Category Archives: Internet censorship

Second edition

Banking security, Electronic voting, Internet censorship, Privacy technology, Security economics, Security engineering

The second edition of my book “Security Engineering” came out three weeks ago. Wiley have now got round to sending me the final electronic version of the book, plus permission to put half a dozen of the chapters online. They’re now available for download here.

The chapters I’ve put online cover security psychology, banking systems, physical protection, APIs, search, social networking, elections and terrorism. That’s just a sample of how our field has grown outwards in the seven years since the first edition.

Enjoy!

Index on Censorship: Shifting Borders

Internet censorship

The latest issue of the journal “Index on Censorship” is dedicated to the topic of Internet censorship and features an article, “Shifting Borders”, by Ross Anderson and me. In it, we argue that it is wrong to claim that the Internet is free from barriers. They exist, and while often aligning with national boundaries they are hopefully lower.

However, the changing nature of the end-to-end principle is increasing the significance of barriers that stem from industry structure — which companies are hosting controversial information, where they do business, what markets do they compete in and what corporate partnerships are involved. The direction these take will have a significant impact on the scale of Internet censorship.

The rest of the journal is well worth reading, with authors including Xeni Jardin, David Weinberger and Jimmy Wales. I can especially recommend taking a look at Nart Villeneuve’s article, “Evasion Tactics”, also published on his blog. Unfortunately access to the full online version is restricted to subscribers.

Web content labelling

Internet censorship, Security economics

As we all know, the web contains a certain amount of content that some people don’t want to look at, and/or do not wish their children to look at. Removing the material is seldom an option (it may well be entirely lawfully hosted, and indeed many other people may be perfectly happy for it to be there). Since centralised blocking of such material just isn’t going to happen, the best way forward is the installation of blocking software on the end-user’s machine. This software will have blacklists and whitelists provided from a central server, and it will provide some useful reassurance to parents that their youngest children have some protection. Older children can of course just turn the systems off, as has recently been widely reported for the Australian NetAlert system.

A related idea is that websites should rate themselves according to widely agreed criteria, and this would allow visitors to know what to expect on the site. Such ratings would of course be freely available, unlike the blocking software which tends to cost money (to pay for the people making the whitelists and blacklists).

I’ve never been a fan of these self-rating systems whose criteria always seem to be based on a white, middle-class, presbyterian view of wickedness, and — at least initially — were hurriedly patched together from videogame rating schemes. More than a decade ago I lampooned the then widely hyped RSACi system by creating a site that scored “4 4 4 4”, the highest (most unacceptable) score in every category: http://www.happyday.demon.co.uk/awful.htm and just recently, I was reminded of this in the context of an interview for an EU review of self-regulation.

Continue reading Web content labelling →

Should there be a Best Practice for censorship?

Internet censorship, Privacy technology

A couple of weeks ago, right at the end of the Oxford Internet Institute conference on The Future of Free Expression on the Internet, the question was raised from the platform as to whether it might be possible to construct a Best Current Practice (BCP) framework for censorship?

If — the argument ran — IF countries were transparent about what they censored, IF there was no overblocking (the literature’s jargon for collateral damage), IF it was done under a formal (local) legal framework, IF there was the right of appeal to correct inadvertent errors, IF … and doubtless a whole raft more of “IFs” that a proper effort to develop a BCP would establish. IF… then perhaps censorship would be OK.

I spoke against the notion of a BCP from the audience at the time, and after some reflection I see no reason to change my mind.

There will be many more subtle arguments — much as there are will be more IFs to consider, but I can immediately see two insurmountable objections.

The first is that a BCP will inevitably lead to far more censorship, but now with the apparent endorsement of a prestigious organisation: “The OpenNet Initiative says that blocking the political opposition’s websites is just fine!” Doubtless some of the IFs in the BCP will address open political processes, and universal human rights … but it will surely come down to quibbling about language: terrorist/freedom-fighter; assassination/murder; dissent/rebellion; opposition/traitor.

The second, and I think the most telling, objection is that it will reinforce the impression that censoring the Internet can actually be achieved! whereas the evidence piles up that it just isn’t possible. All of the schemes for blocking content can be evaded by those with technical knowledge (or access to the tools written by others with that knowledge). Proxies, VPNs, Tor, fragments, ignoring resets… the list of evasion technologies is endless.

