RSA非对称密钥加解密使用示例

一、简介：

　　RSA加密算法是最常用的非对称加密算法，CFCA在证书服务中离不了它。RSA是第一个比较完善的公开密钥算法，它既能用于加密，也能用于数字签名。这个算法经受住了多年深入的密码分析，虽然密码分析者既不能证明也不能否定RSA的安全性，但这恰恰说明该算法有一定的可信性，目前它已经成为最流行的公开密钥算法。
二、RSA的公钥、私钥的组成，以及加密、解密的公式
　　
三、使用方式：
　　① 假设A、B机器进行通信，已A机器为主；
　　② A首先需要用自己的私钥为发送请求数据签名，并将公钥一同发送给B；
　　③ B收到数据后，需要用A发送的公钥进行验证，已确保收到的数据是未经篡改的；
　　④ B验签通过后，处理逻辑，并把处理结果返回，返回数据需要用A发送的公钥进行加密（公钥加密后，只能用配对的私钥解密）；
　　⑤ A收到B返回的数据，使用私钥解密，至此，一次数据交互完成。
　　
四、代码示例：
1、第一步获取私钥，为签名做准备。

/**     * 读取私钥  返回PrivateKey     * @param path  包含私钥的证书路径     * @param password  私钥证书密码     * @return 返回私钥PrivateKey     * @throws KeyStoreException     * @throws NoSuchAlgorithmException     * @throws CertificateException     * @throws IOException     * @throws UnrecoverableKeyException     */    private static PrivateKey getPrivateKey(String path,String password)            throws KeyStoreException, NoSuchAlgorithmException, CertificateException,            IOException, UnrecoverableKeyException {        KeyStore ks = KeyStore.getInstance("PKCS12");        FileInputStream fis = new FileInputStream(path);        char[] nPassword = null;        if ((password == null) || password.trim().equals("")) {            nPassword = null;        } else {            nPassword = password.toCharArray();        }        ks.load(fis, nPassword);        fis.close();        Enumeration<String> en = ks.aliases();        String keyAlias = null;        if (en.hasMoreElements()) {            keyAlias = (String) en.nextElement();        }        return (PrivateKey) ks.getKey(keyAlias, nPassword);    }

2、签名示例：通过第一步得到的私钥，进行签名操作，具体请看以下代码：

/**     * 私钥签名： 签名方法如下：BASE64(RSA(MD5(src),privatekey))，其中src为需要签名的字符串，privatekey是商户的CFCA证书私钥。     * @param plainText 待签名字符串     * @param path 签名私钥路径     * @param password  签名私钥密码     * @return 返回签名后的字符串     * @throws Exception     */    public static String sign(String plainText,String path,String password)            throws Exception  {        /*         * MD5加密         */        MessageDigest md5 = MessageDigest.getInstance("MD5");        md5.update(plainText.getBytes("utf-8"));        byte[] digestBytes = md5.digest();        /*         * 用私钥进行签名 RSA         * Cipher负责完成加密或解密工作，基于RSA         */        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");        //ENCRYPT_MODE表示为加密模式        cipher.init(Cipher.ENCRYPT_MODE, getPrivateKey(path, password));        //加密        byte[] rsaBytes = cipher.doFinal(digestBytes);        //Base64编码        return Base64.byteArrayToBase64(rsaBytes);

3、B收到数据后，需要使用A提供的公钥信息进行验签，此处使用公钥的N、E进行验签首先通过公钥N、E得到公钥PublicKey，如下：

/**      * 根据公钥n、e生成公钥     * @param modulus   公钥n串     * @param publicExponent  公钥e串     * @return 返回公钥PublicKey     * @throws Exception     */    public static PublicKey getPublickKey(String modulus, String publicExponent)            throws Exception {        KeySpec publicKeySpec = new RSAPublicKeySpec(                new BigInteger(modulus, 16), new BigInteger(publicExponent, 16));        KeyFactory factory = KeyFactory.getInstance("RSA");        PublicKey publicKey = factory.generatePublic(publicKeySpec);        return publicKey;    }

得到公钥PublicKey后，再去验证签名，代码如下：

/**     * 用公钥证书进行验签     * @param message  签名之前的原文     * @param cipherText  签名     * @param pubKeyn 公钥n串     * @param pubKeye 公钥e串     * @return boolean 验签成功为true,失败为false     * @throws Exception     */    public static boolean verify(String message, String cipherText,String pubKeyn,            String pubKeye) throws Exception {        Cipher c4 = Cipher.getInstance("RSA/ECB/PKCS1Padding");        // 根据密钥，对Cipher对象进行初始化,DECRYPT_MODE表示解密模式        c4.init(Cipher.DECRYPT_MODE, getPublickKey(pubKeyn,pubKeye));        // 解密        byte[] desDecTextBytes = c4.doFinal(Base64.base64ToByteArray(cipherText));        // 得到前置对原文进行的MD5        String md5Digest1 = Base64.byteArrayToBase64(desDecTextBytes);        MessageDigest md5 = MessageDigest.getInstance("MD5");        md5.update(message.getBytes("utf-8"));        byte[] digestBytes = md5.digest();        // 得到商户对原文进行的MD5        String md5Digest2 = Base64.byteArrayToBase64(digestBytes);        // 验证签名        if (md5Digest1.equals(md5Digest2)) {            return true;        } else {            return false;        }    }

