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[原创]DASCTF 2023六月挑战赛 二进制专项 RE writeup
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发表于: 2023-6-5 12:27
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常年不去上早八课的人,今天居然在八点前就醒了,要问为什么?这比赛从早上八点打到晚上八点>...<(悲)
不过,咱们队伍在下午就把逆向题ak了~居然没有坐牢到晚上(●'◡'●)
动态调试,题目里有个inline hook,在这里打个断点
那么网址就是Just_An_APIH00k11.com
die查一下壳
有sleep反调试,把sleep nop掉
这里读取了名称为cod的资源,用resource hacker把资源复制下来
然后向下执行,这里是一个对cod资源进行解密的地方
这里要注意的是如果检测到调试器,那么byte_7FF6DA64F000[3]将会被赋值为36
所以要把这个if语句通过修改ZF标志位的方式来绕过反调试
cod资源解密脚本如下
用ida打开,看到有花指令
nop一下,主要的改动有这几处
于是得到如下的伪代码
看算法是魔改的RC4,exp如下
查个壳,是python逆向
用pyinstxtractor脱一下
用在线网站看一下ez_py.pyc的源代码
用ida反编译bin1失败,看来是被加密了
用这个代码看一下字节码
在最后面得到了这个
那么解密代码如下
反编译出来是这个
那根据提示我们把上面的解密脚本稍作修改
然后用ida反编译bin2__
那么这就是正常的逆向题了
btea函数里面是这个,这是一个xxtea算法
写一下exp
在这个地方动调
可以发现数组的下标在0~12之间循环
我们随便打开一个BMP类型的文件,用010看看
对于BMP类型的文件前两个字节必定是43 4D
既然这个加密的bmp的每一个字节进行的都是异或,那我们可以将前两个字节异或看看
n和c是密钥enc_by_dasctf的第2个和第3个字符,按照这个序列,我们向后将密钥向后延申看看后面的情况如何
所以我们写个脚本,从密钥的第二位开始,循环异或
得到flag
查一下壳,是go逆向
用这个脚本恢复一下go符号https://github.com/renshareck/IDAGolangHelper_SupportGo1.20
依次点击如下按钮
首先判断key正确与否,看来这是个rsa
用yafu解一下p和q
然后解出密钥
再往后看,
动调了一下看到iv和key都是一样的
所以直接写个exp把加密的文件解密
运行一下解密出的exe,就得到flag了
arr = [0x18, 0x57, 0x68, 0x64]
with open('COD101.bin', 'rb') as f:
b = f.read()
b = bytearray(b)
for i in range(len(b)):
b[i] = b[i] ^ arr[i % 4]
with open('COD_de.bin', 'wb') as f:
f.write(b)
arr = [0x18, 0x57, 0x68, 0x64]
with open('COD101.bin', 'rb') as f:
b = f.read()
b = bytearray(b)
for i in range(len(b)):
b[i] = b[i] ^ arr[i % 4]
with open('COD_de.bin', 'wb') as f:
f.write(b)
class RC4:
def __init__(self, key) -> None:
self.key = key
self.S = 0
self.__rc4_init__()
def __rc4_init__(self):
S = [i for i in range(256)]
j = 0
for i in range(256):
j = (2 * j + S[i] + key[i % len(key)]) % 256
S[i], S[j] = S[j], S[i]
self.S = S
def rc4_encrypt(self, plain) -> list:
i = 0
j = 0
cipher = []
cnt = 0
for p in plain:
p = (p + 256 - cnt % 0xd) % 256
cnt += 1
i = (i + j) % 256
j = (j + self.S[i]) % 256
self.S[i], self.S[j] = self.S[j], self.S[i]
tmp = self.S[(self.S[i] + self.S[j] + j) % 256]
k = p ^ tmp
cipher.append(k)
return cipher
key = [0x5D , 0x42 , 0x62 , 0x29 , 0x3, 0x36 , 0x47 , 0x41 , 0x15, 0x36]
data = [0xF7, 0x2E, 0x34, 0xF0, 0x72, 0xCF, 0x5E, 0x0A, 0xBB, 0xEC, 0xB1, 0x2B, 0x70, 0x88, 0x88, 0xED,
0x46, 0x38, 0xDB, 0xDA, 0x6C, 0xBD, 0xD4, 0x06, 0x77, 0xF2, 0xCF, 0x56, 0x88, 0xC6, 0x31, 0xD2,
0xB7, 0x5A, 0xC1, 0x42, 0xB0, 0xF4, 0x48, 0x37, 0xF5, 0x2C, 0xF5, 0x58]
rc4 = RC4(key)
