西湖论剑 2024

Last updated on January 30, 2024 pm

MZ，babycpp

MZ

核心逻辑在这

输入48位flag后，利用flag作为索引，然后与取得值相比较，最后再换表

尝试爆破一下，发现符合要求的字符很少，那么可以考虑从第一个字符开始爆破，这里搓了一个idapython脚本，方便看值，然后就是不断调试程序，不断尝试输入。

由于题目所说flag有意义且爆破出的字符也比较少，所以手动爆破效率也挺高的

结合题目说flag有意义，边爆边猜会快一点

Somet1mes_ch0ice_i5_more_import@nt_tHan_effort~!

babycpp

有两处主要逻辑，先看第一处

一直跟进去会看到一个循环

跟进操作

就是一个挺标准的TEA类算法了，动调可以拿到Key和delta，不过需要对TEA加密比较熟悉，才能反应过过来哪个变量是什么

还有一处加密是最终比较的上一行

跟进去

也挺长的，不过关键在后面

可以发现就是对TEA之后的密文进行异或和加法

但有个坑，就是前面有一个swap语句

我一直以为是只是交换值，没想到还交换了地址的内容，导致我一直卡在这里，最终在赛后一个钟才发现这个问题，比较遗憾。

解密就很简单了，先打表把最后的异或哪些常量给打出来，然后就是TEA逆运算

from ctypes import *

key = [0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476]

def decrypt(v1, v2):
    sum = c_uint32(0xdeadbeef * 256)
    for i in range(256):
        sum.value -= 0xdeadbeef
        v2.value -= (((v1.value >> 3) ^ (v1.value << 6)) + v1.value) ^ (sum.value + key[(sum.value >> 0xb) & 3])
        v1.value -= (((v2.value >> 7) ^ (v2.value << 2)) + v2.value) ^ (sum.value + key[sum.value & 3])

    for i in range(4):
        print(chr((v1.value >> (8 * i)) & 0xff), end='')
    for i in range(4):
        print(chr((v2.value >> (8 * i)) & 0xff), end='')
    # return v1.value, v2.value

enc = [0x33, 0xb2, 0x49, 0x8c, 0x39, 0xdd, 0x60, 0x5f, 0x5f, 0x77, 0x72, 0xab, 0x38, 0xd9, 0xed, 0xe7, 0xf3, 0xf0, 0x66,
       0x67, 0x16, 0xc8, 0x53, 0x80, 0x71, 0xb2, 0xfa, 0x5e, 0x7c, 0x2b, 0xbb, 0xb, 0xe5, 0x88, 0x82, 0xb, 0x6, 0x8c,
       0x8d, 0xad, 0x47, 0xb5, 0x85, 0xbb, 0x6, 0x8d, 0x1, 0x2b]

tabel1 = [0x31, 0xee, 0x17, 0x80, 0xe3, 0x2d, 0xa, 0xe5, 0x53, 0x33, 0x9e, 0x2e, 0x1d, 0x5, 0x6f, 0xb4, 0x51, 0x9a,
          0x36, 0x5c, 0xbd, 0x8, 0xa2, 0x34, 0xa3, 0x65, 0x59, 0x62, 0xae, 0xef, 0xd, 0xd0, 0xbc, 0x30, 0x81, 0xeb,
          0x8c, 0xe8, 0x22, 0xfd, 0x7e, 0x4a, 0x1e, 0x10, 0x27, 0xdd, 0x5a, 0xa4, 0xb, 0x29, 0xd5, 0x61, 0x9c, 0x48,
          0x6e, 0x7d, 0xf1, 0xbe, 0x90, 0xb3, 0x55, 0x1b, 0x74, 0x89, 0x60, 0x6c, 0xc1, 0x76, 0x3b, 0x8f, 0xd4, 0x6b,
          0x44, 0xe7, 0x49, 0x1f, 0xfb, 0x7c, 0x5b, 0xf, 0x86, 0xa8, 0xb0, 0xa7, 0xcf, 0x5e, 0xc9, 0xcc, 0x13, 0xb6,
          0x3, 0x4d, 0xd1, 0xe4, 0x6d, 0xbb, 0xf4, 0xa1, 0x37, 0xf9, 0x0, 0x38, 0xfe, 0x14, 0x42, 0x3c, 0x4c, 0x7a, 0xc,
          0x6a, 0x26, 0x1, 0xa6, 0x70, 0x2, 0x87, 0xe2, 0x4, 0x45, 0x50, 0x3e, 0x58, 0xa9, 0x52, 0x23, 0x82, 0x20, 0x7f,
          0x39, 0x75, 0xc6, 0xb7, 0x9b, 0xf8, 0x21, 0xa0, 0x8e, 0xc2, 0xba, 0xd2, 0x35, 0x5f, 0xbf, 0x6, 0x16, 0xc3,
          0x32, 0xab, 0xb2, 0x68, 0x2c, 0xf7, 0xad, 0x96, 0x9, 0x8a, 0x2a, 0xf5, 0x8b, 0x7b, 0x19, 0x8d, 0x4e, 0x93,
          0xff, 0x78, 0xec, 0xd7, 0x25, 0x9d, 0xd3, 0x64, 0xca, 0xaa, 0xcb, 0xd8, 0xe0, 0x24, 0x46, 0xb5, 0xd6, 0xd9,
          0xc7, 0xe, 0x98, 0xaf, 0x85, 0xfc, 0x41, 0x94, 0x91, 0xc8, 0xc4, 0x63, 0x84, 0xf6, 0xc0, 0x7, 0x69, 0x88,
          0x1c, 0x11, 0x18, 0x3a, 0x72, 0x47, 0x4b, 0xf0, 0xde, 0x73, 0x66, 0xda, 0xea, 0x54, 0xf2, 0xa5, 0x3d, 0x79,
          0x71, 0x1a, 0x15, 0x3f, 0x40, 0x92, 0xcd, 0xc5, 0xb9, 0x57, 0xdf, 0xac, 0xfa, 0x99, 0x95, 0x5d, 0xe1, 0x77,
          0x9f, 0xdc, 0x56, 0xb8, 0x43, 0xe9, 0x12, 0x2f, 0x83, 0x2b, 0x28, 0x4f, 0xe6, 0xf3, 0xdb, 0xce, 0xb1, 0x97,
          0xed, 0x67, 0xab]

xor1 = []
add = []
xor2 = []
index = 0
sum_ = 0

for i in range(48):
    index = index + 1

    sum_ = (sum_ + tabel1[index]) % 256

    tabel1[sum_], tabel1[index] = tabel1[index], tabel1[sum_]

    v15 = (tabel1[index] + tabel1[sum_]) % 256

    xor1.append(tabel1[v15])
    xor2.append(tabel1[sum_])
    add.append(tabel1[index])

enc_2 = []
for i in range(len(enc)):
    enc_2.append((c_uint8(((enc[i] ^ xor2[i]) - add[i]) ^ xor1[i])).value)

tea = []
for i in range(0, len(enc), 4):
    tea.append((enc_2[i]) | (enc_2[i + 1] << 8) | (enc_2[i + 2] << 16) | (enc_2[i + 3] << 24))


for i in range(0, len(tea), 2):
    decrypt(c_uint32(tea[i]), c_uint32(tea[i + 1]))
    
   # df8d8ab87c22a396041f9bde6a40c4987c22a396041f9bde