from Crypto.Util.number import *
from functools import reduce
import operator
from secret import flag, n, k
def comb(n, k):
if k > n :
return 0
k = min(k, n - k)
u = reduce(operator.mul, range(n, n - k, -1), 1)
d = reduce(operator.mul, range(1, k + 1), 1)
return u // d
def encrypt(msg, n, k):
msg = bytes_to_long(msg.encode('utf-8'))
if msg >= comb(n, k):
return -1
m = ['1'] + ['0' for i in range(n - 1)]
for i in range(1, n + 1):
if msg >= comb(n - i, k):
m[i-1]= '1'
msg -= comb(n - i, k)
k -= 1
m = int(''.join(m), 2)
i, z = 0, [0 for i in range(n - 1)]
c = 0
while (m > 0):
if m % 4 == 1:
c += 3 ** i
m -= 1
elif m % 4 == 3:
c += 2 * 3 ** i
m += 1
m //= 2
i += 1
return c
enc = encrypt(flag, n, k)
print('enc =', enc)
