背景
RSA加密明文最大长度117字节，解密要求密文最大长度为128字节，所以过长数据在加密和解密的过程中需要分块进行。
RSA加密对明文的长度是有限制的，如果加密数据过大会抛出如下异常：
Exception in thread “main” javax.crypto.IllegalBlockSizeException: Data must not be longer than 117 bytes
实际使用说明
项目中使用加密，一般情况主要有两种目的
第一种：数据不可见，直接使用密文传输
第二种：数据可见，但是接收方需要验签名，防止数据被篡改。
综上：
一般情况下，使用加签防止数据篡改就可以适应绝大数的需求了，第一种方式加密传输，如果数据比较大可能会超出最大限制,而且加密耗时长，使用加签，验签方式速度较快，也是业界比较流行的数据传输安全方式。
RSA超出最大限制解决之分段加解密
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公钥/私钥/签名工具包
* 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
*
* @author 码农猿
*/
public class RSAUtils {
/**
* 加密算法RSA
*/
private static final String KEY_ALGORITHM = "RSA";
/**
* 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";
/**
* 签名算法
*/
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
* 当密钥位数为1024时,解密密文最大是 128
* 当密钥位数为2048时需要改为 256 不然会报错（Decryption error）
*/
private static final int MAX_DECRYPT_BLOCK = 128;
/**
* 默认key大小
*/
private static final int DEFAULT_KEY_SIZE = 1024;
/**
* 生成密钥对(公钥和私钥)
*
* @return
* @throws Exception
*/
public static Map<String, Object> initKey() throws Exception {
return initKey(DEFAULT_KEY_SIZE);
}
/**
* 生成密钥对(公钥和私钥)
*
* @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;
}
/**
* 公钥加密
*
* @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);
return encrypt(data, KeyFactory.getInstance(KEY_ALGORITHM), keyFactory.generatePublic(x509KeySpec));
}
/**
* 私钥加密
*
* @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);
return encrypt(data, keyFactory, privateK);
}
/**
* 私钥解密
*
* @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);
return decrypt(encryptedData, keyFactory, keyFactory.generatePrivate(pkcs8KeySpec));
}
/**
* 公钥解密
*
* @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);
return decrypt(encryptedData, keyFactory, publicK);
}
/**
* 用私钥对信息生成数字签名
*
* @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());
}
/**
* 校验数字签名
*
* @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));
}
/**
* 获取私钥
*
* @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());
}
/**
* 获取公钥
*
* @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());
}
/**
* 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 {
// 对数据加密
Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
cipher.init(Cipher.ENCRYPT_MODE, key);
return encryptAndDecrypt(data, cipher, MAX_ENCRYPT_BLOCK);
}
/**
* 加密解密分段处理公共方法
*/
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;
// 对数据分段加密
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 {
//生成公钥与私钥
Map<String, Object> initKeyMap = RSAUtils.initKey(1024);
//公钥
String publicKey = RSAUtils.getPublicKey(initKeyMap);
//私钥
String privateKey = RSAUtils.getPrivateKey(initKeyMap);
System.out.println("公钥 长度: " + publicKey.length() + " 值: " + publicKey);
System.out.println("私钥 长度: " + privateKey.length() + " 值: " + privateKey);
StringBuilder str = new StringBuilder();
for (int i = 0; i < 2000; i++) {
str.append("我爱祖国|");
}
byte[] bytes1 = RSAUtils.encryptByPublicKey(str.toString().getBytes(), publicKey);
byte[] bytes2 = RSAUtils.decryptByPrivateKey(bytes1, privateKey);
System.out.println();
System.out.println("****** 公钥加密 私钥解密 start ******");
System.out.println("加密前长度 ：" + str.toString().length());
System.out.println("加密后 ：" + Base64.encodeBase64String(bytes1));
System.out.println("解密后 ：" + new String(bytes2));
System.out.println("解密后长度 ：" + new String(bytes2).length());
System.out.println("****** 公钥加密 私钥解密 end ******");
System.out.println();
byte[] bytes3 = RSAUtils.encryptByPrivateKey(str.toString().getBytes(), privateKey);
byte[] bytes4 = RSAUtils.decryptByPublicKey(bytes3, publicKey);
System.out.println("****** 私钥加密 公钥解密 start ******");
System.out.println("加密前长度 ：" + str.toString().length());
System.out.println("加密后 ：" + Base64.encodeBase64String(bytes3));
System.out.println("解密后 ：" + new String(bytes4));
System.out.println("解密后长度 ：" + new String(bytes4).length());
System.out.println("****** 私钥加密 公钥解密 end ******");
}
结果示例
RSA加签与验签
public static void main(String[] args) throws Exception {
//生成公钥与私钥
Map<String, Object> initKeyMap = RSAUtils.initKey(1024);
//公钥
String publicKey = RSAUtils.getPublicKey(initKeyMap);
//私钥
String privateKey = RSAUtils.getPrivateKey(initKeyMap);
System.out.println("公钥 长度: " + publicKey.length() + " 值: " + publicKey);
System.out.println("私钥 长度: " + privateKey.length() + " 值: " + privateKey);
StringBuilder str = new StringBuilder();
for (int i = 0; i < 2000; i++) {
str.append("我爱祖国|");
}
//加签
String sign = RSAUtils.sign(str.toString().getBytes(), privateKey);
//验签
boolean verify = RSAUtils.verify(str.toString().getBytes(), publicKey, sign);
System.out.println();
System.out.println("****** 加签 start ******");
System.out.println("签名 sign: " + sign);
System.out.println("验签结果: " + verify);
System.out.println("****** 加签 end ******");
}
结果示例
