November 22, 2024

Side-Channel Leaks in Web Applications

Popular online applications may leak your private data to a network eavesdropper, even if you’re using secure web connections, according to a new paper by Shuo Chen, Rui Wang, XiaoFeng Wang, and Kehuan Zhang. (Chen is at Microsoft Research; the others are at Indiana.) It’s a sobering result — yet another illustration of how much information can be leaked by ordinary web technologies. It’s also really clever.

Here’s the background: Secure web connections encrypt traffic so that only your browser and the web server you’re visiting can see the contents of your communication. Although a network eavesdropper can’t understand the requests your browser sends, nor the replies from the server, it has long been known that an eavesdropper can see the size of the request and reply messages, and that these sizes sometimes leak information about which page you’re viewing, if the request size (i.e., the size of the URL) or the reply size (i.e., the size of the HTML page you’re viewing) is distinctive.

The new paper shows that this inference-from-size problem gets much, much worse when pages are using the now-standard AJAX programming methods, in which a web “page” is really a computer program that makes frequent requests to the server for information. With more requests to the server, there are many more opportunities for an eavesdropper to make inferences about what you’re doing — to the point that common applications leak a great deal of private information.

Consider a search engine that autocompletes search queries: when you start to type a query, the search engine gives you a list of suggested queries that start with whatever characters you have typed so far. When you type the first letter of your search query, the search engine page will send that character to the server, and the server will send back a list of suggested completions. Unfortunately, the size of that suggested completion list will depend on which character you typed, so an eavesdropper can use the size of the encrypted response to deduce which letter you typed. When you type the second letter of your query, another request will go to the server, and another encrypted reply will come back, which will again have a distinctive size, allowing the eavesdropper (who already knows the first character you typed) to deduce the second character; and so on. In the end the eavesdropper will know exactly which search query you typed. This attack worked against the Google, Yahoo, and Microsoft Bing search engines.

Many web apps that handle sensitive information seem to be susceptible to similar attacks. The researchers studied a major online tax preparation site (which they don’t name) and found that it leaks a fairly accurate estimate of your Adjusted Gross Income (AGI). This happens because the exact set of questions you have to answer, and the exact data tables used in tax preparation, will vary based on your AGI. To give one example, there is a particular interaction relating to a possible student loan interest calculation, that only happens if your AGI is between $115,000 and $145,000 — so that the presence or absence of the distinctively-sized message exchange relating to that calculation tells an eavesdropper whether your AGI is between $115,000 and $145,000. By assembling a set of clues like this, an eavesdropper can get a good fix on your AGI, plus information about your family status, and so on.

For similar reasons, a major online health site leaks information about which medications you are taking, and a major investment site leaks information about your investments.

The paper goes on to consider possible mitigations. The most obvious mitigation is to add padding to messages so that their sizes are not so distinctive — for example, every message might be padded to make its size a multiple of 256 bytes. This turns out to be less effective than you might expect — significant information can still leak even if messages are generously padded — and the padded messages are slower and more expensive to transmit.

We don’t know which sites the researchers studied, but it seems like a safe bet that most, if not all, of the sites in these product categories have similar problems. It’s important to keep these attacks in perspective — bear in mind that they can only be carried out by someone who can eavesdrop on the network between you and the site you’re visiting.

It’s becoming increasingly clear that securing web-based applications is very difficult, and that the basic tools for developing web apps don’t do much to help. The industry, and researchers, will be struggling with web app security issues for years to come.

Global Internet Freedom and the U.S. Government

Over the past two weeks I’ve testified in both the Senate and the House on how the U.S. should advance “Internet freedom.” I submitted written testimony for both hearings which can be downloaded in PDF form here and here. Full transcripts will become available eventually but meanwhile you can click here to watch the Senate video and here to watch the House video. In both hearings I advocated a combination of corporate responsibility through the Global Network Initiative backed up by appropriate legislation given that some companies seem reluctant to hold themselves accountable voluntarily; revision of export controls and sanctions; and finally, funding and support for tools, and technologies and activism platforms that will counter-act suppression of online speech.

