公钥私解和私钥公解的应用RSA的加密
/**
?* RSA 工具类。提供加密，解密，生成密钥对等方法。
?* 需要到http://www.bouncycastle.org下载bcprov-jdk14-123.jar。
?* RSA加密原理概述?
?* RSA的安全性依赖于大数的分解，公钥和私钥都是两个大素数（大于100的十进制位）的函数。?
?* 据猜测，从一个密钥和密文推断出明文的难度等同于分解两个大素数的积?
?* ===================================================================?
?* （该算法的安全性未得到理论的证明）?
?* ===================================================================?
?* 密钥的产生：?
?* 1.选择两个大素数 p,q ,计算 n=p*q;?
?* 2.随机选择加密密钥 e ,要求 e 和 (p-1)*(q-1)互质?
?* 3.利用 Euclid 算法计算解密密钥 d , 使其满足 e*d = 1(mod(p-1)*(q-1)) (其中 n,d 也要互质)?
?* 4:至此得出公钥为 (n,e) 私钥为 (n,d)?
?* ===================================================================?
?* 加解密方法：?
?* 1.首先将要加密的信息 m(二进制表示) 分成等长的数据块 m1,m2,...,mi 块长 s(尽可能大) ,其中 2^s<n?
?* 2:对应的密文是： ci = mi^e(mod n)?
?* 3:解密时作如下计算： mi = ci^d(mod n)?
?* ===================================================================?
?* RSA速度?
?* 由于进行的都是大数计算，使得RSA最快的情况也比DES慢上100倍，无论 是软件还是硬件实现。?
?* 速度一直是RSA的缺陷。一般来说只用于少量数据 加密。
?*文件名：RSAUtil.java<br>
?*@author 董利伟<br>
?*版本:<br>
?*描述：<br>
?*创建时间:2008-9-23 下午09:58:16<br>
?*文件描述：<br>
?*修改者：<br>
?*修改日期：<br>
?*修改描述：<br>
?*/
public class RSAUtil {
?//密钥对
?private KeyPair keyPair = null;
?
?/**
? * 初始化密钥对
? */
?public RSAUtil(){
??try {
???this.keyPair = this.generateKeyPair();
??} catch (Exception e) {
???e.printStackTrace();
??}
?}
?
?/**
?* 生成密钥对
?* @return KeyPair
?* @throws Exception
?*/
?private KeyPair generateKeyPair() throws Exception {
??try {
???KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA",new org.bouncycastle.jce.provider.BouncyCastleProvider());
???//这个值关系到块加密的大小，可以更改，但是不要太大，否则效率会低
???final int KEY_SIZE = 1024;
???keyPairGen.initialize(KEY_SIZE, new SecureRandom());
???KeyPair keyPair = keyPairGen.genKeyPair();
???return keyPair;
??} catch (Exception e) {
???throw new Exception(e.getMessage());
??}
?
?}
?/**
?* 生成公钥
?* @param modulus
?* @param publicExponent
?* @return RSAPublicKey
?* @throws Exception
?*/
?private RSAPublicKey generateRSAPublicKey(byte[] modulus, byte[] publicExponent) throws Exception {
?
??KeyFactory keyFac = null;
??try {
???keyFac = KeyFactory.getInstance("RSA", new org.bouncycastle.jce.provider.BouncyCastleProvider());
??} catch (NoSuchAlgorithmException ex) {
??throw new Exception(ex.getMessage());
??}
??RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger(modulus), new BigInteger(publicExponent));
??try {
???return (RSAPublicKey) keyFac.generatePublic(pubKeySpec);
??} catch (InvalidKeySpecException ex) {
???throw new Exception(ex.getMessage());
??}
?
