GFW主动探测系统研究报告

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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Mon, Aug 03, 2020

Announcing the Release of GreatFire Appmaker

GreatFire (https://en.greatfire.org/), a China-focused censorship monitoring organization, is proud to announce that we have developed and released a new anti-censorship tool that will enable any blocked media outlet, blogger, human rights group, or civil society organization to evade censors and get their content onto the phones of millions of readers and supporters in China and other countries that censor the Internet.

GreatFire has built an Android mobile app creator, called “GreatFire AppMaker”, that can be used by organizations to unblock their content for users in China and other countries. Organizations can visit a website (https://appmaker.greatfire.org/) which will compile an app that is branded with the organization’s own logo and will feature their own, formerly blocked content. The app will also contain a special, censorship-circumventing web browser so that users can access the uncensored World Wide Web. The apps will use multiple strategies, including machine learning, to evade advanced censorship tactics employed by the Chinese authorities.  This project will work equally well in other countries that have China-like censorship restrictions. For both organizations and end users, the apps will be free, fast, and extremely easy to use.

This project was inspired by China-based GreatFire’s first-hand experience with our own FreeBrowser app (https://freebrowser.org/en) and desire to help small NGOs who may not have the in-house expertise to circumvent Chinese censorship. GreatFire’s anti-censorship tools have worked in China when others do not. FreeBrowser directs Chinese internet users to normally censored stories from the app’s start page (http://manyvoices.news/).

Fri, Jul 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.

Mon, Jun 10, 2019

Apple Censoring Tibetan Information in China

Apple has a long history of censorship when it comes to information about Tibet. In 2009, it was revealed that several apps related to the Dalai Lama were not available in the China App Store. The developers of these apps were not notified that their apps were removed. When confronted with these instances of censorship, an Apple spokesperson simply said that the company “continues to comply with local laws”.

In December, 2017, at a conference in China, when asked about working with the Chinese authorities to censor the Apple App Store, Tim Cook proclaimed:

"Your choice is: do you participate, or do you stand on the sideline and yell at how things should be. And my own view very strongly is you show up and you participate, you get in the arena because nothing ever changes from the sideline."

In the ten years since Apple was first criticized for working with the Chinese authorities to silence already marginalized voices, what has changed? Apple continues to strictly follow the censorship orders of the Chinese authorities. When does Tim Cook expect that his company will help to bring about positive change in China?

Based on data generated from https://applecensorship.com, Apple has now censored 29 popular Tibetan mobile applications in the China App Store. Tibetan-themed apps dealing with news, religious study, tourism, and even games are being censored by Apple. A full list of the censored apps appear below.

Thu, Jun 06, 2019

Report Shines Spotlight on Apple’s Censorship Practices in China

The newest Ranking Digital Rights Corporate Accountability Index makes recommendations on what companies and governments need to do in order to improve the protection of internet users’ human rights around the world. Ranking Digital Rights (RDR) works to promote freedom of expression and privacy on the internet by creating global standards and incentives for companies to respect and protect users’ rights.

In their 2019 Accountability Index, RDR looks at the policies of 24 of the world’s most important internet companies in respect to freedom of expression and privacy and highlights the companies that have made improvements and those companies that need to do more. RDR notes that:

Insufficient transparency makes it easier for private parties, governments, and companies themselves to abuse their power over online speech and avoid accountability.

In particular, the report highlights how Apple has abused their power over online speech, and notes instances of this in China. According to the report, Apple has not disclosed data around the content that it removes from its App Store when faced with requests from the government authorities.

While [Apple] disclosed data about government requests to restrict accounts, it disclosed no data about content removal requests, such as requests to remove apps from its App Store. Apple revealed little about policies and practices affecting freedom of expression, scoring below all other U.S. companies in this category.

The report makes intelligent and sensible recommendations for governments. However, the recommendations also highlight how difficult it is to have these discussions with governments like China’s.

Thu, Nov 30, 2017

About those 674 apps that Apple censored in China

Apple opened the door on its censorship practices in China - but just a crack.
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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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