K3RN3LCTF 2021

ctf

Word count: 363Reading time: 2 min

 2021/11/15 

Kiddie Pool

`Vieta's Poly`

Python Code:

You have to solve 100 math problems to get the flag

There are three types of math problems

sum of the roots
sum of the reciprocals of the roots

sum of the squares of the roots

from pwn import *
import re
import sympy
import numpy as np
port = 2236
# context.log_level = 'debug' #will print all input and output for debugging purposes
conn = remote("ctf.k3rn3l4rmy.com",port) #enter the address and the port here as strings. For example nc 0.0.0.0 5000 turns into remote('0.0.0.0', 5000)
def get_input(): #function to get one line from the netcat
    input = conn.recvline().strip().decode()
    return input
def parse(my_poly):
    '''
    TODO: Parse polynomial
    For example, parse("x^3 + 2x^2 - x + 1") should return [1,2,-1,1]
    '''
    # my_poly = "2*x**2+7*x-3"
    my_poly = my_poly.replace("^", "**").replace(my_poly[0], "*x").replace("*x", my_poly[0], 1)
    x = sympy.Symbol('x')
    my_poly = sympy.polys.polytools.poly_from_expr(my_poly)[0]
    coeffs = my_poly.coeffs()
    return coeffs
for _ in range(4): get_input() #ignore challenge flavortext
for i in range(100):
    type = get_input()
    coeffs = parse(get_input())
    print(coeffs)

    ans = 0
    if 'sum of the roots' in type:
        #TODO: Find answer
        print("sum of the roots")
        ans = -1*coeffs[1]
    elif 'sum of the reciprocals of the roots' in type:
        #TODO: Find answer
        print("sum of the reciprocals of the roots")
        ans = -1*coeffs[-2]//coeffs[-1]
    elif 'sum of the squares of the roots' in type:
        #TODO: Find answer
        print("sum of the squares of the roots")
        ans = coeffs[1]**2-2*coeffs[2]
    print(ans)
    conn.sendline(str(ans)) #send answer to server
    get_input()
conn.interactive() #should print flag if you got everything right