nsec2021-hymn-backup_app.py

from flask import Flask
from flask import g
from flask import redirect, render_template, request, send_file, make_response, session, url_for
from captcha.image import ImageCaptcha
from io import BytesIO
from Crypto.Cipher import ARC4
from Crypto.Hash import SHA
from Crypto.Random import get_random_bytes
import base64
import string
import random



app = Flask(__name__)
cache = {}
cache['foo'] = 1


@app.after_request
def add_header(response):
    response.headers['Cache-Control'] = 'no-store, public, max-age=0'
    return response



@app.route('/',methods=['GET','POST'])
def index():
    if request.method == "POST":
        if ('CT' not in request.cookies):
            return redirect('/')
        else:
            if (int(request.cookies.get('CT').split("|")[1]) != int(cache['foo']-1)):
                
                resp = make_response(render_template('index.html', tries=0))
                resp.set_cookie('CT',make_struct(get_random_string(),0,cache['foo']))
                cache['foo'] = cache['foo'] +1
                return resp
            gh = parse_struct(request.cookies.get('CT'))
            verse = request.form.get('verse')
            original_verse = gh.split('|')[0]
            current_tries = int(gh.split('|')[1])
            # SUCCESsS
            if (current_tries > 10000000000000000):
                return "THE FLAG IS XXXXXXXXXXXXX" #TODO: Add real flag
            if (verse == original_verse):
                letters = get_random_string()
                tries = current_tries + 1
                struct = make_struct(letters,tries,cache['foo'])
                resp = make_response(render_template('index.html',tries=tries,msg='Good job. You still have a few more to do'))
                resp.set_cookie('CT',struct)
                cache['foo'] = cache['foo'] + 1
                return resp
            else:
                letters = get_random_string()
                struct = make_struct(letters,0,cache['foo'])
                resp = make_response(render_template('index.html',tries=0, msg='Sorry, you said your hymn wrong. I was expecting : ' + original_verse))
                resp.set_cookie('CT',struct)
                cache['foo'] = cache['foo'] + 1
                return resp
    if request.method == "GET":
        if ( 'CT' not in request.cookies):
            letters = get_random_string()
            struct = make_struct(letters,0,cache['foo'])
            resp = make_response(render_template('index.html',tries=0))
            resp.set_cookie('CT',struct)
            cache['foo'] = cache['foo'] +1
            return resp
        else:
            gh = parse_struct(request.cookies.get('CT'))
            letters = get_random_string()
            tries = int(gh.split('|')[1])
            struct = make_struct(letters,tries,cache['foo'])
            resp = make_response(render_template('index.html',tries=tries))
            resp.set_cookie('CT',struct)
            cache['foo'] = cache['foo'] + 1
            return resp




@app.route('/captcha')
def captcha():
    if ('CT' not in request.cookies):
    # Value | num tries | ctr
        return redirect('/')
    else:
        try:
            z = parse_struct(request.cookies.get('CT'))
        except:
            z = get_random_string() + "|0000000000000000000000000|"+str(cache['foo'])
        image = ImageCaptcha(fonts=['x.ttf'],  height=300, width=600, font_sizes=[70])
        letters = z.split('|')[0]
        data = image.generate(letters)
        resp =  make_response(send_file(data, cache_timeout=-1, mimetype='image/png', as_attachment=False))
        return resp

def get_random_string():
    letters = string.ascii_lowercase
    result_str = ''.join(random.choice(letters) for i in range(10))
    return result_str

def make_struct(letters, tries, ctr):
    x = letters + "|" + str(tries).zfill(24) + "|" + str(ctr)
    y = base64.b64encode(encrypt(ctr,x)).decode('UTF-8')+"|" + str(ctr)
    return y

def parse_struct(ct):
    ctr = ct.split("|")[1]
    try:
        zz = base64.b64decode(ct.split("|")[0])
    except:
        zz= make_struct(get_random_string,0,cache['foo']).split('|')[0]
    if (ctr != cache['foo']-1):
        rr = decrypt(cache['foo']-1,zz).decode('UTF-8')
        if (int(rr.split('|')[2]) != int(cache['foo']-1)):
            print(rr.split('|')[2])
            raise ValueError

        if (int(rr.split('|')[2]) != int(ctr)):
            raise ValueError
            return False
        return rr
    else: 
        return get_random_strings + "|" + str(0).zfill(24) + "|" + cache['foo']


def decrypt(ctr, msg):
    x = int(cache['foo']-1)
    key = b'BRING YOUR OWN KEY'
    nonce = str(x%2048).encode('UTF-8')
    tempkey = SHA.new(key+nonce).digest()
    cipher = ARC4.new(tempkey)
    msg =cipher.decrypt(msg)
    return msg

def encrypt(ctr, msg):
    key = b'BRING YOUR OWN KEY'
    nonce = str(ctr%2048).encode('UTF-8')
    tempkey = SHA.new(key+nonce).digest()
    cipher = ARC4.new(tempkey)
    msg = cipher.encrypt(msg.encode('UTF-8'))
    return msg