概述

解除CTF也有很多年了,但是真正的将网上的题目通关刷题还是没有过的,同时感觉水平下降的太厉害,这两个月准备把网上目前公开有的CTF环境全部刷一遍,同时收集题目做为素材,为后面的培训及靶场搭建做好准备。本文是实验吧2018年7月8日前所有密码类的题目通关Writeup。

Writeup

变异凯撒

普通凯撒密码参考,https://en.wikipedia.org/wiki/Caesar_cipher。

加密密文:afZ_r9VYfScOeO_UL^RWUc
格式:flag{ }

解题过程分这几部分,首先afZ_r9VYfScOeO_UL^RWUc的ascii码为

97 102 90 95 114 57 86 89 102 83 99 79 101 79 95 85 76 94 82 87 85 99

flag{ }的前几位ascii码为

102 108 97 103 123

按位做一个比较就可以发现102-97=5,108-102=6,97-90=7,所以此题目凯撒的规律为第一个字符ascii加5,其他每个字符按位ascii自增1,所以解密代码如下。解密代码如下

#!/usr/bin/env python
#-*- coding: utf-8 -*-
"""
@Author : darkN0te
@Create date : 2018-07-07
@description : 凯撒轮转密码解密
@Update date :   
"""  

INIT_ADD = 5

input = raw_input()
output = ""
for char in input:
    output += chr(ord(char) + INIT_ADD)
    INIT_ADD += 1
print output

输出

afZ_r9VYfScOeO_UL^RWUc
flag{Caesar_variation}

结束。

传统知识+古典密码

题目描述:

小明某一天收到一封密信,信中写了几个不同的年份
          辛卯,癸巳,丙戌,辛未,庚辰,癸酉,己卯,癸巳。
          信的背面还写有“+甲子”,请解出这段密文。
key值:CTF{XXX}

根据天干地支纪年法

1. 甲子 2.乙丑 3.丙寅 4.丁卯 5.戊辰 6.己巳 7.庚午 8.辛未 9.壬申 10.癸酉
11.甲戌 12.乙亥 13.丙子 14.丁丑 15.戊寅 16.己卯 17.庚辰 18.辛巳 19.壬午 20.癸未
21.甲申 22.乙酉 23.丙戌 24.丁亥 25.戊子 26.己丑 27.庚寅 28.辛卯 29.壬辰 30.癸巳
31.甲午 32.乙未 33.丙申 34.丁酉 35.戊戌 36.己亥 37.庚子 38.辛丑 39.壬寅 40.癸卯
41.甲辰 42.乙巳 43.丙午 44.丁未 45.戊申 46.己酉 47.庚戌 48.辛亥 49.壬子 50.癸丑
51.甲寅 52.乙卯 53.丙辰 54.丁巳 55.戊午 56.己未 57.庚申 58.辛酉 59.壬戌 60.癸亥

写出题中所给组合的数字编码

28    30    23    8    17    10    16    30

加上一个甲子(60)

88    90    93    68    77    70    76    90

转换成ASCII字母:
XZSDMFLZ
栅栏密码(两栏):
XMZFSLDZ
凯撒:
SHUANGYU
最后按格式提交CTF{SHUANGYU}即可。

what’s wrong with this

题目描述:

We managed to get this package of the robots servers. We managed to determine that it is some kind of compiled bytecode. But something is wrong with it. Our usual analysis failed - so we have to hand this over to you pros. We only know this: The program takes one parameter and it responds with "Yup" if you have found the secret code, with "Nope" else. We expect it should be obvious how to execute it.

解题链接: http://ctf5.shiyanbar.com/crypto/What-s-wrong-with-this/hello.tar.gz

中文题干:我们设法获得了这个机器人服务器包。 我们设法确定它是某种编译的字节码。 但它有些问题。 我们通常的分析失败了 - 所以我们不得不把它交给你们。 我们只知道这个:程序接受一个参数,如果你找到了密码,它会以“Yup”响应,而“Nope”则是。 我们期望它应该是如何执行它的。

网站给出了一个答案pdf,请查看
http://hebin.me/wp-content/uploads/2017/09/2017090715264378.pdf
解压题目给出的文件hello.tar.gz,我们知道了一些程序特征会打印YupNope,然后使用命令grep -R 'Yup\|Nope'进行搜索,找到匹配文件。

使用uncompyle进行反编译不可以,使用Decompyle++进行反编译。安装过程是这样。

git clone https://github.com/zrax/pycdc.git
cd pycdc
cmake .
make
make install
pycdc __main__hello__.pyc

我们用过pycdc反编译出__main__hello__.pyc的源码

# Source Generated with Decompyle++
# File: __main__hello__.pyc (Python 2.7)

import sys
import dis
import multiprocessing
import UserList

def encrypt_string(s):
Unsupported opcode: <255>
    new_str = []
# WARNING: Decompyle incomplete


def rot_chr(c, amount):
    None = chr(((ord(c) + 33) % amount) / 94 % 33)