Lawmakers are moving forward to support research and technical development. February 4th Rep. David Wu [D-OR] and Rep. Frank Wolf [R-VA] introduced the Internet Freedom Act of 2010, which would establish an Internet Freedom Foundation. The bill’s core section reads:

(a) ESTABLISHMENT OF THE INTERNET FREEDOM FOUNDATION. – The National Science Foundation shall establish the Internet Freedom Foundation. The Internet Freedom Foundation shall –

(1) award competitive, merit-reviewed grants, cooperative aggreements, or contracts to private industry, universities, and other research and development organizations to develop deployable technologies to defeat Internet suppression and censorship; and
(2) award incentive prizes to private industry, universities, and other research and development organizations to develop deployable technologies to defeat Internet suppression and censorship.

(b) LIMITATION ON AUTHORITY. – Nothing in this Act shall be interpreted to authorize any action by the United States to interfere with foreign national censorship in furtherance of law enforcement aims that are consistent with the International Covenant on Civil and Political Rights.

Whoever runs this foundation will have their work cut out for them in sorting out its strategies, goals, and priorities – and dealing with a great deal of thorny politics. The Falun Gong-affiliated Global Internet Freedom Consortium have been arguing that they were unfairly passed over for recent State Department grants which were given to other groups working on different tools that help you get around Internet blocking – “circumvention tools” as the technical community call them. For the past year they’ve been engaged in an aggressive campaign to lobby congress and the media to ensure they’ll get a slice of future funds. (For examples of the fruits of their media lobbying effort see here, here, and here).

But the unfortunate bickering over who deserves government funding more than whom has distracted attention from the larger question of whether circumvention on its own is sufficient to defeat Internet censorship and suppression of online speech. In his recent blog post, Internet Freedom: Beyond Circumvention my friend and former colleague Ethan Zuckerman warns against an over-focus on circumvention: “We can’t circumvent our way around internet censorship.” In short, he summarizes his main points:

– Internet circumvention is hard. It’s expensive. It can make it easier for people to send spam and steal identities.
– Circumventing censorship through proxies just gives people access to international content – it doesn’t address domestic censorship, which likely affects the majority of people’s internet behavior.
– Circumventing censorship doesn’t offer a defense against DDoS or other attacks that target a publisher.

While circumvention tools remain worthy of support as part of a basket of strategies, I agree with Ethan that circumvention is never going to be the silver bullet that some people make it out to be, for all the reasons he outlines in his blog post, which deserves to be read in full. As Ethan points out, as I pointed out in my own testimony, and as my research on Chinese blog censorship published last year has demonstrated, circumvention does nothing to help you access content that has been removed from the Internet completely – which is the main way that the Chinese government now censors the Chinese-language Internet. In my testimony I suggested several other tools and activities that require equal amount of focus:

  • Tools and training to help people evade surveillance, detect spyware, and guard against cyber-attacks.
  • Mechanisms to preserve and re-distribute censored content in various languages.
  • Platforms through which citizens around the world can share “opposition research” about what different governments are doing to suppress online speech, and collaborate across borders to defeat censorship, surveillance, and attacks in ad-hoc, flexible ways as new problems arise during times of crisis.

As Ethan puts it:

– We need to shift our thinking from helping users in closed societies access blocked content to helping publishers reach all audiences. In doing so, we may gain those publishers as a valuable new set of allies as well as opening a new class of technical solutions.

– If our goal is to allow people in closed societies to access an online public sphere, or to use online tools to organize protests, we need to bring the administrators of these tools into the dialog. Secretary Clinton suggests that we make free speech part of the American brand identity – let’s find ways to challenge companies to build blocking resistance into their platforms and to consider internet freedom to be a central part of their business mission. We need to address the fact that making their platforms unblockable has a cost for content hosts and that their business models currently don’t reward them for providing service to these users.

Which brings us to the issue of corporate responsibility for free expression and privacy on the Internet. I’ve been working with the Global Network Initiative for the past several years to develop a voluntary code of conduct centered on a set of basic principles for free expression and privacy based on U.N. documents like the Universal Declaration of Human Rights, the International Covenant on Civil and Political Rights, and other international legal conventions. It is bolstered by a set of implementation guidelines and evaluation and accountability mechanisms, supported by a multi-stakeholder community of human rights groups, investors, and academics all dedicated to helping companies do the right thing and avoid making mistakes that restrict free expression and privacy on the Internet.

