def store_flags(self, team, round):
from gameserver import cheapMethodFromRoundNumber, cheapMethods, GameServer, GameServerCrypto, SHA512_HEX_LEN, \
methods
flagsStored = 0
method = cheapMethodFromRoundNumber(round)
flagIndex = cheapMethods.index(method)
flagId = self.get_flag_id(team, round, 0)
flag = self.get_flag(team, round, flagIndex)
msg = GameServer.generatePlaintext() % flag
# Check if the flag is already stored
# We could in theory just try to store the flag and check for an IntegrityException from sqlite.
# However, this approach might not work if teams tinker with their DB layout.
flagAlreadyStored = True
try:
GameServer.retrieveCipher(team.ip, PORT, flagId)
except FlagMissingException:
flagAlreadyStored = False
if not flagAlreadyStored:
cipher, params, msg = GameServerCrypto.encrypt(msg, method)
paramHash = msg[-SHA512_HEX_LEN:]
self.store(team, round, f"paramhash_{flagIndex}", paramHash)
self.store(team, round, f"msg_{flagIndex}", msg)
GameServer.storeCipher(team.ip, PORT, flagId, cipher, params)
flagsStored += 1
flagIndex = methods.index("schwenk")
flagId = self.get_flag_id(team, round, 1)
flag = self.get_flag(team, round, flagIndex)
msg = GameServer.generatePlaintext() % flag
flagAlreadyStored = True
try:
GameServer.retrieveCipher(team.ip, PORT, flagId)
except FlagMissingException:
flagAlreadyStored = False
if not flagAlreadyStored:
cipher, params, msg = GameServerCrypto.schwenkNew(
msg, skipKeyAndIV=False)
paramHash = GameServerCrypto.parameterHash(params)
self.store(team, round, f"paramhash_{flagIndex}", paramHash)
self.store(team, round, "schwenk_msg",
msg) # Random key + IV are added.
GameServer.storeCipher(team.ip, PORT, flagId, cipher, params)
flagsStored += 1
return flagsStored
# print(e)
continue
# No try here: At this point, we are very sure that we have decrypted correctly so far. Backtracking here would also be rather messy.
c_plain = c_elem.nthRoot(
k_b_out.toNumber() ^ xorParams[blockIndex]).toString()
if not isValidPlaintext(c_plain):
continue
plain = c_plain + plain
print("Found plaintext fragment:", c_plain)
bFound = True
break
if not bFound:
raise Exception("Decryption failed.")
remainingCipher = remainingCipher[:-bExpected - bOffset]
k_next_out = k_b_out
IV_next_out = IV_b_out
return plain.decode("utf-8")
if __name__ == "__main__":
assert len(sys.argv) >= 4, "Needs flag ids in fourth argument"
target = sys.argv[1]
flagIds = sys.argv[3].split(",")
for flagId in flagIds:
cipher, params = GameServer.retrieveCipher(target, PORT, flagId)
if params["method"] == "schwenk":
plain = exploit(cipher, params)
print(plain)