plain = rc4.rc4_encrypt(data)
print(''.join(map(chr,plain)))
class RC4:
def __init__(self, key) -> None:
self.key = key
self.S = 0
self.__rc4_init__()
def __rc4_init__(self):
S = [i for i in range(256)]
j = 0
for i in range(256):
j = (2 * j + S[i] + key[i % len(key)]) % 256
S[i], S[j] = S[j], S[i]
self.S = S
def rc4_encrypt(self, plain) -> list:
i = 0
j = 0
cipher = []
cnt = 0
for p in plain:
p = (p + 256 - cnt % 0xd) % 256
cnt += 1
i = (i + j) % 256
j = (j + self.S[i]) % 256
self.S[i], self.S[j] = self.S[j], self.S[i]
tmp = self.S[(self.S[i] + self.S[j] + j) % 256]
k = p ^ tmp
cipher.append(k)
return cipher
key = [0x5D , 0x42 , 0x62 , 0x29 , 0x3, 0x36 , 0x47 , 0x41 , 0x15, 0x36]
data = [0xF7, 0x2E, 0x34, 0xF0, 0x72, 0xCF, 0x5E, 0x0A, 0xBB, 0xEC, 0xB1, 0x2B, 0x70, 0x88, 0x88, 0xED,
0x46, 0x38, 0xDB, 0xDA, 0x6C, 0xBD, 0xD4, 0x06, 0x77, 0xF2, 0xCF, 0x56, 0x88, 0xC6, 0x31, 0xD2,
0xB7, 0x5A, 0xC1, 0x42, 0xB0, 0xF4, 0x48, 0x37, 0xF5, 0x2C, 0xF5, 0x58]
rc4 = RC4(key)
plain = rc4.rc4_encrypt(data)
print(''.join(map(chr,plain)))
#!/usr/bin/env python# visit https://tool.lu/pyc/ for more information# Version: Python 3.11import ctypes
from time import *
from ctypes import *
from ctypes import wintypes
from hashlib import md5
class _STARTUPINFO(Structure):
_fields_ = [
('cb', c_ulong),
('lpReserved', c_char_p),
('lpDesktop', c_char_p),
('lpTitle', c_char_p),
('dwX', c_ulong),
('dwY', c_ulong),
('dwXSize', c_ulong),
('dwYSize', c_ulong),
('dwXCountChars', c_ulong),
('dwYCountChars', c_ulong),
('dwFillAttribute', c_ulong),
('dwFlags', c_ulong),
('wShowWindow', c_ushort),
('cbReserved2', c_ushort),
('lpReserved2', c_char_p),
('hStdInput', c_ulong),
('hStdOutput', c_ulong),
('hStdError', c_ulong)]
class _PROCESS_INFORMATION(Structure):
_fields_ = [
('hProcess', c_void_p),
('hThread', c_void_p),
('dwProcessId', c_ulong),
('dwThreadId', c_ulong)]
StartupInfo = _STARTUPINFO()
ProcessInfo = _PROCESS_INFORMATION()
key1 = bytes(md5(b'bin1bin1bin1').hexdigest().encode())
file = open('bin1', 'rb').read()
arr = range(len(file))()
open('bin1', 'wb').write(bytes(arr))
sleep(0)
bet = ctypes.windll.kernel32.CreateProcessA(b'bin1', ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), byref(StartupInfo), byref(ProcessInfo))
ctypes.windll.kernel32.WaitForSingleObject(ctypes.c_int(ProcessInfo.hProcess), ctypes.c_int(-1))
open('bin1', 'wb').write(file)
#!/usr/bin/env python# visit https://tool.lu/pyc/ for more information# Version: Python 3.11import ctypes
from time import *
