First price at CISCN2022!

👴开门见山就是一句：👴今年是国一！

虽然今年是我打过最抽象的ctf，但是👴国一，👴不计较！

初赛

crypto

签到

签到题就是个抽象玩意，整了个什么电报机，发一串密文过去就行

ISO9798

抽象黑盒aes，随便打一串东西过去，然后按顺序把第二块和第一块再打回去就行了（

可信计算

这可能是最抽象的两道题

基于挑战码的双向认证

我还在研究题目的时候，我队pwn手突然告诉我他出了，我：？

过去一问，cat /root/cube-shell/instance/flag_server/flag2.txt

给哥们人看傻了

基于挑战码的双向认证2

发现是修了flag文件的权限，哥们就继续看题去了，vim打开的时候一堆告警，然后ls一看，我超，.swp文件赫然屹立在那，反手一个还原准备diff研究，结果又没过多久，pwn手跟我说又出了，我：？？？

过去一问，root弱密码，密码是toor

？？？？？

后来知乎看到个好笑的：

哎，linux怎么提权啊？

没想到你还会pwn？

没，我在做crypto

本次比赛成为自我打ctf以来首个没写一行脚本ak了的比赛，好好好，这题出的好，下次不要再出了

半决赛

首先，再丢wp之前，重中之重的第一件事，都给👴狠狠地把知乎全部看一遍，协办的抽象人，抽象事，还得是我们华东百

所以什么时候才能回到2021华东百永远的家啊（悲

crypto

old

👴就是古典大师！👴就是猜谜的神！

base64+w型栅栏+凯撒

run_faster

开局一堆base64，解密全靠猜

many time pad attack

import Crypto.Util.strxor as xo
import libnum, codecs, numpy as np

def isChr(x):
    if ord('a') <= x and x <= ord('z'): return True
    if ord('A') <= x and x <= ord('Z'): return True
    return False


def infer(index, pos):
    if msg[index, pos] != 0:
        return
    msg[index, pos] = ord(' ')
    for x in range(len(c)):
        if x != index:
            msg[x][pos] = xo.strxor(c[x], c[index])[pos] ^ ord(' ')

def know(index, pos, ch):
    msg[index, pos] = ord(ch)
    for x in range(len(c)):
        if x != index:
            msg[x][pos] = xo.strxor(c[x], c[index])[pos] ^ ord(ch)


dat = []

def getSpace():
    for index, x in enumerate(c):
        res = [xo.strxor(x, y) for y in c if x!=y]
        f = lambda pos: len(list(filter(isChr, [s[pos] for s in res])))
        cnt = [f(pos) for pos in range(len(x))]
        for pos in range(len(x)):
            dat.append((f(pos), index, pos))

c = [codecs.decode(x.strip().encode(), 'hex') for x in open('ciphertext.txt', 'r').readlines()]

msg = np.zeros([len(c), len(c[0])], dtype=int)

getSpace()

dat = sorted(dat)[::-1]
for w, index, pos in dat:
    infer(index, pos)

know(0, 1, 'h')
know(2, 14, 'o')


print('\n'.join([''.join([chr(c) for c in x]) for x in msg]))

key = xo.strxor(c[0], ''.join([chr(c) for c in msg[0]]).encode())
print(key)

