Hackvent_2018/Day 14/decode.py

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2018-12-14 17:11:03 +01:00
#!/usr/bin/python
import math
c = int("2A4C9AA52257B56837369D5DD7019451C0EC04427EB95EB741D0273D55", 16)
t = int("1398ED7F59A62962D5A47DD0D32B71156DD6AF6B46BEA949976331B8E1", 16)
n = int("0D8A7A45D9BE42BB3F03F710CF105628E8080F6105224612481908DC721", 16)
def linear_diophantine_equation(a, b):
if b > a:
return linear_diophantine_equation(b, a)
if b == 0:
return a, 1, 0
d, x, y = linear_diophantine_equation(b, a % b)
return (d, y, x - (a // b) * y)
def multiplicative_inverse(a, b):
d, x, y = linear_diophantine_equation(a, b)
if y < 0:
y = (b if b > a else a) + y
return y
def gcd(a, b):
d, x, y = linear_diophantine_equation(a, b)
return d
# n > t > c
# m = flag
def test_solution(m):
return m**2 % n == c
# m**2 % n = x**2
# m**2 + k*n = c
# m % n = x
# m - k*n = x
# m = x + k * n
# x = int(math.sqrt(c))
#
# while not test_solution(x):
# x += n
# print(hex(x), hex(((x**2)%n)-c))
# print(x)
mult_inverse = multiplicative_inverse(c, n)
d, x, y = linear_diophantine_equation(mult_inverse, mult_inverse*n)
print(hex(d + 6*t - 2*c), test_solution(d + 6*t - 2*c))
# x = math.sqrt(n)
# print(x)
#
# print(test_solution(c * math.sqrt()))
# print(test_solution(math.floor(math.sqrt(c * n))))
# c = (m**2) % n
# c = m*m - k*n
# 1 = (m**2)/c - (k*n)/c
# 1 = (m**2)/c - k*(n/c)
# k = 1
# test = k * n / c
# while test != math.floor(test):
# k += 1
# test = k * n / c
#
# print(k, test)
# x = m*m
# c = x % n
# c = x - k*n
# c = k*n+x
# x ~ (48 56 31 38 2d) ^ 2
# m_guess = int("485631382d616161612d616161612d616161612d616161612d61616161", 16)
# x_guess = m_guess ** 2
# k_guess = (c - x_guess) / n
#
# i = 0
# while not test_solution(m_guess):
# m_guess += 1
# i += 1
#
# print(i, m_guess)
# print(test_solution(math.sqrt(c + n)))
# print(math.sqrt(c))
# c = x**2
# m**2 % n = x**2
# m % n = x
# i = 0
# solutioni = 0
# while i < 100:
# i += 1
# if test_solution(i):
# print(i, i**2%n)
# 4**2 % 13 = 3
# 9**2 % 13 = 3
# 17**2 % 13 = 3
# 22**2 % 13 = 3
# 30**2 % 13 = 3