AES / CFB / NOPADDING（128位），具有密码加盐功能

Question

I've tried running the code for about 3 days now but I am not able to figure out the mistake I've done.

I 'am using AES/CFB/NOPadding in 128 bit with password salting Salt_Len = 8 bytes and IV_Len = 16 bytes

package Firstage;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.SecureRandom;
import java.security.spec.KeySpec;
import java.util.Random;
import java.util.Scanner;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;

public class Thealgorithm1 
{

    static Scanner get = new Scanner(System.in);
    private static final String ALGORITHM = "AES";
    private static final String ALGORITHM_MODE ="AES/CFB/NoPadding";
    private static String password;

    public static void encrypt(File inputFile, File outputFile)
            throws Exception
    {
        System.out.println("Enetr passprhase");
        password=get.nextLine();

        final Random ivspc = new SecureRandom();
        byte[] ivspec = new byte[16];
        ivspc.nextBytes(ivspec);
        IvParameterSpec enciv = new IvParameterSpec(ivspec);

        FileOutputStream outputstrm = new FileOutputStream(outputFile);
        byte[] outputBytes = doCrypto(Cipher.ENCRYPT_MODE, inputFile,password,enciv);
        System.arraycopy(ivspec, 0,outputBytes , 0, 16);
        outputstrm.write(outputBytes);
        outputstrm.close();
        System.out.println("File encrypted successfully!");
    }

    public static void decrypt(File inputFile, File outputFile)
            throws Exception
    {

        System.out.println("Enter password");
        password=get.nextLine();
        IvParameterSpec hj = null;
        byte[]outpytBytes=doCrypto(Cipher.DECRYPT_MODE, inputFile,password,hj);
        FileOutputStream outputstrm = new FileOutputStream(outputFile);
        outputstrm.write(outpytBytes);
        outputstrm.close();
        System.out.println("File decrypted successfully!");
    }

    private static byte[] doCrypto(int cipherMode, File inputFile,String keyo ,IvParameterSpec ivespec)
            throws Exception {
    /* Derive the key, given password and salt. */
        final Random slt = new SecureRandom();
        byte[] salt = new byte[8];
        slt.nextBytes(salt);


        char[] passkeyo = keyo.toCharArray();
        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        KeySpec spec = new PBEKeySpec(passkeyo, salt, 65536, 128);
        SecretKey tmp = factory.generateSecret(spec);

        SecretKey secret = new SecretKeySpec(tmp.getEncoded(), ALGORITHM);

        FileInputStream fylin = new FileInputStream(inputFile);
        byte[] inputBytes = new byte[(int)inputFile.length()];
        fylin.read(inputBytes);
        fylin.close();

        Cipher cipher = Cipher.getInstance(ALGORITHM_MODE);

        byte[] outputBytes;
        if(cipherMode==2)
        {
            IvParameterSpec ivdec = new IvParameterSpec(inputBytes,0,16);
            cipher.init(cipherMode, secret,ivdec);
        }
        else
        {
            cipher.init(cipherMode, secret, ivespec);
        }


        if(cipherMode==2)
        {
            outputBytes = cipher.doFinal(inputBytes, 16,(inputBytes.length-16));
        }
        else
        {
            outputBytes=cipher.doFinal(inputBytes);
        }


        return outputBytes;

    }

    public static void main(String[] args)
    {

        File inputFile = new File("C:/temp/File.txt");
        File encryptedFile = new File("C:/temp/encryaes.enc");
        File decryptedFile = new File("C:/temp/mydr.txt");


        try {

            Thealgorithm1.encrypt(inputFile, encryptedFile);
            Thealgorithm1.decrypt(encryptedFile, decryptedFile);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }

    }

}

The code encrypts it properly and also decrypts it, but the problem is that what it decrypts is not proper ie there's a fault in the code.

Answer 1

You have two main issues in your code:

1. The key must be exactly the same for encryption and decryption. When you decrypt you are generating a different (random) salt value so, even if you enter the same passphrase, the decryption key is going to be different. You can test this by making the salt a class attribute and only initializing it once.

2. When you do this inside the encrypt method:

    System.arraycopy(ivspec, 0,outputBytes , 0, 16); 

You are writing over the first 16 bytes of the encrypted output. My simple suggestion is to do something like this:

byte[] outputBytes = doCrypto(Cipher.ENCRYPT_MODE, inputFile, password, enciv);
byte[] outputBytesWithIV = new byte[outputBytes.length + 16];
System.arraycopy(ivspec, 0, outputBytesWithIV, 0, 16);
System.arraycopy(outputBytes, 0, outputBytesWithIV, 16, outputBytes.length);
outputstrm.write(outputBytesWithIV);

Answer 2

You have two problems:

• during encryption, you're overwriting a the first 16 bytes of the ciphertext with the IV. An easy fix is to write the IV to the stream instead of using System.arraycopy() . Change

   System.arraycopy(ivspec, 0,outputBytes , 0, 16); 

  to

   outputstrm.write(ivspec); 

• You're using a different salts during encryption and decryption, because you're always generating a new one. You should also write the salt in front of the ciphertext beside the IV and read it back during decryption.
  You could also just use one of the two: generate a 16 byte salt and write that in front of the ciphertext. Then you can use a static IV, because the semantic property is achieved from the random salt.