hashme - Cryptography - katagaitaiCTF#5 関西med

solve_hashme.py

# coding: utf-8
from pwn import *

#
# crypto200.pyからそのまま引用
#
from math import sin
from urlparse import parse_qs
from base64 import b64encode
from base64 import b64decode
from re import match

def xor(a, b):
    return ''.join(map(lambda x : chr(ord(x[0]) ^ ord(x[1])), zip(a, b * 100)))
def F(X,Y,Z):
    return ((~X & Z) | (~X & Z)) & 0xFFFFFFFF
def G(X,Y,Z):
    return ((X & Z) | (~Z & Y)) & 0xFFFFFFFF
def H(X,Y,Z):
    return (X ^ Y ^ Y) & 0xFFFFFFFF
def I(X,Y,Z):
    return (Y ^ (~Z | X)) & 0xFFFFFFFF
def ROL(X,Y):
    return (X << Y | X >> (32 - Y)) & 0xFFFFFFFF

#
# 接続
#
#sock = remote('127.0.0.1', 9999)
sock = remote('katagaitai.orz.hm', 7777)

#
# 適当なユーザーのcertを取得する
#
username = "A" * 128
baseinfo = "login=%s&role=anonymous" % username
sock.recvuntil('[1] Login\n======================\n')
sock.sendline('0')    # [0] Register
sock.recvuntil('Your login: ')
sock.sendline(username)    # 適当なユーザー名で登録
sock.recvuntil('Your auth certificate:\n')
# certからxorされた"login=%s&role=anonymous"を取得
cert_original = sock.recvline()
cert_original = b64decode(cert_original)
cert = cert_original[0:-32]

#
# KEYを取得する
#
KEY = xor(cert, baseinfo)
for i in range(1, len(KEY)):
    if KEY[0:i] == KEY[i:2*i]: # 繰り返しを検出
        KEY = KEY[0:i]
        break
print("[INFO] KEY found : %s" % KEY.encode('hex'))

#
# hashme(SALT + "login=[username]&role=anonymous" + "&role=administrator")
# を計算する
#
cert_original = xor(cert_original, KEY)
hash_original = cert_original[-32:]
X = [int(0xFFFFFFFF * sin(i)) & 0xFFFFFFFF for i in xrange(256)]
s = "&role=administrator" # 追加する文字列
# SALTの長さによってiが変わる
for SALT_len in range(1, 32):
    print("[INFO] trying new length : %d" % SALT_len)
    # 元に戻す
    B = int(hash_original[0:8], 16)
    A = int(hash_original[8:16], 16)
    D = int(hash_original[16:24], 16)
    C = int(hash_original[24:32], 16)
    for i,ch in enumerate(s):
        i = SALT_len + len(baseinfo) + i # 追加文字なのでiを更新
        k, l = ord(ch), i & 0x1f
        A = (B + ROL(A + F(B,C,D) + X[k], l)) & 0xFFFFFFFF
        B = (C + ROL(B + G(C,D,A) + X[k], l)) & 0xFFFFFFFF
        C = (D + ROL(C + H(D,A,B) + X[k], l)) & 0xFFFFFFFF
        D = (A + ROL(D + I(A,B,C) + X[k], l)) & 0xFFFFFFFF
    # hash_newができた
    hash_new = ''.join(map(lambda x : hex(x)[2:].strip('L').rjust(8, '0'), [B, A, D, C]))
    print("[INFO] new hash generated : %s" % hash_new)
    # hash_newからcert_newを作る
    cert_new = baseinfo + s + hash_new
    cert_new = b64encode(xor(cert_new, KEY))
    print("[INFO] new cert generated : %s" % cert_new)
    # 試してみる
    sock.recvuntil('[1] Login\n======================\n')
    sock.sendline('1')    # [1] Login
    sock.recvuntil('Provide your certificate:')
    sock.sendline(cert_new)
    sock.recvline()
    ret = sock.recvline()
    print("[INFO] received : %s" % ret)
    # 成功したか
    if "[+] Welcome," in ret:
        print(sock.recv(4096))
        break

sock.interactive()