java中RSA加解密的实现

public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
HashMap<String, Object> map = RSAUtils.getKeys();
//生成公钥和私钥
RSAPublicKey publicKey = (RSAPublicKey) map.get("public");
RSAPrivateKey privateKey = (RSAPrivateKey) map.get("private");

//模
String modulus = publicKey.getModulus().toString();
//公钥指数
String public_exponent = publicKey.getPublicExponent().toString();
//私钥指数
String private_exponent = privateKey.getPrivateExponent().toString();
//明文
String ming = "123456789";
//使用模和指数生成公钥和私钥
RSAPublicKey pubKey = RSAUtils.getPublicKey(modulus, public_exponent);
RSAPrivateKey priKey = RSAUtils.getPrivateKey(modulus, private_exponent);
//加密后的密文
String mi = RSAUtils.encryptByPublicKey(ming, pubKey);
System.err.println(mi);
//解密后的明文
ming = RSAUtils.decryptByPrivateKey(mi, priKey);
System.err.println(ming);

}

package yyy.test.rsa;


import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
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 javax.crypto.Cipher;


public class RSAUtils {


/**
* 生成公钥和私钥
* @throws NoSuchAlgorithmException 
*
*/
public static HashMap<String, Object> getKeys() throws NoSuchAlgorithmException{
HashMap<String, Object> map = new HashMap<String, Object>();
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;
}
}