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PublicKey;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.util.HashMap;
import java.util.Map;

/**
 * RSA加密工具
 */
public class RSAUtil {

    public static final String PUBLIC_KEY = "RSA_Public_Key";
    public static final String PRIVATE_KEY = "RSA_Private_Key";

    /**
     * 初始化密鑰
     * @return
     * @throws Exception
     */
    public static Map initKey() throws Exception{
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(1024);//512-65536 & 64的倍數(shù)
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();

        Map keyMap = new HashMap();
        keyMap.put(PUBLIC_KEY, publicKey);
        keyMap.put(PRIVATE_KEY, privateKey);
        return keyMap;
    }

    public static RSAPublicKey getPublicKey(Map keyMap) {
        return (RSAPublicKey) keyMap.get(PUBLIC_KEY);
    }

    public static RSAPrivateKey getPrivateKey(Map keyMap){
        return (RSAPrivateKey) keyMap.get(PRIVATE_KEY);
    }

    /**
     * 使用公鑰對(duì)數(shù)據(jù)進(jìn)行加密
     * @param data
     * @param publicKey
     * @return
     * @throws Exception
     */
    public static byte[] encrypt(byte[] data, RSAPublicKey publicKey) throws Exception{
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE,publicKey);
        return cipher.doFinal(data);
    }

    /**
     * 使用私鑰解密
     * @param data
     * @param privateKey
     * @return
     * @throws Exception
     */
    public static byte[] decrypt(byte[] data, RSAPrivateKey privateKey) throws Exception{
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE,privateKey);
        return cipher.doFinal(data);
    }

    public static void main(String[] args) throws Exception {
        String data = "周杰倫-東風(fēng)破";
        Map keyMap = initKey();

        byte[] miwen = encrypt(data.getBytes(),getPublicKey(keyMap));
        System.out.println("加密后的內(nèi)容："+BytesToHex.fromBytesToHex(miwen));

        byte[] plain = decrypt(miwen, getPrivateKey(keyMap));
        System.out.println("解密后的內(nèi)容："+new String(plain));

    }
}