java RSA加密解密實現（含分段加密）

該工具類中用到了BASE64，須要藉助第三方類庫：javabase64-1.3.1.jar

下載地址：http://download.csdn.net/detail/centralperk/5025595

 

注意：
RSA加密明文最大長度117字節，解密要求密文最大長度爲128字節，因此在加密和解密的過程當中須要分塊進行。
RSA加密對明文的長度是有限制的，若是加密數據過大會拋出以下異常：

Exception in thread "main" javax.crypto.IllegalBlockSizeException: Data must not be longer than 117 bytes  
    at com.sun.crypto.provider.RSACipher.a(DashoA13*..)  
    at com.sun.crypto.provider.RSACipher.engineDoFinal(DashoA13*..)  
    at javax.crypto.Cipher.doFinal(DashoA13*..) 

 

RSAUtils.java

package security;

import java.io.ByteArrayOutputStream;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
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;

/** *//**
 * <p>
 * RSA公鑰/私鑰/簽名工具包
 * </p>
 * <p>
 * 羅納德·李維斯特（Ron [R]ivest）、阿迪·薩莫爾（Adi [S]hamir）和倫納德·阿德曼（Leonard [A]dleman）
 * </p>
 * <p>
 * 字符串格式的密鑰在未在特殊說明狀況下都爲BASE64編碼格式<br/>
 * 因爲非對稱加密速度極其緩慢，通常文件不使用它來加密而是使用對稱加密，<br/>
 * 非對稱加密算法能夠用來對對稱加密的密鑰加密，這樣保證密鑰的安全也就保證了數據的安全
 * </p>
 * 
 * @author IceWee
 * @date 2012-4-26
 * @version 1.0
 */
public class RSAUtils {

    /** *//**
     * 加密算法RSA
     */
    public static final String KEY_ALGORITHM = "RSA";
    
    /** *//**
     * 簽名算法
     */
    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

    /** *//**
     * 獲取公鑰的key
     */
    private static final String PUBLIC_KEY = "RSAPublicKey";
    
    /** *//**
     * 獲取私鑰的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;

    /** *//**
     * <p>
     * 生成密鑰對(公鑰和私鑰)
     * </p>
     * 
     * @return
     * @throws Exception
     */
    public static Map<String, Object> genKeyPair() throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        keyPairGen.initialize(1024);
        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;
    }
    
    /** *//**
     * <p>
     * 用私鑰對信息生成數字簽名
     * </p>
     * 
     * @param data 已加密數據
     * @param privateKey 私鑰(BASE64編碼)
     * 
     * @return
     * @throws Exception
     */
    public static String sign(byte[] data, String privateKey) throws Exception {
        byte[] keyBytes = Base64Utils.decode(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PrivateKey privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initSign(privateK);
        signature.update(data);
        return Base64Utils.encode(signature.sign());
    }

    /** *//**
     * <p>
     * 校驗數字簽名
     * </p>
     * 
     * @param data 已加密數據
     * @param publicKey 公鑰(BASE64編碼)
     * @param sign 數字簽名
     * 
     * @return
     * @throws Exception
     * 
     */
    public static boolean verify(byte[] data, String publicKey, String sign)
            throws Exception {
        byte[] keyBytes = Base64Utils.decode(publicKey);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PublicKey publicK = keyFactory.generatePublic(keySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initVerify(publicK);
        signature.update(data);
        return signature.verify(Base64Utils.decode(sign));
    }

    /** *//**
     * <P>
     * 私鑰解密
     * </p>
     * 
     * @param encryptedData 已加密數據
     * @param privateKey 私鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPrivateKey(byte[] encryptedData, String privateKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.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;
        // 對數據分段解密
        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;
    }

    /** *//**
     * <p>
     * 公鑰解密
     * </p>
     * 
     * @param encryptedData 已加密數據
     * @param publicKey 公鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPublicKey(byte[] encryptedData, String publicKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.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;
        // 對數據分段解密
        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;
    }