from ctypes import *
from ctypes import wintypes
from hashlib import md5
class _STARTUPINFO(Structure):
_fields_ = [
('cb', c_ulong),
('lpReserved', c_char_p),
('lpDesktop', c_char_p),
('lpTitle', c_char_p),
('dwX', c_ulong),
('dwY', c_ulong),
('dwXSize', c_ulong),
('dwYSize', c_ulong),
('dwXCountChars', c_ulong),
('dwYCountChars', c_ulong),
('dwFillAttribute', c_ulong),
('dwFlags', c_ulong),
('wShowWindow', c_ushort),
('cbReserved2', c_ushort),
('lpReserved2', c_char_p),
('hStdInput', c_ulong),
('hStdOutput', c_ulong),
('hStdError', c_ulong)]
class _PROCESS_INFORMATION(Structure):
_fields_ = [
('hProcess', c_void_p),
('hThread', c_void_p),
('dwProcessId', c_ulong),
('dwThreadId', c_ulong)]
StartupInfo = _STARTUPINFO()
ProcessInfo = _PROCESS_INFORMATION()
key1 = bytes(md5(b'bin1bin1bin1').hexdigest().encode())
file = open('bin1', 'rb').read()
arr = range(len(file))()
open('bin1', 'wb').write(bytes(arr))
sleep(0)
bet = ctypes.windll.kernel32.CreateProcessA(b'bin1', ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), ctypes.c_int(0), byref(StartupInfo), byref(ProcessInfo))
ctypes.windll.kernel32.WaitForSingleObject(ctypes.c_int(ProcessInfo.hProcess), ctypes.c_int(-1))
open('bin1', 'wb').write(file)
import marshal, dis
f = open("ez_py.pyc", "rb").read()
code = marshal.loads(f[16:]) #这边从16位开始取因为是python3 python2从8位开始取
dis.dis(code)import marshal, dis
f = open("ez_py.pyc", "rb").read()
code = marshal.loads(f[16:]) #这边从16位开始取因为是python3 python2从8位开始取
dis.dis(code)Disassembly of <code object <listcomp> at 0x00000297CC7F8E70, file "ez_py.py", line 59>:
59 0 RESUME 0
2 BUILD_LIST 0
4 LOAD_FAST 0 (.0)
>> 6 FOR_ITER 50 (to 108)
8 STORE_FAST 1 (i)
10 LOAD_GLOBAL 0 (key1)
22 LOAD_FAST 1 (i)
24 LOAD_GLOBAL 3 (NULL + len)
36 LOAD_GLOBAL 0 (key1)
48 PRECALL 1
52 CALL 1
62 BINARY_OP 6 (%)
66 BINARY_SUBSCR
76 LOAD_GLOBAL 4 (file)
88 LOAD_FAST 1 (i)
90 BINARY_SUBSCR
100 BINARY_OP 12 (^)
104 LIST_APPEND 2
106 JUMP_BACKWARD 51 (to 6)
>> 108 RETURN_VALUE
Disassembly of <code object <listcomp> at 0x00000297CC7F8E70, file "ez_py.py", line 59>:
59 0 RESUME 0
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最后于 2023-6-5 13:09
被oacia编辑
，原因：
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用python3.11来运行输出ez_py.pyc字节码的代码 |
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为什么我查看字节码提示这个
 dis.dis(marshal.load(f)) ValueError: bad marshal data (unknown type code) |
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用与pyc相同版本的python运行代码就可以查看到字节码了,例如这里的代码你用python3.11运行就不会报错了 |
