安恒2018年9月赛~简单加密

#!/usr/bin/env python
# -*- coding:utf-8 -*- 
from Crypto.Cipher import AES
from Crypto import Random

def encrypt(data, password):
    bs = AES.block_size
    pad = lambda s: s + (bs - len(s) % bs) * chr(bs - len(s) % bs)
    iv = "0102030405060708"
    cipher = AES.new(password, AES.MODE_CBC, iv)
    data = cipher.encrypt(pad(data))
    return data
 
def decrypt(data, password):
    unpad = lambda s : s[0:-ord(s[-1])]
    iv = "0102030405060708"
    cipher = AES.new(password, AES.MODE_CBC, iv)
    data  = cipher.decrypt(data)
    return unpad(data)
    
def generate_passwd(key):
    data_halt = "LvR7GrlG0A4WIMBrUwTFoA==".decode("base64")
    rand_int =  int(decrypt(data_halt, key).encode("hex"), 16)
    round = 0x7DC59612
    result = 1    
    a1 = 0
    while a1 < round:
        a2 = 0
        while a2 < round:
            a3 = 0
            while a3 < round:
                result = result * (rand_int % 0xB18E) % 0xB18E
                a3 += 1
            a2 += 1
        a1 += 1
    return encrypt(str(result), key)
    

if __name__ == '__main__':

    key = raw_input("key:")
    
    if len(key) != 32:
        print "check key length!"
        exit()
    passwd = generate_passwd(key.decode("hex"))
    
    flag = raw_input("flag:")
    
    print "output:", encrypt(flag, passwd).encode("base64")
    
            
        
# key = md5(sha1("flag"))
# output = "u6WHK2bnAsvTP/lPagu7c/K3la0mrveKrXryBPF/LKFE2HYgRNLGzr1J1yObUapw"

通过观察这条语句：result = result * (rand_int % 0xB18E) % 0xB18E

result不会超过0xB18E，于是采用爆破result方式生成passwd。

该程序使用了PyCrypto库，访问http://www.voidspace.org.uk/python/modules.shtml#pycrypto，下载并安装PyCrypto 2.6 for Python 2.7 64bit。

重写程序，爆破。 

#!/usr/bin/env python
# -*- coding:utf-8 -*- 
from Crypto.Cipher import AES
from Crypto import Random
from hashlib import md5, sha1

def encrypt(data, password):
    bs = AES.block_size
    pad = lambda s: s + (bs - len(s) % bs) * chr(bs - len(s) % bs)
    iv = "0102030405060708"
    cipher = AES.new(password, AES.MODE_CBC, iv)
    data = cipher.encrypt(pad(data))
    return data
 
def decrypt(data, password):
    unpad = lambda s : s[0:-ord(s[-1])]
    iv = "0102030405060708"
    cipher = AES.new(password, AES.MODE_CBC, iv)
    data  = cipher.decrypt(data)
    return unpad(data)
    
def generate_passwd(result, key):
    '''
    data_halt = "LvR7GrlG0A4WIMBrUwTFoA==".decode("base64")
    rand_int =  int(decrypt(data_halt, key).encode("hex"), 16)
    round = 0x7DC59612
    result = 1    
    a1 = 0
    while a1 < round:
        a2 = 0
        while a2 < round:
            a3 = 0
            while a3 < round:
                result = result * (rand_int % 0xB18E) % 0xB18E
                a3 += 1
            a2 += 1
        a1 += 1
    '''
    return encrypt(str(result), key)
    
def Md5(input1):
    m1 = md5()
    m1.update(input1)
    return m1.hexdigest()

def Sha1(input1):
    m2 = sha1()
    m2.update(input1)
    return m2.hexdigest()

if __name__ == '__main__':
    '''
    key = raw_input("key:")
    
    if len(key) != 32:
        print "check key length!"
        exit()
    passwd = generate_passwd(key.decode("hex"))
    
    flag = raw_input("flag:")
    
    print "output:", encrypt(flag, passwd).encode("base64")
    '''
    key = Md5(Sha1("flag")).decode("hex")
    output = "u6WHK2bnAsvTP/lPagu7c/K3la0mrveKrXryBPF/LKFE2HYgRNLGzr1J1yObUapw"
    for result in range(0x0B18E):
        passwd = generate_passwd(result, key)
        flag = decrypt(output.decode("base64"), passwd)
        if 'flag' in flag:
            print flag
            break
    print 'ok'

得到结果flag{552d3a0e567542d99694c4d61d1a652e}