JAVA RSA加密公私鑰

RSA加密算法：RSA加密算法是一種非對稱加密算法。解密者擁有私鑰，並且將由私鑰計算生成的公鑰發布給加密者。加密都使用公鑰進行加密，並將密文發送到解密者，解密者用私鑰解密將密文解碼為明文。

RSA 密鑰最少保存 3 個數，n，d，e
ne 組成公鑰，nd 組成私鑰
其中 e 一般固定 65537，因此知道私鑰 nd 就能推出公鑰

如果 e 不是 65537 就不一定能推出了

import org.apache.commons.codec.binary.Base64;
import javax.crypto.Cipher;

import java.math.BigInteger;
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.RSAPublicKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

public class RSAEncrypt {
	private static Map<String, String> keyMap = new HashMap<String, String>();  //用於封裝隨機產生的公鑰與私鑰
	private static Map<String, BigInteger> modMap = new HashMap<>();
	public static void main(String[] args) throws Exception {
		//生成公鑰和私鑰
		genKeyPair();
		//加密字符串
		String message = "license";
		System.out.println("隨機生成的公鑰為:" + keyMap.get("publicKeyString"));
		System.out.println("隨機生成的私鑰為:" + keyMap.get("privateKeyString"));
		String messageEn = encrypt(message,keyMap.get("privateKeyString"));//私鑰加密
		System.out.println(message + "\t加密后的字符串為:" + messageEn);
		String messageDe = decrypt(messageEn,keyMap.get("publicKeyString"));//公鑰解密
		System.out.println("decrypt還原后的字符串為:" + messageDe);
		String messageDeMod = decryptMod(messageEn,modMap.get("publicMod"), modMap.get("publicExp"));
		System.out.println("decryptMod還原后的字符串為:" + messageDeMod);
		String messageDeModStr = decryptModStr(messageEn,keyMap.get("publicModStr"), keyMap.get("publicExpStr"));
		System.out.println("decryptModStr還原后的字符串為:" + messageDeModStr);
	}

	/** 
	 * 隨機生成密鑰對 
	 * @throws NoSuchAlgorithmException 
	 */  
	public static void genKeyPair() throws NoSuchAlgorithmException {  
		// KeyPairGenerator類用於生成公鑰和私鑰對，基於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();  
		RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();   // 得到私鑰  
		RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();  // 得到公鑰  
		String publicKeyString = new String(Base64.encodeBase64(publicKey.getEncoded()));  
		// 得到私鑰字符串  
		String privateKeyString = new String(Base64.encodeBase64((privateKey.getEncoded())));  
		// 將公鑰和私鑰保存到Map
		keyMap.put("publicKeyString",publicKeyString);  
		keyMap.put("privateKeyString",privateKeyString);  
		
		String publicModStr = new String(Base64.encodeBase64((publicKey.getModulus().toByteArray())));
		String publicExpStr = new String(Base64.encodeBase64((publicKey.getPublicExponent().toByteArray())));
		String privateModStr = new String(Base64.encodeBase64((privateKey.getModulus().toByteArray())));
		String privateExpStr = new String(Base64.encodeBase64((privateKey.getPrivateExponent().toByteArray())));
		keyMap.put("publicModStr",publicModStr); 
		keyMap.put("publicExpStr",publicExpStr); 
		keyMap.put("privateModStr",privateModStr); 
		keyMap.put("privateExpStr",privateExpStr); 
		
		modMap.put("publicMod", publicKey.getModulus());
		modMap.put("publicExp", publicKey.getPublicExponent());
		modMap.put("privateMod", privateKey.getModulus());
		modMap.put("privateExp", privateKey.getPrivateExponent());
		
		System.out.println("publicModStr:"+publicModStr);
		System.out.println("publicExpStr:"+publicExpStr);
		System.out.println("publicMod:"+publicKey.getModulus());
		System.out.println("publicExp:"+publicKey.getPublicExponent());
		System.out.println("privateModStr:"+privateModStr);
		System.out.println("privateExpStr:"+privateExpStr);
		System.out.println("privateMod:"+privateKey.getModulus());
		System.out.println("privateExp:"+privateKey.getPrivateExponent());
	}  
	
	/** 
	 * RSA私鑰加密 
	 *  
	 * @param str 
	 *            加密字符串
	 * @param privateKey 
	 *            私鑰 
	 * @return 密文 
	 * @throws Exception 
	 *             加密過程中的異常信息 
	 */  
	public static String encrypt( String str, String privateKey ) throws Exception{
		//base64編碼的公鑰
		byte[] decoded = Base64.decodeBase64(privateKey);
		RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(decoded));
		//RSA加密
		Cipher cipher = Cipher.getInstance("RSA");
		cipher.init(Cipher.ENCRYPT_MODE, priKey);
		String outStr = Base64.encodeBase64String(cipher.doFinal(str.getBytes("UTF-8")));
		return outStr;
	}
	
	/** 
	 * RSA公鑰解密
	 *  
	 * @param str 
	 *            加密字符串
	 * @param publicKey 
	 *            公鑰 
	 * @return 銘文
	 * @throws Exception 
	 *             解密過程中的異常信息 
	 */  
	public static String decrypt(String str, String publicKey) throws Exception{
		//64位解碼加密后的字符串
		byte[] inputByte = Base64.decodeBase64(str.getBytes("UTF-8"));
		//base64編碼的公鑰
		byte[] decoded = Base64.decodeBase64(publicKey);  
		RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(decoded));  
		//RSA解密
		Cipher cipher = Cipher.getInstance("RSA");
		cipher.init(Cipher.DECRYPT_MODE, pubKey);
		String outStr = new String(cipher.doFinal(inputByte));
		return outStr;
	}

	/** 
	 * RSA公鑰解密
	 *  
	 * @param str 
	 *            加密字符串
	 * @param publicMod 
	 *            公鑰模數
	 * @param publicExp 
	 *            公鑰指數
	 * @return 銘文
	 * @throws Exception 
	 *             解密過程中的異常信息 
	 */  
	public static String decryptMod(String str, BigInteger publicMod, BigInteger publicExp) throws Exception{
		//64位解碼加密后的字符串
		byte[] inputByte = Base64.decodeBase64(str.getBytes("UTF-8"));
		
		RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(publicMod, publicExp); 
        RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(pubKeySpec);  
		//RSA解密
		Cipher cipher = Cipher.getInstance("RSA");
		cipher.init(Cipher.DECRYPT_MODE, pubKey);
		String outStr = new String(cipher.doFinal(inputByte));
		return outStr;
	}
	
	/** 
	 * RSA公鑰解密
	 *  
	 * @param str 
	 *            加密字符串
	 * @param publicModStr
	 *            公鑰模數字符串
	 * @param publicExpStr 
	 *            公鑰指數字符串
	 * @return 銘文
	 * @throws Exception 
	 *             解密過程中的異常信息 
	 */  
	public static String decryptModStr(String str, String publicModStr, String publicExpStr) throws Exception{
		//64位解碼加密后的字符串
		byte[] inputByte = Base64.decodeBase64(str.getBytes("UTF-8"));
		
		BigInteger publicMod = new BigInteger(Base64.decodeBase64(publicModStr));
		BigInteger publicExp = new BigInteger(Base64.decodeBase64(publicExpStr));
		RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(publicMod, publicExp); 
        RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(pubKeySpec);  
		//RSA解密
		Cipher cipher = Cipher.getInstance("RSA");
		cipher.init(Cipher.DECRYPT_MODE, pubKey);
		String outStr = new String(cipher.doFinal(inputByte));
		return outStr;
	}

}