Crypto CTF 2021 | Linda

#cryptoctf2021

#!/usr/bin/env python3

from Crypto.Util.number import *
from math import gcd
from flag import flag

def keygen(p):
    while True:
        u = getRandomRange(1, p)
        if pow(u, (p-1) // 2, p) != 1:
            break
    x = getRandomRange(1, p)
    w = pow(u, x, p)
    while True:
        r = getRandomRange(1, p-1)
        if gcd(r, p-1) == 1:
            y = x * inverse(r, p-1) % (p-1)
            v = pow(u, r, p)
            return u, v, w

def encrypt(m, pubkey):
    p, u, v, w = pubkey
    assert m < p
    r, s = [getRandomRange(1, p) for _ in '01']
    ca = pow(u, r, p)
    cb = pow(v, s, p)
    cc = m * pow(w, r + s, p) % p
    enc = (ca, cb, cc)
    return enc

def die(*args):
    pr(*args)
    quit()

def pr(*args):
    s = " ".join(map(str, args))
    sys.stdout.write(s + "\n")
    sys.stdout.flush()

def sc():
    return sys.stdin.readline().strip()

def main():
    border = "+"
    pr(border*72)
    pr(border, "  .:::::: LINDA Cryptosystem has high grade security level ::::::.  ", border)
    pr(border, "  Can you break this cryptosystem and find the flag?                ", border)
    pr(border*72)

    pr('| please wait, preparing the LINDA is time consuming...')
    from secret import p
    u, v, w = keygen(p)
    msg = bytes_to_long(flag)
    pubkey = p, u, v, w
    enc = encrypt(msg, pubkey)
    while True:
        pr("| Options: \n|\t[E]xpose the parameters \n|\t[T]est the encryption \n|\t[S]how the encrypted flag \n|\t[Q]uit")
        ans = sc().lower()
        if ans == 'e':
            pr(f'| p = {p}')
            pr(f'| u = {u}')
            pr(f'| v = {v}')
            pr(f'| w = {w}')
        elif ans == 's':
            print(f'enc = {enc}')
        elif ans == 't':
            pr('| send your message to encrypt: ')
            m = sc()
            m = bytes_to_long(m.encode('utf-8'))
            pr(f'| encrypt(m) = {encrypt(m, pubkey)}')
        elif ans == 'q':
            die("Quitting ...")
        else:
            die("Bye ...")

if __name__ == '__main__':
    main()

ElGamal暗号っぽい？　何もわからずに言っています