CCTF_Public/writeups/vol9_rnd1/ratoto/to_players/ratoto.py

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2022-09-10 10:53:53 +00:00
#!/usr/bin/env sage
from Crypto.Util.number import *
from random import *
from flag import flag
def keygen(nbit, l):
p = getPrime(nbit)
pubkey = []
for _ in range(l):
r, s = getPrime(nbit), getPrime(nbit >> 1)
pubkey.append(r * p + s)
return p, pubkey
def encrypt(msg, pubkey, size, nbit):
bmsg = bin(bytes_to_long(msg))[2:]
ENC, ERR = [], [getRandomNBitInteger(nbit >> 2) for _ in range(len(pubkey))]
I = [[getRandomRange(0, l) for _ in range(size)] for _ in range(len(bmsg))]
J = I.copy()
shuffle(J)
for i in range(len(bmsg)):
BSE = [pubkey[_] for _ in I[i]]
NSE = [ERR[_] for _ in J[i]]
ENC.append((p - 1337) * sum(BSE) + 31337 * sum(NSE) + int(bmsg[i]))
return ENC
nbit, l, size = 128, 19, 5
p, pubkey = keygen(nbit, l)
ENC = encrypt(flag, pubkey, size, nbit)
print(f'p = SECRET')
print(f'pubkey = CENSORED')
print(f'ENC = {ENC}')