    /** *//**
     * <p>
     * 公鑰加密
     * </p>
     * 
     * @param data 源數據
     * @param publicKey 公鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPublicKey(byte[] data, String publicKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.decode(publicKey);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        // 對數據加密
        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;
        // 對數據分段加密
        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;
    }

    /** *//**
     * <p>
     * 私鑰加密
     * </p>
     * 
     * @param data 源數據
     * @param privateKey 私鑰(BASE64編碼)
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPrivateKey(byte[] data, String privateKey)
            throws Exception {
        byte[] keyBytes = Base64Utils.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;
        // 對數據分段加密
        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;
    }

    /** *//**
     * <p>
     * 獲取私鑰
     * </p>
     * 
     * @param keyMap 密鑰對
     * @return
     * @throws Exception
     */
    public static String getPrivateKey(Map<String, Object> keyMap)
            throws Exception {
        Key key = (Key) keyMap.get(PRIVATE_KEY);
        return Base64Utils.encode(key.getEncoded());
    }

    /** *//**
     * <p>
     * 獲取公鑰
     * </p>
     * 
     * @param keyMap 密鑰對
     * @return
     * @throws Exception
     */
    public static String getPublicKey(Map<String, Object> keyMap)
            throws Exception {
        Key key = (Key) keyMap.get(PUBLIC_KEY);
        return Base64Utils.encode(key.getEncoded());
    }

}

Base64Utils.java

package security;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

import it.sauronsoftware.base64.Base64;

/** *//**
 * <p>
 * BASE64編碼解碼工具包
 * </p>
 * <p>
 * 依賴javabase64-1.3.1.jar
 * </p>
 * 
 * @author IceWee
 * @date 2012-5-19
 * @version 1.0
 */
public class Base64Utils {

    /** *//**
     * 文件讀取緩衝區大小
     */
    private static final int CACHE_SIZE = 1024;
    
    /** *//**
     * <p>
     * BASE64字符串解碼爲二進制數據
     * </p>
     * 
     * @param base64
     * @return
     * @throws Exception
     */
    public static byte[] decode(String base64) throws Exception {
        return Base64.decode(base64.getBytes());
    }
    
    /** *//**
     * <p>
     * 二進制數據編碼爲BASE64字符串
     * </p>
     * 
     * @param bytes
     * @return
     * @throws Exception
     */
    public static String encode(byte[] bytes) throws Exception {
        return new String(Base64.encode(bytes));
    }
    
    /** *//**
     * <p>
     * 將文件編碼爲BASE64字符串
     * </p>
     * <p>
     * 大文件慎用，可能會致使內存溢出
     * </p>
     * 
     * @param filePath 文件絕對路徑
     * @return
     * @throws Exception
     */
    public static String encodeFile(String filePath) throws Exception {
        byte[] bytes = fileToByte(filePath);
        return encode(bytes);
    }
    
    /** *//**
     * <p>
     * BASE64字符串轉回文件
     * </p>
     * 
     * @param filePath 文件絕對路徑
     * @param base64 編碼字符串
     * @throws Exception
     */
    public static void decodeToFile(String filePath, String base64) throws Exception {
        byte[] bytes = decode(base64);
        byteArrayToFile(bytes, filePath);
    }
    
    /** *//**
     * <p>
     * 文件轉換爲二進制數組
     * </p>
     * 
     * @param filePath 文件路徑
     * @return
     * @throws Exception
     */
    public static byte[] fileToByte(String filePath) throws Exception {
        byte[] data = new byte[0];
        File file = new File(filePath);
        if (file.exists()) {
            FileInputStream in = new FileInputStream(file);
            ByteArrayOutputStream out = new ByteArrayOutputStream(2048);
            byte[] cache = new byte[CACHE_SIZE];
            int nRead = 0;
            while ((nRead = in.read(cache)) != -1) {
                out.write(cache, 0, nRead);
                out.flush();
            }
            out.close();
            in.close();
            data = out.toByteArray();
         }
        return data;
    }
    
