chall.sage.py

# This file was *autogenerated* from the file chall.sage
from sage.all_cmdline import *   # import sage library

_sage_const_2 = Integer(2); _sage_const_256 = Integer(256); _sage_const_189 = Integer(189); _sage_const_16 = Integer(16); _sage_const_4 = Integer(4); _sage_const_0 = Integer(0); _sage_const_1 = Integer(1)#!/usr/bin/sage
import hashlib
import re

with open("flag.txt", "rb") as f:
    FLAG = f.read()
    assert re.match(rb"Hero{[0-9a-zA-Z_]{90}}", FLAG)

F = FiniteField(_sage_const_2 **_sage_const_256  - _sage_const_189 )
R = PolynomialRing(F, "x")
H = lambda n: int(hashlib.sha256(n).hexdigest(), _sage_const_16 )
C = lambda x: [H(x[i : i + _sage_const_4 ]) for i in range(_sage_const_0 , len(FLAG), _sage_const_4 )]

f = R(C(FLAG))

points = []
for _ in range(f.degree()):
    r = F.random_element()
    points.append([r, f(r)])
print(points)

try:
    flag = input(">").encode().ljust(len(FLAG))

    g = R(C(flag))

    for p in points:
        if g(p[_sage_const_0 ]) != p[_sage_const_1 ]:
            print("Wrong flag!")
            break
    else:
        print("Congrats!")
except Exception:
    pass