aesandrsa.txt

高级加密标准（AES）是一个用来代替数据加密标准（DES）的算法。目前使用的一般为128,196和256位密钥

   //讀入AES密鑰
   in = new ObjectInputStream(new FileInputStream("aesKey.txt"));
   Key key = (Key)in.readObject();
   in.close();
   
   //加密AES密鑰
   Cipher cipher = Cipher.getInstance("RSA");
   cipher.init(Cipher.WRAP_MODE,publicKey);
   byte[] wrappedKey = cipher.wrap(key);
   //加密后的AES寫入文件中
   DataOutputStream out = new DataOutputStream(new FileOutputStream("rasDecode.txt"));
   out.writeInt(wrappedKey.length);
   out.write(wrappedKey);
   
   //讀入要加密的文件
   InputStream input = new FileInputStream("encode.txt");
   cipher = Cipher.getInstance("AES");
   cipher.init(Cipher.ENCRYPT_MODE, key);
   //用AES密鑰加密要加密的文件
   AESImpl.crypt(input, out, cipher);
   input.close();
   out.close();
  }catch (Exception e) {
   e.printStackTrace();
  }
 }
 
 public void decode(){
  try{
   //讀入要解密的文件，其中包括用RAS算法加密AES的密鑰內容
   DataInputStream in = new DataInputStream(new FileInputStream("rasDecode.txt"));
   int length = in.readInt();
   byte[] wrappedKey = new byte[length];
   in.read(wrappedKey,0,length);
   
   //讀入RSA的私有密鑰文件
   ObjectInputStream keyIn = new ObjectInputStream(new FileInputStream("privateKey.txt"));
   Key privateKey = (Key)keyIn.readObject();
   keyIn.close();
   
   //用RSA私有密鑰解密加密的AES密鑰
   Cipher cipher = Cipher.getInstance("RSA");
   cipher.init(Cipher.UNWRAP_MODE, privateKey);
   Key key = cipher.unwrap(wrappedKey, "AES", Cipher.SECRET_KEY);
   
   OutputStream out = new FileOutputStream("encode.txt");
   cipher = Cipher.getInstance("AES");
   cipher.init(Cipher.DECRYPT_MODE, key);
   //用解密的AES密鑰解密加密的文件
   AESImpl.crypt(in, out, cipher);
   in.close();
   out.close();
  }catch (Exception e) {
   e.printStackTrace();
  }
 }
 
 public static void main(String[] args){
  RSAImpl _rsa = new RSAImpl();
  //_rsa.createKey();
  //_rsa.encode();
  _rsa.decode();
 }

}



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);
     } 
 
 }