    /** *//**
     * <p>
     * 二進制數據寫文件
     * </p>
     * 
     * @param bytes 二進制數據
     * @param filePath 文件生成目錄
     */
    public static void byteArrayToFile(byte[] bytes, String filePath) throws Exception {
        InputStream in = new ByteArrayInputStream(bytes);   
        File destFile = new File(filePath);
        if (!destFile.getParentFile().exists()) {
            destFile.getParentFile().mkdirs();
        }
        destFile.createNewFile();
        OutputStream out = new FileOutputStream(destFile);
        byte[] cache = new byte[CACHE_SIZE];
        int nRead = 0;
        while ((nRead = in.read(cache)) != -1) {   
            out.write(cache, 0, nRead);
            out.flush();
        }
        out.close();
        in.close();
    }
    
    
}

RSATester.java

package security;

import java.util.Map;

public class RSATester {

    static String publicKey;
    static String privateKey;

    static {
        try {
            Map<String, Object> keyMap = RSAUtils.genKeyPair();
            publicKey = RSAUtils.getPublicKey(keyMap);
            privateKey = RSAUtils.getPrivateKey(keyMap);
            System.err.println("公鑰: \n\r" + publicKey);
            System.err.println("私鑰： \n\r" + privateKey);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    public static void main(String[] args) throws Exception {
        test();
        testSign();
    }

    static void test() throws Exception {
        System.err.println("公鑰加密——私鑰解密");
        String source = "這是一行沒有任何意義的文字，你看完了等於沒看，不是嗎？";
        System.out.println("\r加密前文字：\r\n" + source);
        byte[] data = source.getBytes();
        byte[] encodedData = RSAUtils.encryptByPublicKey(data, publicKey);
        System.out.println("加密後文字：\r\n" + new String(encodedData));
        byte[] decodedData = RSAUtils.decryptByPrivateKey(encodedData, privateKey);
        String target = new String(decodedData);
        System.out.println("解密後文字: \r\n" + target);
    }

    static void testSign() throws Exception {
        System.err.println("私鑰加密——公鑰解密");
        String source = "這是一行測試RSA數字簽名的無心義文字";
        System.out.println("原文字：\r\n" + source);
        byte[] data = source.getBytes();
        byte[] encodedData = RSAUtils.encryptByPrivateKey(data, privateKey);
        System.out.println("加密後：\r\n" + new String(encodedData));
        byte[] decodedData = RSAUtils.decryptByPublicKey(encodedData, publicKey);
        String target = new String(decodedData);
        System.out.println("解密後: \r\n" + target);
        System.err.println("私鑰簽名——公鑰驗證簽名");
        String sign = RSAUtils.sign(encodedData, privateKey);
        System.err.println("簽名:\r" + sign);
        boolean status = RSAUtils.verify(encodedData, publicKey, sign);
        System.err.println("驗證結果:\r" + status);
    }
    
}

 

本身改進的：

package com.gd.rps.rb.service.util;

import org.apache.geronimo.mail.util.Base64;

import net.sf.json.JSONObject;

import java.io.ByteArrayOutputStream;
import java.security.Key;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import javax.crypto.Cipher;

/**
 * RSA加解密
 * @author jiafuwei
 * created at 2017/6/8
 */
public class UseRSAUtil {
    
    /** *//** 
     * 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; 

    public static final String KEY_ALGORITHM = "RSA";
    private static KeyFactory keyFactory = null;
    public static String PrivateKey = "私鑰。。。";
    public static String publicKey="公鑰。。。";

    static {
        try {
            keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        } catch (NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * 解密方法
     * @param dataStr 要解密的數據
     * @return 解密後的原數據
     * @throws Exception
     */
    public static String decrypt(String dataStr) throws Exception{
        //要加密的數據
        System.out.println("要解密的數據:"+dataStr);
        //對私鑰解密
        Key decodePrivateKey = getPrivateKeyFromBase64KeyEncodeStr(PrivateKey);
        //Log.i("機密",""+decodePrivateKey);
        Cipher cipher = Cipher.getInstance(KEY_ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, decodePrivateKey);
        byte[] encodedData = Base64.decode(dataStr);
        byte[] decodedData = cipher.doFinal(encodedData);
        String decodedDataStr = new String(decodedData,"utf-8");
        System.out.println("私鑰解密後的數據:"+decodedDataStr);
        return decodedDataStr;
    }