　至此，签名验签已经完毕
　
4、提供一个从.cer文件读取公钥的方法：

/**     * 读取公钥cer     * @param path .cer文件的路径  如：c:/abc.cer     * @return  base64后的公钥串     * @throws IOException     * @throws CertificateException     */    public static String getPublicKey(String path) throws IOException,    CertificateException{        InputStream inStream = new FileInputStream(path);        ByteArrayOutputStream out = new ByteArrayOutputStream();        int ch;        String res = "";        while ((ch = inStream.read()) != -1) {            out.write(ch);        }        byte[] result = out.toByteArray();        res = Base64.byteArrayToBase64(result);        return res;    }

代码封装

package utils;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公钥/私钥/签名工具包 * </p> * <p> * 罗纳德·李维斯特（Ron [R]ivest）、阿迪·萨莫尔（Adi [S]hamir）和伦纳德·阿德曼（Leonard [A]dleman） * </p> * <p> * 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<br/> * 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，<br/> * 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 * </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";    /**     * 签名算法     */    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";    /**     * 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;    /**     * <p>     * 生成密钥对(公钥和私钥)     * </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>     * 用私钥对信息生成数字签名     * </p>     *      * @param data     *            已加密数据     * @param privateKey     *            私钥(BASE64编码)     *      * @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>     * 校验数字签名     * </p>     *      * @param data     *            已加密数据     * @param publicKey     *            公钥(BASE64编码)     * @param sign     *            数字签名     *      * @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>     * 私钥解密     * </p>     *      * @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 = 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;        // 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;    }    /**     * <p>     * 公钥解密     * </p>     *      * @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 = 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;        // 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;    }    /**     * <p>     * 公钥加密     * </p>     *      * @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 = Base64Utils.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;    }    /**     * <p>     * 私钥加密     * </p>     *      * @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 = 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;        // 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;    }    /**     * <p>     * 获取私钥     * </p>     *      * @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 Base64Utils.encode(key.getEncoded());    }    /**     * <p>     * 获取公钥     * </p>     *      * @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 Base64Utils.encode(key.getEncoded());    }}

Base64Utils文件

package utils;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 com.sun.org.apache.xml.internal.security.utils.Base64;  /** * <p> * BASE64编码解码工具包 * </p> * <p> * 依赖javabase64-1.3.1.jar * </p> *  * @author IceWee * @date 2012-5-19 * @version 1.0 */public class Base64Utils {    /**     * 文件读取缓冲区大小     */    private static final int CACHE_SIZE = 1024;    /**     * <p>     * BASE64字符串解码为二进制数据     * </p>     *      * @param base64     * @return     * @throws Exception     */    public static byte[] decode(String base64) throws Exception {        return Base64.decode(base64.getBytes());    }    /**     * <p>     * 二进制数据编码为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>     * 将文件编码为BASE64字符串     * </p>     * <p>     * 大文件慎用，可能会导致内存溢出     * </p>     *      * @param filePath 文件绝对路径     * @return     * @throws Exception     */    public static String encodeFile(String filePath) throws Exception {        byte[] bytes = fileToByte(filePath);        return encode(bytes);    }    /**     * <p>     * BASE64字符串转回文件     * </p>     *      * @param filePath 文件绝对路径     * @param base64 编码字符串     * @throws Exception     */    public static void decodeToFile(String filePath, String base64) throws Exception {        byte[] bytes = decode(base64);        byteArrayToFile(bytes, filePath);    }    /**     * <p>     * 文件转换为二进制数组     * </p>     *      * @param filePath 文件路径     * @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>     * 二进制数据写文件     * </p>     *      * @param bytes 二进制数据     * @param filePath 文件生成目录     */    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();    }}

测试用例：

package util;import java.util.Map;import RSAUtils;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("公钥: \n\r" + publicKey);            System.err.println("私钥： \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("公钥加密——私钥解密");        String source = "这是一行没有任何意义的文字，你看完了等于没看，不是吗？";        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("加密后文字：\r\n" + new String(encodedData));        byte[] decodedData = RSAUtils.decryptByPrivateKey(encodedData, privateKey);        String target = new String(decodedData);        System.out.println("解密后文字: \r\n" + target);    }    static void testSign() throws Exception {        System.err.println("私钥加密——公钥解密");        String source = "这是一行测试RSA数字签名的无意义文字";        System.out.println("原文字：\r\n" + source);        byte[] data = source.getBytes();        byte[] encodedData = RSAUtils.encryptByPrivateKey(data, privateKey);        System.out.println("加密后：\r\n" + new String(encodedData));        byte[] decodedData = RSAUtils.decryptByPublicKey(encodedData, publicKey);        String target = new String(decodedData);        System.out.println("解密后: \r\n" + target);        System.err.println("私钥签名——公钥验证签名");        String sign = RSAUtils.sign(encodedData, privateKey);        System.err.println("签名:\r" + sign);        boolean status = RSAUtils.verify(encodedData, publicKey, sign);        System.err.println("验证结果:\r" + status);    }}

