Java 字节数组与String的相互转换错误
- 遇到的问题：Byte[]数组转化为String,String再转化成Byte数组时，两个字节数组长度不一。
- 问题描述：今天我在学习Java实现的RSA加密算法的时候，将加密后的字节数组用String来存储（为了方便查看以及传输），但是在解密的时候却出错了，代码如下：
package com.yufeng.utils;
/**
* Created by Feng on 2016/6/26.
*/
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import java.io.*;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.util.HashMap;
import java.util.Map;
public class RSAUtil2 {
public static final String PUBLIC = "public";
public static final String PRIVATE = "private";
public static Map generator(){
Map result = new HashMap();
try {
KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
KeyPair pair = generator.generateKeyPair();
result.put(PUBLIC, pair.getPublic());
result.put(PRIVATE,pair.getPrivate());
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return result;
}
public static String encrypt(String message, PublicKey publicKey, String enct){
try {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE,publicKey);
byte[] trst= cipher.doFinal(message.getBytes());
System.out.println(trst.length);
return new String(trst,enct);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (BadPaddingException e) {
e.printStackTrace();
} catch (IllegalBlockSizeException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return "";
}
public static String decrypt(String message,PrivateKey key,String enct){
try {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE,key);
System.out.println(message.getBytes().length);
byte[] trst = cipher.doFinal(message.getBytes());
return new String(trst,enct);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (BadPaddingException e) {
e.printStackTrace();
} catch (IllegalBlockSizeException e) {
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return "";
}
public static void main(String[] args) {
Map keyPair = generator();
String message = "test";
String result = encrypt(message, (PublicKey) keyPair.get(PUBLIC), "UTF-8");
System.out.println(result);
System.out.println(decrypt(result, (PrivateKey) keyPair.get(PRIVATE),"UTF-8"));
}
}
其中，我在加密和解密的函数中输出了两个字节数组的长度，结果如下：
3.问题分析：String底层是以Char数组记录的，Byte会转化成Char，因为Char和Byte的长度不同，所以在转化的过程中会对Byte进行整合，主要是用0填充.
4.解决方案：将字节转化为两位BCD码
以下别人是封装好的一个类：
package com.yufeng.utils;
import javax.crypto.Cipher;
import java.math.BigInteger;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.RSAPrivateKeySpec;
import java.security.spec.RSAPublicKeySpec;
import java.util.HashMap;
import java.util.Map;
/**
* Created by Feng on 2016/6/26.
*/
public class RSAUtils {
/**
* 生成公钥和私钥
* @throws NoSuchAlgorithmException
*/
public static HashMap getKeys() throws NoSuchAlgorithmException {
HashMap map = new HashMap();
KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
keyPairGen.initialize(1024);
KeyPair keyPair = keyPairGen.generateKeyPair();
RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
map.put("public", publicKey);
map.put("private", privateKey);
return map;
}
/**
* 使用模和指数生成RSA公钥
* 注意：【此代码用了默认补位方式，为RSA/None/PKCS1Padding，不同JDK默认的补位方式可能不同，如Android默认是RSA
* /None/NoPadding】
*
* @param modulus 模
* @param exponent 指数
* @return
*/
public static RSAPublicKey getPublicKey(String modulus, String exponent) {
try {
BigInteger b1 = new BigInteger(modulus);
BigInteger b2 = new BigInteger(exponent);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
RSAPublicKeySpec keySpec = new RSAPublicKeySpec(b1, b2);
return (RSAPublicKey) keyFactory.generatePublic(keySpec);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
/**
* 使用模和指数生成RSA私钥
* 注意：【此代码用了默认补位方式，为RSA/None/PKCS1Padding，不同JDK默认的补位方式可能不同，如Android默认是RSA
* /None/NoPadding】
*
* @param modulus 模
* @param exponent 指数
* @return
*/