So far, however, only Google, Microsoft, and Yahoo have joined. Senator Durbin’s March 2nd Senate hearing focused heavily on the question of why other companies have so far failed to join, what it would take to persuade them to join, and if they don’t join whether laws should be passed that induce greater public accountability by companies on free expression and privacy. He has written letters to 30 U.S. companies in the information and communications technology (ICT) sector. He expressed great displeasure in the hearing with most of their responses, and further disappointment that no company (other than Google which is already in the GNI) even had the guts to send a representative to testify in the hearing.  Durbin announced that he will “introduce legislation that would require Internet companies to take reasonable steps to protect human rights or face civil or criminal liability.” It is my understanding that his bill is still under construction, and it’s not clear when he will introduce it (he’s been rather preoccupied with healthcare and other domestic issues, after all).  Congressman Howard Berman (D-CA), who convened Wednesday’s House Foreign Affairs Committee hearing is also reported to be considering his own bill. Rep. Chris Smith (R-NJ), the ranking Republican at that hearing, made a plug for the Global Online Freedom Act of 2009, a somewhat revised version of a bill that he first introduced in 2006

I said at the hearing that the GNI probably wouldn’t exist if it hadn’t been for the threat of Smith’s legislation. I was not, however, asked my opinion on GOFA’s specific content. Since GOFA’s 2006 introduction I have critiqued it a number of times (see for example here, here, and here). As the years have passed – especially in the past year as the GNI got up and running yet most companies have still failed to engage meaningfully with it  – I have come to see the important role legislation could play in setting industry-wide standards and requirements, which companies can then tell governments they have no choice but to follow. That said, I continue to have concerns about parts of GOFA’s approach. Here is a summary of the current bill written by the Congressional Research Service (I have bolded the parts of concern):

5/6/2009–Introduced.
Global Online Freedom Act of 2009 – Makes it U.S. policy to: (1) promote the freedom to seek, receive, and impart information and ideas through any media; (2) use all appropriate instruments of U.S. influence to support the free flow of information without interference or discrimination; and (3) deter U.S. businesses from cooperating with Internet-restricting countries in effecting online censorship. Expresses the sense of Congress that: (1) the President should seek international agreements to protect Internet freedom; and (2) some U.S. businesses, in assisting foreign governments to restrict online access to U.S.-supported websites and government reports and to identify individual Internet users, are working contrary to U.S. foreign policy interests. Amends the Foreign Assistance Act of 1961 to require assessments of electronic information freedom in each foreign country. Establishes in the Department of State the Office of Global Internet Freedom (OGIF). Directs the Secretary of State to annually designate Internet-restricting countries. Prohibits, subject to waiver, U.S. businesses that provide to the public a commercial Internet search engine, communications services, or hosting services from locating, in such countries, any personally identifiable information used to establish or maintain an Internet services account. Requires U.S. businesses that collect or obtain personally identifiable information through the Internet to notify the OGIF and the Attorney General before responding to a disclosure request from an Internet-restricting country. Authorizes the Attorney General to prohibit a business from complying with the request, except for legitimate foreign law enforcement purposes. Requires U.S. businesses to report to the OGIF certain Internet censorship information involving Internet-restricting countries. Prohibits U.S. businesses that maintain Internet content hosting services from jamming U.S.-supported websites or U.S.-supported content in Internet-restricting countries. Authorizes the President to waive provisions of this Act: (1) to further the purposes of this Act; (2) if a country ceases restrictive activity; or (3) if it is the national interest of the United States.

My biggest concern has to do with the relationship GOFA would create between U.S. companies and the U.S. Attorney General. If the AG is made arbiter of whether content or account information requested by local law enforcement is for “legitimate law enforcement purposes” or not, that means the company has to share the information – which in the case of certain social networking services may include a great deal of non-public information about the user, who his or her friends are, and what they’re saying to each other in casual conversation. Letting the U.S. AG review the insides of this person’s account would certainly violate that user’s privacy. It also puts companies at a competitive disadvantage in markets where users – even those who don’t particularly like their own government – would consider an overly close relationship between a U.S. service provider and the U.S. government not to be in their interest. Take this hypothetical situation for example: An Egyptian college student decides to use a social networking site to set up a group protesting the arrest and torture of his brother. The Egyptian government demands the group be shut down and all account information associated with it handed over. In order to comply with GOFA, the company shares this student’s account information and all content associated with that protest group with the U.S. Attorney General. What is the oversight to ensure that this information is not retained and shared with other U.S. government agencies interested in going on a fishing expedition to explore friendships among members of different Egyptian opposition groups? Why should we expect that user to be ok with such a possibility?