    public  static Key getPrivateKeyFromBase64KeyEncodeStr(String keyStr) {
        byte[] keyBytes = Base64.decode(keyStr);
        // 取得私鑰
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        Key privateKey=null;
        try {
            privateKey = keyFactory.generatePrivate(pkcs8KeySpec);
        } catch (InvalidKeySpecException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return privateKey;
    }

    /**
     * 獲取base64加密後的字符串的原始公鑰
     * @param keyStr
     * @return
     */
    public static Key getPublicKeyFromBase64KeyEncodeStr(String keyStr) {
        byte[] keyBytes = Base64.decode(keyStr);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        Key publicKey = null;
        try {
            publicKey = keyFactory.generatePublic(x509KeySpec);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return publicKey;
    }

    /**
     * 公鑰加密方法
     * @param dataStr 要加密的數據
     * @param dataStr 公鑰base64字符串
     * @return 加密後的base64字符串
     * @throws Exception
     */
    public static String encryptPublicKey(String dataStr) throws Exception{
        //要加密的數據
        System.out.println("要加密的數據:"+dataStr);
        byte[] data = dataStr.getBytes();
        // 對公鑰解密
        Key decodePublicKey = getPublicKeyFromBase64KeyEncodeStr(publicKey);
        // 對數據加密
        Cipher cipher = Cipher.getInstance(KEY_ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, decodePublicKey);
        byte[] encodedData = cipher.doFinal(data);
        String encodedDataStr = new String(Base64.encode(encodedData));
        System.out.println("公鑰加密後的數據:"+encodedDataStr);
        return encodedDataStr;
    }
    
    /**
     * 使用公鑰進行分段加密
     * @param dataStr 要加密的數據
     * @return 公鑰base64字符串
     * @throws Exception
     */
    public static String encryptByPublicKey(String dataStr)  
            throws Exception {  
        //要加密的數據
        System.out.println("要加密的數據:"+dataStr);
        byte[] data = dataStr.getBytes();
        // 對公鑰解密
        Key decodePublicKey = getPublicKeyFromBase64KeyEncodeStr(publicKey);
         
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);  
        // 對數據加密  
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());  
        cipher.init(Cipher.ENCRYPT_MODE, decodePublicKey);  
        int inputLen = data.length;  
        ByteArrayOutputStream out = new ByteArrayOutputStream();  
        int offSet = 0;  
        byte[] cache;  
        int i = 0;  
        // 對數據分段加密  
        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(); 
        String encodedDataStr = new String(Base64.encode(encryptedData));
        System.out.println("公鑰加密後的數據:"+encodedDataStr);
        return encodedDataStr;  
    } 

    /**
     * 使用私鑰進行分段解密
     * @param dataStr 使用base64處理過的密文
     * @return 解密後的數據
     * @throws Exception
     */
    public static String decryptByPrivateKey(String dataStr)  
            throws Exception {  
        
        byte[] encryptedData = Base64.decode(dataStr);
        
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);  
        Key decodePrivateKey = getPrivateKeyFromBase64KeyEncodeStr(PrivateKey);
        
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());  
        cipher.init(Cipher.DECRYPT_MODE, decodePrivateKey);  
        int inputLen = encryptedData.length;  
        ByteArrayOutputStream out = new ByteArrayOutputStream();  
        int offSet = 0;  
        byte[] cache;  
        int i = 0;  
        // 對數據分段解密  
        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();  
        String decodedDataStr = new String(decryptedData,"utf-8");
        System.out.println("私鑰解密後的數據:"+decodedDataStr);
        return decodedDataStr;  
    } 
    
    
    public static void main(String[] args) throws Exception {
       
    }
}