/**
* 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()))));
}
}