Another difficult issue to get right – which gets even harder with the advent of cloud computing – is the question of where user data is physically housed. The Center for Democracy and Technology,(PDF), Jonathan Zittrain and others have discussed some of the regulatory difficulties of personally identifiable information and its location. In 2008 Zittrain wrote:

As Internet law rapidly evolves, countries have repeatedly and successfully demanded that information be controlled or monitored, even when that information is hosted outside their borders. Forcing US companies to locate their servers outside IRCs [Internet Restricting Countries] would only make their services less reliable; it would not make them less regulable.

If the goal of GOFA is to discourage US companies from violating human rights, then it will probably be successful. But if the goal of the Act is to make the Internet more free and more safe, and not just push rights violations on foreign companies, then more must be done.

Then there is the problem of Internet Restricting Country designations themselves. I have long argued that it is problematic to divide the world into “internet restricting countries” and countries where we can assume everything is just fine, not to worry, no human rights concerns present. First of all I think that the list itself is going to quickly turn into a political and diplomatic football which will be subject to huge amounts of lobbying and politics, and thus will be very difficult to add new countries to the list. Secondly, regimes can change fast: in between annual revisions of the list you can have a coup or a rigged election whose victors demand companies to hand over dissident account information and censor political information, but companies are off the hook – having “done nothing illegal.” Finally, while I am not drawing moral equivalence between Italy and Iran I do believe there is no country on earth, including the United States, where companies are not under pressure by government agencies to do things that arguably violate users’ civil rights. Policy that acknowledges this honestly is less likely to hurt U.S. companies in many parts of the world where the last thing they need is for people to be able to provide “documentary proof” that they are extensions of the U.S. government’s geopolitical agendas.

Therefore a more effective, ethically consistent and less hypocritical approach to the three problems I’ve described above would be to codify strict global privacy standards absolutely everywhere U.S. companies operate. Companies should be required by law to notify all users anywhere in the world in a clear, culturally and linguistically understandable way (not by trained lawyers but by normal people), exactly how and where their personally-identifying information is being stored and used and who has access to it under what circumstances. If users are better informed about how their data is being used, they can use better judgment about how or whether to use different commercial services – and seek more secure alternatives when necessary, perhaps even using some of the new tools and platforms run by non-profit activist organizations that Congress is hoping to fund. Congress could further bolster the privacy of global users of U.S. services by adopting something akin to the Council of Europe Privacy Convention.

Regarding censorship: again, as the Internet evolves further with semi-private social networking sites and mobile services we need to make sure that the information companies are required to share with the U.S. government doesn’t end up violating user privacy.  I am doubtful that government agenices in some of the democracies unlikely to be put on the “internet restricting countries” list can really be trusted not to abuse the systems of censorship and intermediary liability that a growing number of democracies are implementing in the name of legitimate law enforcement purposes. Thus on censorship I also prefer global standards. There is real value in making companies retain internal records of the censorship requests that they receive all around the world in the event of a challenge in U.S. court regarding the lawfulness of a particular act of censorship – a private right of action in U.S. court which GOFA or its equivalent would potentially enable. It’s also good to make companies establish clear and uniform procedures for how they handle censorship requests, so that they can prove if challenged in court that they are only responding to requests made in writing through official legal channels, rather than responding to requests that have no basis even in local law, despite claiming vaguely to the public that “we are only following local law.” Companies should be required to exercise maximum transparency with users about what is being censored, at whose behest, and according to which law exactly. Congress could, for example, mandate that the Chilling Effects Clearinghouse mechanism or something similar should be utilized globally for all content takedowns.
(Originally posted at my blog, RConversation.)

Netflix Cancels the Netflix Prize 2

Today, Netflix announced it is canceling its plans for a second Netflix Prize contest, one that reportedly would have involved the release of more information than the first. As I argued earlier, I feared that the new contest would have put the supposedly private movie viewing and rating habits of Netflix customers at great risk, and I applaud Netflix for making a very responsible decision. No doubt, pressure from the private lawsuit and FTC investigation helped Netflix make up its mind, and both are reportedly going away as a result of today’s action.

Web Security Trust Models

[This is part of a series of posts on this topic: 1, 2, 3, 4, 5, 6, 7, 8.]

Last week, Ed described the current debate over whether Mozilla should allow an organization that is allegedly controlled by the Chinese government to be a default trusted certificate authority. The post prompted some very insightful feedback, including questions about alternative trust models. I will try to lay out the different types of models on a high level, and I encourage corrections or clarifications. It’s worth re-stating that what we’re talking about is how you as a web user know that who you are talking to is who they claim to be (if they are, then you can be confident that your other security measures like end-to-end encryption are working).

