Question

I got confused in an assignment 😀
given a UML diagram I had to Implement a course management application, one part is the Student class as follow

    public class Student extends Person implements Encryptable {
    private String program;
    private Vector<Course> courses;

//constructor. 
    public Student(String Name, String pnr, String tel, String prog) {
            super(Name, pnr, tel);
            program = prog;
            courses = new Vector<Course>();
        }
/* implementation of related methods 
  ......  */

        @Override
    public void encrypt(String password) {
    }

    @Override
    public void decrypt(String password) {  
    }

all other classes and all related setters and getters of this class are implemented also the Encryptable interface is as follow

public interface Encryptable {

    public void encrypt(String password);
    public void decrypt(String password);
}

in an earlier task I had implemented a class “PassworCrypter” that I should use that class

public class PasswordCrypter {
    Cipher ecipher;
    Cipher dcipher;
    SecretKey key;
    DESKeySpec dks;
    SecretKeyFactory skf;
    byte[] psword;

    public PasswordCrypter(String password) {

        try {
            psword = password.getBytes("UTF-16");
            dks = new DESKeySpec(psword);
            skf = SecretKeyFactory.getInstance("DES");
            key = skf.generateSecret(dks);
            ecipher = Cipher.getInstance("DES");
            ecipher.init(Cipher.ENCRYPT_MODE, key);
            dcipher = Cipher.getInstance("DES");
            dcipher.init(Cipher.DECRYPT_MODE, key);
        } catch (NoSuchAlgorithmException e) {
            throw new CrypterException(e);
        } catch (NoSuchPaddingException e) {
            throw new CrypterException(e);
        } catch (InvalidKeyException e) {
            throw new CrypterException(e);
        } catch (InvalidKeySpecException e) {
            throw new CrypterException(e);
        } catch (UnsupportedEncodingException e) {
            throw new CrypterException(e);
        }

    }

    public byte[] encrypt(byte[] array) {

        try {
            return ecipher.doFinal(array);
        } catch (IllegalBlockSizeException e) {
            throw new CrypterException(e);
        } catch (BadPaddingException e) {
            throw new CrypterException(e);
        }
    }

    public byte[] decrypt(byte[] array) {

        try {
            return dcipher.doFinal(array);
        } catch (IllegalBlockSizeException e) {
            throw new CrypterException(e);
        } catch (BadPaddingException e) {
            throw new CrypterException(e);
        }
    }
}

I should use PasswordCrypter class on local and inherited fields of the Student
class. When a Student object is encrypted it should not be possible to get data
such as a student’s name without first calling decrypt. A Student object should
always be encrypted except for when you need to access any of its data.
can any one give me idea or tell me how should I encrypt this damn student 🙂

Answer 1

I think you have problem in Encryptable. The signature of the method should be

public void encrypt(Encrypter enc);
public void decrypt(Decrypter dec);

Where you can define two separate interfaces Encrypter and Decrypter. so finally you can use PasswordCrypter as central class which implements these two methods.

 public class PasswordCrypter implements Encrypter,Decrypter  {

So now inside your Student class you can do

public void encrypt(Encrypter enc) {
   byte[] programbytes = enc.encrypt(program);
}

public void encrypt(Decrypter dec) {
   program = dec.decrypt(programbytes);
}