拿到密码W@_0u_Y0u_C@n_R3@11y_D@nc3_b@by

解压之后的东西显然一个是字典一个是hash，john爆破就完了

这题很离谱，t非常小，导致加密性很差，只要有t个人的数据基本就能恢复函数f(x)了，题目最后改了y0和y1，但是后面还有很多的数据，直接用后面的就行了

sigma = [(7,[297321905442622086655777122878347065868,311772637731397992755988835643237309539,258409395646949644587189814494650948892,229661884007090559984271007393218884878,210755618260134386557578317684284231344,42629503464484411074530409224833347744,87967363214749550457151328532891556884],[157737545918213953755327108333947991114,317872077880940679809614010825371698417,86624037161883155206577260542472171215,317028281506890684277032990811191697980,258465451871053539349471730150916835415,153264157207783262444002861546206936120,289000922263555251522752972082118420994]),(6,[284334878252345214914712482285696924991,165926984986379306821357416122362386359,193637829384529193495630025917170738695,334882665693477520093059906349807755805,268900344625159440411103370834067861440,91280291221404377771897658696028311940,194953122620210846204934290972270327939],[262772073226095364909240613130896626446,25045221876552835532755896106687587027,290132234127387762127754534163582347803,80323928284560765486185338101062119046,63130854914629293225876778792832543500,194242464018353077430988407022608500272,240358378198563571900194429955390922636]),(17035696356725523435736689352030103776,[16310928756724449650677618214978002701,174336045848228030779714764020238703557,89970216714490906504041327043501903033,282986139634559662214090998546272252057,339756653680570402572151189598090053491,226753195189776187233360667707631451395,302393844239337444779445791166076726499],[83693785572982730284187343563453427812,214382896695971150381852644184906500093,31159746526526831505464896928473401209,109689344372495890477346170739794680979,29464723212738599605243411728123573920,75125389557289762047890120501768842472,83648594694726104892013738976521242930]),(38112363242026170740607299231457590593,[280000669740991152715116414064868844069,117811978751516994318608886491996928160,219066592573340196843386896082513768757,266149851847970337077776861076744575928,273302369856624536044807995922274461035,173837090212655468667252338987442545651,50087494512497153546666189839574987813],[73484909955976133758554085839755813985,168471312867111360682072380440949499624,83002489231793947696180306610753347913,181850915483480478365724927212070209022,31988378704099854892369800287869533334,164069190306115241515513330672566738572,20968485724549308806624305705098823296]),(76205233544349126480906642720404032012,[305030447654966106812630819156617224327,257813469706458852963999235126479482896,19646572578527020171226397193701594536,3096227741298015254290242781056337079,193144454612049425264096843609040583875,131663867163342491996417738843070115893,225042609653050824400550143744526504013],[208200244179108274626478654760656272041,277206679130540511812071164296954433046,133008232900469968393807801737445456047,238187942999310821463031176837431989322,335849605574781654583052890135691606436,43803219416914764604640200649104568720,276238575687619035021067058885214417017]),(204686711424689899259236245265099671151,[55330193663121150614151839948543176192,25374040475906722895551110102466752751,332336287589555261940407367033926210828,236841791562130849608160123633242883485,55132078392822701591355541344100417356,210710935440224596506310010347651890748,246494841359851005113390287205601666834],[339473507188035864234953276558636239614,89814961534867822212610057802248875196,159676081157870578324052534325163446042,278059126074846033027152940362124597383,34703917213859578532087467475347648823,165380347281896132594808120070625786348,139330263516220676740626115157795922525]),(209876243505419239230507609298903863123,[231630314654660388240597169920746438098,319108745154870162781675696472178978700,136580385441834975057798631246982481820,183577018802271270939653308168737951908,323824187627341537434200499585439611550,311284989895183246538067216295958716481,5852988257601121115352692251212404181],[262250385316363078475977443655961217681,44659897377225764927692903931629165495,110331796885242604675024331721197688011,156069809351174897850410833685907713393,71518006372186014009593799874320845431,215822592720683375077289686677881608555,217455673260072965643775624241188442131])]
xlist = [141586027935236199910852696821624556539, 40666427516342492776926786656956980320, 211934535135753616032329255822871485104, 72848036554241506309424877106561776890, 294883308555980411146995456458745170680, 80828132368001405431441629923575932026, 305927509378389767202094045755269682626]

p=340282366920938463463374607431768211507
t=2
n=7
F=GF(p)

key = []
tlist = []
ylist = []
for i in range(n):
    ylist.append(sigma[i][0])
    tlist.append(sigma[i][1])
    key.append(sigma[i][2])

B = []
for i in range(2, n):
    qwq = []
    temp = 1
    for j in range(2, n):
        qwq.append(temp)
        temp = temp * xlist[i] % p
    B.append(qwq)
B = Matrix(F, B)
B = B.inverse()
A = Matrix(F, ylist[2:])
A = A.transpose()
C = B*A
print(C)

