alibabactf-2024-misc-af540a50/solution/solve.sh

#!/bin/bash
# Copyright (c) 2026 Alibaba Group and its affiliates

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# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


# ============================================================
# Challenge: aliyunctf-2024-Misc-af540a50
# Writeup (from instruction.md) - commented out below.
# ============================================================
#
#
# > 以下为解题 writeup 全文，供参考。
#
# # sentiment_analyze writeup
# 没有给附件，只有一个端口。
#
# 连接上去是一个pow，很容易，基本上1s左右。
#
# 通过pow后，会询问是否需要训练集。
#
# ![img](img/wps1.jpg)
#
#  之后会进行15次询问
#
# ![img](img/wps2.jpg)
#
#  如果顺利答对，进入下一轮，否则游戏结束，同时有时间限制，不得超过2s给出答案。
#
# ![img](img/wps3.jpg)
#
# 本题由于样本集过小（总数据量1.5w左右）。选手也可以通过大量轮询方法获取所有的数据集进行直接枚举，不过这种方法将会耗费大量时间，不推荐。
#
# 如果是随机猜测语句情绪的话，则可能性在pow(1/3, 15) ≈ 0.00000006，几乎不可能做到。
#
# 推荐的做法如下：
#
# 1. 准备数据集：将提供的40条数据按照格式进行解析，提取出 sentiment 和 text。将其划分为训练集。
# 2. 特征提取：对文本进行特征提取，一种常用的方法是使用词袋模型。将文本转换为向量表示，统计文本中每个词语在该文本中出现的次数或使用其他统计特征表示。
# 3. 计算类别的先验概率：根据训练集中的 sentiment，统计每个类别的先验概率。
# 4. 计算特征的条件概率：对于每个特征（词语），计算在给定类别下的条件概率。可以使用词频或其他统计方法来估计条件概率。
# 5. 进行分类预测：对于测试集中的每个样本，根据贝叶斯定理和条件独立性假设计算后验概率，并选择具有最高后验概率的类别作为预测结果。
# 6. 错误重试：当预测失败后，旧的数据集仍作为下一次连接的基础训练集，这样即可获取更多的样本数量。
#
# 最终的wp如下：
#
# ```python
# import re
# from sklearn.feature_extraction.text import CountVectorizer
# from sklearn.naive_bayes import MultinomialNB
# from hashlib import sha256
# from pwn import *
# DEBUG = False
#
# host, port = 'xxx.xxx.xxx.xxx', 9999
#
# def pass_pow():
#     log_level = context.log_level
#     context.log_level = 'critical'
#     # print('pass pow')
#     if DEBUG:
#         io.sendlineafter(b'answer: ', b'debugs')
#         return
#     info = io.recvline()
#     answer_size = info.count(b'?')
#     # sha256(("k22pzjh2d5m7yjphqpdm1xaisnc" + "?????").encode()) = 0a867d05f8b83e20fcff89aa46ccd435967e6639bdcd4b3e7e88fc6376343d72\n
