Need help creating an exception for wrong password in decrypt method
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Thread: Need help creating an exception for wrong password in decrypt method

  1. #1
    Join Date
    Nov 2006
    Posts
    32

    Need help creating an exception for wrong password in decrypt method

    The following code works but I am trying to prevent decrypting a file if you have the wrong key.


    // Example code showing how to use Java's Password-Based encryption. This
    // example is a simplified form of the code in the documentation for the
    // java cryptography architecture.
    import java.awt.image.BufferedImage;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    import java.security.GeneralSecurityException;
    //import java.security.NoSuchAlgorithmException;
    import javax.crypto.Cipher;
    import javax.crypto.CipherInputStream;
    import javax.crypto.CipherOutputStream;
    //import javax.crypto.NoSuchPaddingException;
    import javax.crypto.SecretKey;
    import javax.crypto.SecretKeyFactory;
    import javax.imageio.ImageIO;
    import javax.crypto.spec.DESKeySpec;


    public class sample
    {

    static String key = "squirrel123";
    static String key1 = "squirrel1234";

    public static void main(String[] arg) throws Exception
    {


    encryptFile(key, "c:\\users\\test\\rose.jpg",
    "c:\\users\\test\\encrypt.jpg","JPG");

    decryptFile(key1, "c:\\users\\test\\encrypt.jpg",
    "c:\\users\\test\\decrypted_output.jpg","JPG");


    }



    public static void encryptFile(String key, String nonEncryptedFile, String EncryptedFile, String typeFile) throws GeneralSecurityException, FileNotFoundException
    {


    DESKeySpec dks = new DESKeySpec(key.getBytes());
    SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
    SecretKey desKey = skf.generateSecret(dks);
    Cipher pbeCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");


    if((typeFile.equals("JPG"))||
    (typeFile.equals("GIF"))||
    (typeFile.equals("PNG"))||
    (typeFile.equals("BMP")))
    {

    File inputFile = new File(nonEncryptedFile);

    BufferedImage input = null;

    pbeCipher.init(Cipher.ENCRYPT_MODE, desKey);

    try
    {
    input = ImageIO.read(inputFile);
    }
    catch (IOException e)
    {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }

    FileOutputStream output = null;

    try
    {
    output = new FileOutputStream(EncryptedFile);
    }
    catch
    (FileNotFoundException e)
    {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }

    CipherOutputStream cos = new CipherOutputStream(output, pbeCipher);

    try
    {
    ImageIO.write(input,typeFile,cos);
    }
    catch (IOException e1)
    {
    // TODO Auto-generated catch block
    e1.printStackTrace();
    }

    try
    {
    cos.close();
    }
    catch (IOException e)
    {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }
    }



    }


    public static void doCopy(InputStream is, OutputStream os) throws IOException
    {
    byte[] bytes = new byte[64];
    int numBytes;
    while ((numBytes = is.read(bytes)) != -1) {
    os.write(bytes, 0, numBytes);
    }
    os.flush();
    os.close();
    is.close();
    }

    public static void decryptFile(String key, String encryptedFile, String decryptedFile, String typeFile)throws GeneralSecurityException, FileNotFoundException
    {

    DESKeySpec dks = new DESKeySpec(key1.getBytes());
    SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
    SecretKey desKey = skf.generateSecret(dks);
    Cipher pbeCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");

    try
    {
    pbeCipher.init(Cipher.DECRYPT_MODE, desKey);

    System.out.println("Decrypt mode!");

    // Decrypt the ciphertext and then print it out.
    FileInputStream output = null;

    if((typeFile.equals("JPG"))||
    (typeFile.equals("GIF"))||
    (typeFile.equals("PNG"))||
    (typeFile.equals("BMP")))
    {

    try {
    output = new FileInputStream(encryptedFile);
    } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }

    CipherInputStream cis = new CipherInputStream(output, pbeCipher);
    BufferedImage input = null;
    try {
    input = ImageIO.read(cis);
    } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }
    FileOutputStream out = null;
    try {
    out = new FileOutputStream(decryptedFile);
    } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }
    try {
    ImageIO.write(input,typeFile, out);
    } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }
    try {
    cis.close();
    } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    }

    }


    } catch (IOException e ){
    System.out.println("invalid");
    }

    }

    }
    Last edited by liftthis; October 3rd, 2012 at 03:05 PM.

  2. #2
    Join Date
    May 2006
    Location
    UK
    Posts
    4,473

    Re: Need help creating an exception for wrong password in decrypt method

    Please use code tags when posting code.
    The following code works but I am trying to prevent decrypting a file if you have the wrong key
    What does your code do now if you enter the wrong key - how can it decrypt the file if the Key is incorrect?
    Posting code? Use code tags like this: [code]...Your code here...[/code]
    Click here for examples of Java Code

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