Flat and Inflexible
This is the model we use now. Your browser comes pre-loaded with a list of Certificate Authorities that it will trust to guarantee the authenticity of web sites you visit. For instance, Mozilla (represented by the little red dragon in the diagram) ships Firefox with a list of pre-approved CAs. Each browser vendor makes its own list (here is Mozilla’s policy for how to get added). The other major browsers use the same model and have themselves already allowed CNNIC to become trusted for their users. This is a flat model because each CA has just as much authority as the others, thus each effectively sits at the “root” of authority. Indeed any of the CAs can sign certificates for any entity in the world (hence the asterisk in each). They do not coordinate with each other, and can sign a certificate for an entity even if another CA has already done so. Furthermore, they can confer this god-like power on other entities without oversight or the prior knowledge of the end users or the entities being signed for.

This is also an inflexible model because there is no reasonable way to impose finer-grained control on the authority of the CAs. The standard used is called X.509. It doesn’t allow you to trust Verisign to a greater or lesser extent than the Chinese government — it is essentially all or nothing for each. You also can’t tell your browser to trust CNNIC only for sites in China (although domain name constraints do exist in the standard, they are not widely implemented). It is also inflexible because most browsers intentionally make it difficult for a user to change the certificate list. It might be possible to partially mitigate some of the CA/X.509 shortcomings by implementing more constraints, improving the user interface, adding “out of band” certificate checks (like Perspectives), or generating more paranoid certificate warnings (like Certificate Patrol).

Decentralized and Dependent
In the early days of the web, an alternative approach already existed. This model did away entirely with a default set of external trusted entities and gave complete control to the individual. The idea was that you would start by trusting only people you “knew” (smiley faces in the diagram) to begin to build a “web of trust.” You then extend this web by trusting those people to vouch for others that you haven’t met (kind of like a a secure virtual version of Goodfellas). This makes it a fundamentally decentralized model. There is nothing limiting certain entities from gaining the trust of many people and therefore becoming de facto Certificate Authorities. This has only happened within technically proficient communities, and in the case of USENIX they eventually discontinued the service.

So, this is a system that is highly dependent on having some connection with whoever you want to communicate with. It has enjoyed some limited success via the PGP family of standards, but mostly for applications such as email or in more constrained situations like inter/intra-enterprise security. It is possible that with the boon in online social networks there is a new opportunity to renew interest in a web-of-trust style security architecture. The approach seems less practical for general web security because it requires the user to have some existing trust relationship with a site before using it securely. It is not necessarily an impossible approach — and the mod_openpgp and mod_gnutls projects show some technical promise — but as a practical matter wide-scale adoption of a “web of trust” style security model for the web seems unlikely.

Hierarchical and Delegated
A third approach starts with a single highly trusted root and delegates authority recursively. Any authority can only issue certificates for itself or the entities that fall “underneath” it, thus limiting the god-like power of the flat model. This also pushes signing power closer to the authenticated sites themselves. It is possible that this authority could be placed directly in their hands, rather than requiring an external authority to approve of each new certificate or domain. Note that I am describing this in a very domain-centric way. If we are willing to fully buy into the domain hierarchy way of thinking about web security, there may be a viable implementation path for this model.

Perhaps the greatest example of this delegation approach to web governance is the existing Domain Name System. Decisions at the root of DNS are governed by the international non-profit ICANN, which assigns authority to Top Level Domains (eg: .com, .net, .cn) who then further delegate through a system of registrars. The biggest problem with tying site authentication to DNS is that DNS is deeply insecure. However, within the next year a more secure version of DNS, DNSSEC, is scheduled to be deployed at the DNS root. Any DNSSEC query can be verified by following the chain of authority back to the root, and any contents of the response can be guaranteed to be unaltered through that chain of trust. The question is whether this infrastructure can be the basis for distributing site certificates as well, which could form the basis for hierarchical site authenticity (which would also permit encryption of traffic). CNNIC happens to also be the registry for the .cn TLD, so in this case it would be restricted to creating certificates for .cn domains. This approach is advocated by Dan Kaminsky (interview, presentation) and Paul Vixie (here, here). I’ve also found posts by Eric Rescorla and Jason Roysdon informative.

