I’m quite pleased with mine - it has five passwords for each of the three levels of difficulty. With a little help from my good friend, Mr Google, I managed to create three arrays of five passwords (I tried to do a 3x5 array but got absolutely nowhere with that!), then it picks one at random each time you select a level. 
using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Random = System.Random;
public class Hacker : MonoBehaviour
{
int level;
enum Screen { MainMenu, Password, Win };
Screen currentScreen = Screen.MainMenu;
string[] passwordsL1 = new string[5] { "books", "shelf", "password", "font", "borrow" };
string[] passwordsL2 = new string[5] { "prisoner", "handcuffs", "holster", "uniform", "arrest" };
string[] passwordsL3 = new string[5] { "starfield", "telescope", "environment", "exploration", "astronauts" };
Random random = new Random();
string strPassword;
int passwordIndex;
// Start is called before the first frame update
void Start()
{
ShowMainMenu();
}
void ShowMainMenu()
{
currentScreen = Screen.MainMenu;
passwordIndex = random.Next(1, 5);
Terminal.ClearScreen();
Terminal.WriteLine("Welcome to Hacker™ v0.21");
Terminal.WriteLine("");
Terminal.WriteLine("Which system would you like to hack?");
Terminal.WriteLine("");
Terminal.WriteLine("Press 1 for the local library");
Terminal.WriteLine("Press 2 for the local police station");
Terminal.WriteLine("Press 3 for NASA");
Terminal.WriteLine("");
Terminal.WriteLine("Enter your selection: ");
Terminal.WriteLine("");
}
void OnUserInput(string input)
{
if (input == "menu")
{
level = 0;
ShowMainMenu();
}
else if (currentScreen == Screen.MainMenu)
{
RunMainMenu(input);
}
else if (currentScreen == Screen.Password)
{
RunCheckPassword(input);
}
}
private void RunMainMenu(string input)
{
if (input == "1")
{
level = 1;
strPassword = passwordsL1[passwordIndex];
StartGame();
}
else if (input == "2")
{
level = 2;
strPassword = passwordsL2[passwordIndex];
StartGame();
}
else if (input == "3")
{
level = 3;
strPassword = passwordsL3[passwordIndex];
StartGame();
}
else
{
Terminal.WriteLine("Syntax Error: " + input);
}
}
private void StartGame()
{
currentScreen = Screen.Password;
Terminal.WriteLine("You have chosen level " + level + ".");
Terminal.WriteLine("");
Terminal.WriteLine("Please enter the password:");
}
private void RunCheckPassword(string input)
{
if (input == strPassword)
{
Terminal.WriteLine("Congratulations! You have successfully guessed the password!");
Terminal.WriteLine("");
currentScreen = Screen.Win;
}
else
{
Terminal.WriteLine("Incorrect password entered - please try again.");
Terminal.WriteLine("");
Terminal.WriteLine("Please enter the password:");
}
}
// Update is called once per frame
void Update()
{
}
}