One of the best ways of spreading data to multiple sites is to attempt to remove it, and every few years some organisation demonstrates this again. Although ad hoc replication doesn’t necessarily scale — there’s plenty of schemes in the literature for doing it on an industrial scale.

It’s cliched to trot out John Gilmore’s observation that “the Internet treats censorship as a defect and routes around it“, but over-familiarity with the phrase should not hide its underlying truth.

So, in my view, a BCP will merely be used by the wicked as a fig-leaf for their activity, and by the ignorant to prop up their belief that it’s actually possible to block the content they don’t believe should be visible. A BCP is a thoroughly bad idea, and should not be further considered.

Results of global Internet filtering survey

Internet censorship, News coverage

At their conference in Oxford, the OpenNet Initiative have released the results from their first global Internet filtering survey. This announcement has been widely covered in the media.

Out of the 41 countries surveyed, 25 were found to impose filtering, though the topics blocked and extent of blocking varies dramatically.

Results can be seen on the filtering map and an URL checker. The full report, including detailed country and region summaries, will be published in the book “Access Denied: The Practice and Policy of Global Internet Filtering“.

23rd Chaos Communication Congress

Banking security, Cryptology, Hardware & signals, Internet censorship, Privacy technology

23C3 logoThe 23rd Chaos Communication Congress will be held later this month in Berlin, Germany on 27–30 December. I will be attending to give a talk on Hot or Not: Revealing Hidden Services by their Clock Skew. Another contributor to this blog, George Danezis, will be talking on An Introduction to Traffic Analysis.

This will be my third time speaking at the CCC (I previously talked on Hidden Data in Internet Published Documents and The Convergence of Anti-Counterfeiting and Computer Security in 2004 then Covert channels in TCP/IP: attack and defence in 2005) and I’ve always had a great time but this year looks to be the best yet. Here are a few highlights from the draft programme, although I am sure there are many great talks I have missed.

It’s looking like a great line-up, so I hope many of you can make it. See you there!

With a single bound it was free!

Banking security, Cryptology, Hardware & signals, Internet censorship, Legal issues, Meta, News coverage, Security economics, Security engineering

My book on Security Engineering is now available online for free download here.

I have two main reasons. First, I want to reach the widest possible audience, especially among poor students. Second, I am a pragmatic libertarian on free culture and free software issues; I believe many publishers (especially of music and software) are too defensive of copyright. I don’t expect to lose money by making this book available for free: more people will read it, and those of you who find it useful will hopefully buy a copy. After all, a proper book is half the size and weight of 300-odd sheets of laser-printed paper in a ring binder.

I’d been discussing this with my publishers for a while. They have been persuaded by the experience of authors like David MacKay, who found that putting his excellent book on coding theory online actually helped its sales. So book publishers are now learning that freedom and profit are not really in conflict; how long will it take the music industry?

Protocol design is hard — Flaws in ScatterChat

Cryptology, Internet censorship, Privacy technology

At the recent HOPE conference, the “secure instant messaging (IM) client”, ScatterChat, was released in a blaze of publicity. It was designed by J. Salvatore Testa II to allow human rights and democracy activists to securely communicate while under surveillance. It uses cryptography to protect confidentiality and authenticity, and integrates Tor to provide anonymity and is bundled with an easy to use user interface. Sadly not everything is as good as it sounds.

When I first started supervising undergraduates at Cambridge, Richard Clayton explained that the real purpose of the security course was to teach students not to invent the following (in increasing order of importance): protocols, hash functions, block ciphers and modes of operation. Academic literature is scattered with the bones of flawed proposals for all of these, despite being designed by very capable and experienced cryptographers. Instead, wherever possible, implementors should use peer-reviewed building blocks, as normally there is already a solution which can do the job, but has withstood more analysis and so is more likely to be secure.

Unfortunately, ScatterChat uses both a custom protocol and mode of operation, neither which are as secure as hoped. While looking at the developer documentation I found a few problems and reported them to the author. As always, there is the question of whether such vulnerabilities should be disclosed. It is likely that these problems would be discovered eventually, so it is better for them to be caught early and users allowed to take precautions, rather than attackers who independently find the weaknesses being able to exploit them with impunity. Also, I hope this will serve as a cautionary tale, reminding software designers that cryptography and protocol design is fraught with difficulties so is better managed through open peer-review.

