Question

Using Java: implement a program with the following features. Thanks

• Produce a menu for the user with 3 choices.
  1. Add a new user
  2. Attempt login
  3. See all users
• If the user chooses #1, prompt them for a username (a string). Then a password (a string). Using SHA-2 hash the password they gave you, and store the resulting username and hashed password in a datastructure of your choice. (It can be 2 arrays, one for usernames, one for hashed passwords).
• If the user chooses #2, prompt them for a username and password. When they enter the username, first search to see if you have a matching username stored. If you don't give them a "unknown user" error. When they enter their password, hash it with SHA-2 again, and compare the resulting hash with the stored hash for that user. If they are correct print "Login successful", if not "Login failed".
• If the user chooses #3, print out all the usernames and hashed passwords you have.
• Note: When hashing the password you can use any strength SHA that is supported by your language. You'll likely need to use a salt when you calculate the hash, that can be hardcoded in your application.
• Note: You do not have to use files or databases to store the username/password hashes. They'll only be in memory

Answer 1

Here is the requried program with proper comments:

package users;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Scanner;

public class Users {

        //Constant Salt for SHA algorithm
        private static final String SALT = "SALTSAMPLE";

        //MAx Array Size declared to avoid array out of bound exception
        private static final int MAX_USERS=100;

        //User name and password arrays
        private static String[] userNames=new String[100];      
        private static String[] passwords=new String[100];

        //Constructor
        public Users() {

        }

        public static void main(String[] args) {
                //Scanner for input
                Scanner sc=new Scanner(System.in);
                //variable to take choice
                int choice=0;
                //keep track of user count
                int userCount=0;
                do {
                        System.out.println("Enter Your choice:\nAdd new user(1)\nAttempt Login(2)\nSee all Users(3)\nExit(4):");
                        //get choice
                        choice=sc.nextInt();
                        //Variables to get user name
                        String userName="";
                        //variable to get password
                        String password="";
                        //variable to keep hashed password
                        String hashedPassword="";
                        sc.nextLine();
                        switch (choice) {
                        //For adding new user
                        case 1:
                                System.out.println("Enter User Name:");
                                userName=sc.nextLine();
                                System.out.println("Enter password:");
                                password=sc.nextLine();
                                hashedPassword=getSecurePassword(password);
                                //check if maximum users reached
                                if(userCount<MAX_USERS) {
                                        //If not add user
                                        userNames[userCount]=userName;
                                        passwords[userCount]=hashedPassword;
                                        //increase user count
                                        userCount++;
                                }
                                else {
                                        System.out.println("Max User count reached");
                                }
                                //usernameAndPasswords.put(userName, hashedPassword);
                                break;
                                //For attemptig login   
                        case 2:
                                System.out.println("Enter User Name:");
                                userName=sc.nextLine();

                                boolean islogin=false;
                                boolean isuserfound=false;
                                for(int i=0;i<userCount;i++) {
                                        if(userNames[i].equalsIgnoreCase(userName)) {
                                                isuserfound=true;
                                                break;
                                        }
                                }
                                if(!isuserfound) {
                                        System.out.println("Unknown User");

                                }
                                else {
                                        System.out.println("Enter password:");
                                        password=sc.nextLine();
                                        hashedPassword=getSecurePassword(password);
                                        for(int i=0;i<userCount;i++) {
                                                if(passwords[i].equalsIgnoreCase(hashedPassword)) {
                                                        System.out.println("Login successful");
                                                        islogin=true;
                                                        break;
                                                }
                                        }

                                        if(!islogin)
                                                System.out.println("Login failed");
                                }
                                break;

                                //for printing all users
                        case 3:
                                for(int i=0;i<userCount;i++) {
                                        System.out.println("User Name : "+userNames[i] +" Password : "+passwords[i]);
                                }

                                break;
                        default:
                                break;                                  
                        }
                        System.out.println();
                }
                while(choice!=4);
                System.out.println("Program Exited");
        }

        /**
         * Generates a hashed password using SHA-256 and constant SALT
         * @param password: password to be hashed
         * @return: hashed password
         */
        public static String getSecurePassword(String password) {

                String generatedPassword = null;
                try {
                        MessageDigest md = MessageDigest.getInstance("SHA-256");
                        md.update(SALT.getBytes());
                        byte[] bytes = md.digest(password.getBytes());
                        StringBuilder sb = new StringBuilder();
                        for (int i = 0; i < bytes.length; i++) {
                                sb.append(Integer.toString((bytes[i] & 0xff) + 0x100, 16).substring(1));
                        }
                        generatedPassword = sb.toString();
                } catch (NoSuchAlgorithmException e) {
                        e.printStackTrace();
                }
                return generatedPassword;
        }
}

Program output:

Enter Your choice:
Add new user(1)
Attempt Login(2)
See all Users(3)
Exit(4):
1
Enter User Name:
user 1
Enter password:
password 1

Enter Your choice:
Add new user(1)
Attempt Login(2)
See all Users(3)
Exit(4):
1
Enter User Name:
user2
Enter password:
password2

Enter Your choice:
Add new user(1)
Attempt Login(2)
See all Users(3)
Exit(4):
2
Enter User Name:
user3
Unknown User

Enter Your choice:
Add new user(1)
Attempt Login(2)
See all Users(3)
Exit(4):
2
Enter User Name:
user 1
Enter password:
password 1
Login successful

Enter Your choice:
Add new user(1)
Attempt Login(2)
See all Users(3)
Exit(4):
3
User Name : user 1 Password : 7d9eeb5d8a1dd61574701e03449851cfe6b7c82fda377479e3389365c510a497
User Name : user2 Password : 0ba240ed711e7da851d7b661c7a7d7c873e7b08924c6cf30b7fd84557640f14e

Enter Your choice:
Add new user(1)
Attempt Login(2)
See all Users(3)
Exit(4):
4

Program Exited

Console output screen shot: