desencrypt.java

this code implements the DES algorithm for a file in JAVA

package des;


import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;
import java.security.Key; 
import java.security.SecureRandom; 
import javax.crypto.Cipher; 
import javax.crypto.KeyGenerator; 
import javax.swing.JOptionPane;

/** 
* 
* 使用DES加密与解密,可对byte[],String类型进行加密与解密 密文可使用String,byte[]存储. 
* 
* 方法: void getKey(String strKey)从strKey的字条生成一个Key 
* 
* String getEncString(String strMing)对strMing进行加密,返回String密文 String 
* getDesString(String strMi)对strMin进行解密,返回String明文 
* 
* byte[] getEncCode(byte[] byteS)byte[]型的加密 byte[] getDesCode(byte[] 
* byteD)byte[]型的解密 
*/ 

public class DesEncrypt { 
	Key key; 
	/** 
	* 根据参数生成KEY 
	* 
	* @param strKey 
	*/ 
	public void getKey(String strKey) { 
	
		try { 
				KeyGenerator _generator = KeyGenerator.getInstance("DES"); 
				_generator.init(new SecureRandom(strKey.getBytes())); 
				this.key = _generator.generateKey(); 
				_generator = null; 		
		} 
		catch (Exception e) 
		{ 
			e.printStackTrace(); 
		} 
	} 

	/** 
	* 加密String明文输入,String密文输出 
	* 
	* @param strMing 
	* @return 
	*/ 
	public String getEncString(String strMing) { 
		byte[] byteMi = null; 
		byte[] byteMing = null; 
	
		String strMi = ""; 
	
		try { 	
				return byte2hex(getEncCode(strMing.getBytes())); 
	
				// byteMing = strMing.getBytes("UTF8"); 
				// 	byteMi = this.getEncCode(byteMing); 
				// 	strMi = new String( byteMi,"UTF8"); 
		}
		catch (Exception e) 
		{ 
			e.printStackTrace();
		} 
		finally 
		{ 
			byteMing = null;
			byteMi = null;
		} 
		return strMi; 
	} 

	/** 
	* 解密 以String密文输入,String明文输出 
	* 
	* @param strMi 
	* @return 
	*/ 
	public String getDesString(String strMi) { 
		byte[] byteMing = null; 
		byte[] byteMi = null; 
	
		String strMing = ""; 
	
		try { 
	
				return new String(getDesCode(hex2byte(strMi.getBytes()))); 
	
				// byteMing = this.getDesCode(byteMi); 
				// strMing = new String(byteMing,"UTF8"); 
	
		}
		catch (Exception e) 
		{ 
			e.printStackTrace(); 
		}
		finally 
		{ 
			byteMing = null; 
			byteMi = null; 
		} 
	
		return strMing; 

	} 

	/** 
	 	* 加密以byte[]明文输入,byte[]密文输出 
	* 
	* @param byteS 
	* @return 
	*/ 
	private byte[] getEncCode(byte[] byteS) { 
		byte[] byteFina = null; 
		Cipher cipher; 
	
		try { 
				cipher = Cipher.getInstance("DES"); 
				cipher.init(Cipher.ENCRYPT_MODE, key); 
				byteFina = cipher.doFinal(byteS); 
		}
		catch (Exception e) 
		{ 
			e.printStackTrace();
		}
		finally 
		{ 
			cipher = null;
		} 
	
		return byteFina; 

	} 

	/** 
	 	* 解密以byte[]密文输入,以byte[]明文输出 
	* 
	* @param byteD 
	* @return 
	*/ 
	private byte[] getDesCode(byte[] byteD) 
	{ 

