RSA加密图片出错

Question

这个问题搞了好几天了，还是没弄出来，代码如下：
[code="java"]
import javax.crypto.Cipher;
import java.security.*;
import java.security.spec.RSAPublicKeySpec;
import java.security.spec.RSAPrivateKeySpec;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.io.*;
import java.math.BigInteger;

public class RSAUtil {

/**
 * 生成密钥对
 * @return KeyPair
 * @throws EncryptException
 */
public static KeyPair generateKeyPair() throws Exception {
    try {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
        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;
       } 
    finally{}
}
/**
 * 生成公钥
 * @param modulus
 * @param publicExponent
 * @return RSAPublicKey
 * @throws EncryptException
 */
public static RSAPublicKey generateRSAPublicKey(byte[] modulus, byte[] publicExponent) throws Exception {
    KeyFactory keyFac = null;
    try {
        keyFac = KeyFactory.getInstance("RSA");
    } catch (NoSuchAlgorithmException ex) {
        throw new Exception(ex.getMessage());
    }

    RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger(modulus), new BigInteger(publicExponent));
    try {
        return (RSAPublicKey) keyFac.generatePublic(pubKeySpec);
    }  finally{}
}
/**
 * 生成私钥
 * @param modulus
 * @param privateExponent
 * @return RSAPrivateKey
 * @throws EncryptException
 */
public static RSAPrivateKey generateRSAPrivateKey(byte[] modulus, byte[] privateExponent) throws Exception {
    KeyFactory keyFac = null;
    try {
        keyFac = KeyFactory.getInstance("RSA");
    } catch (NoSuchAlgorithmException ex) {
        throw new Exception(ex.getMessage());
    }

    RSAPrivateKeySpec priKeySpec = new RSAPrivateKeySpec(new BigInteger(modulus), new BigInteger(privateExponent));
    try {
        return (RSAPrivateKey) keyFac.generatePrivate(priKeySpec);
    }  finally{}
}
/**
 * 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 EncryptException
 */
public static byte[] encrypt(Key key, byte[] data) throws Exception {
    try {
        Cipher cipher = Cipher.getInstance("RSA");
        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;
    } 
    finally{}
}
/**
 * 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 EncryptException
 */
public static byte[] decrypt(Key key, byte[] raw) throws Exception {
    try {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, key);
        int blockSize = cipher.getBlockSize();
        ByteArrayOutputStream bout = new ByteArrayOutputStream(64);
        int j = 0;

        while (raw.length - j * blockSize > 0) {
            if (raw.length - j * blockSize > blockSize)
                bout.write(cipher.doFinal(raw, j * blockSize, blockSize));
            else
                bout.write(cipher.doFinal(raw, j * blockSize, raw.length - j * blockSize));

            j++;
        }

        return bout.toByteArray();
    }  finally{}
}
/**
 *
 * @param args
 * @throws Exception
 */
public static void main(String[] args) throws Exception {
    File file=null;
    FileInputStream in = new FileInputStream("d:/MyPhoto.jpg");
    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();
    RSAPublicKey recoveryPubKey = RSAUtil.generateRSAPublicKey(pubModBytes,pubPubExpBytes);
    byte[] raw = RSAUtil.encrypt(priKey, orgData);
    file = new File("d:/Photo.dat");
    OutputStream out = new FileOutputStream(file);
    out.write(raw);
    out.close();
    byte[] data = RSAUtil.decrypt(recoveryPubKey, raw);
    file = new File("d:/Photo.jpg");
    out = new FileOutputStream(file);
    out.write(data);
    out.flush();
    out.close();

}

}
[/code]

在MyEclipse运行时错误提示为：
Exception in thread "main" java.lang.ArithmeticException: / by zero
at RSA.RSAUtil.encrypt(RSAUtil.java:84)
at RSA.RSAUtil.main(RSAUtil.java:152)

希望有人能给解决一下，先谢谢了

Answer 1

因为不是基础的算法，所以得到的blockSize=0
[quote]int blockSize = cipher.getBlockSize(); [/quote]

可以参考http://binglanhuoli.iteye.com/blog/347692 来实现。