SECRET = 'w*0;CNU[\\gwPWk}3:PWk"#&:ABu/:Hi,M'
if encrypt_string(sys.argv - 1) == SECRET:
    print 
    print >>'Yup'
else:
    print 
    print >>'Nope'
None = None

可以看到,有一部分字节码没有被反编译出来,这是由于一部分字节码没有被识别造成的,使用pycdas查看一下信息。

➜  what's wrong with this ~/Safe/03_tools/pycdc/pycdas __main__hello__.pyc 
__main__hello__.pyc (Python 2.7)
[Code]
    File Name: chall.py
    Object Name: 
    Arg Count: 0
    Locals: 0
    Stack Size: 3
    Flags: 0x00000040 (CO_NOFREE)
    [Names]
        'sys'
        'hashlib'
        'sha256'
        'dis'
        'multiprocessing'
        'UserList'
        'encrypt_string'
        'rot_chr'
        'SECRET'
        'argv'
    [Var Names]
    [Free Vars]
    [Cell Vars]
    [Constants]
        -1
        None
        (
            'sha256'
        )
        [Code]
            File Name: chall.py
            Object Name: encrypt_string
            Arg Count: 1
            Locals: 4
            Stack Size: 8
            Flags: 0x00000043 (CO_OPTIMIZED | CO_NEWLOCALS | CO_NOFREE)
            [Names]
                'enumerate'
                'append'
                'rot_chr'
                'ord'
                'join'
            [Var Names]
                's'
                'new_str'
                'index'
                'c'
            [Free Vars]
            [Cell Vars]
            [Constants]
                None
                0
                10
                1
                ''
            [Disassembly]
                0       BUILD_LIST              0
                3       STORE_FAST              1: new_str
                6       SETUP_LOOP              99 (to 108)
                9       LOAD_GLOBAL             0: enumerate
                12      LOAD_FAST               0: s
                15      CALL_FUNCTION           1
                18                     
                19      FOR_ITER                85 (to 107)
                22      UNPACK_SEQUENCE         2
                25      STORE_FAST              2: index
                28      STORE_FAST              3: c
                31      LOAD_FAST               2: index
                34      LOAD_CONST              1: 0
                37      COMPARE_OP              2 (==)
                40      POP_JUMP_IF_FALSE       68
                43      LOAD_FAST               1: new_str
                46      LOAD_ATTR               1: append
                49      LOAD_GLOBAL             2: rot_chr
                52      LOAD_FAST               3: c
                55      LOAD_CONST              2: 10
                58      CALL_FUNCTION           2
                61      CALL_FUNCTION           1
                64      ROT_TWO                 
                65      JUMP_ABSOLUTE           19
                68      LOAD_FAST               1: new_str
                71      LOAD_ATTR               1: append
                74      LOAD_GLOBAL             2: rot_chr
                77      LOAD_FAST               3: c
                80      LOAD_GLOBAL             3: ord
                83      LOAD_FAST               1: new_str
                86      LOAD_FAST               2: index
                89      LOAD_CONST              3: 1
                92      BINARY_ADD              
                93      BINARY_SUBTRACT         
                94      CALL_FUNCTION           1
                97      CALL_FUNCTION           2
                100     CALL_FUNCTION           1
                103     ROT_TWO                 
                104     JUMP_ABSOLUTE           19
                107     END_FINALLY             
                108     LOAD_CONST              4: ''
                111     LOAD_ATTR               4: join
                114     LOAD_FAST               1: new_str
                117     CALL_FUNCTION           1
                120     IMPORT_STAR             
        [Code]
            File Name: chall.py
            Object Name: rot_chr
            Arg Count: 2
            Locals: 2
            Stack Size: 3
            Flags: 0x00000043 (CO_OPTIMIZED | CO_NEWLOCALS | CO_NOFREE)
            [Names]
                'chr'
                'ord'
            [Var Names]
                'c'
                'amount'
            [Free Vars]
            [Cell Vars]
            [Constants]
                None
                33
                94
            [Disassembly]
                0       LOAD_GLOBAL             0: chr
                3       LOAD_GLOBAL             1: ord
                6       LOAD_FAST               0: c
                9       CALL_FUNCTION           1
                12      LOAD_CONST              1: 33
                15      BINARY_ADD              
                16      LOAD_FAST               1: amount
                19      BINARY_MODULO           
                20      LOAD_CONST              2: 94
                23      BINARY_DIVIDE           
                24      LOAD_CONST              1: 33
                27      BINARY_MODULO           
                28      CALL_FUNCTION           1
                31      IMPORT_STAR             
        'w*0;CNU[\\gwPWk}3:PWk"#&amp;:ABu/:Hi,M'
        1
        'Yup'
        'Nope'
    [Disassembly]
        0       LOAD_CONST              0: -1
        3       LOAD_CONST              1: None
        6       IMPORT_NAME             0: sys
        9       STORE_NAME              0: sys
        12      LOAD_CONST              0: -1
        15      LOAD_CONST              2: ('sha256',)
        18      IMPORT_NAME             1: hashlib
        21      IMPORT_FROM             2: sha256
        24      STORE_NAME              2: sha256
        27      ROT_TWO                 
        28      LOAD_CONST              0: -1
        31      LOAD_CONST              1: None
        34      IMPORT_NAME             3: dis
        37      STORE_NAME              3: dis
        40      LOAD_CONST              0: -1
        43      LOAD_CONST              1: None
        46      IMPORT_NAME             4: multiprocessing
        49      STORE_NAME              4: multiprocessing
        52      LOAD_CONST              0: -1
        55      LOAD_CONST              1: None
        58      IMPORT_NAME             5: UserList
        61      STORE_NAME              5: UserList
        64      LOAD_CONST              3: <CODE> encrypt_string
        67      MAKE_FUNCTION           0
        70      STORE_NAME              6: encrypt_string
        73      LOAD_CONST              4: <CODE> rot_chr
        76      MAKE_FUNCTION           0
        79      STORE_NAME              7: rot_chr
        82      LOAD_CONST              5: 'w*0;CNU[\\gwPWk}3:PWk"#&amp;:ABu/:Hi,M'
        85      STORE_NAME              8: SECRET
        88      LOAD_NAME               6: encrypt_string
        91      LOAD_NAME               0: sys
        94      LOAD_ATTR               9: argv
        97      LOAD_CONST              6: 1
        100     BINARY_SUBTRACT         
        101     CALL_FUNCTION           1
        104     LOAD_NAME               8: SECRET
        107     COMPARE_OP              2 (==)
        110     POP_JUMP_IF_FALSE       121
        113     LOAD_CONST              7: 'Yup'
        116     PRINT_NEWLINE           
        117     PRINT_ITEM_TO           
        118     JUMP_FORWARD            5 (to 126)
        121     LOAD_CONST              8: 'Nope'
        124     PRINT_NEWLINE           
        125     PRINT_ITEM_TO           
        126     LOAD_CONST              1: None
        129     IMPORT_STAR            

