GFW主动探测系统研究报告

Analyzer是GreatFire的第一个项目,在2011年上线后,它一如以往的为大家提供测试服务直至今日。现在,我们做了一个新的项目叫做"Blocky",欢迎大家试用这个全新的版本!如果您对此有任何意见和建议,请发送邮件到support@greatfire.org

英文原文来自 https://blog.torproject.org/blog/learning-more-about-gfws-active-probing...

Roya, David, Nick, nweaver, Vern, 和我刚刚完成了关于GFW主动探测系统的研究。这个系统在几年前就被用来探测翻墙工具,比如Tor。我们在之前的博文中介绍过GFW主动探测系统是如何工作的。但有几个问题我们没有回答。比如这个系统的物理结构是怎样的。那些用来主动探测的IP是归GFW所有的么? 有猜测GFW短时间内劫持了部分IP来用来主动探测,但没有证据。这次研究回答了这些问题。

因为这个实验是网络检测,我们从收集数据开始。我们创建了3个数据库,包括了GFW主动探测的小时/月份/年份的数据。这3个不同时段的数据库让我们从不同角度了解GFW主动探测的工作原理。我们公开了其中的两个数据库,你可以重复我们的实验,或者自己分析。

  • 通常来说,如果Tor的某个网桥代理被GFW检测并封锁,它会一直被封锁。但是这意味着网桥代理完全无法访问吗? 我们让中国的VPS一直连接我们控制的网桥代理。我们发现,每25小时,中国的VPS可以短暂的连接到我们的代理网桥。下图显示了这个现象。每个数据点表示中国的VPS试图与网桥代理建立连接。中国联通和中国教育网都有这个周期性现象。有时候,网络安全设备在更新规则时会默认允许所有流量,但我们不知道GFW周期性现象是不是因为这个原因导致的。

  • 我们找到了规律,GFW主动探测的TCP头暗示那几千个IP都来自与同一个地方。下图显示了数据包的初始序号和时间。每个数据点都是一个主动探测连接。如果每个主动探测都是从不同地方发出的,我们应该看到随机的数据点,因为数据包的初始序号是随机选择的。但是下图显示主动探测连接虽然来自不同IP,但是非常有规律。我们认为主动探测的初始序号是按照时间产生的。

 

  • 我们发现GFW主动探测不仅仅针对了Tor。GFW还对 SoftEther 和GoAgent进行了主动探测。这说明主动探测系统是模块化的。GFW工程师能比较简单的对新翻墙软件改进主动探测功能。

  • GFW能(部分的)模拟  vanilla Tor protocol, obfs2, and obfs3 来主动探测网桥代理。有趣的是, node-Tor 因为是使用JavaScript 编写而导致不同的代码实现,从而对主动探测免疫。人为修改了Tor回复能躲避GFW的主动探测,但这应该不是长久之计。

  • 在2012年,主动探测系统每15分钟扫描一次。但现在,主动探测系统能实时扫描。平均来说,中国用户连接Tor网桥代理后半秒内就有主动探测连接。

  • 我们使用 traceroute 发现,GFW的主动探测系统是有状态的,但没有办法重组TCP流。

 

幸运的是,我们有 pluggable transports 来防止主动探测。ScrambleSuitobfs4 能使用预先分享的密钥来防止主动探测。 Meek 使用CDN来代理流量,虽然这不能阻止主动探测,但封锁造成的额外伤害会很大。我们在开发翻墙工具的同时需要注重可用性。大力开发的翻墙工具若很难使用,是没有价值的。这是用户界面的重要性所在。

最后,这是我们的论文数据库和代码,和研究页面。若你有任何问题和反馈,欢迎联系我们

 

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星期一, 11月 25, 2024

China’s New Effort to Achieve Cyber Sovereignty

How Real-Name Registration policies create an “ideological firewall” that chills dissent by eliminating user anonymity and selectively restricting transnational access to Chinese social media apps.

星期四, 8月 10, 2023

1.4 million people used FreeBrowser to circumvent the Great Firewall of Turkmenistan

Since 2021, the authorities in Turkmenistan have taken exceptional measures to crack down on the use of circumvention tools. Citizens have been forced to swear on the Koran that they will not use a VPN. Circumvention tool websites have been systematically blocked. Arbitrary searches of mobile devices have also taken place and have even targeted school children and teachers.

The government has also blocked servers hosting VPNs which led to “near complete” internet shutdowns on several occasions in 2022. Current reports indicate that 66 hosting providers, 19 social networks and messaging platforms, and 10 leading content delivery networks (CDNs), are blocked in the country. The government presumably is unconcerned about the negative economic impact that such shutdowns can cause.

星期五, 3月 18, 2022

Well-intentioned decisions have just made it easier for Putin to control the Russian Internet

This article is in large part inspired by a recent article from Meduza (in Russian).

Since the beginning of the war in Ukraine, Russian users have had problems accessing government websites and online banking clients. Browsers began to mark these sites as unsafe and drop the connection. The reason is the revocation of digital security certificates by foreign certificate authorities (either as a direct consequence of sanctions or as an independent, good will move); without them, browsers do not trust sites and “protect” their users from them.