		Cipher cipher; 
		byte[] byteFina = null; 

		try { 

				cipher = Cipher.getInstance("DES"); 
				cipher.init(Cipher.DECRYPT_MODE, key); 
				byteFina = cipher.doFinal(byteD); 
		}
		catch (Exception e) 
		{ 
			e.printStackTrace(); 
		}
		finally
		{ 
			cipher = null; 
		} 

		return byteFina; 
	} 

	/** 
	* 二行制转字符串 
	* 
	* @param b 
	* @return 
	*/ 
	public static String byte2hex(byte[] b) 
	{
		// 一个字节的数， 
		// 转成16进制字符串 
		String hs = ""; 
		String stmp = ""; 

		for (int n = 0; n < b.length; n++) 
		{ 
			// 整数转成十六进制表示 
			stmp = (java.lang.Integer.toHexString(b[n] & 0XFF)); 
			if (stmp.length() == 1) 
				hs = hs + "0" + stmp; 
			else 
				hs = hs + stmp; 
		} 
		return hs.toUpperCase(); // 转成大写 
	} 

	public static byte[] hex2byte(byte[] b) 
	{ 
		if ((b.length % 2) != 0) 
			throw new IllegalArgumentException("长度不是偶数"); 
		
		byte[] b2 = new byte[b.length / 2]; 
		
		for (int n = 0; n < b.length; n += 2) 
		{ 
			String item = new String(b, n, 2); 

			// 	两位一组，表示一个字节,把这样表示的16进制字符串，还原成一个进制字节 
			b2[n / 2] = (byte) Integer.parseInt(item, 16); 
		} 
		return b2; 
	} 

	public static void main(String[] args) 
	{ 
		
		System.out.println("hello"); 
		DesEncrypt des = new DesEncrypt(); //实例化一个对像 
		des.getKey("a"); //生成密匙 
		String strEnc,strDes ;
		/*
		String strEnc = des.getEncString("abcdabcd"); //加密字符串,返回String的密文 
		System.out.println(strEnc); 
		String strDes = des.getDesString(strEnc); //把String 类型的密文解密 
		System.out.println(strDes); 
		*/
		//new DesEncrypt(); 
		
		
		FormattedInput in = new FormattedInput();
		int choice = 0;
		
		try
		{
			File inFile ;//= new File("dataToDec.dat");//dataToDec.dat//dataToEnc.dat
			FileInputStream fis ;//= new FileInputStream(inFile);
			BufferedReader d ;//= new BufferedReader (new InputStreamReader(fis));
			String temp = "\0";
			
			File outFile ;//= new File("dataDecrypted.dat");//dataDecrypted.dat//dataEncrypted.dat
			FileOutputStream fos ;//= new  FileOutputStream(outFile);
			DataOutputStream dos ;//= new DataOutputStream (fos);
			
	
			for(;;){
				JOptionPane.showMessageDialog(null,"Enter 1 to encrypt\n"+
						"Enter 2 to decrypt\n"+"Enter 9 to quit","Guide",JOptionPane.INFORMATION_MESSAGE);
				
				try {
					choice = in.readInt("Enter a number");
				}
				catch(Exception e){
					JOptionPane.showMessageDialog(null,e.getMessage()+"\nTry again",
				    		 "Enter your choice",JOptionPane.ERROR_MESSAGE);
					continue;
				}
				switch(choice){
				case 1:
					inFile = new File("dataToEnc.dat");
					fis = new FileInputStream(inFile);
					d = new BufferedReader (new InputStreamReader(fis));
					
					outFile = new File("dataEncrypted.dat");
					fos = new  FileOutputStream(outFile);
					dos = new DataOutputStream (fos);
										
					while(!temp.equals(null))
					{
						temp = d.readLine();
						if(!temp.equals(null))
						{
							strEnc = des.getEncString(temp);
							dos.writeBytes(strEnc+"\r\n");
						}
						

					}

					
					fis.close();
					break;
				case 2:
					inFile = new File("dataToDec.dat");
					fis = new FileInputStream(inFile);
					d = new BufferedReader (new InputStreamReader(fis));
					
					outFile = new File("dataDecrypted.dat");
					fos = new  FileOutputStream(outFile);
					dos = new DataOutputStream (fos);
					
					while(!temp.equals(null))
					{
						temp = d.readLine();
						if(!temp.equals(null))
						{
							strDes = des.getDesString(temp); //把String 类型的密文解密 
							dos.writeBytes(strDes+"\r\n");
						}
		
