RSA加密與解密

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情況下都爲BASE64編碼格式<br/>
 * 由於非對稱加密速度極其緩慢，一般文件不使用它來加密而是使用對稱加密，<br/>
 * 非對稱加密算法可以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，可能會導致內存溢出
     * </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();
    }


}

測試用例：

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數字簽名的無意義文字";
        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);
    }

}

生成RSA密鑰、保存到文件、從文件讀取、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' };

}

Java中RSA非對稱密鑰加解密使用示例

一、簡介：

　　RSA加密算法是最常用的非對稱加密算法，CFCA在證書服務中離不了它。RSA是第一個比較完善的公開密鑰算法，它既能用於加密，也能用於數字簽名。這個算法經受住了多年深入的密碼分析，雖然密碼分析者既不能證明也不能否定RSA的安全性，但這恰恰說明該算法有一定的可信性，目前它已經成爲最流行的公開密鑰算法。

　　二、RSA的公鑰、私鑰的組成，以及加密、解密的公式可見於下表

　　三、使用方式：

　　① 假設A、B機器進行通信，已A機器爲主；

　　② A首先需要用自己的私鑰爲發送請求數據簽名，並將公鑰一同發送給B；

　　③ B收到數據後，需要用A發送的公鑰進行驗證，已確保收到的數據是未經篡改的；

　　④ B驗籤通過後，處理邏輯，並把處理結果返回，返回數據需要用A發送的公鑰進行加密（公鑰加密後，只能用配對的私鑰解密）；

　　⑤ A收到B返回的數據，使用私鑰解密，至此，一次數據交互完成。

　　四、代碼示例：

　　1、第一步獲取私鑰，爲簽名做準備。

/**
     * 讀取私鑰  返回PrivateKey
     * @param path  包含私鑰的證書路徑
     * @param password  私鑰證書密碼
     * @return 返回私鑰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、簽名示例：通過第一步得到的私鑰，進行簽名操作，具體請看以下代碼：

/**
     * 私鑰簽名： 簽名方法如下：BASE64(RSA(MD5(src),privatekey))，其中src爲需要簽名的字符串，
privatekey是商戶的CFCA證書私鑰。
     * @param plainText 待簽名字符串
     * @param path 簽名私鑰路徑
     * @param password  簽名私鑰密碼
     * @return 返回簽名後的字符串
     * @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();
        /*
         * 用私鑰進行簽名 RSA
         * Cipher負責完成加密或解密工作，基於RSA
         */
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        //ENCRYPT_MODE表示爲加密模式
        cipher.init(Cipher.ENCRYPT_MODE, getPrivateKey(path, password));
        //加密
        byte[] rsaBytes = cipher.doFinal(digestBytes);
        //Base64編碼
        return Base64.byteArrayToBase64(rsaBytes);}

3、B收到數據後，需要使用A提供的公鑰信息進行驗籤，此處使用公鑰的N、E進行驗籤

　　首先通過公鑰N、E得到公鑰PublicKey，如下：

/**
     * 根據公鑰n、e生成公鑰
     * @param modulus   公鑰n串
     * @param publicExponent  公鑰e串
     * @return 返回公鑰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;
    }

得到公鑰PublicKey後，再去驗證簽名，代碼如下：

/**
     * 用公鑰證書進行驗籤
     * @param message  簽名之前的原文
     * @param cipherText  簽名
     * @param pubKeyn 公鑰n串
     * @param pubKeye 公鑰e串
     * @return boolean 驗籤成功爲true,失敗爲false
     * @throws Exception
     */
    public static boolean verify(String message, String cipherText,String pubKeyn,
            String pubKeye) throws Exception {
        Cipher c4 = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        // 根據密鑰，對Cipher對象進行初始化,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));
        // 得到前置對原文進行的MD5
        String md5Digest1 = Base64.byteArrayToBase64(desDecTextBytes);
        MessageDigest md5 = MessageDigest.getInstance("MD5");
        md5.update(message.getBytes("utf-8"));
        byte[] digestBytes = md5.digest();
        // 得到商戶對原文進行的MD5
        String md5Digest2 = Base64.byteArrayToBase64(digestBytes);
        // 驗證簽名
        if (md5Digest1.equals(md5Digest2)) {
            return true;
        } else {
            return false;
        }
    }

　至此，簽名驗籤已經完畢

　　4、提供一個從.cer文件讀取公鑰的方法：

/**
     * 讀取公鑰cer
     * @param path .cer文件的路徑  如：c:/abc.cer
     * @return  base64後的公鑰串
     * @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;
    }