主要逻辑server.py
import random
from flask import Flask,request
app = Flask(__name__)
FLAG = "INSA{655e6_is_T0_Much}"
def is_ascii(s):
return len(s) == len(s.encode())
def encrypt_string(st,dest_char_list):
binlist = ['{0:08b}'.format(ord(x), 'b') for x in st]
return ''.join([chr(dest_char_list[int(i+j,2)]) for i,j in zip(binlist[::2], binlist[1::2])])
def isprintable(s, codec='utf8'):
try: s.encode(codec)
except UnicodeEncodeError: return False
else: return True
list_decodable=[ i for i in range(100,100000) if isprintable(chr(i))]
@app.route('/',methods=['POST'])
def handle():
if request.method == 'POST':
sample = request.form.get('sample')
if sample:
if is_ascii(sample):
for _ in range(random.randint(0, 9)):
random.shuffle(list_decodable)
encrypted_input = encrypt_string(sample,list_decodable)
encrypted_flag = encrypt_string(FLAG,list_decodable)
return("Your encrypted sample is %s and the flag is %s !\n" % (encrypted_input,encrypted_flag))
else :
return("Only Ascii characters are allowed\n")
else :
return ("Param 'sample' is expected\n")
else:
return ("FAIL: HTTP method not allowed (%s)\n") % (request.method)
if __name__ == '__main__':
app.run(host='0.0.0.0')
本质上就是将输入的sample和flag同时进行一次encrypt_string操作。
encrypt_string中首先将明文每个字符格式化为二进制字节形式binlist：
binlist = ['{0:08b}'.format(ord(x), 'b') for x in 'deadbeaf']
'''
['01100100',
'01100101',
'01100001',
'01100100',
'01100010',
'01100101',
'01100001',
'01100110']
'''
然后将明文binlist奇数项和偶数位项成若干二元组( b 2 i , b 2 i + 1 ) (b_{2i},b_{2i+1})(b 2 i ,b 2 i +1 )
zz=zip(binlist[::2],binlist[1::2])
list(zz)
'''
[('01100100', '01100101'),
('01100001', '01100100'),
('01100010', '01100101'),
('01100001', '01100110')]
'''
再将每个二元组中两个二进制值相连，转为数字
[int(i+j,2) for i,j in zip(binlist[::2], binlist[1::2])]
最后在dest_char_list中找到对应需要的字符输出。
看到这里解题思路就比较清晰了，将flag字符串INSA{655e6_is_T0_Much}中的字符两两分组，可以分为11组。sample可以一次发送或多次发送进行分组枚举，只要sample中的两两分组能覆盖flag中的分组，就可以通过sample密文和flag密文对照完成最终解密。
Original: https://blog.csdn.net/figfig55/article/details/128094678
Author: 山猪儿烦不得
Title: crypto-base65536(INS‘hAck 2018)
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