/integrity.py Secret
Created
March 22, 2017 06:08
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#!/usr/bin/python -u | |
from Crypto.Cipher import AES | |
from hashlib import md5 | |
from Crypto import Random | |
from signal import alarm | |
BS = 16 | |
pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS) | |
unpad = lambda s : s[0:-ord(s[-1])] | |
class Scheme: | |
def __init__(self,key): | |
self.key = key | |
def encrypt(self,raw): | |
raw = pad(raw) | |
raw = md5(raw).digest() + raw | |
iv = Random.new().read(BS) | |
cipher = AES.new(self.key,AES.MODE_CBC,iv) | |
return ( iv + cipher.encrypt(raw) ).encode("hex") | |
def decrypt(self,enc): | |
enc = enc.decode("hex") | |
iv = enc[:BS] | |
enc = enc[BS:] | |
cipher = AES.new(self.key,AES.MODE_CBC,iv) | |
blob = cipher.decrypt(enc) | |
checksum = blob[:BS] | |
data = blob[BS:] | |
if md5(data).digest() == checksum: | |
return unpad(data) | |
else: | |
return | |
key = Random.new().read(BS) | |
scheme = Scheme(key) | |
flag = open("flag",'r').readline() | |
alarm(30) | |
print "Welcome to 0CTF encryption service!" | |
while True: | |
print "Please [r]egister or [l]ogin" | |
cmd = raw_input() | |
if not cmd: | |
break | |
if cmd[0]=='r' : | |
name = raw_input().strip() | |
if(len(name) > 32): | |
print "username too long!" | |
break | |
if pad(name) == pad("admin"): | |
print "You cannot use this name!" | |
break | |
else: | |
print "Here is your secret:" | |
print scheme.encrypt(name) | |
elif cmd[0]=='l': | |
data = raw_input().strip() | |
name = scheme.decrypt(data) | |
if name == "admin": | |
print "Welcome admin!" | |
print flag | |
else: | |
print "Welcome %s!" % name | |
else: | |
print "Unknown cmd!" | |
break | |
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