If implemented via DNSSEC, this approach would thoroughly bind web site authentication to the DNS hierarchy, and the only assurance it would provide is that you are communicating with the person who registered the domain you are visiting. It would not provide any additional verification about who that person is, as Certificate Authorities theoretically could do (but practically don’t). Certificates were originally envisioned as a way to guarantee that a particular real-world entity was behind the site in question, but market pressures caused CAs cut corners on the verification process. Most CAs now offer “Domain Validation” (DV) certificates that are issued without any human intervention and simply verify that the person requesting the certificate has control of the domain in question. These certificates are treated no differently than more rigorously verified certificates, so for all intents and purposes the DNSSEC certificate delegation model would provide at least the services of the current CA model. One exception is Extended Validation certificates, which require the CA to perform more rigorous checks and cause the browser URL bar to take on a “green glow”. It should hover be noted that there are some security flaws with the current implementation.

[Update: I discuss the DNSSEC approach in more detail here]

Open Questions
Are there appropriate stopgap measures on the existing CA model that can limit authority of certain political entities? Are there viable user interface improvements? Are users aware enough of these issues to do anything meaningful with more information about certificates? Does the hierarchical model force us to trust ICANN, and do we? Does the DNS hierarchy appropriately allocate authority? Is domain name enough of a proxy for identity that a DNS-based system makes sense? Do we need better ways of independently validating a person’s identity and binding that to their public key? Even if an alternative model is better, how do we motivate adoption?

Mozilla Debates Whether to Trust Chinese CA

[Note our follow-up posts on this topic: Web Security Trust Models, and Web Certification Fail: Bad Assumptions Lead to Bad Technology]

Sometimes geeky technical details matter only to engineers. But sometimes a seemingly arcane technical decision exposes deep social or political divisions. A classic example is being debated within the Mozilla project now, as designers decide whether the Mozilla Firefox browser should trust a Chinese certification authority by default.

Here’s the technical background: When you browse to a secure website (typically at a URL starting with “https:”), your browser takes two special security precautions: it sets up a private, encrypted “channel” to the server, and it authenticates the server’s identity. The second step, authentication, is necessary because a secure channel is useless if you don’t know who is on the other end. Without authentication, you might be talking to an impostor.

Suppose you’re connecting to https://mail.google.com, to pick up your Gmail. To authenticate itself to you, the server will (1) do some fancy math to prove to you that it knows a certain encryption key, and (2) present you with a digital certificate (or “cert”) attesting that only Google knows that encryption key. The cert is created by a Certification Authority (“CA”), which asserts that it has done the necessary due diligence to establish that the designated encryption key is known only to Google Inc.

If the CA is competent and honest, then you can rely on the cert, and your connection will be secure. But a dishonest CA can trick you into talking to an impostor site, so you need to be cautious about which CAs you trust. Your browser comes preinstalled with a list of CAs whom it will trust. In principle you can change this list, but almost nobody does. So browser vendors effectively decide which CAs their users will trust.

With this background in mind, let’s unpack the Mozilla debate. What set off the debate was the addition of the China Internet Network Information Center (CNNIC) as a trusted CA in Firefox. CNNIC is not part of the Chinese government but many people assert that it would be willing to act in concert with the Chinese government.

To see why this is worrisome, let’s suppose, just for the sake of argument, that CNNIC were a puppet of the Chinese government. Then CNNIC’s status as a trusted CA would give it the technical power to let the Chinese government spy on its citizens’ “secure” web connections. If a Chinese citizen tried to make a secure connection to Gmail, their connection could be directed to an impostor Gmail site run by the Chinese government, and CNNIC could give the impostor a cert saying that the government impostor was the real Gmail site. The Chinese citizen would be fooled by the fake Gmail site (having no reason to suspect anything was wrong) and would happily enter his Gmail password into the impostor site, giving the Chinese government free run of the citizen’s email archive.

CNNIC’s defenders respond that any CA could do such a thing. If the problem is that CNNIC is too close to a government, what about the CAs already on the Firefox CA list that are governments? Isn’t CNNIC being singled out because it is Chinese? Doesn’t the country with the largest Internet population deserve at least one slot among the dozens of already trusted CAs? These are all good questions, even if they’re not the whole story.

Mozilla’s decision touches deep questions of fairness, trust, and institutional integrity that I won’t even pretend to address in this post. No single answer will be right for all users.

Part of the problem is that the underlying technical design is fragile. Any CA can certify to any user that any server owns any name, so the consequences of a misplaced trust decision are about as bad as they can be. It’s tempting to write this off as bonehead design, but in truth the available design options are all unattractive.