					}

					fis.close();
					break;
				
				case 9:
					JOptionPane.showMessageDialog(null,"Thank you for your use" ,
							"Ending program",JOptionPane.INFORMATION_MESSAGE);
					return;
				default:
					JOptionPane.showMessageDialog(null,"Invalid selection" ,
							"Error",JOptionPane.ERROR_MESSAGE);
					break;
				}
			}
			
		}
		catch (NullPointerException e)
		{
			if(choice==1) 
				JOptionPane.showMessageDialog(null,"The data has been encrypted." ,
						"Ending program",JOptionPane.INFORMATION_MESSAGE);
			else
				JOptionPane.showMessageDialog(null,"The data has been decrypted." ,
						"Ending program",JOptionPane.INFORMATION_MESSAGE);
				
		}
		catch (EOFException e)
		{
			System.out.println("Empty File.");	
		}
		catch (FileNotFoundException e)
		{
			System.out.println("FileStreamsTest: " + e);
		}
		catch (IOException e)
		{
			System.err.println("FileStreamsTest: " + e);
				
		}

					
	} 

}


//a class for a standard input I define for users including checking the validity of data input
//by users
class FormattedInput{
	private final int MaxStudentNum = 100000;
	public String readString(String str){
		String strInput;
		strInput = JOptionPane.showInputDialog("Please enter "+str);
		return strInput;
	}
	
	public double readDouble(String str){
		String strInput;
		double input = 0;
		int maxTries = 5;
				
		for(;;){
			try{
					strInput = JOptionPane.showInputDialog("Please enter "+str);
			     	input = Double.parseDouble(strInput);
			     	if(input>100000||input<0){
			     		if(--maxTries == 0){
							JOptionPane.showMessageDialog(null,"ERROR INPUT.Terminating...",
						    		 "Enter the number",JOptionPane.ERROR_MESSAGE);
							System.exit(1);
						}
			     		JOptionPane.showMessageDialog(null,"Out of Range.Try again.",
					    		 "Enter the number(Range from 0 to MaxStudentNum)",
					    		 JOptionPane.ERROR_MESSAGE);
						continue;
				
			     	}	
			     	return input;
			}
			catch(Exception e){
				if(--maxTries == 0){
					JOptionPane.showMessageDialog(null,"ERROR INPUT.Terminating...",
				    		 "Enter the number",JOptionPane.ERROR_MESSAGE);
					System.exit(1);
				}
				JOptionPane.showMessageDialog(null,e.getMessage()+"\nTry again.",
			    		 "Enter the number",JOptionPane.ERROR_MESSAGE);
				continue;
			}
		}
		
	}
	
	public int readInt(String str){
		String strInput;
		int input=0;
		int maxTries = 5;
				
		for(;;){
			try{
					strInput = JOptionPane.showInputDialog("Please enter "+str);
			     	input = Integer.parseInt(strInput);
			     	if(input>100000||input<0){
			     		if(--maxTries == 0){
							JOptionPane.showMessageDialog(null,"ERROR INPUT.Terminating...",
						    		 "Enter the number",JOptionPane.ERROR_MESSAGE);
							System.exit(1);
						}
			     		JOptionPane.showMessageDialog(null,"Out of Range.Try again.",
					    		 "Enter the number(Range from 0 to MaxStudentNum)",
					    		 JOptionPane.ERROR_MESSAGE);
						continue;
				
			     	}	
			     	return input;
			}
			catch(Exception e){
				if(--maxTries == 0){
					JOptionPane.showMessageDialog(null,"ERROR INPUT.Terminating...",
				    		 "Enter the number",JOptionPane.ERROR_MESSAGE);
					System.exit(1);
				}
				JOptionPane.showMessageDialog(null,e.getMessage()+"\nTry again.",
			    		 "Enter the number",JOptionPane.ERROR_MESSAGE);
				continue;
			}
		}
		
	}
	
	private int readToken(){
		try{
			ttype = tokenizer.nextToken();
			return ttype;
		}
		catch(IOException e){
			e.printStackTrace(System.err);
			System.exit(1);
		}
		return 0;
	}
	private StreamTokenizer tokenizer = new StreamTokenizer (new BufferedReader(new 
			InputStreamReader(System.in)));
	private int ttype;
}