public static RSAPrivateKey getPrivateKey(String modulus, String exponent) {
try {
BigInteger b1 = new BigInteger(modulus);
BigInteger b2 = new BigInteger(exponent);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
RSAPrivateKeySpec keySpec = new RSAPrivateKeySpec(b1, b2);
return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
/**
* 公钥加密
*
* @param data
* @param publicKey
* @return
* @throws Exception
*/
public static String encryptByPublicKey(String data, RSAPublicKey publicKey)
throws Exception {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
// 模长
int key_len = publicKey.getModulus().bitLength() / 8;
// 加密数据长度 <= 模长-11
String[] datas = splitString(data, key_len - 11);
String mi = "";
//如果明文长度大于模长-11则要分组加密
for (String s : datas) {
mi += bcd2Str(cipher.doFinal(s.getBytes()));
}
return mi;
}
/**
* 私钥解密
*
* @param data
* @param privateKey
* @return
* @throws Exception
*/
public static String decryptByPrivateKey(String data, RSAPrivateKey privateKey)
throws Exception {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
//模长
int key_len = privateKey.getModulus().bitLength() / 8;
byte[] bytes = data.getBytes();
byte[] bcd = ASCII_To_BCD(bytes, bytes.length);
System.err.println(bcd.length);
//如果密文长度大于模长则要分组解密
String ming = "";
byte[][] arrays = splitArray(bcd, key_len);
for (byte[] arr : arrays) {
ming += new String(cipher.doFinal(arr));
}
return ming;
}
/**
* ASCII码转BCD码
*/
public static byte[] ASCII_To_BCD(byte[] ascii, int asc_len) {
byte[] bcd = new byte[asc_len / 2];
int j = 0;
for (int i = 0; i < (asc_len + 1) / 2; i++) {
bcd[i] = asc_to_bcd(ascii[j++]);
bcd[i] = (byte) (((j >= asc_len) ? 0x00 : asc_to_bcd(ascii[j++])) + (bcd[i] << 4));
}
return bcd;
}
public static byte asc_to_bcd(byte asc) {
byte bcd;
if ((asc >= '0') && (asc <= '9'))
bcd = (byte) (asc - '0');
else if ((asc >= 'A') && (asc <= 'F'))
bcd = (byte) (asc - 'A' + 10);
else if ((asc >= 'a') && (asc <= 'f'))
bcd = (byte) (asc - 'a' + 10);
else
bcd = (byte) (asc - 48);
return bcd;
}
/**
* BCD转字符串
*/
public static String bcd2Str(byte[] bytes) {
char temp[] = new char[bytes.length * 2], val;
for (int i = 0; i < bytes.length; i++) {
val = (char) (((bytes[i] & 0xf0) >> 4) & 0x0f);
temp[i * 2] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
val = (char) (bytes[i] & 0x0f);
temp[i * 2 + 1] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
}
return new String(temp);
}
/**
* 拆分字符串
*/
public static String[] splitString(String string, int len) {
int x = string.length() / len;
int y = string.length() % len;
int z = 0;
if (y != 0) {
z = 1;
}
String[] strings = new String[x + z];
String str = "";
for (int i = 0; i < x + z; i++) {
if (i == x + z - 1 && y != 0) {
str = string.substring(i * len, i * len + y);
} else {
str = string.substring(i * len, i * len + len);
}
strings[i] = str;
}
return strings;
}
/**
* 拆分数组
*/
public static byte[][] splitArray(byte[] data, int len) {
int x = data.length / len;
int y = data.length % len;
int z = 0;
if (y != 0) {
z = 1;
}
byte[][] arrays = new byte[x + z][];
byte[] arr;
for (int i = 0; i < x + z; i++) {
arr = new byte[len];
if (i == x + z - 1 && y != 0) {
System.arraycopy(data, i * len, arr, 0, y);
} else {
System.arraycopy(data, i * len, arr, 0, len);
}
arrays[i] = arr;
}
return arrays;
}
public static void main(String[] args) throws Exception {
HashMap keyPair = getKeys();
String message = "加密信息";
String result = encryptByPublicKey(message, (RSAPublicKey) keyPair.get("public"));
System.out.println(result);
System.out.println(decryptByPrivateKey(result, (RSAPrivateKey) keyPair.get("private")));
}
} 参考：
http://www.ruanyifeng.com/blog/2007/10/ascii_unicode_and_utf-8.html
http://yuncode.net/code/c_54c21d8781bae60