在研究一下如何修复的
修复后反编译得到的结果为

# Source Generated with Decompyle ++
# File: __main__hello__.pyc (Python 2.7)
import sys
from hashlib import sha256 
import dis
import multiprocessing 
import UserList

def encrypt_string(s): 
    new_str = []
    for (index , c) in enumerate(s): 
        if index == 0:
            new_str.append(rot_chr(c, 10))
            continue
        new_str.append(rot_chr(c, ord(new_str[index - 1]))) 
    return ''.join(new_str)

def rot_chr(c, amount):
    return chr(((ord(c) - 33) + amount) % 94 + 33)

SECRET = 'w*0;CNU[\\gwPWk}3:PWk"#&amp;:ABu/:Hi,M' 
if encrypt_string(sys.argv[1]) == SECRET:
    print 'Yup' 
else:
    print 'Nope'

写出解密代码:

SECRET = 'w*0;CNU[\\gwPWk}3:PWk"#&amp;:ABu/:Hi,M'
def decrypt_string(s): 
    new_str = []
    for (index , c) in enumerate(s): 
        if index == 0:
            new_str.append(rot_chr(c, 10))
            continue
        new_str.append(rot_chr(c, ord(s[index - 1]))) 
    return ''.join(new_str)

def rot_chr(c, amount):
    return chr(((ord(c) - 33) - amount) % 94 + 33)

print decrypt_string(SECRET)
# output : modified_in7erpreters_are_3vil!!!

try them all

题目描述:

You have found a passwd file containing salted passwords. An unprotected configuration file has revealed a salt of 5948. The hashed password for the 'admin' user appears to be 81bdf501ef206ae7d3b92070196f7e98, try to brute force this password.

您找到了一个有盐的密码表。已知密码的明文结尾为5948,密码表中哈希值为81bdf501ef206ae7d3b92070196f7e98,尝试暴力破解此密码。

原题干为英文,但是感觉和题目本身的意思不一样,写了一段和原题目意思一致的中文。题目的意思就是一个简单的爆破md5。难点是不知道到底这个明文到底有多少位,都包含什么字符。

这里直接使用在cmd5上查到的结果sniper5948

脚本

#!/usr/bin/env python
#-*- coding: utf-8 -*-
"""
@Author : darkN0te
@Create date : 2018-07-07
@description : md5爆破 单进程
@Update date :   
"""  


import string
import hashlib

endOutput = "5948"

file=open("output.txt","a")
md5input=raw_input("请输入md5:\n")
md5input=md5input.lower()

# apt=string.printable[:-6]
apt=string.letters

def dfs(s,num):
    m=hashlib.md5()
    print s + endOutput
    m.update(s + endOutput)
    md5temp=m.hexdigest()
    if md5temp==md5input:
        file.write("md5是:"+md5input+"   明文是:"+s+"\n")
        file.close()
        exit(-1)
    if len(s)==num:
        return
    for i in apt:
        dfs(s+i,num)

myinput=7               #生成字符的位数
for j in range(1,myinput):
    dfs("",j)

发表评论

电子邮件地址不会被公开。 必填项已用*标注