生成RSA密钥、保存到文件、从文件读取、加密、解密等操作

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.SecureRandom;   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 javax.crypto.Cipher;   import org.apache.commons.configuration.ConfigurationException;   import org.apache.commons.configuration.PropertiesConfiguration;   import org.bouncycastle.jce.provider.BouncyCastleProvider;   public class RSATest {       public static void main(String[] args) {           try {               RSATest encrypt = new RSATest();               String encryptText = "encryptText";               // Generate keys               KeyPair keyPair = encrypt.generateKey();               RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();               RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();               byte[] e = encrypt.encrypt(publicKey, encryptText.getBytes());               byte[] de = encrypt.decrypt(privateKey, e);               System.out.println(toHexString(e));               System.out.println(toHexString(de));           } catch (Exception e) {               e.printStackTrace();           }       }       public KeyPair generateKey() throws NoSuchAlgorithmException {           KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");           keyPairGen.initialize(1024, new SecureRandom());           KeyPair keyPair = keyPairGen.generateKeyPair();           return keyPair;       }       public void saveKey(KeyPair keyPair, String publicKeyFile,               String privateKeyFile) throws ConfigurationException {           PublicKey pubkey = keyPair.getPublic();           PrivateKey prikey = keyPair.getPrivate();           // save public key           PropertiesConfiguration publicConfig = new PropertiesConfiguration(                   publicKeyFile);           publicConfig.setProperty("PULIICKEY", toHexString(pubkey.getEncoded()));           publicConfig.save();           // save private key           PropertiesConfiguration privateConfig = new PropertiesConfiguration(                   privateKeyFile);           privateConfig.setProperty("PRIVATEKEY",                   toHexString(prikey.getEncoded()));           privateConfig.save();       }       /**       * @param filename       * @param type：       *            1-public 0-private       * @return       * @throws ConfigurationException       * @throws NoSuchAlgorithmException       * @throws InvalidKeySpecException       */      public Key loadKey(String filename, int type)               throws ConfigurationException, NoSuchAlgorithmException,               InvalidKeySpecException {           PropertiesConfiguration config = new PropertiesConfiguration(filename);           KeyFactory keyFactory = KeyFactory.getInstance("RSA",                   new BouncyCastleProvider());           if (type == 0) {               // privateKey               String privateKeyValue = config.getString("PULIICKEY");               PKCS8EncodedKeySpec priPKCS8 = new PKCS8EncodedKeySpec(                       toBytes(privateKeyValue));               PrivateKey privateKey = keyFactory.generatePrivate(priPKCS8);               return privateKey;           } else {               // publicKey               String privateKeyValue = config.getString("PRIVATEKEY");               X509EncodedKeySpec bobPubKeySpec = new X509EncodedKeySpec(                       toBytes(privateKeyValue));               PublicKey publicKey = keyFactory.generatePublic(bobPubKeySpec);               return publicKey;           }       }       /**       * Encrypt String.       *        * @return byte[]       */      protected byte[] encrypt(RSAPublicKey publicKey, byte[] data) {           if (publicKey != null) {               try {                   Cipher cipher = Cipher.getInstance("RSA",                           new BouncyCastleProvider());                   cipher.init(Cipher.ENCRYPT_MODE, publicKey);                   return cipher.doFinal(data);               } catch (Exception e) {                   e.printStackTrace();               }           }           return null;       }       /**       * Basic decrypt method       *        * @return byte[]       */      protected byte[] decrypt(RSAPrivateKey privateKey, byte[] raw) {           if (privateKey != null) {               try {                   Cipher cipher = Cipher.getInstance("RSA",                           new BouncyCastleProvider());                   cipher.init(Cipher.DECRYPT_MODE, privateKey);                   return cipher.doFinal(raw);               } catch (Exception e) {                   e.printStackTrace();               }           }           return null;       }       public static String toHexString(byte[] b) {           StringBuilder sb = new StringBuilder(b.length * 2);           for (int i = 0; i < b.length; i++) {               sb.append(HEXCHAR[(b[i] & 0xf0) >>> 4]);               sb.append(HEXCHAR[b[i] & 0x0f]);           }           return sb.toString();       }       public static final byte[] toBytes(String s) {           byte[] bytes;           bytes = new byte[s.length() / 2];           for (int i = 0; i < bytes.length; i++) {               bytes[i] = (byte) Integer.parseInt(s.substring(2 * i, 2 * i + 2),                       16);           }           return bytes;       }       private static char[] HEXCHAR = { '0', '1', '2', '3', '4', '5', '6', '7',               '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };   }

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