?}
?/**
?* 生成私钥
?* @param modulus
?* @param privateExponent
?* @return RSAPrivateKey
?* @throws Exception
?*/
?private RSAPrivateKey generateRSAPrivateKey(byte[] modulus, byte[] privateExponent) throws Exception {
??KeyFactory keyFac = null;
??try {
???keyFac = KeyFactory.getInstance("RSA", new org.bouncycastle.jce.provider.BouncyCastleProvider());
??} catch (NoSuchAlgorithmException ex) {
???throw new Exception(ex.getMessage());
??}
??RSAPrivateKeySpec priKeySpec = new RSAPrivateKeySpec(new BigInteger(modulus), new BigInteger(privateExponent));
??try {
???return (RSAPrivateKey) keyFac.generatePrivate(priKeySpec);
??} catch (InvalidKeySpecException ex) {
???throw new Exception(ex.getMessage());
??}
?}
?/**
?* 加密
?* @param key 加密的密钥
?* @param data 待加密的明文数据
?* @return 加密后的数据
?* @throws Exception
?*/
?public byte[] encrypt(Key key, byte[] data) throws Exception {
??try {
???Cipher cipher = Cipher.getInstance("RSA", new org.bouncycastle.jce.provider.BouncyCastleProvider());
???cipher.init(Cipher.ENCRYPT_MODE, key);
???//获得加密块大小，如:加密前数据为128个byte，而key_size=1024 加密块大小为127 byte,加密后为128个byte;
???//因此共有2个加密块，第一个127 byte第二个为1个byte
???int blockSize = cipher.getBlockSize();
???int outputSize = cipher.getOutputSize(data.length);//获得加密块加密后块大小
???int leavedSize = data.length % blockSize;
???int blocksSize = leavedSize != 0 ? data.length / blockSize + 1 : data.length / blockSize;
???byte[] raw = new byte[outputSize * blocksSize];
???int i = 0;
???while (data.length - i * blockSize > 0) {
????if (data.length - i * blockSize > blockSize)
????cipher.doFinal(data, i * blockSize, blockSize, raw, i * outputSize);
????else
????cipher.doFinal(data, i * blockSize, data.length - i * blockSize, raw, i * outputSize);
????//这里面doUpdate方法不可用，查看源代码后发现每次doUpdate后并没有什么实际动作除了把byte[]放到ByteArrayOutputStream中
????//，而最后doFinal的时候才将所有的byte[]进行加密，可是到了此时加密块大小很可能已经超出了OutputSize所以只好用dofinal方法。
????i++;
???}
???return raw;
??} catch (Exception e) {
??throw new Exception(e.getMessage());
??}
?}
?/**
?* 解密
?* @param key 解密的密钥
?* @param raw 已经加密的数据
?* @return 解密后的明文
?* @throws Exception
?*/
?public byte[] decrypt(Key key, byte[] raw) throws Exception {
??try {
???Cipher cipher = Cipher.getInstance("RSA", new org.bouncycastle.jce.provider.BouncyCastleProvider());
???cipher.init(cipher.DECRYPT_MODE, key);
???int blockSize = cipher.getBlockSize();
???ByteArrayOutputStream bout = new ByteArrayOutputStream(64);
???int j = 0;
???while (raw.length - j * blockSize > 0) {
????bout.write(cipher.doFinal(raw, j * blockSize, blockSize));
????j++;
???}
???return bout.toByteArray();
??} catch (Exception e) {
???throw new Exception(e.getMessage());
??}
?}
?
?/**
? * 返回公钥
? * @return
? * @throws Exception
? */
?public RSAPublicKey getRSAPublicKey() throws Exception{
??
??//获取公钥
??RSAPublicKey pubKey = (RSAPublicKey) keyPair.getPublic();
??//获取公钥系数(字节数组形式)
??byte[] pubModBytes = pubKey.getModulus().toByteArray();
??//返回公钥公用指数(字节数组形式)
??byte[] pubPubExpBytes = pubKey.getPublicExponent().toByteArray();
??//生成公钥
??RSAPublicKey recoveryPubKey = this.generateRSAPublicKey(pubModBytes,pubPubExpBytes);
??return recoveryPubKey;
?}
?
?/**
? * 获取私钥
? * @return
? * @throws Exception
? */
?public RSAPrivateKey getRSAPrivateKey() throws Exception{
??
??//获取私钥
??RSAPrivateKey priKey = (RSAPrivateKey) keyPair.getPrivate();
??//返回私钥系数(字节数组形式)
??byte[] priModBytes = priKey.getModulus().toByteArray();
??//返回私钥专用指数(字节数组形式)
??byte[] priPriExpBytes = priKey.getPrivateExponent().toByteArray();
??//生成私钥
??RSAPrivateKey recoveryPriKey = this.generateRSAPrivateKey(priModBytes,priPriExpBytes);
??return recoveryPriKey;
?}
?
?
?/**
?* 测试
?* @param args
?* @throws Exception
?*/
?public static void main(String[] args) throws Exception {
??
??RSAUtil rsa = new RSAUtil();
??String str = "董利伟";
??RSAPublicKey pubKey = rsa.getRSAPublicKey();
??RSAPrivateKey priKey = rsa.getRSAPrivateKey();
??System.out.println("加密后==" + new String(rsa.encrypt(pubKey,str.getBytes())));
??System.out.println("解密后==" + new String(rsa.decrypt(priKey, rsa.encrypt(pubKey,str.getBytes()))));
?}
}
