javax.crypto.IllegalBlockSizeException: last block

问题:

i am creating android application that encrypt and decrypt a string the encrypt method work fine but the problem is in the decrypt method . the system display an error in the log cat : javax.crypto.IllegalBlockSizeException: last block incomplete in decryption

can anyone help me to fix this error ??

MainActivity.java

package com.devleb.encdecapp;

import java.io.UnsupportedEncodingException;
import java.security.GeneralSecurityException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;

import android.app.Activity;
import android.os.Bundle;
import android.util.Base64;
import android.util.Log;
import android.view.ContextMenu;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

public class MainActivity extends Activity implements OnClickListener {
    // views for the layout
    Spinner spin;
    EditText edit_txt_pass;
    static EditText edit_txt_enc_string;
    EditText edit_txt_raw;
    static EditText edit_txt_dec_string;
    Button btn_encrypt, btn_decrypt, btn_clear;

    private static SecretKey SKey;
    static String cyphertext = "";
    static String STReditTxtPass;
    String strPaddingencryption;
    static int iterations = 1000;
    private static final String[] items = { "Padding Key derivation",
            "SHA1PRNG key derivation", "PBKDF2 key derivation",
            "PKCS#12 key derivation" };

    private static final String TAG = MainActivity.class.getSimpleName();
    private static final String[] Passwords = { "password", "cryptography",
            "cipher", "algorithm", "qwerty" };

    // mesage that will be binded with the key to generate the cypher text
    private static String PlainText = "this is the text that will be encrypted";

    // the list that will be used for the OnItemSelection method
    private static final int PADDING_ENC_IDX = 0;
    private static final int SHA1PRNG_ENC_IDX = 1;
    private static final int PBKDF2_ENC_IDX = 2;
    private static final int PKCS12_ENC_IDX = 3;

    byte[] salt = { (byte) 0x11, (byte) 0x9B, (byte) 0xC6, (byte) 0xFE,
            (byte) 0x33, (byte) 0x44, (byte) 0x55, (byte) 0x77 };;

    static byte[] ivBytes = { 0, 0, 0, 0, 0, 0, 0, 0 };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        KeyGenerator kg = null;
        try {
            kg = KeyGenerator.getInstance("DES");
        } catch (NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        SKey = kg.generateKey();

        // creation of the spinner with setting Array adapter and
        // DropDownresourse
        spin = (Spinner) findViewById(R.id.spiner);
        spin.setOnItemSelectedListener(new OnItemSelectedListener() {

            @Override
            public void onItemSelected(AdapterView<?> arg0, View arg1,
                    int arg2, long arg3) {
                // TODO Auto-generated method stub

            }

            @Override
            public void onNothingSelected(AdapterView<?> arg0) {
                // TODO Auto-generated method stub

            }
        });

        ArrayAdapter<String> aa = new ArrayAdapter<String>(this,
                android.R.layout.simple_spinner_item, items);
        aa.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
        spin.setAdapter(aa);
        // end of the spinner code

        edit_txt_pass = (EditText) findViewById(R.id.editTxtPass);
        edit_txt_enc_string = (EditText) findViewById(R.id.editTxtEncString);
        edit_txt_raw = (EditText) findViewById(R.id.editTxtRawKey);
        edit_txt_dec_string = (EditText) findViewById(R.id.editTxtDecString);

        btn_encrypt = (Button) findViewById(R.id.btnEncrypt);
        btn_encrypt.setOnClickListener(this);

        btn_decrypt = (Button) findViewById(R.id.btnDecrypt);
        btn_decrypt.setOnClickListener(this);

        btn_clear = (Button) findViewById(R.id.btnClear);
        btn_clear.setOnClickListener(this);

        // / for registering the editText to the Context Menu
        registerForContextMenu(edit_txt_pass);

    }

    // for the ciphering of the plainText using the base 64
    public static String toBase64(byte[] bytes) {
        return Base64.encodeToString(bytes, Base64.NO_WRAP);
    }

    public static byte[] fromBase64(byte[] bytes) {
        // return Base64.encodeToString(bytes, Base64.NO_WRAP);
        return Base64.decode(bytes, Base64.DEFAULT);
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v,
            ContextMenuInfo menuInfo) {
        // TODO Auto-generated method stub

        int groupId = 0;
        menu.add(groupId, 1, 1, "password");
        menu.add(groupId, 2, 2, "cryptography");
        menu.add(groupId, 3, 3, "cipher");
        menu.add(groupId, 4, 4, "algorithm");
        menu.add(groupId, 5, 5, "qwerty");

        super.onCreateContextMenu(menu, v, menuInfo);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        // TODO Auto-generated method stub

        return getText(item);

