2022年春秋杯easy_python

方法一

直接看到题目文件

  3           0 LOAD_CONST               1 (204)
              3 LOAD_CONST               2 (141)
              6 LOAD_CONST               3 (44)
              9 LOAD_CONST               4 (236)
             12 LOAD_CONST               5 (111)
             15 LOAD_CONST               6 (140)
             18 LOAD_CONST               6 (140)
             21 LOAD_CONST               7 (76)
             24 LOAD_CONST               3 (44)
             27 LOAD_CONST               8 (172)
             30 LOAD_CONST               9 (7)
             33 LOAD_CONST               9 (7)
             36 LOAD_CONST              10 (39)
             39 LOAD_CONST              11 (165)
             42 LOAD_CONST              12 (70)
             45 LOAD_CONST               9 (7)
             48 LOAD_CONST              10 (39)
             51 LOAD_CONST              13 (166)
             54 LOAD_CONST              11 (165)
             57 LOAD_CONST              14 (134)
             60 LOAD_CONST              14 (134)
             63 LOAD_CONST               6 (140)
             66 LOAD_CONST               1 (204)
             69 LOAD_CONST              11 (165)
             72 LOAD_CONST               9 (7)
             75 LOAD_CONST              10 (39)
             78 LOAD_CONST              15 (230)
             81 LOAD_CONST               6 (140)
             84 LOAD_CONST              11 (165)
             87 LOAD_CONST              12 (70)
             90 LOAD_CONST               3 (44)
             93 LOAD_CONST               8 (172)
             96 LOAD_CONST              16 (102)
             99 LOAD_CONST              17 (6)
            102 LOAD_CONST               6 (140)
            105 LOAD_CONST               1 (204)
            108 LOAD_CONST              15 (230)
            111 LOAD_CONST              15 (230)
            114 LOAD_CONST               7 (76)
            117 LOAD_CONST              18 (198)
            120 LOAD_CONST              19 (38)
            123 LOAD_CONST              20 (175)
            126 BUILD_LIST              42
            129 STORE_FAST               0 (flag)

  4         132 SETUP_LOOP              54 (to 189)
            135 LOAD_GLOBAL              0 (range)
            138 LOAD_CONST              21 (42)
            141 CALL_FUNCTION            1
            144 GET_ITER            
        >>  145 FOR_ITER                40 (to 188)
            148 STORE_FAST               1 (i)

  5         151 LOAD_FAST                0 (flag)
            154 LOAD_FAST                1 (i)
            157 BINARY_SUBSCR       
            158 LOAD_CONST              22 (5)
            161 BINARY_RSHIFT       
            162 LOAD_FAST                0 (flag)
            165 LOAD_FAST                1 (i)
            168 BINARY_SUBSCR       
            169 LOAD_CONST              23 (3)
            172 BINARY_LSHIFT       
            173 BINARY_OR           
            174 LOAD_CONST              24 (255)
            177 BINARY_AND          
            178 LOAD_FAST                0 (flag)
            181 LOAD_FAST                1 (i)
            184 STORE_SUBSCR        
            185 JUMP_ABSOLUTE          145
        >>  188 POP_BLOCK           
        >>  189 LOAD_CONST               0 (None)
            192 RETURN_VALUE        

显然这是一段python文件的字节码,看到129行之前的一连串的赋值语句，加上数组名字叫做flag我们可以知道这个就是我们需要解密的明文，那么我们再看接下来的加密部分
132 SETUP_LOOP 54 (to 189)
看到这个指令，就是进行一个循环，也就是189-54=135
那么就是135行到189行设置了一个循环,迭代器是0-42

可以看到循环的主要内容就是，首先拿到flag[i]的值然后右移5位
然后再取flag[i]的值，然后左移3位,然后将两个值进行位或运算之后再与255再存入flag[i]

方法二

直接请ai

exp

python:

flag = [204, 141, 44, 236, 111, 140, 140, 76, 44, 172, 7, 7, 39, 165, 70, 7, 39, 166, 165, 134, 134, 140, 204, 165, 7, 39, 230, 140, 165, 70, 44, 172, 102, 6, 140, 204, 230, 230, 76, 198, 38, 175]

for i in range(42):
    flag[i] = (flag[i] >> 5) | (flag[i] << 3) & 255
    print(chr(flag[i]),end='')

C++

#include<iostream>
using namespace std;
int main()
{
    int enc[] = {
        204, 141, 44, 236, 111, 140, 140, 76, 44, 172, 7, 7,
        39, 165, 70, 7, 39, 166, 165, 134, 134, 140, 204, 165,
        7, 39, 230, 140, 165, 70, 44, 172, 102, 6, 140, 204,
        230, 230, 76, 198, 38, 175
    };
    for(int i =  0 ; i < 42 ; i ++ )
    {
        printf("%c",(enc[i]>>5|enc[i]<<3)%0xFFF);
    }
}