#     ques = info[9: 41 - answer_size]
#     hashed = info[61 : -1].decode()
#     # print(ques, hashed, answer_size)
#     crack = lambda x: sha256(ques+x.encode()).hexdigest() == hashed
#     result = iters.bruteforce(crack, 'abcdefghijklmnopqrstuvwxyz0123456789', length = answer_size, method='fixed')
#     io.sendlineafter(b'answer: ', result.encode())
#     context.log_level = log_level
#     return 
#
# def get_training(train_size = 40):
#     log_level = context.log_level
#     context.log_level = 'critical'
#     _sentiments = []
#     _texts = []
#     io.sendlineafter(b'Do you want to training? (y/n) ', b'y', timeout = 1)
#     io.recvuntil(b'sentiment: ')
#     for _ in range(train_size - 1):
#         info = io.recvuntil(b'\nsentiment: ', drop = True, timeout = 1).decode()
#         result = re.findall(r'(.+?), text: (.+)', info)
#         if not result:
#             continue
#         sentiment, text = result[0]
#         _sentiments.append(sentiment)
#         _texts.append(text)
#         # print(_, len(_texts), text)
#     info = io.recvuntil(b'\nNow', drop = True, timeout = 1).decode()
#     result = re.findall(r'(.+?), text: (.+)', info)
#     if result:
#         sentiment, text = result[0]
#         _sentiments.append(sentiment)
#         _texts.append(text)
#     context.log_level = log_level
#     return _sentiments, _texts
#
# sentiments = []
# texts = []
#
# context.log_level = 'critical'
# io = remote(host, port)
#
# pass_pow()
#
# _sentiments, _texts = get_training()
# sentiments += _sentiments
# texts += _texts
# print('data nums', len(sentiments), len(texts))
# # pause()
# print('run this..')
# # 特征提取
# vectorizer = CountVectorizer()
# X = vectorizer.fit_transform(texts)
#
# # 训练朴素贝叶斯分类器
# classifier = MultinomialNB()
# classifier.fit(X, sentiments)
#
# # 进行预测
# print('doing')
# io.sendlineafter(b'Do you want to start challenge? (y/n) ', b'y', timeout = 1)
#
# _round = 1
# while True:
#     io.recvuntil(b', text: ', timeout = 1)
#     test_text = io.recvline(timeout = 1).strip().decode()
#     test_vector = vectorizer.transform([test_text])
#     prediction = classifier.predict(test_vector)[0]
#
#     print(f"forecast: {_round} {prediction} {test_text in texts}")
#     io.sendlineafter(b'Please input the answer: ', prediction.encode(), timeout = 1)
#     result = io.recvuntil(b' ', drop=True, timeout = 1)
#     if b'Congratulations!' == result:
#         context.log_level = 'debug'
#         io.unrecv(result)
#         break
#     elif result == b'Round':
#         _round += 1
#         continue
#     io.close()
#     io = remote(host, port)
#     pass_pow()
#     _sentiments, _texts = get_training()
#     sentiments += _sentiments
#     texts += _texts
#     print('data nums', len(sentiments), len(texts))
#
#     # 重新训练
#     vectorizer = CountVectorizer()
#     X = vectorizer.fit_transform(texts)
#     classifier = MultinomialNB()
#     classifier.fit(X, sentiments)
#     _round = 0
#     io.sendlineafter(b'Do you want to start challenge? (y/n) ', b'y', timeout = 1)
# result = io.recvuntil(b'}')
# print(result)
# io.close()
#
# ```
#
# 经过测试，大概在获取4000条左右数据量后，识别准确率达到80%，将可能获取flag。
#
# ![img](img/wps4.jpg)
#
# ![image-20240311162229435](img/image-20240311162229435.png)
#
# ===== sentiment_analyze_exp.py =====
# # coding=utf-8
# import re
# from sklearn.feature_extraction.text import CountVectorizer
# from sklearn.naive_bayes import MultinomialNB
# from hashlib import sha256
# from pwn import *
# DEBUG = False
#
# host, port = '47.99.106.207', 9999
#
# def pass_pow():
#     log_level = context.log_level
#     context.log_level = 'critical'
#     # print('pass pow')
#     if DEBUG:
#         io.sendlineafter(b'answer: ', b'debugs')
#         return
#     info = io.recvline()
#     answer_size = info.count(b'?')