        // return super.onContextItemSelected(item);
    }

    private boolean getText(MenuItem item) {
        // TODO Auto-generated method stub

        int menuItemId = item.getItemId();

        if (menuItemId == 1) {
            edit_txt_pass.setText("password");
        }
        if (menuItemId == 2) {
            edit_txt_pass.setText("cryptography");
        }
        if (menuItemId == 3) {
            edit_txt_pass.setText("cipher");
        }
        if (menuItemId == 4) {
            edit_txt_pass.setText("algorithm");
        }
        if (menuItemId == 5) {
            edit_txt_pass.setText("qwerty");
        }
        STReditTxtPass = edit_txt_pass.getText().toString();

        Log.w("the String of the Password text", STReditTxtPass);
        return false;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub

        if (v == btn_encrypt) {

            encryptPadding(PlainText, salt);
        } else if (v == btn_clear) {
            edit_txt_enc_string.setText("");
        } else if (v == btn_decrypt) {
            decryptPadding(cyphertext, salt);
        }
    }

    public static String encryptPadding(String plaintext, byte[] salt) {
        try {

            Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");

            cipher.init(Cipher.ENCRYPT_MODE, SKey);

            byte[] cipherText = cipher.doFinal(PlainText.getBytes("UTF-8"));

            cyphertext = String.format("%s%s%s", toBase64(salt), "]",
                    toBase64(cipherText));
            edit_txt_enc_string.setText(cyphertext);
            return cyphertext;
        } catch (GeneralSecurityException e) {
            throw new RuntimeException(e);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }

    public static String decryptPadding(String ctext, byte[] salt) {
        try {

            Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");

            IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
            cipher.init(Cipher.DECRYPT_MODE, SKey, ivSpec);

            byte[] plaintxt = cipher.doFinal(cyphertext.getBytes("UTF-8"));

            PlainText = String.format("%s%s%s", fromBase64(salt), "]",
                    fromBase64(plaintxt));
            edit_txt_dec_string.setText(PlainText);
            return PlainText;
        } catch (GeneralSecurityException e) {
            throw new RuntimeException(e);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }

}

回答1:

I think you have something backwards regarding salt and encryption in generel.

You have this where you do something with the result of the encryption:

cyphertext = String.format("%s%s%s", toBase64(salt), "]", toBase64(cipherText));

Then you try to decrypt the generated string above. That is not possible. You must decrypt the same byte array you get back (you call it cipherText).

Please read up on security if this is anything serious. The salt is used to generate the KEY which you dont.

Well. Here goes (but you really need to work on the rest of the solution and read up on security):

public static String encryptPadding(String plaintext, byte[] salt) {
    try {

        Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");

        IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
        cipher.init(Cipher.ENCRYPT_MODE, SKey, ivSpec);

        byte[] cipherText = cipher.doFinal(PlainText.getBytes("UTF-8"));

        cyphertext = Base64.encodeToString(cipherText, Base64.DEFAULT);
        edit_txt_enc_string.setText(cyphertext);
        return cyphertext;
    } catch (GeneralSecurityException e) {
        throw new RuntimeException(e);
    } catch (UnsupportedEncodingException e) {
        throw new RuntimeException(e);
    }
}

public static String decryptPadding(String ctext, byte[] salt) {
    try {

        Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");

        IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
        cipher.init(Cipher.DECRYPT_MODE, SKey, ivSpec);

        byte[] plaintxt = cipher.doFinal(Base64.decode(cyphertext, Base64.DEFAULT));

        PlainText = new String(plaintxt, "UTF-8");
        edit_txt_dec_string.setText(PlainText);
        return PlainText;
    } catch (GeneralSecurityException e) {
        throw new RuntimeException(e);
    } catch (UnsupportedEncodingException e) {
        throw new RuntimeException(e);
    }
}