The most serious of the three vulnerabilities was published today in an advisory (technical version), assigned CVE-2006-4021, from the ScatterChat author, but I also found two lesser ones. The three vulnerabilities are as follows (in increasing order of severity): Continue reading Protocol design is hard — Flaws in ScatterChat →

Ignoring the "Great Firewall of China"

Internet censorship, News coverage

The Great Firewall of China is an important tool for the Chinese Government in their efforts to censor the Internet. It works, in part, by inspecting web traffic to determine whether or not particular words are present. If the Chinese Government does not approve of one of the words in a web page (or a web request), perhaps it says “f” “a” “l” “u” “n”, then the connection is closed and the web page will be unavailable — it has been censored.

This user-level effect has been known for some time… but up until now, no-one seems to have looked more closely into what is actually happening (or when they have, they have misunderstood the packet level events).

It turns out [caveat: in the specific cases we’ve closely examined, YMMV] that the keyword detection is not actually being done in large routers on the borders of the Chinese networks, but in nearby subsidiary machines. When these machines detect the keyword, they do not actually prevent the packet containing the keyword from passing through the main router (this would be horribly complicated to achieve and still allow the router to run at the necessary speed). Instead, these subsiduary machines generate a series of TCP reset packets, which are sent to each end of the connection. When the resets arrive, the end-points assume they are genuine requests from the other end to close the connection — and obey. Hence the censorship occurs.

However, because the original packets are passed through the firewall unscathed, if both of the endpoints were to completely ignore the firewall’s reset packets, then the connection will proceed unhindered! We’ve done some real experiments on this — and it works just fine!! Think of it as the Harry Potter approach to the Great Firewall — just shut your eyes and walk onto Platform 9¾.

Ignoring resets is trivial to achieve by applying simple firewall rules… and has no significant effect on ordinary working. If you want to be a little more clever you can examine the hop count (TTL) in the reset packets and determine whether the values are consistent with them arriving from the far end, or if the value indicates they have come from the intervening censorship device. We would argue that there is much to commend examining TTL values when considering defences against denial-of-service attacks using reset packets. Having operating system vendors provide this new functionality as standard would also be of practical use because Chinese citizens would not need to run special firewall-busting code (which the authorities might attempt to outlaw) but just off-the-shelf software (which they would necessarily tolerate).

There’s a little more to this story (but not much) and all is revealed in our academic paper (Clayton, Murdoch, Watson) which will be presented at the 6th Workshop on Privacy Enhancing Technologies being held here in Cambridge this week.

NB: There’s also rather more to censorship in China than just the “Great Firewall” keyword detecting system — some sites are blocked unconditionally, and it is necessary to use other techniques, such as proxies, to deal with that. However, these static blocks are far more expensive for the Chinese Government to maintain, and are inherently more fragile and less adaptive to change as content moves around. So there remains real value in exposing the inadequacy of the generic system.

The bottom line though, is that a great deal of the effectiveness of the Great Chinese Firewall depends on systems agreeing that it should work … wasn’t there once a story about the Emperor’s New Clothes ?

Censoring science

Internet censorship, Legal issues, News coverage

I’ve written a rebuttal in today’s Guardian to an article that appeared last week by Martin Rees, the President of the Royal Society. Martin argued that science should be subjected to more surveillance and control in case terrorists do bad things with it.

Those of us who work with cryptography and computer security have been subjected to a lot of attempts by governments to restrict what we do and publish. It’s a long-running debate: the first book written on cryptology in English, by Bishop John Wilkins in 1641, remarked that ‘If all those useful Inventions that are liable to abuse, should therefore be concealed, there is not any Art or Science which might be lawfully profest’. (John, like Martin, was Master of Trinity in his day.)

In 2001–2, the government put an export control act through Parliament which, in its original form, would have required scientists working on subjects with possible military applications (that is, most subjects) to get export licenses before talking to foreigners about our work. FIPR colleagues and I opposed this; we organised Universities UK, the AUT, the Royal Society, the Conservatives and the Liberals to bring in an amendment in the Lords creating a research exemption for scientists. We mustn’t lose that. If scientists end up labouring under the same bureaucratic controls as companies that sell guns, then both science and nonproliferation will be seriously weakened.

Some people love to worry: Martin wrote a whole book wondering about how the human race will end. But maybe we should rather worry about something a bit closer to hand — how our civilisation will end. If a society turns inwards and builds walls to keep the barbarians out, then competition abates, momentum gets lost, confidence seeps away, and eventually the barbarians win. Imperial Rome, Ming Dynasty China, … ?