java中RSA分段加解密與加簽驗簽

 背景

RSA加密明文最大長度117字節，解密要求密文最大長度為128字節，所以過長數據在加密和解密的過程中需要分塊進行。
RSA加密對明文的長度是有限制的，如果加密數據過大會拋出如下異常：

Exception in thread “main” javax.crypto.IllegalBlockSizeException: Data must not be longer than 117 bytes

實際使用說明

項目中使用加密，一般情況主要有兩種目的
第一種：數據不可見，直接使用密文傳輸
第二種：數據可見，但是接收方需要驗簽名，防止數據被篡改。

綜上：
一般情況下，使用加簽防止數據篡改就可以適應絕大數的需求了，第一種方式加密傳輸，如果數據比較大可能會超出最大限制,而且加密耗時長，使用加簽，驗簽方式速度較快，也是業界比較流行的數據傳輸安全方式。

RSA超出最大限制解決之分段加解密

package com.rsa.demo.util;


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;


/** * RSA公鑰/私鑰/簽名工具包 * 字符串格式的密鑰在未在特殊說明情況下都為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 * * @author 碼農猿 */
public class RSAUtils {
    /** * 加密算法RSA */
    private static final String KEY_ALGORITHM = "RSA";
    /** * 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";
    /** * 簽名算法 */
    private static final String SIGNATURE_ALGORITHM = "MD5withRSA";
    /** * 常量0 */
    private static final int ZERO = 0;
    /** * RSA最大加密明文最大大小 */
    private static final int MAX_ENCRYPT_BLOCK = 117;
    /** * RSA最大解密密文最大大小 * 當密鑰位數為1024時,解密密文最大是 128 * 當密鑰位數為2048時需要改為 256 不然會報錯（Decryption error） */
    private static final int MAX_DECRYPT_BLOCK = 128;
    /** * 默認key大小 */
    private static final int DEFAULT_KEY_SIZE = 1024;

    /** * 生成密鑰對(公鑰和私鑰) * * @return * @throws Exception */
    public static Map<String, Object> initKey() throws Exception {
        return initKey(DEFAULT_KEY_SIZE);
    }

    /** * 生成密鑰對(公鑰和私鑰) * * @return * @throws Exception */
    public static Map<String, Object> initKey(int keySize) throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        keyPairGen.initialize(keySize);
        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;
    }


    /** * 公鑰加密 * * @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);
        return encrypt(data, KeyFactory.getInstance(KEY_ALGORITHM), keyFactory.generatePublic(x509KeySpec));
    }


    /** * 私鑰加密 * * @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);
        return encrypt(data, keyFactory, privateK);
    }


    /** * 私鑰解密 * * @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);
        return decrypt(encryptedData, keyFactory, keyFactory.generatePrivate(pkcs8KeySpec));
    }


    /** * 公鑰解密 * * @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);
        return decrypt(encryptedData, keyFactory, publicK);

    }


    /** * 用私鑰對信息生成數字簽名 * * @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());
    }


    /** * 校驗數字簽名 * * @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));
    }


    /** * 獲取私鑰 * * @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());
    }


    /** * 獲取公鑰 * * @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());
    }

    /** * 解密公共方法 */
    private static byte[] decrypt(byte[] data, KeyFactory keyFactory, Key key) throws Exception {

        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, key);
        return encryptAndDecrypt(data, cipher, MAX_DECRYPT_BLOCK);
    }

    /** * 加密公共方法 */
    private static byte[] encrypt(byte[] data, KeyFactory keyFactory, Key key) throws Exception {
        // 對數據加密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, key);
        return encryptAndDecrypt(data, cipher, MAX_ENCRYPT_BLOCK);
    }


    /** * 加密解密分段處理公共方法 */
    private static byte[] encryptAndDecrypt(byte[] data, Cipher cipher, int maxSize) throws Exception {
        int inputLen = data.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = ZERO;
        byte[] cache;
        int i = ZERO;
        // 對數據分段加密
        while (inputLen - offSet > ZERO) {
            if (inputLen - offSet > maxSize) {
                cache = cipher.doFinal(data, offSet, maxSize);
            } else {
                cache = cipher.doFinal(data, offSet, inputLen - offSet);
            }
            out.write(cache, ZERO, cache.length);
            i++;
            offSet = i * maxSize;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }

}

分段加解密使用示例

public static void main(String[] args) throws Exception {
        //生成公鑰與私鑰
        Map<String, Object> initKeyMap = RSAUtils.initKey(1024);
        //公鑰
        String publicKey = RSAUtils.getPublicKey(initKeyMap);
        //私鑰
        String privateKey = RSAUtils.getPrivateKey(initKeyMap);
        System.out.println("公鑰 長度: " + publicKey.length() + " 值: " + publicKey);
        System.out.println("私鑰 長度: " + privateKey.length() + " 值: " + privateKey);

        StringBuilder str = new StringBuilder();
        for (int i = 0; i < 2000; i++) {
            str.append("我愛祖國|");
        }


        byte[] bytes1 = RSAUtils.encryptByPublicKey(str.toString().getBytes(), publicKey);
        byte[] bytes2 = RSAUtils.decryptByPrivateKey(bytes1, privateKey);

        System.out.println();
        System.out.println("****** 公鑰加密 私鑰解密 start ******");
        System.out.println("加密前長度 ：" + str.toString().length());
        System.out.println("加密后 ：" + Base64.encodeBase64String(bytes1));
        System.out.println("解密后 ：" + new String(bytes2));
        System.out.println("解密后長度 ：" + new String(bytes2).length());
        System.out.println("****** 公鑰加密 私鑰解密 end ******");

        System.out.println();
        byte[] bytes3 = RSAUtils.encryptByPrivateKey(str.toString().getBytes(), privateKey);
        byte[] bytes4 = RSAUtils.decryptByPublicKey(bytes3, publicKey);

        System.out.println("****** 私鑰加密 公鑰解密 start ******");
        System.out.println("加密前長度 ：" + str.toString().length());
        System.out.println("加密后 ：" + Base64.encodeBase64String(bytes3));
        System.out.println("解密后 ：" + new String(bytes4));
        System.out.println("解密后長度 ：" + new String(bytes4).length());
        System.out.println("****** 私鑰加密 公鑰解密 end ******");


    }

結果示例

RSA加簽與驗簽

  public static void main(String[] args) throws Exception {
        //生成公鑰與私鑰
        Map<String, Object> initKeyMap = RSAUtils.initKey(1024);
        //公鑰
        String publicKey = RSAUtils.getPublicKey(initKeyMap);
        //私鑰
        String privateKey = RSAUtils.getPrivateKey(initKeyMap);
        System.out.println("公鑰 長度: " + publicKey.length() + " 值: " + publicKey);
        System.out.println("私鑰 長度: " + privateKey.length() + " 值: " + privateKey);

        StringBuilder str = new StringBuilder();
        for (int i = 0; i < 2000; i++) {
            str.append("我愛祖國|");
        }

        //加簽
        String sign = RSAUtils.sign(str.toString().getBytes(), privateKey);
        //驗簽
        boolean verify = RSAUtils.verify(str.toString().getBytes(), publicKey, sign);

        System.out.println();
        System.out.println("****** 加簽 start ******");
        System.out.println("簽名 sign: " + sign);
        System.out.println("驗簽結果: " + verify);
        System.out.println("****** 加簽 end ******");

    }

結果示例