2020网鼎杯青龙组部分题目WP

0x00 Crypto之boom

下载下来是个exe文件，拖到cmd运行（切记一定不要双击，用cmd打开）

找个md5网站解密，得到明文

输入后得到一个方程组，解方程组（找个就不用说了，初中知识）

输入有又出现一个方程：

解出来输入x可得flag：

0x01 Reverse之signal

用IDA逆向后，可得关键算法：


他是将一串数字做了不同操作符运算，得到一个ascii码，即为flag，于是写出爆破payload如下：

# -*- coding: UTF-8 -*-
code = [10,4,16,8,3,5,1,4,32,8,5,3,1,3,2,8,11,1,12,8,4,4,1,5,3,8,3,33,1,11,8,11,1,4,9,8,3,32,1,2,81,8,4,36,1,12,8,11,1,5,2,8,2,37,1,2,54,8,4,65,1,2,32,8,5,1,1,5,3,8,2,37,1,4,9,8,3,32,1,2,65,8,12,1,7,34,7,63,7,52,7,50,7,114,7,51,7,24,7,167,7,49,7,241,7,40,7,132,7,193,7,30,7,122]
result = [34,63,52,50,114,51,24,167,49,241,40,132,193,30,122]
flag = []
def encode(x,code):
	i=0
	achar=0
	while(i<len(code)):
		if code[i]==2:
			achar=x+code[i+1]
			i+=2
		elif code[i]==3:
			achar=x-code[i+1]
			i=i+2
		elif code[i]==4:
			achar=x^code[i+1]
			i=i+2
		elif code[i]==5:
			achar=x*code[i+1]
			i=i+2
		elif code[i]==8:
			x=achar
			i=i+1
		elif code[i]==11:
			achar=x-1
			i=i+1
		elif code[i]==12:
			achar=x+1
			i=i+1
	return achar

def run(result,code):
	for x in range(1,127):
		if(encode(x,code)==result):
			flag.append(chr(x))
			
if __name__ == '__main__':
	cur_code = []
	result_i = 0
	for i in range(len(code)):
		if code[i] == 10:
			continue
		if i < len(code) - 1 and code[i+1] != 1 and code[i] == 1:
			run(result[result_i],cur_code)
			cur_code = []
			result_i = result_i + 1
		else:
			cur_code.append(code[i])
	print("flag is = flag{" + ''.join(flag) + '}')