2020年最后的一次比赛,共三场,一直想复盘一下再写WP的,最终还是咕了。。。
鲲鹏计算专场独自解了两道逆向+一道半Crypto+两道RealWorld,也是校队第一次进XCTF分站赛前十
鸿蒙专场AK了5道逆向+1道RealWorld,可惜当天起得晚了点加上中午有点事,基本都是四血,不过此次队友十分给力,短暂登过顶,最终也苟进了第五,算是2020年最好的成绩了!
鲲鹏计算专场 - Crypto
combinelfsr
lfsr,参考https://www.anquanke.com/post/id/184828
z3 求 R1,R2
R2= 90307
R1 = 13706
1 | from z3 import * |
1 | # from z3 |
flag{d0b570e1-5292-4381-9d71-d6edab490854}
RRSSAA
简单的rsa,总共有三部分,part1直接解,part2利用韦达定理解
1 | from Crypto.Util.number import * |
flag{4c2fd4e6-44de-445f-8c34-1235464de2de}
鲲鹏计算 && 鸿蒙专场 - Reverse
逆向部分WP写得比较简单,较为详细的wp可以参考师妹的博客https://c10udlnk.top/2020/12/29/wpFor-2020XCTF/
mips
三个迷宫,走完就行,这道题多解
1 | g = [0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000000, 0x00000003, 0x00000000, 0x00000001, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000000, 0x00000001, 0x00000000, 0x00000001, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000000, 0x00000001, 0x00000000, 0x00000001, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000000, 0x00000001, 0x00000000, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000000, 0x00000000, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000001, 0x00000000, 0x00000001, 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0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000004, 0x00000000, 0x00000000] |
pypy
解包,反编译 https://github.com/extremecoders-re/pyinstxtractor/wiki/Extracting-Linux-ELF-binaries
rc4,这里注意python3的encode
1 | # from Crypto.Cipher import ARC4 |
re123
chm文件,用chmdecompiler反编译,doc.htm有一段base64编码的powershell shellcode,解base64
执行,得到一个pe,补文件头,可以看到就是一个简单的后门,aes加密,密文,密钥直接给出,直接解即可
1 | key = b'\x2b\x7e\x15\x16\x28\xae\xd2\xa6\xab\xf7\x15\x88\x09\xcf\x4f\x3c' |
flag{youcangues}
crash
crash包含多个可执行文件,binwalk分离获取主程序,password校验算法为按字节xor 0x17,之后每四个字节取md5和常量比对
1 | # "bf2b36d56f5757c13cad80494b385e78" |
flag{ux1cy1x4iltkahbc9nu1nk00d9akpp7w}
arm
arm架构,程序输入key和flag,用key作为随机数种子(取低8位)初始化随机数池,作为常数(取低8位+1)形成42元一次方程组,output.txt就是方程组的ans。
hook程序地址00107A0,使程序直接打印生成的随机数序列,共42*42个
之后只要遍历一个字节的key,尝试解方程即可
1 | import pexpect |
82:
dict_values([198, 136, 219, 156, 107, 228, 152, 7, 239, 63, 97, 127, 134, 5, 247, 131, 109, 75, 96, 180, 241, 173, 57, 211, 49, 224, 157, 9, 34, 243, 129, 199, 1, 244, 31, 17, 157, 171, 252, 249, 64, 91])
xor table getflag
1 | arr=[0xA0, 0xE4, 0xBA, 0xFB, 0x10, 0xDD, 0xAC, 0x65, 0x8D, 0x0B, 0x57, 0x1A, 0xE4, 0x28, 0x96, 0xB3, 0x0C, 0x79, 0x4D, 0x80, 0x90, 0x99, 0x58, 0xFE, 0x50, 0xD3, 0xF9, 0x3C, 0x0F, 0xC1, 0xE3, 0xA6, 0x39, 0xC3, 0x28, 0x75, 0xF8, 0xC9, 0xC8, 0xCD, 0x78, 0x26] |
flag{94bb46eb-a0a2-4a4a-a3d5-2ba877deb448}
arm_pe
windows-arm架构,无环境,静态硬刚
普莱费尔密码
密钥表
1 | CREIH |
密文
KIMLXDWRZXTHXTHQTXTXHZWC
按规则解密即可
YE SM AY BE YO UC AN RU NA NA RM PE
flag{YESMAYBEYOUCANRUNANARMPE}
puzzle
mips架构
一个华容道游戏,八数码问题,用现成的算法算出走的方向
1 | #include <iostream> |
base64换表求解
1 | import base64 |
flag{8xOi6R2k8xOk6R2i7xOm}
鲲鹏计算 && 鸿蒙专场 - RealWorld
realworld这几道都比较简单,有手就行
AESbaby
arm架构,买个鲲鹏处理器的云服务器编译即可
抄个aes,table优化成52/62,百分之五十概率能打通,分段传shellcode,exp打通概率百分之二十左右
远程exp
1 | from base64 import * |
可执行文件源码
1 |
|
Hash
老规矩,随便找个sha256源码,鲲鹏编译,大概百分之二的概率能出
exp
1 | from base64 import * |
main.c
1 | /********************************************************************* |
sha256.h
1 | /********************************************************************* |
sha256.c
1 | /********************************************************************* |
flag{QuiCK_H4sh_cbDbdBdcd6}
luaplayground01
鸿蒙系统运行的lua,execute被禁用,通过io读文件,hexencode分段读取
1 | function bin2hex(s) |
简单逆向
1 | b = [0x9C, 0x6D, 0xE7, 0x56, 0x06, 0xD2, 0x0D, 0xEB, 0xDD, 0xF0, 0x9E, 0xB7, 0xFB, 0xE6, 0xEC, 0x3B, 0xB7, 0x5E, 0x75, 0x53, 0xD6, 0x83, 0x75, 0xAF, 0x18, 0xF7, 0x99, 0x95, 0xF2, 0xC1, 0xF2, 0xDB, 0x9F, 0x65, 0xB4, 0x06, 0x49, 0x87, 0x58, 0xE2, 0xDE, 0xB5, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00] |
flag{cd8e88ac-b8f6-4de5-b4d4-1dded274611f}