java安全，RSA算法。

一般加密原理是，由用户共有的公共密钥和传输数据的用户直接有的私有密钥组成。每次加密的时候，都是由一定算法随机生成一对密钥，用密钥加密所需加密的文件，用公钥加密密钥，然后将这些一起传输给目标用户，目标用户将数据处理后，又按照此密钥加密，然后传输回去。

这样的优点别人很难破解，网络上的数据无法定位，而且产生的密钥是随机的。

接下来这个例子就是java核心技术卷2高级特性安全性一章的最后一个例子。

import java.io.*;
import java.security.*;
import javax.crypto.*;
import javax.crypto.interfaces.*;
import javax.crypto.spec.*;
public class RSATest ...{

    private static final int KEYSIZE = 512;

    /** *//**
     * @param args
     */
    public static void main(String[] args) ...{
        // TODO Auto-generated method stub
        try...{
            if(args[0].equals("-genkey"))...{
                KeyPairGenerator keyPair = KeyPairGenerator.getInstance("RSA");
                SecureRandom random = new SecureRandom();
                keyPair.initialize(KEYSIZE, random);
                KeyPair keyP = keyPair.generateKeyPair();
                ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(args[1]));
                oos.writeObject(keyP.getPublic());
                oos.close();
                oos = new ObjectOutputStream(new FileOutputStream(args[2]));
                oos.writeObject(keyP.getPrivate());
                oos.close();
            }else if(args[0].equals("-encrypt"))...{
                KeyGenerator keygen = KeyGenerator.getInstance("AES");
                SecureRandom random = new SecureRandom();
                keygen.init(random);
                SecretKey key = keygen.generateKey();
                
                ObjectInputStream kin = new ObjectInputStream(new FileInputStream(args[3]));
                Key publicKey = (Key)kin.readObject();
                kin.close();
                
                Cipher cipher = Cipher.getInstance("RSA");
                System.out.println(cipher.getAlgorithm());
                cipher.init(Cipher.WRAP_MODE,publicKey);
                byte[] wrappedKey = cipher.wrap(key);
                DataOutputStream out = new DataOutputStream(new FileOutputStream(args[2]));
                out.writeInt(wrappedKey.length);
                out.write(wrappedKey);
                
                InputStream in = new FileInputStream(args[1]);
                cipher = Cipher.getInstance("AES");
                cipher.init(Cipher.ENCRYPT_MODE, key);
                crypt(in,out,cipher);
                in.close();
                out.close();
                
            }else...{
                DataInputStream in = new DataInputStream(new FileInputStream(args[1]));
                int length = in.readInt();
                byte []wrappedKey = new byte[length];
                in.read(wrappedKey,0,length);
                
                ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream(args[3]));
                Key privateKey = (Key) keyIn.readObject();
                keyIn.close();
                
                Cipher cipher = Cipher.getInstance("RSA");
                cipher.init(Cipher.UNWRAP_MODE, privateKey);
                Key key = cipher.unwrap(wrappedKey, "AES", Cipher.SECRET_KEY);
                
                OutputStream out = new FileOutputStream(args[2]);
                cipher = Cipher.getInstance("AES");
                cipher.init(Cipher.ENCRYPT_MODE, key);
                crypt(in,out,cipher);
                in.close();
                out.close();
            }
        }catch(Exception e)...{
            e.printStackTrace();
        }
    }

    private static void crypt(InputStream in, OutputStream out, Cipher cipher)throws IOException,GeneralSecurityException ...{
        // TODO Auto-generated method stub
        int blockSize = cipher.getBlockSize();
        int outputSize = cipher.getOutputSize(blockSize);
        byte[] inBytes = new byte[blockSize];
        byte[] outputBytes = new byte[outputSize];
        int inLength = 0;
        boolean more = true;
        while(more)...{
            inLength = in.read(inBytes);
            if(inLength == blockSize)...{
                int outLength = cipher.update(inBytes, 0,blockSize,outputBytes);
                out.write(outputBytes, 0, outLength);
            }else 
                more = false;
        }
        if(inLength>0)
            outputBytes = cipher.doFinal(inBytes, 0, inLength);
        else
            outputBytes = cipher.doFinal();
        out.write(outputBytes);
    }

}

 

运行的时候，先在eclipse里面运行的参数里加上-genkey public.key private.key

生成两个文件，就是用于加密的公钥和私钥。

然后运行的参数里面加上-encrypt textFile encryptedFile public.key对第二个参数对应的文件加密，第三个参数对应的就是生成的加密过的文件。

最后运行-decrypt encryptedFile decryptedFile private.key对文件进行解密。