最近有一个外部合作项目要求在数据传输过程中使用RSA加密算法对数据进行加密，所以需要编写一个加解密的工具类，因为对方不是java语言，所以是各自实现的这个工具，实现了一个加解密的工具。
package org.dreams.transaction.rsa;
import org.apache.commons.codec.binary.Base64;
import org.apache.commons.io.IOUtils;
import javax.crypto.Cipher;
import java.io.ByteArrayOutputStream;
import java.security.*;
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 java.util.HashMap;
import java.util.Map;
public class RSAUtils {
public static final String CHARSET = "UTF-8";
public static final String RSA_ALGORITHM = "RSA";
public static Map<String, String> createKeys(int keySize) {
//为RSA算法创建一个KeyPairGenerator对象
KeyPairGenerator kpg;
try {
kpg = KeyPairGenerator.getInstance(RSA_ALGORITHM);
} catch (NoSuchAlgorithmException e) {
throw new IllegalArgumentException("No such algorithm-->[" + RSA_ALGORITHM + "]");
}
//初始化KeyPairGenerator对象,密钥长度
kpg.initialize(keySize);
//生成密匙对
KeyPair keyPair = kpg.generateKeyPair();
//得到公钥
Key publicKey = keyPair.getPublic();
String publicKeyStr = Base64.encodeBase64URLSafeString(publicKey.getEncoded());
//得到私钥
Key privateKey = keyPair.getPrivate();
String privateKeyStr = Base64.encodeBase64URLSafeString(privateKey.getEncoded());
Map<String, String> keyPairMap = new HashMap<String, String>();
keyPairMap.put("publicKey", publicKeyStr);
keyPairMap.put("privateKey", privateKeyStr);
return keyPairMap;
}
/**
* 得到公钥
*
* @param publicKey 密钥字符串（经过base64编码）
* @throws Exception
*/
public static RSAPublicKey getPublicKey(String publicKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
//通过X509编码的Key指令获得公钥对象
KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(Base64.decodeBase64(publicKey));
RSAPublicKey key = (RSAPublicKey) keyFactory.generatePublic(x509KeySpec);
return key;
}
/**
* 得到私钥
*
* @param privateKey 密钥字符串（经过base64编码）
* @throws Exception
*/
public static RSAPrivateKey getPrivateKey(String privateKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
//通过PKCS#8编码的Key指令获得私钥对象
KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(Base64.decodeBase64(privateKey));
RSAPrivateKey key = (RSAPrivateKey) keyFactory.generatePrivate(pkcs8KeySpec);
return key;
}
/**
* 公钥加密
*
* @param data
* @param publicKey
* @return
*/
public static String publicEncrypt(String data, RSAPublicKey publicKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET), publicKey.getModulus().bitLength()));
} catch (Exception e) {
throw new RuntimeException("加密字符串[" + data + "]时遇到异常", e);
}
}
/**
* 私钥解密
*
* @param data
* @param privateKey
* @return
*/
public static String privateDecrypt(String data, RSAPrivateKey privateKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, privateKey);
return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data), privateKey.getModulus().bitLength()), CHARSET);
} catch (Exception e) {
throw new RuntimeException("解密字符串[" + data + "]时遇到异常", e);
}
}
/**
* 私钥加密
*
* @param data
* @param privateKey
* @return
*/
public static String privateEncrypt(String data, RSAPrivateKey privateKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET), privateKey.getModulus().bitLength()));
} catch (Exception e) {
throw new RuntimeException("加密字符串[" + data + "]时遇到异常", e);
}
}
/**
* 公钥解密
*
* @param data
* @param publicKey
* @return
*/
public static String publicDecrypt(String data, RSAPublicKey publicKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, publicKey);
return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data), publicKey.getModulus().bitLength()), CHARSET);
} catch (Exception e) {
throw new RuntimeException("解密字符串[" + data + "]时遇到异常", e);
}
}
private static byte[] rsaSplitCodec(Cipher cipher, int opmode, byte[] datas, int keySize) {
int maxBlock = 0;
if (opmode == Cipher.DECRYPT_MODE) {
maxBlock = keySize / 8;
} else {
maxBlock = keySize / 8 - 11;
}
ByteArrayOutputStream out = new ByteArrayOutputStream();
int offSet = 0;
byte[] buff;
int i = 0;
try {
while (datas.length > offSet) {
if (datas.length - offSet > maxBlock) {
buff = cipher.doFinal(datas, offSet, maxBlock);
} else {
buff = cipher.doFinal(datas, offSet, datas.length - offSet);
}
out.write(buff, 0, buff.length);
i++;
offSet = i * maxBlock;
}
} catch (Exception e) {
throw new RuntimeException("加解密阀值为[" + maxBlock + "]的数据时发生异常", e);
}
byte[] resultDatas = out.toByteArray();
IOUtils.closeQuietly(out);
return resultDatas;
}
public static void main(String[] args) throws Exception {
Map<String, String> keyMap = RSAUtils.createKeys(1024);
String publicKey = keyMap.get("publicKey");
String privateKey = keyMap.get("privateKey");
System.out.println("公钥: \n\r" + publicKey);
System.out.println("私钥： \n\r" + privateKey);
System.out.println("公钥加密 —— 私钥解密");
String str = "对于新兴事物,\n" +
"第一看不见，\n" +
"第二看不起,\n" +
"第三看不懂，\n" +
"第四来不及!";
System.out.println("\r明文：\r\n" + str);
System.out.println("\r明文大小：\r\n" + str.getBytes().length);
String encodedData = RSAUtils.publicEncrypt(str, RSAUtils.getPublicKey(publicKey));
System.out.println("密文：\r\n" + encodedData);
String decodedData = RSAUtils.privateDecrypt(encodedData, RSAUtils.getPrivateKey(privateKey));
System.out.println("解密后文字: \r\n" + decodedData);
}
}
实现基本上就是这样，都是大同小异。
- RSA加密算法对于加密数据的长度是有要求的。一般来说，明文长度小于等于密钥长度（Bytes）-11。解决这个问题需要对较长的明文进行分段加解密，这个上面的代码已经实现了。
- 一旦涉及到双方开发，语言又不相同，不能够采用同一个工具的时候，切记要约定以下内容。
a）约定双方的BASE64编码
b）约定双方分段加解密的方式。我踩的坑也主要是这里，不仅仅是约定大家分段的大小，更重要的是分段加密后的拼装方式。doFinal方法加密完成后得到的仍然是byte[]，因为最终呈现的是编码后的字符串，所以你可以分段加密，分段编码和分段加密，一次编码两种方式（上面的代码采用的是后一种，也推荐采用这一种）。相信我不是所有人的脑回路都一样的，尤其是当他采用的开发语言和你不通时。
