ITI0011:harjutus 16

Kirjeldus

Kirjutada programm, mis loeb etteantud properties-failist kasutajanime ja parooli ning salvestab turvalisema variandi teise faili. Teise faili salvestatakse sama kasutaja andmed, aga parool on soolatud räsina (salted hash). Mõlemad failid on properties-tüüpi failid (vt viiteid allpool).

Algne fail (user.properties):

username=Juku
password=raskeparool123

Teie peate implementeerima failist lugemise ja kirjutamise meetodid - vastavalt readUserDataFromFile ja saveNewUserDataToFile.

Programm kontrollib, kas on olemas räsitud parooliga fail "newUser.properties". Kui see puudub, siis tehakse see fail SaveNewUserDataToFile meetodiga. Uues failis peavad olema võtmesõnad: "username", "password" ja "salt". Kui aga käivitamisel eksisteerib "newUser.properties" mõnest eelnevast käitamisest, siis programm kutsub esile authenticate meetodi, mis laseb kasutajal parooli pakkuda.

Esmalt oleks mõistlik realiseerida readUserDataFromFile meetod, kuna uue faili andmed on otseses sõltuvuses meie antud faili sisust - mida võib vabalt muuta, aga kindlasti peavad olema võtmesõnad "username" ja "password". Meetod readUserDataFromFile peab tagastama HashMap tüüpi objekti, mille võtmed ja väärtused on täpselt need, mis user.properties failis.

Lugemine soolatud räsimise kohta: https://crackstation.net/hashing-security.htm

Kui pikad tekstid pole päris Teie rada, siis järgmine link on ka piisav lugemine: http://security.stackexchange.com/questions/51959/why-are-salted-hashes-more-secure

Kiire ülevaade Java Propertiesist: http://www.mkyong.com/java/java-properties-file-examples/

Mall

<source lang="java"> /**

* Created by odin on 20.04.15.
*/

import java.io.*; import java.security.MessageDigest; import java.util.HashMap; import java.util.Properties; import java.util.Scanner;

public class Main {

   private static final String INPUT_FILE   = "user.properties";
   private static final String OUTPUT_FILE  = "newUser.properties";
   private static final int LENGTH_OF_SALT  = 10;
   private static final int MAX_CHANCES_COUNT = 3;

   public static void main(String[] args) {
       try {
           // check whether a user with a hashed password already exists
           if(new File(OUTPUT_FILE).isFile()) {
               HashMap<String, String> data = readUserDataFromFile(OUTPUT_FILE);
               if (data == null) {
               	System.out.println("Data from " + OUTPUT_FILE + " cannot be read");
               	System.exit(2);
               }
               String username = data.get("username");
               String password = data.get("password");
               String salt     = data.get("salt");
               authenticate(username, password, salt);
           } else {
               // "register" new user with salted hash
               HashMap<String, String> data = readUserDataFromFile(INPUT_FILE);
               if (data == null) {
               	System.out.println("data cannot be read");
               	System.out.println("(file does not exist, is corrupted, "
               			+ "or readUserDataFromFile not implemented).");
               	System.out.println("Exiting.");
               	System.exit(1);
               }
               String username = data.get("username");
               String password = data.get("password");
               String salt     = md5MyString("saltyRandomString").substring(0, LENGTH_OF_SALT);
               password        = md5MyString(password + salt);
               saveNewUserData(username, password, salt);
           }
       } catch (Exception e) {
           e.printStackTrace();
       }
   }

   private static void authenticate(String username, String password, String salt) throws Exception {
       Scanner userInput = new Scanner(System.in);
       String guess;
       System.out.println("Hello, You now have " + MAX_CHANCES_COUNT + " chances to guess " + username + "'s password.");
       int chances;
       for (chances = MAX_CHANCES_COUNT - 1; chances >= 0; chances--) {
           guess = userInput.next();
           if (md5MyString(guess + salt).equals(password)) {
               System.out.println("That's correct!");
               break;
           } else if (chances > 0) {
               System.out.println("That's invalid! " + chances + " guess" + (chances > 1 ? "es" : "") + " left.");
           }
       }
       if (chances < 0)
           System.out.println("Sorry, You didn't guess " + username + "'s password");
   }

   private static HashMap<String, String> readUserDataFromFile(String filename) throws IOException {
       return null;
   }

   private static void saveNewUserData(String username, String password, String salt) throws IOException {
   }

   /*
   * Maagia, sellest ei pea aru saama.
   * tl;dr:
   * Hashimist on vaja, et andmete hoiustamisel poleks
   * privaatsed andmed (loe: paroolid) lihtsasti loetavad
   * */
   private static String md5MyString(String str) throws Exception {
       MessageDigest m = MessageDigest.getInstance("MD5");
       m.update(str.getBytes("UTF8"));
       byte s[] = m.digest();
       String result = "";
       for (int i = 0; i < s.length; i++) {
           result += Integer.toHexString((0x000000ff & s[i]) | 0xffffff00).substring(6);
       }
       return result;
   }

} </source>