However, these actions, caused - or at least triggered by - a desire to punish Russia for their gruesome actions in Ukraine, will have long-lasting consequences for Russian netizens.

Digital certificates are needed to confirm that the site the user wants to visit is not fraudulent. The certificates contain encryption keys to establish a secure connection between the site and the user. It is very easy to understand whether a page on the Internet is protected by a certificate. One need just look at the address bar of the browser. If the address begins with the https:// prefix, and there is a lock symbol next to the address, the page is protected. By clicking on this lock, you can see the status of the connection, the name of the Certification Authority (CA) that issued the certificate, and its validity period.

There are several dozen commercial and non-commercial organizations in the world that have digital root certificates, but 3/4 of all certificates are issued by only five of the largest companies. Four of them are registered in the USA and one is registered in Belgium.

星期一, 8月 03, 2020

GreatFire 应用生成器 发布

GreatFire (https://en.greatfire.org/) 是一家专注于中国的审查监督组织,我们自豪地宣布一个新的反审查工具,该工具将使任何被屏蔽的媒体、博客、人权组织或民间社会组织反制审查,将其内容得以传播到中国和其他互联网审查国家的数百万读者和支持者的手机上。

GreatFire 已经构建了一个名为“GreatFire 应用生成器”的网页程序,任何组织可以使用它来为中国和其他国家的用户解锁他们的内容。任何人可以访问 (https://appmaker.greatfire.org/),该网站将编译一个带有自己logo的应用,并将包含他们以前被封锁的内容。该应用还将包含一个特殊的、绕过审查的网络浏览器,以便用户可以访问未经审查的网络。这些应用将使用包括机器学习在内的多种策略来规避中国当局先进的审查策略。这个项目在其他有类似中国的审查限制的国家也同样有效。对于组织和最终用户而言,这些应用将免费、快速且非常易于使用。

这个项目的灵感来自于GreatFire自己的应用 自由浏览(https://freebrowser.org/en)的第一手经验,并希望帮助那些可能没有内部专业知识来规避中国审查制度的小型非政府组织。GreatFire的反审查工具在中国发挥了作用,而其他工具却没有。自由浏览可以引导中国的互联网用户从应用的首页进入被僧所内容的导航(http://manyvoices.news/)。

   

人权基金会 (HRF) 已经使用 GreatFire 应用生成器 创建了一个应用程序HRF 在全球范围内促进和保护人权。该组织的使命是确保自由在世界范围内得到维护和促进。 HRF 的网站 在中国被封锁, 但现在中国任何人都可以 下载 HRF Android 应用程序 并访问该网站的信息。

“现在是中国政府防火墙倒塌的时候了,”人权基金会战略顾问王珍妮说。 “与我们在 GreatFire 的朋友一起,我们致力于击败中国的审查制度——在每一部手机。”

GreatFire 应用生成器 的起源可以追溯到 2014 年,当时开放技术基金 (OTF) 支持 GreatFire 的“依附的自由”实验。该项目直接导致了 2015 年中国政府的大规模网络攻击,后来被称为“大炮”。 OTF 还为 GreatFire 开发 AppleCensorship.com,该网站正在跟踪苹果对包括香港在内的全球应用商店的审查情况。

自由浏览 是“大炮”攻击的直接结果,五年后,我们很高兴能够向任何可能遭受中国当局审查的组织提供我们的方法。 

星期五, 7月 24, 2020

Apple, anticompetition, and censorship

On July 20, 2020, GreatFire wrote to all 13 members of the Subcommittee on Antitrust, Commercial and Administrative Law of the U.S. House Committee on the Judiciary, requesting a thorough examination into Apple’s practice of censorship of its App Store, and an investigation into how the company collaborates with the Chinese authorities to maintain its unique position as one of the few foreign tech companies operating profitably in the Chinese digital market.  

This letter was sent a week before Apple CEO TIm Cook will be called for questioning in front of the Subcommittee on Antitrust, Commercial and Administrative Law. The CEOs of Amazon, Google and Facebook will also be questioned on July 27, as part of the Committee’s ongoing investigation into competition in the digital marketplace.

This hearing offers an opportunity to detail to the Subcommittee how Apple uses its closed operating ecosystem to not only abuse its market position but also to deprive certain users, most notably those in China, of their right to download and use apps related to privacy, secure communication, and censorship circumvention.

We hope that U.S. House representatives agree with our view that Apple should not be allowed to do elsewhere what would be considered as unacceptable in the U.S. Chinese citizens are not second class citizens. Private companies such as Apple compromise themselves and their self-proclaimed values of freedom and privacy when they collaborate with the Chinese government and its censors.

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And I have just completed a GFW Active Detection System. The system in a few years ago was used to detect circumvention tools, such as Tor. We are introduced in a previous blog post how GFW active detection system works. But there are several questions we did not answer. For example, the physical structure of the system is like. Those for active detection of IP is owned by GFW all of it? There is speculation GFW short time hijacked a part of the IP to be used to take the initiative to detect, but there is no evidence. This study answers these questions.

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