cncjq

from pwn import *
import re
import json

conn = remote('socket.cryptohack.org', 13372)
s = conn.recv(1024)
conn.send(json.dumps({"option":"get_flag"}))
s = conn.recv(1024)
num = re.findall(r': (.*)\n', s.decode())[0]
data = num[1:-2]

cncjq

from scalar_multiplication import scalar_mul
import hashlib

if __name__ == "__main__":
    QA, nB = (815, 3190), 1829
    key = scalar_mul(nB, QA)[0]
    flag = hashlib.sha1(b'%f' % key).hexdigest()
    print('crypto{%s}' % flag)
    
'''codes for scalar_mul and point_addition are below:

cncjq

import gmpy2
from point_addition import add_ecc

O = (0, 0)
def scalar_mul(n, p):
    q, r = p, O
    while n > 0:
        if n % 2 == 1:
            r = add_ecc(r, q)
        q, n = add_ecc(q, q), n // 2

cncjq

import gmpy2

O = (0, 0)
def add_ecc(p, q):
    if p == O:
        return q
    elif q == O:
        return p
    elif p[0] == q[0] and p[1]==-q[1]:
        return O