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import javax.crypto.Cipher;

import java.security.*;

import java.security.spec.RSAPublicKeySpec;

import java.security.spec.RSAPrivateKeySpec;

import java.security.spec.InvalidKeySpecException;

import java.security.interfaces.RSAPrivateKey;

import java.security.interfaces.RSAPublicKey;

import java.io.*;

import java.math.BigInteger;

/**

* RSA 工具類。提供加密，解密，生成密62616964757a686964616fe59b9ee7ad9431333234326339鑰對等方法。

* 需要到http://www.bouncycastle.org下載bcprov-jdk14-123.jar。

* @author xiaoyusong

* mail: xiaoyusong@etang.com

* msn:xiao_yu_song@hotmail.com

* @since 2004-5-20

*

*/

public class RSAUtil {

/**

* 生成密鑰對

* @return KeyPair

* @throws EncryptException

*/

public static KeyPair generateKeyPair() throws EncryptException {

try {

KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA",

new org.bouncycastle.jce.provider.BouncyCastleProvider());

final int KEY_SIZE = 1024;//沒什么好說的了，這個值關系到塊加密的大小，可以更改，但是不要太大，否則效率會低

keyPairGen.initialize(KEY_SIZE, new SecureRandom());

KeyPair keyPair = keyPairGen.genKeyPair();

return keyPair;

} catch (Exception e) {

throw new EncryptException(e.getMessage());

}

}

/**

* 生成公鑰

* @param modulus

* @param publicExponent

* @return RSAPublicKey

* @throws EncryptException

*/

public static RSAPublicKey generateRSAPublicKey(byte[] modulus, byte[] publicExponent) throws EncryptException {

KeyFactory keyFac = null;

try {

keyFac = KeyFactory.getInstance("RSA", new org.bouncycastle.jce.provider.BouncyCastleProvider());

} catch (NoSuchAlgorithmException ex) {

throw new EncryptException(ex.getMessage());

}

RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger(modulus), new BigInteger(publicExponent));

try {

return (RSAPublicKey) keyFac.generatePublic(pubKeySpec);

} catch (InvalidKeySpecException ex) {

throw new EncryptException(ex.getMessage());

}

}

/**

* 生成私鑰

* @param modulus

* @param privateExponent

* @return RSAPrivateKey

* @throws EncryptException

*/

public static RSAPrivateKey generateRSAPrivateKey(byte[] modulus, byte[] privateExponent) throws EncryptException {

KeyFactory keyFac = null;

try {

keyFac = KeyFactory.getInstance("RSA", new org.bouncycastle.jce.provider.BouncyCastleProvider());

} catch (NoSuchAlgorithmException ex) {

throw new EncryptException(ex.getMessage());

}

RSAPrivateKeySpec priKeySpec = new RSAPrivateKeySpec(new BigInteger(modulus), new BigInteger(privateExponent));

try {

return (RSAPrivateKey) keyFac.generatePrivate(priKeySpec);

} catch (InvalidKeySpecException ex) {

throw new EncryptException(ex.getMessage());

}

}

/**

* 加密

* @param key 加密的密鑰

* @param data 待加密的明文數據

* @return 加密后的數據

* @throws EncryptException

*/

public static byte[] encrypt(Key key, byte[] data) throws EncryptException {

try {

Cipher cipher = Cipher.getInstance("RSA", new org.bouncycastle.jce.provider.BouncyCastleProvider());

cipher.init(Cipher.ENCRYPT_MODE, key);

int blockSize = cipher.getBlockSize();//獲得加密塊大小，如：加密前數據為128個byte，而key_size=1024 加密塊大小為127 byte,加密后為128個byte;因此共有2個加密塊，第一個127 byte第二個為1個byte

int outputSize = cipher.getOutputSize(data.length);//獲得加密塊加密后塊大小

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);

//這里面doUpdate方法不可用，查看源代碼后發現每次doUpdate后并沒有什么實際動作除了把byte[]放到ByteArrayOutputStream中，而最后doFinal的時候才將所有的byte[]進行加密，可是到了此時加密塊大小很可能已經超出了OutputSize所以只好用dofinal方法。

i++;

}

return raw;

} catch (Exception e) {

throw new EncryptException(e.getMessage());

}

}

/**

* 解密

* @param key 解密的密鑰

* @param raw 已經加密的數據

* @return 解密后的明文

* @throws EncryptException

*/

public static byte[] decrypt(Key key, byte[] raw) throws EncryptException {

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 EncryptException(e.getMessage());

}

}

/**

*

* @param args

* @throws Exception

*/

public static void main(String[] args) throws Exception {

File file = new File("test.html");

FileInputStream in = new FileInputStream(file);

ByteArrayOutputStream bout = new ByteArrayOutputStream();

byte[] tmpbuf = new byte[1024];

int count = 0;

while ((count = in.read(tmpbuf)) != -1) {

bout.write(tmpbuf, 0, count);

tmpbuf = new byte[1024];

}

in.close();

byte[] orgData = bout.toByteArray();

KeyPair keyPair = RSAUtil.generateKeyPair();

RSAPublicKey pubKey = (RSAPublicKey) keyPair.getPublic();

RSAPrivateKey priKey = (RSAPrivateKey) keyPair.getPrivate();

byte[] pubModBytes = pubKey.getModulus().toByteArray();

byte[] pubPubExpBytes = pubKey.getPublicExponent().toByteArray();

byte[] priModBytes = priKey.getModulus().toByteArray();

byte[] priPriExpBytes = priKey.getPrivateExponent().toByteArray();

RSAPublicKey recoveryPubKey = RSAUtil.generateRSAPublicKey(pubModBytes,pubPubExpBytes);

RSAPrivateKey recoveryPriKey = RSAUtil.generateRSAPrivateKey(priModBytes,priPriExpBytes);

byte[] raw = RSAUtil.encrypt(priKey, orgData);

file = new File("encrypt_result.dat");

OutputStream out = new FileOutputStream(file);

out.write(raw);

out.close();

byte[] data = RSAUtil.decrypt(recoveryPubKey, raw);

file = new File("decrypt_result.html");

out = new FileOutputStream(file);

out.write(data);

out.flush();

out.close();

}

}

http://book.77169.org/data/web5409/20050328/20050328__3830259.html

這個行吧

http://soft.zdnet.com.cn/software_zone/2007/0925/523319.shtml

再參考這個吧

http://topic.csdn.net/t/20040427/20/3014655.html

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