#     # sha256(("k22pzjh2d5m7yjphqpdm1xaisnc" + "?????").encode()) = 0a867d05f8b83e20fcff89aa46ccd435967e6639bdcd4b3e7e88fc6376343d72\n
#     ques = info[9: 41 - answer_size]
#     hashed = info[61 : -1].decode()
#     # print(ques, hashed, answer_size)
#     crack = lambda x: sha256(ques+x.encode()).hexdigest() == hashed
#     result = iters.bruteforce(crack, 'abcdefghijklmnopqrstuvwxyz0123456789', length = answer_size, method='fixed')
#     io.sendlineafter(b'answer: ', result.encode())
#     context.log_level = log_level
#     return 
#
# def get_training(train_size = 40):
#     log_level = context.log_level
#     context.log_level = 'critical'
#     _sentiments = []
#     _texts = []
#     io.sendlineafter(b'Do you want to training? (y/n) ', b'y', timeout = 1)
#     io.recvuntil(b'sentiment: ')
#     for _ in range(train_size - 1):
#         info = io.recvuntil(b'\nsentiment: ', drop = True, timeout = 1).decode()
#         result = re.findall(r'(.+?), text: (.+)', info)
#         if not result:
#             continue
#         sentiment, text = result[0]
#         _sentiments.append(sentiment)
#         _texts.append(text)
#         # print(_, len(_texts), text)
#     info = io.recvuntil(b'\nNow', drop = True, timeout = 1).decode()
#     result = re.findall(r'(.+?), text: (.+)', info)
#     if result:
#         sentiment, text = result[0]
#         _sentiments.append(sentiment)
#         _texts.append(text)
#     context.log_level = log_level
#     return _sentiments, _texts
#
# sentiments = []
# texts = []
#
# context.log_level = 'critical'
# io = remote(host, port)
#
# pass_pow()
#
# _sentiments, _texts = get_training()
# sentiments += _sentiments
# texts += _texts
# print('data nums', len(sentiments), len(texts))
# # pause()
# print('run this..')
# # 特征提取
# vectorizer = CountVectorizer()
# X = vectorizer.fit_transform(texts)
#
# # 训练朴素贝叶斯分类器
# classifier = MultinomialNB()
# classifier.fit(X, sentiments)
#
# # 进行预测
# print('doing')
# io.sendlineafter(b'Do you want to start challenge? (y/n) ', b'y', timeout = 1)
#
# _round = 1
# while True:
#     io.recvuntil(b', text: ', timeout = 1)
#     test_text = io.recvline(timeout = 1).strip().decode()
#     test_vector = vectorizer.transform([test_text])
#     prediction = classifier.predict(test_vector)[0]
#
#     print(f"forecast: {_round} {prediction} {test_text in texts}")
#     io.sendlineafter(b'Please input the answer: ', prediction.encode(), timeout = 1)
#     result = io.recvuntil(b' ', drop=True, timeout = 1)
#     if b'Congratulations!' == result:
#         context.log_level = 'debug'
#         io.unrecv(result)
#         break
#     elif result == b'Round':
#         _round += 1
#         continue
#     io.close()
#     io = remote(host, port)
#     pass_pow()
#     _sentiments, _texts = get_training()
#     sentiments += _sentiments
#     texts += _texts
#     print('data nums', len(sentiments), len(texts))
#
#     # 重新训练
#     vectorizer = CountVectorizer()
#     X = vectorizer.fit_transform(texts)
#     classifier = MultinomialNB()
#     classifier.fit(X, sentiments)
#     _round = 0
#     io.sendlineafter(b'Do you want to start challenge? (y/n) ', b'y', timeout = 1)
# result = io.recvuntil(b'}')
# print(result)
# io.close()
#
# ## Hints
#
# - 服务入口包含基于哈希的简易计算题，需根据给定前缀与目标值特征进行本地穷举求解。
# - 核心交互机制在于训练数据的累积性：预测失败后断开重连不会清空历史数据，旧样本会作为基础与新数据合并。
# - 题目实质为文本情感分类任务，可采用词袋模型进行文本向量化，并配合多项式朴素贝叶斯算法构建分类器。
# - 单次会话提供的样本量有限，需设计自动化流程循环连接、持续抓取新数据以逐步扩充训练集规模。
# - 随着数据集不断增大，模型对未知句子的预测准确率将稳步提升，达到较高水平后即可稳定完成多轮次挑战。
#
# ============================================================
# End of Writeup
# ============================================================

# --- Direct flag solution ---
# Decode and write the flag so that running this script solves the challenge.
mkdir -p /logs/agent
echo -n 'YWxpeXVuY3Rme04wXzBOM19rbk9XXzVlbnQxTTNOdF9BbjQxWTJFXzdING5fWTB1fQ==' | base64 -d > /logs/agent/flag.txt