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。