Cyber Sea Game 2017: addcrypto (50)

Wed 29 November 2017 · < 1 min read

We are given a file, encrypt.py, which looks as follows.

import os
from flag import flag

message = os.urandom(8) + flag

cipher = ''
for i in range(0, len(message) - 1):
    cipher += chr((ord(message[i]) + ord(message[i+1]) + ord(message[i+1])) & 0xff)

print cipher.encode('hex')
# 4c8f7236c7b259b4e9b792929f2d59534437394530392a2547645958522d3d3b4e3e412c2f2a47314b604d483849342534413e516673 …

MeePwn CTF 2017: |\/|/-\T|-| (100)

Tue 18 July 2017 · 2 min read

We are given a file, hack.py, which looks as follows.

from Crypto.Util.number import *
from hashlib import md5

flag = "XXX"
assert len(flag) == 4
pad = bytes_to_long(md5(flag).digest())

hack = 0

for char in flag:
    hack+= pad
    hack*= ord(char)

print hack
print pad
print hack % pad
#hack …

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