RSA对文件进行加密和解密

package author.estone.rsa;

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 工具类。提供加密，解密，生成密钥对等方法。
 * 
 */
public class RSAUtil {

	/**
	 * 生成密钥对
	 * 
	 * @return KeyPair
	 * @throws
	 */
	public static KeyPair generateKeyPair() {
		try {
			KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA",
					new org.bouncycastle.jce.provider.BouncyCastleProvider());
			final int KEY_SIZE = 1024;// 没什么好说的了，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
			keyPairGen.initialize(KEY_SIZE, new SecureRandom());
			KeyPair keyPair = keyPairGen.genKeyPair();
			return keyPair;
		} catch (Exception e) {
			return null;
		}
	}

	/**
	 * 生成公钥
	 * 
	 * @param modulus
	 * @param publicExponent
	 * @return RSAPublicKey
	 * @throws
	 */
	public static RSAPublicKey generateRSAPublicKey(byte[] modulus,
			byte[] publicExponent) {
		KeyFactory keyFac = null;
		try {
			keyFac = KeyFactory.getInstance("RSA",
					new org.bouncycastle.jce.provider.BouncyCastleProvider());
		} catch (NoSuchAlgorithmException ex) {

		}

		RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger(
				modulus), new BigInteger(publicExponent));
		try {
			return (RSAPublicKey) keyFac.generatePublic(pubKeySpec);
		} catch (InvalidKeySpecException ex) {
			return null;
		}
	}

	/**
	 * 生成私钥
	 * 
	 * @param modulus
	 * @param privateExponent
	 * @return RSAPrivateKey
	 * @throws
	 */
	public static RSAPrivateKey generateRSAPrivateKey(byte[] modulus,
			byte[] privateExponent) {
		KeyFactory keyFac = null;
		try {
			keyFac = KeyFactory.getInstance("RSA",
					new org.bouncycastle.jce.provider.BouncyCastleProvider());
		} catch (NoSuchAlgorithmException ex) {

		}

		RSAPrivateKeySpec priKeySpec = new RSAPrivateKeySpec(new BigInteger(
				modulus), new BigInteger(privateExponent));
		try {
			return (RSAPrivateKey) keyFac.generatePrivate(priKeySpec);
		} catch (InvalidKeySpecException ex) {
			return null;
		}
	}

	/**
	 * 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
	 */
	public static byte[] encrypt(Key key, byte[] data) {
		try {
			Cipher cipher = Cipher.getInstance("RSA",
					new org.bouncycastle.jce.provider.BouncyCastleProvider());
			cipher.init(Cipher.ENCRYPT_MODE, key);
			int blockSize = cipher.getBlockSize();// 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 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) {
			return null;
		}
	}

	/**
	 * 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
	 */
	public static byte[] decrypt(Key key, byte[] raw) {
		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) {
			return null;
		}
	}

	/**
	 * 
	 * @param args
	 * @throws Exception
	 */
	public static void main(String[] args) throws Exception {
		
		// 读取要加密的文件
		File file = new File("d:/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();
		
		// 对数据文件进行加密处理
		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);

		// 对文件进行加密
		byte[] raw = RSAUtil.encrypt(priKey, orgData);
		file = new File("encrypt_result.dat");
		OutputStream out = new FileOutputStream(file);
		out.write(raw);
		out.close();
		
		// 对文件进行解密
		byte[] data = RSAUtil.decrypt(recoveryPubKey, raw);
		file = new File("decrypt_result.html");
		out = new FileOutputStream(file);
		out.write(data);
		out.flush();
		out.close();
	}
}

 code from :

http://code.google.com/p/jsc4/source/browse/trunk/JSC4/src/eticketApplet/RSAUtil.java?spec=svn35&r=35