决赛

破烂疫情，又是延期又是线上，没去成南开，也没法抄流量，我那时候天天喊的最多的话，大概是寄了

不过👴是国一！好！

先丢个榜

我宣布，决赛就是帆哥哥爆杀之日！（白泽哥太猛了，根本打不过

线上比个赛，又是双机位又是录屏的

Day1

web_unserialize_game

一眼反序列化，先反手把反序列化入口扬了，fix万事

然后break的payload如下

1
2
3

$a=new Game();
$a->setAB("create_function","}EVAL(\$_POST['a']);//");
echo urlencode(serialize($a));

web_just

www.zip泄漏源码，修了半天都修不过去，最后还得是szz哥哥，把白名单全🐑了，然后fix成功了，好好好好好好

web_so_easy_4_u

先发现了几个api

api/save.php存数据

api/get.php读数据

刚开始一直在看hash怎么算，后来想到可以直接把hash赋值了，越界读../../../../../../../flag

然后修的话，break之后能任意文件读，把save.php读出来把.和/过滤掉即可

web_backdoor

这题是真的骚，虽然开源了我还没来得及复现，但是比赛的时候我一直修不好，让我以为这题的check写的非常认真的时候，szz哥哥跟我说修好了，把__sleep里原来的return注释掉，换成return “aa”;，我：？好好好好好好

Day2

web_HouTai

进行一个对黑名单的补

// const blacklists = [`"`, `\\`, `|`, `&`, `+`, `-`, `*`, `/`, `^`];
const blacklists = [`"`, `\\`, `|`, `&`, `+`, `-`, `*`, `/`, `^`, `#`];
// const blackwords = [`select`, `drop`, `insert`, `update`, `delete`, `like`, `order`, `truncate`, `create`, `reg`, `sub`, `left`, `right`, `mid`, `if`, `log`, `pro`, `func`, `history`, `file`, `plugin`, `role`, `collation`, `event`];
const blackwords = [`select`, `drop`, `insert`, `update`, `delete`, `like`, `order`, `truncate`, `create`, `reg`, `sub`, `left`, `right`, `mid`, `if`, `log`, `pro`, `func`, `history`, `file`, `plugin`, `role`, `collation`, `event`, `union`, `database`, `flag`];

web_flasf

接着补黑名单，然后urlopen和read有ssrf，换成request访问然后就突然好了

web_即将上线的项目

前台是个命令执行，直接读flag就行了name=system&content=cat /flaaaaaaggggggggggg&B1=提交

这题是真的恶心，丢个rce给你，不让你杀system函数，check拿着system在根目录乱跑，exp的payload又多的要命，修，修个🔨

这题多给了10次fix机会，不过每次都是patch失败 check不通过或者patch失败 check通过 exp通过幸运二选一罢了

赛后

比赛打完了，这会写博客已经忘的差不多了，我只记得有个最nt的机制是这个

截屏2022-08-24 12.28.18

我还记得我replace打成了repalce，等我发现之后硬是最后五分钟不让我交了😅

头一次拿国一，腾讯会议里的颁奖典礼也没多少意思，抽奖的时候抽了个二等奖，不过我的蓝牙耳机已经堆成山了，所以成功和Dbt👴exchange了一下，好！

Summary

第二年国赛了啊，总算是把国一拿到了，但是还是没有公费旅游，没有茶歇，没有线下真人awd，倒是有大中午的Asuri集体直播干饭

本来想回学校再看看👴这逆天学校还有什么破烂要求，结果👴开学前夕摇身一变中风险，完事解封了这逆天学校还是不让返校，看着身边的好兄弟们都上学去了，我只能憋在家里等着学校安排，没学上，没班上，在学校还得看人脸色，👴多少也有些可悲了罢

tnnd，既然学校不让去，那👴就直接去字节上班去喽

First price at CISCN2022!

初赛

crypto

签到

ISO9798

可信计算

基于挑战码的双向认证

基于挑战码的双向认证2

半决赛

crypto

old

run_faster

share_Masker

决赛

Day1

web_unserialize_game

web_just

web_so_easy_4_u

web_backdoor

Day2

web_HouTai

web_flasf

web_即将上线的项目

赛后

Summary